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2019
2nd International Conference on Building Materials and Materials Engineering - ICBMM 2018, Chastre, Carlos, and Mendonça Paulo , September 26-28,, Volume 278, Lisbon, Portugal, p.168, (2019) Abstract

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Assessment of the influence of gravity load in RC beams’ critical zones subjected to cyclic loading, Gião, Rita, Lúcio Valter, and Chastre Carlos , Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures, May, 27-29, 2019, Kraków, Poland, p.497-504, (2019) Abstract

The aim of the present paper is to evaluate the gravity loads effect in the behaviour of reinforced concrete beams critical zones subjected to cyclic loads. A numerical study to assess the influence of gravity load on RC beam critical zones subjected to cyclic loading is presented, assuming the level of gravity load as a variable parameter. For this purpose, the non-linear model was previously validated with an experimental campaign carried out on RC beam connection subject to cyclic loading with and without gravity loads. The consideration of the gravity load effects led to an accumulation of negative (hogging) deformation and the formation of an unidirectional plastic hinge. In order to validate this behaviour in an overall structural response, a non-linear numerical analysis of a RC frame system under cyclic loads, subject to different levels of gravity load, is also presented. The numerical results are analysed in terms of global hysterical response, accumulated energy dissipation and equivalent viscous damping ratio. In this numerical study was observed that the hysteretic response depends on the load path. In the presence of higher gravity loads levels, the structure hysteretic behaviour exhibits higher damage levels and the failure mechanism is prone to the formation of four plastic hinges. This phenomenon is analysed and discuss in the present paper. © Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019.

Reliability of the bond strength of recycled coarse aggregate concrete, Pacheco, João, de Brito Jorge, Chastre Carlos, and Evangelista Luís , Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures, May, 27-29, 2019, Kraków, Poland, p.913-920, (2019) Abstract

An analysis on the effect of the incorporation of coarse recycled concrete aggregates on the bond strength between concrete and embedded steel reinforcement is presented. The model’s uncertainty of the Level I provision of the anchorage length of fib Bulletin 72 on ribbed steel/recycled aggregate concrete bond is quantified. Afterwards, reliability analyses on the bond strength are made and a partial safety factor for the anchorage length of recycled concrete elements is proposed. The model’s uncertainty is evaluated through data from pullout tests, the only type of bond test that has been so far performed extensively on recycled aggregate concrete specimens. The limitations of this test in reproducing the bond of actual structural elements is discussed, and the model’s uncertainty is converted to that of lap splice tests. The bond strength of recycled aggregate concrete design was found to be less reliable than that of natural aggregate concrete, especially in the absence of confining reinforcement. For concrete with full recycled aggregate incorporation, a 25% increase in the anchorage length is proposed. Additional testing on the bond strength of lapped splices or beam-end specimens is recommended.

Towards the structural codification of recycled aggregate concrete, Pacheco, João Nuno, de Brito Jorge, Chastre Carlos, and Evangelista Luís , UKIERI Concrete Congress. Concrete: The Global Builder, March 5-8, 2019, Jalandhar, Punjab, India, (2019) Abstract

This paper analyses the studies made so far on the variability and reliability of recycled aggregate concrete. Since recycled aggregate concrete is seen by different agents of the construction industry as a variable material and no structural code has specifically been calibrated to its use, its role as a structural material is limited. Such calibration is hindered since specific research on the statistical and probabilistic data of recycled aggregate concrete properties is lacking.Investigations on the probabilistic knowledge of recycled aggregates and recycled aggregate concrete properties are discussed, and the studies made so far on the reliability of recycled aggregate concrete elements are summarised. Final remarks regarding the future prospects towards the consensual acceptance of recycled aggregate concrete structures are provided.

Scatter of constitutive models of the mechanical properties of concrete: comparison of major international codes, Pacheco, João Nuno, de Brito Jorge, Chastre Carlos, and Evangelista Luís , Journal of Advanced Concrete Technology, March 19, 2019, Volume 17, Number 3, p.102-125, (2019) AbstractWebsite

An investigation on the scatter of code-type constitutive models that relate compressive strength (fc) with tensile strength (fct) and Young’s modulus (Ec) of standard concrete specimens is presented. The influence of the mix design on the accuracy of the fc vs. fct and fc vs. Ecrelationships is discussed, with emphasis on the lithological type and morphology of the coarse aggregates. The uncertainty of the constitutive models is analysed in probabilistic terms and random variables that model the uncertainty of the fc vs. fct and fc vs. Ec relationships are proposed for reliability analyses of serviceability limit states. The suitability of the models proposed is assessed through preliminary conservative estimates of their design values.

Monotonic and quasi-static cyclic bond response of CFRP-to-steel joints after salt fog exposure, Yang, Yongming, Biscaia Hugo, Silva Manuel A. G., and Chastre Carlos , Composites Part B: Engineering, 2019/07/01/, Volume 168, p.532-549, (2019) AbstractWebsite

Deterioration of adhesively bonded CFRP/steel systems in salt fog environment, i.e., deicing salts and ocean environments, has to be taken into account in the design of steel strengthened structures. In the present work, monotonic and quasi-static cyclic loading were applied to CFRP-to-steel double strap joints for two kinds of CFRP laminates after being aged for a period of 5000 h to evaluate the bond behavior. The bonded joints exposed to salt fog had a different failure mode than that observed in the control specimens (0 h of exposure). The severe reduction of the maximum bond stress resulted from damage initiation that occurred in the corrosion region of the steel substrate, associated with final partial rupture on the corroded steel substrate around the edge of the bonded area: it was also correlated with reduced load carrying capacity. Results of pseudo-cyclic tests showed that the relationship between a local damage parameter (D) and normalized local dissipated energy (Wd/Gf) and the normalized slip increment (ΔS/ΔSult) exhibited almost the same trend in the un-aged and aged bonded joints. The normalized slip increment can be seen as a direct indicator for the local and global damage for the un-aged and aged bonded joints. However, monotonic and quasi-static cyclic tests results revealed that the stress concentration due to local corrosion of steel substrate could lead to brittle rupture or accelerated cumulative damage once the aged bonded interface had become weaker. The bonded joints have exhibited also a smaller relative deformation capacity between CFRP and steel.

Statistical analysis of Portuguese ready-mixed concrete production, Pacheco, João Nuno, de Brito Jorge, Chastre Carlos, and Evangelista Luís , Construction and Building Materials, 2019/06/10/, Volume 209, p.283-294, (2019) AbstractWebsite

This paper evaluates and compares the statistics of compressive strength data from three Portuguese ready-mixed concrete plants. A hierarchical model showed that different groups of concrete strength records are not statistically equivalent, even if they were produced in the same plant and using the same concrete composition. This finding is related to autocorrelation. For the same specified strength class, compositions produced less often result in higher average compressive strength and variability. The statistics of one of the plants were quite different from those of the others, even though the concrete of this plant also complied with the specifications. It was found that the average compressive strength of a mix may be quite dependent on the plant that produced it, even if the compressive strength complies with quality control specifications. Conformity with the target slump and strength class was checked following the conformity criteria of EN 206-1 for continuous production. Nonconformity with slump is more frequent than failure to comply with the strength class. A bias factor for reliability analyses was proposed.

Uncertainty models of reinforced concrete beams in bending: code comparison and recycled aggregate incorporation, Pacheco, J., de Brito J., Chastre C., and Evangelista L. , Journal of Structural Engineering, 2019/04/01, Volume 145, Number 4, p.04019013, (2019) AbstractWebsite

The bias factor of the Eurocode 2 [CEN (European Committee for Standardization) (2008). Eurocode 2: Design of ConcreteStructures–Part 1-1: General Rules and Rules for Buildings] and ACI 318 [ACI (American Concrete Institute) (2014). Building CodeRequirements for Structural Concrete and Commentary] flexural resistance models of reinforced concrete beams are compared withemphasis on the effect of the incorporation of coarse recycled aggregates sourced from concrete waste. The bias factor of the yielding momentcalculations according to both codes is also investigated, and the bias in the cracking moment when Eurocode 2 material clauses are used. Thedatabase was composed of 174 beams, and the criteria that led to its development are discussed. The effect of recycled aggregate incorporationon the statistical descriptors of the bias factor is evaluated and probabilistic modeling using lognormal distributions is argued for. Preliminarypartial safety factors for the bias factor of recycled aggregate concrete beams are proposed. No significant differences in the bias of theultimate moment were found between the two comparison vectors: Eurocode 2 versus ACI 318 specifications and recycled versus naturalcoarse aggregate. The bias of the cracking moment increased when coarse recycled aggregates were incorporated, most probably due to thehigher heterogeneity of recycled aggregates.

Experimental investigation on the variability of the main mechanical properties of concrete produced with coarse recycled concrete aggregates, Pacheco, J., de Brito J., Chastre C., and Evangelista L. , Construction and Building Materials, 2019/03/20/, Volume 201, p.110-120, (2019) AbstractWebsite

Research on the variability of the properties of recycled aggregate concrete is lacking and is necessary for the development of reliability analyses and code calibration procedures. This paper presents an experimental programme on the within-batch variability of the compressive strength, Young’s modulus, and splitting tensile strength of several recycled and natural aggregate concrete mixes. The influence of the recycled concrete aggregates on the mechanical properties and variability of concrete is analysed and discussed and benchmarks with standard predictions for the variability of natural aggregate concrete are made. It was found that full recycled aggregate concrete incorporation did not increase the variability of any of the properties tested, but intermediate ratios of recycled aggregate incorporation did. The properties of high-strength concrete mixes were more variable than that of all other mixes, irrespective of recycled aggregate incorporation. All properties of all compositions were suitably modelled by normal distributions. The coarse recycled aggregates were sourced from concrete waste.

Bond durability of CFRP laminates-to-steel joints subjected to freeze-thaw, Yang, Yongming, Silva Manuel A. G., Biscaia Hugo, and Chastre Carlos , Composite Structures, 2019/03/15/, Volume 212, p.243-258, (2019) AbstractWebsite

The degradation mechanisms of bonded joints between CFRP laminates and steel substrates under severe environmental conditions require more durability data and studies to increase the database and better understand their causes. Studies on bond properties of double-strap CFRP-to-steel bonded joints with two different composite materials as well as adhesive coupons subjected to freeze-thaw cycles for 10,000 h were conducted to reduce that gap. In addition, the equivalent to the number of thermal cycles and their slips induced in the CFRP laminates was replicated by an equivalent (mechanical) loading-unloading history condition imposed by a static tensile machine. The mechanical properties of the adhesive coupons and the strength capacity of the bonded joints were only slightly changed by the artificial aging. It was confirmed that the interfacial bond strength between CFRP and adhesive is critically related to the maximum shear stress and failure mode. The interfacial bond strength between adhesive and steel degraded with the aging. However, the equivalent thermal cyclic bond stress caused no detectable damage on the bond because only the interfacial elastic regime was actually mobilized, which confirmed that pure thermal cycles aging, per se, at the level imposed, have a low impact on the degradation of CFRP-to-steel bonded joints.

Estimations of the debonding process of aged joints through a new analytical method, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Composite Structures, 2019/03/01/, Volume 211, p.577-595, (2019) AbstractWebsite

The estimation of the long-term durability of adhesively bonded interfaces between Fiber Reinforced Polymers (FRP) and concrete substrates is crucial because degradation potentiates FRP premature debonding. One of the main reasons for mistrusting the use of FRP composites is the premature debonding phenomenon, which, associated to degradation, has been preventing their widespread use. In this research work, an analytical model is proposed that introduces ageing to estimate the effects of degradation of Glass (G) FRP externally bonded to concrete. Cycles were used to experimentally accelerate ageing of beam specimens, namely, (i) salt fog cycles; (ii) wet-dry cycles with salted water; (iii) temperature cycles between −10 °C and +30 °C; and (iv) temperature cycles between +7.5 °C and +47.5 °C. Based on the experimental results obtained and a corresponding bond-slip curve, the analytical model predicts the complete debonding process between FRP composites and a substrate. Consequently, the temporal evolution of the degradation of the bonded interfaces can be calculated and compared with the initial situation prior to exposure. The effects of the environmental conditions are reported and compared.

Gravity load effects on the behaviour of reinforced concrete beam critical zones subjected to cyclic loads, Gião, Rita, Lúcio Valter, and Chastre Carlos , Engineering Structures, 2019/02/15/, Volume 181, p.503-518, (2019) AbstractWebsite

The aim of the present study was to proceed to a numerical analysis of the gravity load effects on the behaviour of reinforced concrete beam critical zones when subjected to cyclic loads. A parametric study to assess the influence of different levels of gravity load on RC beam critical zones subjected to cyclic loading was carried out. For this purpose, assuming the level of gravity load as a variable parameter, a nonlinear numerical model of a beam-column connection, previously calibrated with experimental data, was used. In order to evaluate the gravity load effects in the global response, a numerical study of a RC frame system is also presented. The numerical results are analysed in terms of global hysteretic response, accumulated energy dissipation and equivalent viscous damping ratio. In this numerical study, it was observed that the hysteretic response depends on the load path. In the presence of higher gravity load levels, the structure hysteretic behaviour exhibits higher damage levels, associated to a failure mechanism corresponding to the formation of four span plastic hinges. Thus, the proper test procedure should involve the imposition of a reverse cyclic displacement history starting each cycle from the gravity load effects.

Ensaios não destrutivos para a inspeção e avaliaçao de edifícios históricos de alvenaria de pedra, Chastre, Carlos, Ludovico-Marques Marco, and Biscaia Hugo , TEST&E 2019 - 2º Congresso de Ensaios e Experimentação em Engenharia Civil, 19-20 February 2, ISEP, Porto, Portugal, p.12, (2019) Abstract

Ao longo da sua vida útil os edifícios históricos estão sujeitos a alterações de uso, a agentes ambientais e a diferentes ações como assentamentos do solo, incêndios, inundações ou sismos, para os quais podem não estar preparados. Além disso, a falta de manutenção contínua ajuda a colocar grande parte desse património em risco devido a problemas estruturais que reduzem sua própria segurança e a dos seus utilizadores. A preservação e mitigação de riscos do património cultural construído requer o uso de ferramentas confiáveis, a fim de avaliar o seu estado de conservação e identificar e prevenir potenciais vulnerabilidades. Os testes destrutivos tradicionais não são possíveis de realizar na maioria dos edifícios históricos, por isso é necessário selecionar testes não destrutivos (NDT) que permitam a caracterização física e mecânica dos materiais e do comportamento da estrutura. Neste artigo apresenta-se uma visão geral de diferentes equipamentos e testes NDT que permitem o levantamento geométrico e o mapeamento dos danos do edifício, a análise petrográfica da pedra de alvenaria, a caracterização das propriedades físicas e mecânicas dos materiais e o comportamento estrutural do edifício.

Ligações coladas entre barras de aço inox exteriormente coladas a elementos de betão: Análise teórica vs. experimental, Biscaia, Hugo, Franco Noel, and Chastre Carlos , TEST&E 2019 - 2º Congresso de Ensaios e Experimentação em Engenharia Civil, 19-20 February 2, ISEP, Porto, Portugal, p.11, (2019) Abstract

Os sistemas de reforço por colagem exterior têm sido alvo de várias abordagens, não só do ponto de vista do tipo de material a utilizar, como também sob o ponto de vista da técnica mais eficiente a seguir. As fibras reforçadas com polímeros (FRP) têm sido, no último par de décadas, alvo de investigação exaustiva, tendo-se verificado que esses sistemas nutrem de ductilidade algo reduzida devido ao descolamento prematuro do material de reforço da superfície de betão. Por conseguinte, o aço inox devidos às suas boas características anticorrosivas e ductilidade apresenta-se como uma alternativa viável aos compósitos de FRP. Assim, com vista a melhorar a ductilidade dos elementos estruturais reforçados, em vez de se recorrer a técnicas de reforço não tradicionais (e.g., Externally Bonded Reinforcement (EBR) ou Near Surface Mounted (NSM)) que estão sempre associadas a roturas prematuras por colagem do elemento de reforço quando a extensão nele instalada está muito aquém do seu valor de rotura, dever-se-á seguir outras técnicas de reforço por colagem. Com vista a interpretar e perceber o desempenho da ligação aço-inox, desenvolveu-se uma campanha experimental em que os ensaios visam em testar e comparar a técnica EBR com uma técnica inovadora e desenvolvida pelos autores (CREatE – Continuous Reinforcement Embedded at Ends) através da realização de ensaios de arrancamento de ligações aço inox/betão. Estes ensaios consistem em aplicar uma força à barra de aço inox segundo uma direção que permite induzir uma rotura da ligação consistente com o Modo II de fratura. A técnica de correlação de imagem digital (DIC) foi utilizada na monitorização de todos estes ensaios tendo-se desenvolvido ainda diferentes modelos, analíticos e numéricos com recurso a um programa de cálculo automático não linear, que permitiram simular os processos de descolamento da ligação aço inox/betão segundo as técnicas EBR e CREatE.

Metodologia para a caraterização física e mecânica de edifícios históricos de pedra utilizando ensaios não destrutivos, Chastre, Carlos, and Ludovico-Marques Marco , TEST&E 2019 - 2º Congresso de Ensaios e Experimentação em Engenharia Civil, 19-20 February 2, ISEP, Porto, Portugal, p.12, (2019) Abstract

Os edifícios históricos como os palácios, castelos, igrejas e templos, são exemplos do património construído e constituem uma parte importante do nosso património cultural. Estas construções históricas incluem normalmente paredes de alvenaria maciça e pedra natural. A salvaguarda do património construído em pedra é de importância inquestionável, pelo que devem ser desenvolvidas e estudadas técnicas de intervenção adequadas em materiais e estruturas. Neste artigo, é apresentada uma metodologia de ensaios não destrutivos para avaliar a conservação de edifícios históricos de pedra e, com base nesta metodologia, é mostrado um caso de estudo na Igreja de São Leonardo, monumento português construído na Atouguia da Baleia no século XIII.

Preface, Chastre, Carlos , 2nd International Conference on Building Materials and Materials Engineering - ICBMM 2018, Volume 278, Lisbon, Portugal, (2019) Abstract

The 2nd International Conference on Building Materials and Materials Engineering (ICBMM 2018) was held at the University of Lisbon, Portugal, from 26 to 28 September, 2018. The objective of the Lisbon conference was to provide a platform for researchers, engineers, academics, as well as industrial professionals from all over the world, to present their research results and development activities in Building Materials and Materials Engineering.ICBMM 2018 was an opportunity for researchers, engineers and academics to further develop Building Materials and Materials Engineering. Attendees benefitted a lot from expert practitioners and researchers who presented the latest trends in theoretical and practical domains of Building Materials and Materials Engineering. Distinguished professors also delivered their keynote speeches on the latest developments in their respective fields. Among the keynote and plenary speakers were Prof. Carlos Chastre from NOVA University of Lisbon, Portugal; Prof. Paulo Mendonça from University of Minho, Portugal; Dr. Mascarenhas Mateus from University of Lisbon, Portugal; Prof. Rudolf Hela from Brno University of Technology, Czech Republic.The current set of conference proceedings present a selection of papers submitted by researchers from a variety of universities, research institutes and industries. All papers were peer-reviewed by conference committee members and a panel of international reviewers who selected the papers to be published based on their quality and relevance to the topic of the conference. This volume presents recent advances in the field of Materials Science and Engineering, Materials Properties, Measuring Methods and Applications, Materials Manufacturing and Processing, Civil and Structural Engineering, Architecture and Urban Planning.We would like to thank all the authors who have contributed to this volume and also the organizing committee, reviewers, speakers, co-chair persons, sponsors and all the conference participantsfor their strong support to ICBMM 2018, making this conference such a great success. We look forward to meeting you in ICBMM 2019!

Probabilistic Conversion of the Compressive Strength of Cubes to Cylinders of Natural and Recycled Aggregate Concrete Specimens, Pacheco, João Nuno, de Brito Jorge, Chastre Carlos, and Evangelista Luís , Materials, Volume 12, Number 2, p.280, (2019) AbstractWebsite

This paper investigates the effect of recycled coarse aggregate incorporation on the relationship between 150 mm cubic and Փ 150 mm cylindrical compressive strength (the reference strength of standards) by comparing data from recycled and natural aggregate concrete compositions in which both cubes and cylinders were tested. A conversion factor from cubic to cylindrical strength is proposed in two versions: A deterministic and a probabilistic one. Such factor has not been studied before and researchers have been converting cubic data as if natural aggregate concrete were tested. The probabilistic factor is intended for reliability analyses on the structural behaviour of recycled aggregate concrete using data from laboratory cube tests. It was found that the incorporation of recycled coarse aggregates sourced from concrete waste significantly decreases the expected value of the factor but the factor’s scatter is relatively unaffected.

A Simple Method for the Determination of the Bond-Slip Model of Artificially Aged Joints, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Journal of Composites for Construction, Volume 23, Number 4, p.04019028, (2019) AbstractWebsite

The durability of adhesively bonded fiber-reinforced polymers (FRP) and concrete substrates has been the subject of recent studies. The degradation of bonded interfaces conjugated with other factors that affect the interface strength may compromise the potentialities of using FRP in externally bonded reinforced (EBR) concrete structures. However, the estimation of the effects of degradation on these bonded interfaces and the analytical methodologies to quantify them are not fully understood. The present work focuses on a local bond-slip model characterized by two parameters for which the values are obtained experimentally. Then, the determination of the local bond-slip relationship of a glass (G) FRP-to-concrete interface can be estimated. The assessment of the degradation of the bonded interface when subjected to cycles of (1) salt fog; (2) wet-dry environments with salt water; (3) temperatures between −10°C and +30°C; and (4) temperatures between +7.5°C and +47.5°C is presented. The results obtained using the proposed bond-slip model led to the conclusion that after 10,000 h of exposure to temperature cycles between −10°C and +30°C, there was a small change in the GFRP-to-concrete interface performance, whereas the effects on the bonded interface for the specimens subjected to temperature cycles between +7.5°C and +47.5°C were far more most severe.

2018
Construção, inovação e pré-fabricação em betão, Chastre, Carlos , Construção Magazine, Novembro/Dezembr, Volume 88, Number Novembro/Dezembro, p.59-61, (2018) AbstractWebsite

Num mundo em constante mutação, as próximas décadas na indústria da construção serão, certamente, muito influenciadas pelos desenvolvimentos nas áreas dos materiais, da informática, do processamento de dados, da industrialização e da automação. A pré-fabricação em betão é, hoje em dia, uma forma de construção segura, económica, durável, sustentável e arquitetonicamente versátil. Trata-se de uma forma industrializada de construção com diversas vantagens, pois permite incorporar, de forma mais rápida, económica, adequada e sustentável, a inovação em materiais, sistemas e processos.A produção em fábrica significa processos de fabrico racionais e eficientes, controlo de qualidade, trabalhadores qualificados, repetição de tarefas, e menor custo de mão-de-obra por m² devido à automação do processo de produção. Deste modo, a industrialização da construção transfere a maioria dos trabalhos do local da obra para a fábrica. As distâncias máximas de transporte por camião deverão variar entre 150 e 350 km, dependendo do tipo de produtos e da rede viária, podendo, em algumas situações, o transporte ser feito por comboio ou por navio, caso em que as distâncias máximas podem aumentar até 2.000 km [3]. Dependendo da acessibilidade do local e da capacidade do sistema de elevação, o processo de montagem em obra deverá ser discutido no início do projeto. Em termos de sustentabilidade, a indústria de pré-fabricação a nível europeu está apostada na redução de 45% de matérias-primas e de 30% do consumo energético. Várias fábricas já reciclam o betão não utilizado e em breve funcionarão num sistema de produção fechado, em que todo os resíduos serão processados e reutilizados [3]. No futuro, o betão pré-fabricado será por excelência o veículo preferido para a introdução dos agregados reciclados na indústria de construção, dado o controlo de qualidade a que é sujeito. O controlo de qualidade na pré-fabricação começa no estudo e preparação do projeto, e continua com a produção das peças de betão e com a entrega e montagem a tempo e horas. O controlo de qualidade durante o processo de fabrico é baseado em quatro pilares fundamentais: pessoas, instalações e equipamentos, matérias-primas e processos de execução, e controlo de qualidade da execução. A maioria das empresas de pré-fabricação possui a certificação ISO-9000.As caraterísticas das estruturas pré-fabricadas permitem adaptá-las, na maioria das situações, às exigências do arquiteto ou do dono de obra, não existindo antagonismo entre a elegância arquitetónica e o aumento da eficiência estrutural (Figura 1). Atualmente, industrialização já não significa um número elevado de peças de betão idênticas, pelo contrário, um processo de produção eficiente pode ser combinado com a mão-de-obra qualificada existente na fábrica, o que permite desenvolver um projeto de arquitetura moderno e sem custos adicionais. A utilização de vãos grandes, sem restrições a possíveis subdivisões com paredes divisórias, permite a flexibilidade do espaço, adaptando-o às necessidades do utilizador, tal como é exigido nos edifícios de escritórios. Quer no passado quer atualmente, a maioria dos edifícios tradicionais são concebidos para uma utilização específica, sem atender a futuras alterações de uso e consequentes remodelações ou demolições. Para obviar a esta desvantagem, a solução passa por fazer uma distinção clara entre a parte estrutural dos edifícios e os acabamentos, possibilitando, desta forma, futuras remodelações sem demolição da estrutura do edifício. Hoje as estruturas pré-fabricadas em betão já são concebidas de acordo com este conceito, dada a capacidade existente nas vigas e pavimentos para vencerem grandes vãos, o que facilita a criação de grandes espaços abertos no interior do edifício. As caraterísticas das lajes alveoladas permitem que as redes de instalações sejam aí incorporadas, e, além disso, pode-se tirar partido da massa térmica do betão da laje para armazenar energia térmica. Os elementos pré-fabricados de betão possibilitam uma ampla variedade de acabamentos, desde superfícies cuidadosamente moldadas até ao betão à vista. Deste modo, o arquiteto dispõe de painéis de fachada, vigas e pilares com formas especiais e com acabamentos de alta qualidade (Figura 2). Além disso, o projetista pode inspecionar e aceitar as peças pré-fabricadas antes de serem transportadas e fixadas no local. Os painéis em betão arquitetónico oferecem uma ampla gama de acabamentos, numa grande variedade de cores e texturas, por exemplo em calcário ou granito, ou através de acabamentos mais complexos em tijoleiras cerâmicas ou em alvenaria de pedra natural ou artificial que seriam extremamente caros se aplicados in situ pelos métodos tradicionais. A pré-fabricação, comparativamente à construção in situ, tem um maior potencial para apresentar estruturas mais económicas, melhor desempenho estrutural e maior durabilidade por causa da otimização dos materiais utilizados, a qual é obtida tendo por base as matérias-primas, os equipamentos de fabricação utilizados e os procedimentos de trabalho cuidadosamente estudados. Os trabalhos de pré-fabricação utilizam equipamento de dosagem e mistura controlados por computador, bem como aditivos e adjuvantes na mistura para obter os desempenhos mecânicos pretendidos. A betonagem e a vibração do betão são realizadas com condições de trabalho e equipamentos ideais. O teor de água pode ser reduzido ao mínimo e a cura também ocorre em circunstâncias controladas. A classe do betão utilizada pode ser adequada às exigências de cada tipo de elemento, de forma a otimizar o uso de materiais mais caros. O betão pré-fabricado oferece uma liberdade de ação considerável para a melhoria da eficiência estrutural, permitindo produtos mais esbeltos e um uso otimizado dos materiais. Maiores vãos e menores alturas úteis podem ser obtidos através da utilização do pré-esforço em vigas e pavimentos. O pré-esforço é frequentemente utilizado na pré-fabricação devido às pistas de pré-tensão existentes e aos fios de pré-esforço serem ancorados por aderência. O betão pré-fabricado pré-esforçado proporciona todas as vantagens construtivas do betão pré-esforçado, mas também a economia na fabricação, devido à reduzida mão-de-obra e à ausência de dispositivos de ancoragem dispendiosos. Outra vantagem do betão pré-fabricado é a melhoria da durabilidade. Contudo, os melhores benefícios são obtidos para os elementos verticais, especialmente para os pilares, onde a capacidade de carga pode aumentar entre 100% a 150% quando a resistência do betão passa de 30 para 90 MPa [3]. As estruturas pré-fabricadas em betão armado e pré-esforçado apresentam, normalmente, uma resistência ao fogo de 60 a 120 minutos ou mais [3]. Atualmente os betões de alto desempenho já são utilizados em algumas estruturas pré-fabricadas e no futuro próximo, em especial em zonas com alguma agressividade ambiental, o betão pré-fabricado verá as armaduras de aço substituídas por armaduras de matérias compósitos. O desempenho das estruturas pré-fabricadas tem sido analisado face a sismos de diferentes intensidades, tendo a maioria registado um bom desempenho, enquanto outras, em especial as mais antigas, mostraram algumas deficiências. A investigação a nível internacional dai resultante, tem sido particularmente útil para melhorar a pormenorização das ligações das estruturas pré-fabricadas, bem como para avaliar a ductilidade geral destas estruturas (que mostrou ser bastante comparável à das estruturas construídas in situ), ajudando assim a definir fatores de comportamento adequados [4].Na última década a Comissão 6 da pré-fabricação, da Federação Internacional do Betão (fib) publicou um conjunto de relatórios técnicos [1-5] sobre edifícios pré-fabricados, dedicados em especial às ligações estruturais [1], às ações acidentais [2], aos painéis sandwich [5], ao projeto de estruturas pré-fabricadas em geral [3] e ao projeto de edifícios em zonas sísmicas [4], onde estes temas são abordados em detalhe e que podem ser uma mais-valia para todos os que se queiram dedicar a esta temática.

Ductilidade e resistência no reforço de pilares de betão armado sem aumento de secção, Chastre, Carlos , Construção Magazine, Março/Abril de 2, Volume 84, Number Março/Abril, p.48-49, (2018) AbstractWebsite

O aumento da resistência e/ou da ductilidade é um objetivo primordial quando se procede ao reforço de pilares. Um método bastante eficaz de aumentar a ductilidade, particularmente em regiões sísmicas, é através do encamisamento com coletes de FRP, uma vez que esta técnica permite uma diminuição da deformação transversal do pilar e a limitação da encurvadura das armaduras longitudinais, aumentando consequentemente a ductilidade do mesmo. Diversos ensaios experimentais permitiram detetar que os incrementos são maiores em secções circulares do que em secções quadradas ou retangulares [1, 2]. A atenuação deste efeito é obtida através do arredondamento dos cantos nos pilares de secção retangular. Contudo, o encamisamento com coletes de FRP, por si só, não aumenta significativamente a resistência do pilar à flexão composta. Para que isso aconteça e se mantenha um nível elevado de ductilidade, é necessário adicionar armaduras longitudinais à armadura do pilar e posteriormente proceder ao encamisamento com colete de FRP. Uma forma muito eficiente de o conseguir, mantendo a seção transversal do pilar, é utilizando o sistema CREatE (Continuous Reinforcement Embedded at Ends) desenvolvido na Universidade NOVA e já anteriormente apresentado nesta coluna, na edição de Junho/Agosto de 2017 [3], para o caso do reforço de vigas. O sistema CREatE foi idealizado para ser utilizado com diversos materiais e diferentes elementos estruturais [4-7], em que é necessário aumentar a sua capacidade resistente através de armaduras pós-instaladas, caracterizando-se pela utilização de armaduras contínuas embutidas nas extremidades do elemento estrutural sem o uso de dispositivos mecânicos para as fixar. Antes da ancoragem da armadura de reforço no interior do elemento, é necessário utilizar uma curva de transição suave para alterar a forma da armadura de reforço e evitar a ocorrência de concentrações de tensões na armadura ou na interface [4, 7, 8]. Este conceito foi aplicado no reforço de pilares realizado no âmbito da tese de doutoramento de Faustino Marques [9].Na Figura 1 é possível observar dois pilares de seção retangular (20x40cm2) encamisados com coletes de 3 camadas de CFRP (200gr/m2) em que foi utilizado o sistema CREatE com armaduras pós-instaladas de aço inox (2x20x5mm2) ou de laminados de CFRP (2x(10+20)×1.4 mm2/face) para reforço longitudinal [7, 8]. Na Figura 2 pode observar-se os resultados dos ensaios experimentais de um conjunto de pilares de seção retangulares sujeitos a esforço axial e a ações horizontais cíclicas. O pilar P11 é o de referência pois, não foi reforçado, enquanto os pilares P12, P15 e P16 foram encamisados com coletes de 3 camadas de CFRP e nos pilares P15 e P16 foi utilizado adicionalmente o sistema CREatE com armaduras pós-instaladas de aço inox (P15) ou de laminados de CFRP (P16) para reforço longitudinal [7]. Na Figura 3 mostra-se a envolvente dos diagramas Força-Deslocamento dos ensaios dos diferentes pilares de seção retangular (P11; P12; P15 e P16), sendo possível de constatar um excelente desempenho não só em termos de ductilidade (incremento de 67%) como de resistência (incrementos entre 29% e 43%, para drifts entre 2 e 4%) dos pilares reforçados com o sistema CREatE relativamente ao pilar de referência não reforçado.

Analyses on the bond transfer between FRP composites and other structural materials, Biscaia, H. C., Chastre C., Cardoso J., and Franco N. , 9th International Conference on Fibre Reinforced Polymer (FRP) Composites in Civil engineering, CICE2018, July 17-19, Paris, France, p.8, (2018) Abstract
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Stainless steel bonded to concrete: An experimental assessment using the DIC technique, Biscaia, Hugo, Franco Noel, and Chastre Carlos , International Journal of Concrete Structures and Materials, January 30, Volume 12, Number 1, (2018) AbstractWebsite

The durability performance of stainless steel makes it an interesting alternative for the structural strengthening of reinforced concrete. Like external steel plates or fibre reinforced polymers, stainless steel can be applied using externally bonded reinforcement (EBR) or the near surface mounted (NSM) bonding techniques. In the present work, a set of single-lap shear tests were carried out using the EBR and NSM bonding techniques. The evaluation of the performance of the bonding interfaces was done with the help of the digital image correlation (DIC) technique. The tests showed that the measurements gathered with DIC should be used with caution, since there is noise in the distribution of the slips and only the slips greater than one-tenth of a millimetre were fairly well predicted. For this reason, the slips had to be smoothed out to make it easier to determine the strains in the stainless steel and the bond stress transfer between materials, which helps to determine the bond–slip relationship of the interface. Moreover, the DIC technique allowed to identify all the states developed within the interface through the load–slip responses which were also closely predicted with other monitoring devices. Considering the NSM and the EBR samples with the same bonded lengths, it can be stated that the NSM system has the best performance due to their higher strength, being observed the rupture of the stainless steel in the samples with bond lengths of 200 and 300 mm. Associated with this higher strength, the NSM specimens had an effective bond length of 168 mm which is 71.5% of that obtained for the EBR specimens (235 mm). A trapezoidal and a power functions are the proposed shapes to describe the interfacial bond–slip relationships of the NSM and EBR systems, respectively, where the maximum bond stress in the former system is 1.8 times the maximum bond stress of the latter one.

Análise experimental de ligações pilar-pilar em torres treliçadas em concreto pré-moldado para suporte de geradores eólicos, Martins, David, Souza Sueli T. M., LUCIO Válter J. G., Chastre Carlos, and Souza Luiz A. S. , Encontro Nacional Betão Estrutural - BE2018, 7 a 9 de novembr, LNEC, Lisboa, Portugal, p.10, (2018) Abstract

Com o crescente consumo de energia elétrica são cada vez mais os países que procuram fontes de energia renovável e limpa, entre elas a eólica. A quantidade de energia produzida é influenciada pela altura das torres, dimensões das pás e potência dos aerogeradores. Quanto maior for a elevação da turbina maiores são a velocidade e estabilidade dos ventos alcançados. A solução de torre treliçada em concreto armado pré-moldado idealizada por Lúcio e Chastre [2] permite a construção de torres altas e é competitiva em relação aos outros sistemas estruturais.As ligações têm uma importância fundamental no comportamento global das estruturas pré-moldadas. A viabilidade da ligação (fácil execução, baixo custo, comportamento/capacidade resistente) é preponderante na viabilização da construção destas torres.Até à data foram estudadas quatro ligações (S1, S2, S3 e S4), sendo neste artigo abordadas apenas as ligações do modelo S3 com junta de 3mm (barras salientes/bainhas corrugadas/selagem com grout) e do modelo S4 com junta de 50 mm (ligações aparafusadas produzidas comercialmente).Através dos resultados experimentais pode-se concluir que o mecanismo de rutura foi o mesmo nos dois modelos e que as soluções estudadas preenchem os requisitos para a sua utilização em estruturas pré-moldadas de concreto armado para suporte de aerogeradores.

Avaliação dos resultados de resistência à compressão de betão pronto produzido em centrais portuguesas, Pacheco, João, de Brito Jorge, Chastre Carlos, and Evangelista Luís , Encontro Nacional Betão Estrutural - BE2018, 7 a 9 de novembr, LNEC, Lisboa, Portugal, p.10, (2018) Abstract

Este artigo avalia se, para especificações de betão correntes, a resistência à compressão de betão pronto é significativamente dependente da central que o produziu, bem como se a variabilidade entre amassaduras de uma determinada composição é dependente da classe de resistência especificada. É apresentado um parâmetro probabilístico que converte a resistência à compressão característica especificada para a resistência à compressão expectável em provetes de betão cúbicos em condições padronizadas.É feita uma análise estatística e probabilística dos resultados de ensaios de resistência à compressão aos 28 dias de betão pronto produzido em três centrais de betão portuguesas durante o ano de 2017. Após a avaliação da representatividade da base de dados analisada, é feito um estudo comparativo dos parâmetros estatísticos dos dados de produção das diferentes centrais e é avaliada a influência da classe de resistência à compressão do betão nestes parâmetros. Define-se e analisa-se um parâmetro probabilístico que converte a resistência à compressão especificada para a resistência potencial de betão, para cubos de 150 mm. Este parâmetro contribui para uma futura proposta de um modelo probabilístico, a ser utilizado em análises de fiabilidade, que converte a resistência à compressão especificada para a resistência à compressão de elementos de betão em obra.Quer a análise estatística dos ensaios de resistência à compressão, quer o parâmetro de conversão são comparados com os resultados de investigações internacionais na área, aferindo-se se a qualidade da produção de betão pronto nacional é semelhante à de outras regiões.

Design method and verification of steel plate anchorages for FRP-to-concrete bonded interfaces, Biscaia, Hugo C., and Chastre Carlos , Composite Structures, 5/15/, Volume 192, p.52-66, (2018) AbstractWebsite

Concrete structures Externally Bonded Reinforced (EBR) with Fibre Reinforced Polymers (FRP) have been studied and used since the end of the last century. However, several issues need to be better studied in order to improve performance. The influence of size of anchorage plates used on Reinforced Concrete (RC) structures strengthened with EBR FRP composites, the external compressive stress to be applied on the anchorage plate and the numerical simulation of this region are some of the topics that need to be more carefully studied in order to clarify the performance of the FRP-to-concrete interface within the anchorage plate region. This study proposes a design methodology to estimate the amount of external compressive stress necessary to be applied on the anchorage plate of EBR systems with FRP composites, in order to avoid premature debonding. The external compressive stress imposed on the FRP composite is intended to simulate the effect produced by a mechanical anchorage system tightened to the EBR system. The results from the design proposal, when compared with the numerical ones, were efficient enough on the prediction of the bond strength improvement of FRP-to-concrete interfaces.

Degradation of EB-GFRP systems due to artificial aging conditions, Biscaia, Hugo, and Chastre Carlos , XVI Portuguese Conference on Fracture (PCF2018), 23-24th April 20, Universidade da Beira Interior, Covilhã, Portugal, (2018) Abstract

The use of adhesively bonded joints between Fiber Reinforced Polymers (FRP) and concrete elements have been spread out in the past decades. However, due to their recent applications, the durability aspects related with these bonded joints requires the use of high safety factors which strongly restricts the mechanical capacity of the FRP composites. The experimental assessment of the degradation of FRP-to-concrete interfaces is an important task because it provides useful data that can be used to calibrate analytical or numerical models with the aim of helping on the correct understanding of the interfacial degradation. In this work, a new and simple interfacial bond-slip model that needs only one parameter to be experimentally defined is proposed. Compared to unaged Glass (G) FRP-to-concrete interfaces, the relative degradation of these bonded interfaces is studied after being subjected to: (i) salt fog cycles; (ii) wet-dry cycles; (iii) temperature cycles between -10ºC and +30ºC; and (iv) between +7.5ºC and +47.5ºC. The subsequent full debonding processes are predicted through an analytical model that takes into account the degradations experimentally determined from the tests.

Theoretical analysis of fracture in double overlap bonded joints with frp composites and thin steel plates, Biscaia, Hugo C., and Chastre Carlos , Engineering Fracture Mechanics, 2018/03/01/, Volume 190, p.435-460, (2018) AbstractWebsite

The effective stress transfer between the fiber reinforced polymers (FRP) and the steel substrate is crucial for the successful retrofit of existing steel structures with FRP composites. However, there are no standard tests for FRP-to-steel interfaces, wherefore different test configurations have been used in recent years to assess the bond behaviour in these interfaces. The present study shows that the choice of test configuration is highly important and leads to different transfer stresses between the FRP and steel composites and consequently, has a direct influence on the strength of the bonded joint. Therefore, it is important to understand the debonding process that occurs in each test and avoid misinterpretations, erroneous analyses and dangerous characterizations of the interfacial behaviour of these interfaces. The current study presents a new analytical approach for the prediction of the debonding of FRP-to-steel interfaces when double-lap pull or double-strap tests are used.

Mechanical response of anchored FRP bonded joints: A nonlinear analytical approach, Biscaia, Hugo Charrinho, Chastre Carlos, Silva Cinderela, and Franco Noel , Mechanics of Advanced Materials and Structures, 2018/02/17, Volume 25, Number 3, p.238-252, (2018) AbstractWebsite

This article presents a nonlinear analytical solution for the prediction of the full-range debonding response of mechanically anchored, fiber-reinforced polymer (FRP) composites from the substrate. The nonlinear analytical approach predicts, for any monotonic loading history or bonded length, the relative displacements (or slips) between materials, the strains in the FRP composite, the bond stresses within the interface, and the stresses developed in the substrate. The load-slip responses of FRP-to-substrate interfaces with short and long bonded lengths are motives of analysis and discussion. The solutions obtained from the proposed approach are also compared with other experimental results found in the literature.

Influência da Variabilidade de Agregados Reciclados de Betão na Fiabilidade de Estruturas de Betão, Pacheco, João Nuno, de Brito Jorge, Chastre Carlos, and Evangelista Luís , 3º Congresso Luso-Brasileiro Materiais de Construção Sustentáveis, 14-16 de feverei, Coimbra, Portugal, (2018) Abstract

A produção de betão com substituição de agregados naturais por agregados reciclados minimiza os impactes da indústria da construção. Contudo, o recurso a este tipo de agregado é limitado devido a dúvidas dos diferentes agentes da indústria da construção e à ausência de regulamentação específica para o projecto de betão com agregados reciclados. A percepção de betões com agregados reciclados como um material heterogéneo com comportamento imprevisível é o principal entrave, quer para a aceitação da indústria, quer para o desenvolvimento de regulamentação. Diferentes aspectos relacionados com o efeitos da variabilidade das propriedades de betão com agregados reciclados na regulamentação de estruturas são abordados conceptualmente: a heterogeneidade dos agregados reciclados, o efeito desta heterogeneidade nas propriedades mecânicas de betão e os efeitos da variabilidade das propriedades de betão na sua fiabilidade estrutural. Os primeiros resultados de uma campanha experimental desenvolvida especificamente para abordar o efeito de agregados grossos reciclados na fiabilidade são apresentados e as suas implicações no projecto de estruturas discutidas. São apresentadas sugestões de desenvolvimentos futuros que visam a calibração de coeficientes parciais de segurança que possibilitem o projecto de estruturas de betão armado dimensionadas segundo o formato do Eurocódigo 2 e mantendo os mesmos níveis de segurança de betão convencional.

CFRP-to-steel bonded joints subjected to cyclic loading: An experimental study, Yang, Yongming, Silva Manuel A. G., Biscaia Hugo, and Chastre Carlos , Composites Part B: Engineering, 1 August 2018, Volume 146, p.28–41, (2018) AbstractWebsite

Pseudo-cyclic and cyclic loading were applied to CFRP-to-steel bonded joints built with two different CFRP laminates. In this paper, the strength capacity and bond-slip curves are presented and compared. The modes of failure are also described and associated with the types of material used, and the observed performances are correlated. The analysis of the results showed a threshold value for loading and amplitude level, below which the cyclic loading caused no detectable damage. For cycles above that limit, the region of the joints around the loaded end presented degradation reflected on the bond-slip stiffness and on the increase of residual deformation. It was found that the normalized dissipated energies either obtained from the bond-slip relationship or from the load-slip response had the same trend. The experimental data allowed also to establish a relationship between the damage developed within the interface and the normalized slip. A preliminary estimate of fatigue limit based on those data is suggested.

Mechanical Response of Anchored FRP bonded joints: A Nonlinear Analytical Approach, Biscaia, Hugo, Chastre Carlos, Silva Cinderela, and Franco Noel , Mechanics of Advanced Materials and Structures, (2018) Abstract

The paper presents a nonlinear analytical solution for the prediction of the full-range debonding response of mechanically-anchored FRP composites from the substrate. The nonlinear analytical approach predicts, for any monotonic loading history or bonded length the relative displacements (or slips) between materials, the strains in the FRP composite, the bond stresses within the interface and the stresses developed in the substrate. The load-slip responses FRP-to-substrate interfaces with a short and a long bonded lengths are motive of analysis and discussion. The solutions obtained from the proposed approach are also compared with other experimental results found in the literature.

Consolidation works on sandstone monuments: A new approach, Ludovico-Marques, Marco, and Chastre Carlos , Handbook of Materials Failure Analysis: With Case Studies from the Construction Industries, p.235-254, (2018) Abstract

Abstract Sandstones are widely used in the building elements of the world’s stone monuments. Alveolization due to salt crystallization-dissolution is the most important degradation pattern found on the Middle Ages’ sandstone façades of St. Leonardo’s Church in Portugal. An outstanding case of widespread distribution of deep and large alveolization patterns found mainly on portals and vaults of its sandstone façades appeared as a result of the past and present proximity of the seashore. On stonewall façades, a new approach of consolidating products’ treatments using the total head was followed in order to allow full absorption of stone. Physical and mechanical tests were carried out on selected representative specimens of varieties of sandstones on the monument. Treatments with ethyl silicates were assessed by means of its effectiveness, harmfulness, and durability. The comparison of results between the application of this new procedure on this stone monument and the traditional intervention treatments highlighted the potential viability of the former to overcome difficult conditions of absorption of consolidating products.

Cyclic loading behaviour of double strap bonded joints with CFRP and aluminium, Biscaia, Hugo, Micaelo Rui, Chastre Carlos, and Cardoso João , Key Engineering Materials , (2018) Abstract

The adhesively bonded joints behaviour under cyclic loading is not yet well understood due to its inherent complexity. Numerical approaches appear, therefore, as the easiest way to simulate such mechanical behaviour. In this work, double strap bonded joints with Carbon Fibres Reinforced Polymers (CFRP) and aluminium are numerically simulated and subjected to a cyclic loading history. In the numerical simulation, the Distinct Element Method (DEM) is used and it is assumed cohesive bi-linear bond-slip models with local damage of the interface. The evaluation of the bonded joints under cyclic loading is made by comparing the results with those simulated with a monotonic loading.

Nondestructive testing methodology to assess the conservation of historic stone buildings and monuments, Chastre, Carlos, and Ludovico-Marques Marco , Handbook of Materials Failure Analysis: With Case Studies from the Construction Industries, p.255-294, (2018) Abstract

Earthquakes, soil settlements, traffic vibrations, and air pollution are some of the actions that can affect historic old buildings. Besides these, the lack of continuous maintenance puts a large part of this heritage in risk due to structural problems that reduce their own safety and that of their users. The preservation and risk mitigation of built cultural heritage require the use of reliable tools in order to assess its state of conservation and to identify and prevent potential vulnerabilities. Having this in mind, it is not possible to carry out destructive tests in most historic old buildings, so it is preferable to opt for nondestructive tests (NDT) or alternative methodologies that allow the physical and mechanical characterization of materials and structure. In this chapter, a general view of NDT methods used in historic buildings to obtain the geometrical information, the damage mapping, the mechanical and physical characterization, and the petrographic analysis of stones is presented. An alternative methodology to physically and mechanically characterize the stone of historic buildings using NDT tests is also proposed. The chapter ends with a case study carried out in the St. Leonard’s Church, a Portuguese monument built in Atouguia da Baleia village in the 13th century, where the alternative methodology here presented was applied. The final results of this study show that the methodology proposed allows the obtention of stress-strain curves in a completely nondestructive way, based on the water absorption coefficient at low pressure.

A simple analytical approach for creep analysis of EB-FRP systems, Biscaia, H., and Chastre C. , Key Engineering Materials , (2018) Abstract

Based on a few experimental results available in the literature, this work presents a simple analytical approach that allows the study of the long-term behaviour of CFRP-to-concrete interfaces under an initial sustaining load. Only the elastic regime is studied, which means that the interfacial maximum bond stress and maximum slip are never exceeded. Therefore, the maximum initial load to be sustained by the joints is limited by its corresponding elastic value. The analytical results provided by the proposed model are compared with some experimental results found in the literature. The results showed strain redistribution throughout the bonded length over the time.

2017
2017 International Conference on Building Materials and Materials Engineering - ICBMM 2017, Chastre, Carlos, and Mendonça Paulo , September 21-23,, Volume 264, Lyon, France, p.159, (2017) Abstract
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CREatE, um sistema inovador de reforço estrutural utilizando compósitos de CFRP, Chastre, Carlos , Construção Magazine, Novembro/Dezembr, Volume 80, Issue Julho/Agosto, Number Novembro/Dezembro, p.46-47, (2017) AbstractWebsite

A procura de soluções de reforço mais duráveis e de fácil aplicação tem levado à utilização crescente dos compósitos de FRP (Fiber Reinforced Polymer) no reforço de estruturas, dada a sua resistência à corrosão, o baixo quociente peso/resistência mecânica, a sua moldabilidade, a facilidade de aplicação e a eliminação de estruturas de suporte. No reforço estrutural de vigas de betão armado com compósitos de FRP, são tradicionalmente utilizados dois tipos de técnicas: os sistemas em que o laminado é colado pelo exterior (EBR - Externally-Bonded Reinforcement) ou aqueles em que o laminado é inserido em rasgos previamente abertos na camada de recobrimento (NSM - Near Surface Mounted). No entanto, as técnicas utilizadas, o comportamento elástico-linear destes materiais e as roturas tendencialmente frágeis das soluções condicionam a sua utilização em estruturas onde se pretende alguma ductilidade. A técnica de reforço NSM apresenta algumas vantagens em relação à técnica EBR, nomeadamente ao nível da proteção das armaduras [1]. Além disso, o desempenho em termos de ductilidade do sistema e resistência final excede a técnica EBR. Contudo, diversos ensaios experimentais [2-5] têm mostrado que roturas prematuras [6] da ligação na interface ou o destacamento do betão na zona do recobrimento entre a face inferior das armaduras ordinárias e as armaduras de reforço podem limitar significativamente a eficiência do sistema, originando modos de rotura frágeis e desperdício de material por falta de otimização da quantidade de material aplicado [1]. A fim de evitar a rotura prematura das soluções de reforço tradicionais (EBR e NSM), foi concebido na Universidade NOVA um sistema inovador de reforço intitulado CREatE (Continuous Reinforcement Embedded at Ends). O sistema CREatE foi idealizado para ser utilizado com diversos materiais [1, 5] e diferentes elementos estruturais, tais como vigas [1, 3], pilares [7], pavimentos [8], lajes ou paredes, em que é necessário aumentar a sua capacidade resistente através de armaduras pós-instaladas. A solução de reforço CREatE caracteriza-se pela utilização de armaduras contínuas embutidas nas extremidades do elemento estrutural sem o uso de dispositivos mecânicos para as fixar. Antes da ancoragem da armadura de reforço no interior do elemento, é necessário utilizar uma curva de transição suave para al terar a forma da armadura de reforço e evitar a concentração de tensões no la minado de CFRP (Carbon Fiber Reinforced Polymer) ou na interface e, desta forma, ter um fluxo gradual de tensões transmitidas à zona de ancoragem existente no interior do elemento. Para validar a solução CREatE foi realizada uma campanha de ensaios à flexão de vigas de betão armado com seção em T, uma altura total de 0,3m, um vão livre de 3,0m e reforçadas com laminados de CFRP recorrendo a diferentes técnicas (EBR, NSM e CREatE). As vigas foram testadas à flexão em 4 pontos, tendo-se obtido resultados promissores (Figura 1), com a eliminação na técnica CREatE dos modos de rotura prematuros. Na Figura 2 é possível observar uma viga ensaiada com a técnica CREatE em que se detetam aberturas de fendas significativas sem que se verifique qualquer rotura prematura do sistema. Além da eliminação dos modos de rotura prematuros, os ensaios comprovam que a técnica CREatE permite o incremento da ductilidade (Figura 1) e a exploração total da capacidade do CFRP [1, 3, 5].

Aging of some GFRP-concrete joints under external pressure, Silva, M. A. G., Biscaia H. C., and Chastre C. , AIS2017 - 6th Asia-Pacific Conference on FRP in Structures, July 19-21 , Singapore, (2017) Abstract

Compressive stresses created by lateral external pressure on laminates are an important factor on success of the use of mechanical anchorage of externally bonded reinforcement (EBR). A program of double shear tests with imposed normal stresses on GFRP plates bonded to a concrete surface and a bond-slip model are described. Results generated numerically are summarized and used as reference values against those obtained after accelerated aging by freeze-thaw cycles, and temperature cycles of the same amplitude but range closer to the glass vitreous temperature. Numerical modelling showed that the bonded length is fully stressed prior to failure. Increasing lateral pressure led to a larger maximum bond stress and strength at the interface. Cohesion, fracture energy and internal friction angle changes are calculated and used to analyze the effects of the aforementioned cycles on the expected behaviour of the GFRP-concrete joints, namely at the interface.

Reforço de vigas em betão armado com armaduras exteriores de FRP, Monteiro, António, Chastre Carlos, Biscaia Hugo, and Franco Noel , Revista Internacional TechITT, Jan. 2017, Volume 15, Number 40, p.48-60, (2017) AbstractWebsite

A utilização de Polímeros Reforçados com Fibras (FRP) no reforço de estruturas de Betão Armado (BA) tem tido cada vez mais aceitação devido à sua elevada resistência e rigidez, baixo peso específico e excelente resistência aos efeitos dos agentes ambientais. No entanto, actualmente, é comum utilizarem-se técnicas de reforço que dificilmente permitem tirar partido da resistência total destes materiais. Com o objectivo de explorar a capacidade total de Polímeros Reforçados com Fibras de Carbono (CFRP), foram estudadas e desenvolvidas duas novas técnicas de reforço de vigas à flexão designadas por Continuous Reinforcement Embedded at Ends (CREatE) e Horizontal Near Surface Mounted Reinforcement (HNSMR). Posteriormente realizou-se um estudo comparativo entre o desempenho destes sistemas de reforço e o de duas outras técnicas já estudadas e usuais, nomeadamente os sistemas Externally Bonded Reinforcement (EBR) e Near Surface Mounted Reinforcement (NSMR). A técnica CREatE provou ser a mais eficaz de todas as alternativas testadas mobilizando a totalidade do compósito de CFRP e dotando as vigas de BA com uma maior capacidade resistente e com uma ductilidade mais elevada.Como complemento deste trabalho experimental, desenvolveu-se também um programa de cálculo em MATLAB, capaz de simular o problema em estudo através de um modelo numérico de análise não linear através do equilíbrio de secções. A representatividade dos dados obtidos foi verificada através de uma análise comparativa entre os valores numéricos e os obtidos experimentalmente.The use of Fiber Reinforced Polymers (FRP) in order to strengthen Reinforced Concrete (RC) structures has been increasingly accepted due to their strength and stiffness, low weight and excellent resistance to the effects of environmental aggressive agents. However, the bonding techniques available and described in the literature can not allow the full use of the mechanical properties of these materials and premature failures are often observed and described by several researchers. In order to explore the full capacity of CFRP composites, two new bonding strengthening techniques of RC beams when subjected to 4-point bending tests were studied and developed. For these new techniques, the designation of Continuous Reinforcement Embedded at Ends (CREatE) and Horizontal Near Surface Mounted Reinforcement (HNSMR) has been assigned. Posteriorly, a comparative study has been carried out between those strengthening systems performance and two traditional techniques, namely, the Externally Bonded Reinforcement (EBR) and Near Surface Mounted Reinforcement (NSMR). The CREatE technique has proved to be the most effective of all alternatives tested, with the full utilization of the CFRP composite and the highest strength, combined with the highest ductility. A code using MATLAB software was developed as a complement of this experimental work, which is able to simulate the problem under study through a nonlinear numerical model based on the equilibrium of sections. The representativeness of the numerical data has been verified afterwards through a comparative analysis between those and the experimental results.

Model uncertainty of recycled aggregate concrete beams subjected to bending, Pacheco, J., de Brito J., Chastre C., and Evangelista L. , HISER International Conference on Advances in Recycling and Management of Construction and Demolition Waste, 21-22-23 June 20, Delft, The Netherlands, (2017) Abstract

This paper investigates whether the model uncertainty of reinforced recycled aggregate concrete (RAC) beams subjected to bending differs from that of reinforced natural aggregate concrete (NAC) beams. An introductory remark concerning the importance of the codification of RAC structural design is made and notions concerning model uncertainties and their role on structural codification are given. Afterwards, the criteria used in the construction of a database of RAC and NAC beams are referred before presenting the key findings of an analysis on the model uncertainty of the cracking, yielding and ultimate moments of beams subjected to four-point bending tests. The analytical moments were calculated following Eurocode 2 provisions. Probabilistic models for model uncertainties are proposed. Negligible differences in the model uncertainty of NAC and RAC beams are reported.

Prediction of the interfacial performance of CFRP laminates and old timber bonded joints with different strengthening techniques, Biscaia, Hugo C., Chastre Carlos, Cruz David, and Viegas André , Composites Part B: Engineering, 1/1/, Volume 108, p.1-17, (2017) AbstractWebsite

Fiber Reinforced Polymers (FRP) is a recent technique to strengthen timber structures and the studies available discussing the debonding between these materials are limited. Therefore, the bond assessment between FRP composites and timber substrates is a topic that needs clarification. The present work analyses the debonding process between Carbon (C) FRP laminates and timber with rupture modes consistent with Mode II interfacial fracture, i.e. with the sliding mode where the bond stresses act parallel to the plane of the bonding surface. Several single-lap shear tests were performed and the experiments showed a nonlinear local behaviour of the CFRP-to-timber interface. An interfacial bond-slip model and its calibration procedure were also presented. Furthermore, the calibrated nonlinear bond-slip model was implemented in a numerical approach where the FRP composite and the adhesive are simulated by linear and nonlinear springs and the substrate is assumed rigid. The following influences on the debonding process of the CFRP-to-timber interface were also analysed: (i) the bonding technique (Externally Bonded Reinforcement - EBR; and Near Surface Mounted - NSM); and (ii) the use of an additional device to mechanically anchor the CFRP laminate. Besides the determination of the effective bond length for each bonding technique, a new concept defining the length beyond which the force at the anchorage device does not decrease with the bonded length and a proposal to estimate its value for any bonded length was also presented and discussed. The experimental tests have shown that the NSM technique has a better performance compared to the EBR technique, independently of the installation of mechanical anchorage devices. In the case of the EBR technique, the strains in the CFRP laminate increased at its vicinities due to the clamping force applied to the anchors, which affected the final strength of the interface.

Analytical model with uncoupled adhesion laws for the bond failure prediction of curved FRP-concrete joints subjected to temperature, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Theoretical and Applied Fracture Mechanics, Volume 89, p.63-78, (2017) Abstract

The strengthening of structures such as columns, beams, arches or slabs with Fibre Reinforced Polymers (FRP) has been the focus of several studies. However, the studies dedicated to the FRP debonding phenomenon of curved bonded joints affected by elevated temperatures are surprisingly limited and no studies on this topic are known, at present, to use nonlinear analytical or numerical approaches. Still, the available studies found in the literature are unanimous in affirming that the debonding phenomenon on such curved interfaces demands the interaction between Fracture Modes I and II. The present work aims to develop an analytical solution capable of simulating the debonding process of curved CFRP-toconcrete interfaces with a constant radius subjected to mechanical and/or thermal loads. Some examples are presented in which the influence of the radius of the interface and the temperature level is analysed. The analytical solution proposed here is based on adhesion laws in which, in the case ofMode II, an exponential bond vs. relative displacement law with temperature dependency is assumed, whereas the Mode I adhesive law is based on a linear with fragile rupture law with the same temperature dependency as Mode II.

Avaliação dos Portais de Pedra Arenítica da Igreja de São Leonardo Utilizando Testes Não Destrutivos, Chastre, Carlos, and Ludovico-Marques Marco , Mecânica Experimental, Volume 28, p.47-54, (2017) AbstractWebsite

Neste artigo é apresentado um resumo das intervenções de conservação realizadas no século passado e dos estudos e testes não destrutivos realizados na última década na Igreja de São Leonardo na Atouguia da Baleia. Em seguida mostra-se o padrão de degradação que ocorre nos portais de arenito da igreja e é analisada a evolução da alveolização que ocorreu nos portais de arenito ao longo dos últimos sessenta a setenta anos. No final, a inspeção visual dos portais de arenito é comparada com um levantamento realizado através de varrimento por laser 3D.

fib Bulletin 84. Precast Insulated Sandwich Panels, Hughes, Simon, Acker Arnold Van, Chastre Carlos, Gasperi Antonello, Jones George, Karutz Holger, Krohn Jason, Laliberté Diane, Lindstrom Gosta, Ronchetti Alessandra, Sennour Larbi, Seshappa Venkatesh, Sthaladipti Saha, Suika Arto, Tillman Mathias, and Tsoukantas Spyros , fib Bulletin 84, Number fib Bulletin, Lausanne, (2017) Abstract

Precast concrete sandwich panels started being used as cladding for buildings, together with the rise of industrial prefabrication, during the mid-20th century. Since then, society and industry have become increasingly aware of energy efficiency in all fields, for both affordability and sustainability consciousness. As such, buildings have been subject to increasingly stringent requirements with the technology of sandwich panels kept continually at the forefront.
Nowadays, sandwich panels have reached the highest standards of functional performance as structural efficiency, flexibility in use, the speed as well as of aesthetic appeal. These combine in building construction with the well-known advantages of prefabrication; such as construction, quality consciousness, durability and sustainability. Sandwich panels have gained more and more important in their field, thus representing quite a significant application within the industry of prefabrication and an important share of the market.
The Commission ‘Prefabrication’ is keen to promote the development of all precast structural concrete products and to transfer the knowledge to practical design and construction. Now filling a strategic gap, by issuing this Guide to Good Practice, which includes design considerations, structural analysis, building physics, use of materials, manufacturing methods, equipment, field performance, and provides a comprehensive overview of the information currently available worldwide. The Commission is particularly proud that this document is a result of close cooperation with PCI and that it will be published by both fib and PCI. This cooperation started six years ago, first with comparing the different approaches to several issues, then progressively integrating up to producing common documents, like this one, that wasn’t yet treated in a specific Guide by either body.

Reforço de Vigas de Betão Armado com Armaduras Pós‑Instaladas de Aço Inox ou de Compósitos de FRP, Chastre, Carlos, Biscaia Hugo, and Franco Noel , Mecânica Experimental, Volume 28, p.39-46, (2017) AbstractWebsite

Neste artigo apresentam-se e analisam-se um conjunto de ensaios realizados em vigas de betão armado reforçadas com armaduras pós-instaladas de aço ou de FRP, incluindo os referentes a uma nova técnica (CREatE) desenvolvida na FCT NOVA. Os resultados experimentais permitiram concluir que a técnica CREatE possibilita aumentos de resistência e ductilidade consideráveis face às técnicas tradicionais.

Application of fuzzy inference system for determining weathering degree of some monument stones in Iran, Heidari, Mojtaba, Chastre Carlos, Torabi-Kaveh Mehdi, Ludovico-Marques Marco, and Mohseni Hassan , Journal of Cultural Heritage, Volume 25, p.41-55, (2017) Abstract

This paper presents a comparative evaluation of efficiencies of different accelerated ageing tests (freezethaw, thermal shock, salt crystallization, dissolution and wetting-drying) and fuzzy inference system in predicting weathering degrees of some monument stones from three historical sites (Anahita Temple, Anobanini reliefs and Eshkaft-e Salman reliefs, Iran). The combined effects of natural weathering processes (heating and cooling, wetting and drying, and freezing and thawing) and climatic information were used for assessing the natural weathering degrees. Finally, the natural weathering degrees were multiplied by time effect coefficients to obtain more realistic natural weathering degrees of the monuments. The predicted natural weathering degrees for Anahita Temple, Anobanini reliefs and Eshkaft-e Salman reliefs are 56%, 61%, and 47%, respectively. These predicted values reasonably support the weathering degrees defined by progressive decay indices (calculated equal to 2.77, 3.42 and 2.66 for Anahita Temple, Anobanini reliefs and Eshkaft-e Salman reliefs, respectively), which means the fuzzy model potentially could accurately predict the weathering of stones.

Bond characteristics of CFRP-to-steel joints, Yang, Yongming, Biscaia Hugo, Chastre Carlos, and Silva Manuel A. G. , Journal of Constructional Steel Research, Volume 138, p.401-419, (2017) Abstract

Carbon Fiber Reinforced Polymer (CFRP) composites have a large potential for strengthening and retrofitting steel parts but due to their premature debonding from steel, further data and research are still required for wider application in such situations. In the present paper, the bond characteristics of CFRP-to-steel joints in pull-pull loaded conditions were studied. Monotonic loading of the double strap joints with different bond lengths was applied and the failure modes and interfacial bond-slip curves were obtained. A tri-linear bondslip model is proposed and it was derived from the experimental data. A closed-form solution approach is also proposed based on the tri-linear bond-slip model. The strength of the CFRP-to-steel interface, the distribution of the relative displacements between bonded materials, the strains developed in the CFRP laminate and the bond stresses along the interface are reported and the closed-form solution is compared with the experimental results. Two cases are selected for presentation: (i) one with the bond length greater than the effective bond length; and, inversely, (ii) one with bond length which is shorter than the effective bond length. The results predicted by the closed-form solutions are shown to be accurate enough when compared to the experiments.

Cáceres-Florencia, patrimonio vivo: Ensayos técnico-arquitectónicos, Salcedo Hernández, José Carlos, Fortea Luna Manuel, Lauria Antonio, Rovero Luisa, Tonietti Ugo, Chastre Carlos, González Jiménez Luis, Matas Casco Miguel, and Saumell Lladó Juan , Suplementos de Investigación en Construcciones Arquitectónicas , Volume 3, Cáceres, p.156, (2017) Abstract
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Characterisation of unidirectional fibre reinforced grout as a strengthening material for RC structures, Gião, Rita, Lúcio Valter, and Chastre Carlos , Construction and Building Materials, Volume 137, p.272-287, (2017) Abstract

The main goal of the present research work is to characterise a unidirectional fibre reinforced grout (UFRG), developed as an alternative material to strengthen RC structures using small thickness jacketing. A high performance cementitious grout reinforced with continuous and unidirectional non-woven steel fibre mat has been developed for this purpose. It was expected that the optimization of the percentage and alignment of the steel fibres would yield a more efficient fibre grout. In fact, the composite should attain higher tensile strength with continuous fibres since the fibre embedment length is enough to prevent fibre pull-out. An experimental programme was carried out to characterise the UFRG’s mechanical properties. Compressive tests were conducted on small thickness tubular specimens to enable the determination of the compressive strength and the static modulus of elasticity. The tensile strength was obtained from splitting tests performed on cubic specimens (DIN 1048-5). Semi-empirical equations, based on the experimental results, are proposed to estimate UFRG’s modulus of elasticity, compressive strength and tensile strength. Two strengthening solutions for RC structures using small thickness CFRP jacketing are presented.

Determination of weathering degree of the Persepolis stone under laboratory and natural conditions using fuzzy inference system, Heidari, Mojtaba, Torabi-Kaveh Mehdi, Chastre Carlos, Ludovico-Marques Marco, Mohseni Hassan, and Akefi Hossein , Construction and Building Materials, Volume 145, p.28-41, (2017) Abstract

Weathering imposes vital effects on stony monuments. Mostly, the degree of weathering is determined by simple test results, ignoring simultaneous effects of various weathering factors. Hence, the main purpose of this study is to develop prediction models with fuzzy inference systems to determine the weathering degree of the Persepolis stone, using various accelerated ageing tests in laboratory condition and to extrapolate the results to the natural condition, considering climatic information. The results suggest reliable conformity between the prediction of the weathering degree of the stone and the weathering degree observed in the Persepolis complex in natural condition.

A Finite Element Based Analysis of Double Strap Bonded Joints with CFRP and Aluminium, Biscaia, Hugo, Cardoso João, and Chastre Carlos , Key Engineering Materials, Volume 754, p.237-240, (2017) Abstract
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A finite element based analysis of double strap bonded joints with CFRP and aluminium, Biscaia, Hugo, Cardoso João, and Chastre Carlos , 16th International Conference on Fracture and Damage Mechanics, Florence, Italy, (2017) Abstract

The bonding between two different materials or between same materials is a quite popular method. Unlike fastener joints, it avoids undesirable stress concentrations and doesn't demand an intrusive application to ensure the good performance of the joint. However, depending on the configuration of the adhesively bonded joint, its performance responds differently and the choice (if possible to make) on the best configuration, i.e. the configuration that originates the highest strength and/or stiffness, may be hard to make. Within this context, several configurationsof aluminium-to-aluminium bonded joints unstrengthened and strengthened with fiber reinforced polymers (FRP) were modelled using a commercial finite element code. The linearity and nonlinearity of the FRP composite and the aluminium were considered, respectively, and the adhesively bonded joints were subjected to a regular displacement that intended to simulate a tensioning load. Also, the nonlinearities of the interfaces were considered in the form of nonlinear cohesive adhesive laws. The fracture Modes I and II were defined trough a bond-slip relation with abi-linear shape and the Mohr-Coulomb failure criterion is used for the coupling of the cohesive adhesive laws of the interface when the debonding process of the bonded joint configuration implies the interaction between both fracture modes, i.e. the joint is under a mixed-mode (Mode I+II) situation. The results are presented and discussed and the configurations of the bonded joints are all compared through bond stress distributions and load-slip responses. The study herein presented is, therefore, a contribution to the analysis of the structural integrity of bonded joints between FRP composites and aluminium substrates, helping also on the choice of the most adequatebonded joint configuration and corresponding reinforcement to be used and applied in practice.

Flexural Strengthening of Old Timber Floors with Laminated Carbon Fiber-Reinforced Polymers, Biscaia, Hugo C., Chastre Carlos, Cruz David, and Franco Noel , Journal of Composites for Construction, Volume 21, Number 1, p.04016073, (2017) AbstractWebsite

A set of three old suspended timber floors were flexurally strengthened with carbon fiber–reinforced polymer (CFRP) strips in order to investigate the effectiveness of externally bonding FRP to their soffits. The specimens were from an old building and 740-mm-wide bands were transferred to the laboratory in order to be tested in a four-point bending test. One specimen was tested with no strengthening system and the results obtained were used as reference values for comparison with the specimens that were externally bonded and reinforced (EBR) with CFRP strips. Two similar EBR systems were studied: (1) keeping both ends of the CFRP strips free of any restriction (traditional technique), and (2) embedding both ends of the CFRP strips into the timber, thus providing a bonding anchorage of the strips (new technique). The installation of the new strengthening system comprises the opening of holes in the timber and the creation of a transition curve between the holes and the timber surface. This transition curve allows a smooth transition of the CFRP laminate between the hole and the timber surface, thus avoiding stress concentrations in this area. After the opening of the holes, the resin is applied inside the hole and on the beam surface, and then the CFRP laminate is mounted. The load-carrying capacity of the specimens, the rupture modes, and the strains and bond stress distributions within the CFRP-to-timber interface are presented. A nonlinear numerical simulation of the specimens based on the midspan cross-sectional equilibrium is also presented. The results showed that the use of the new strengthening system enhances the performance of the specimens when compared with the traditional strengthening system.

Prólogo, Chastre, Carlos , Cáceres-Florencia, patrimonio vivo: Ensayos técnico-arquitectónicos, Volume 3, Cáceres, p.11-15, (2017) Abstract

Este livro apresenta diferentes perspetivas sobre o património arquitetónico em Espanha e Itália, debruçando-se sobre temas que estão na ordem do dia, como a reabilitação do património arquitetónico ou as acessibilidades ao mesmo, sejam elas na forma física ou digital, sendo os autores profundos conhecedores desta área. Nas intervenções a realizar no património edificado é fundamental ter um conhecimento aprofundado do projeto, da história e do processo construtivo da obra, bem como do seu comportamento estrutural. De acordo com o ICOMOS estas intervenções devem ser realizadas utilizando as técnicas mais adequadas, baseadas num diagnóstico apropriado e na compreensão dos materiais existentes. De igual forma, os estudos no edificado monumental devem ser realizados com o menor grau de intrusão e o máximo respeito pela sua integridade física, seguindo os princípios de salvaguarda do património arquitetónico definidos na carta internacional de Atenas.O livro divide‐se em duas grandes áreas: numa, abordam‐se os assuntos que se enquadram essencialmente no âmbito da conservação e reabilitação do património arquitetónico e na outra são apresentados os temas mais dedicados à acessibilidade do público ao património arquitetónico e à sua divulgação online. Os trabalhos apresentados no âmbito da conservação e reabilitação do património arquitetónico seguem na essência as recomendações do ICOMOS em relação à necessidade de compreensão da construção existente, ao desenvolvimento de novas técnicas e dos materiais mais adequados aos trabalhos de conservação e reabilitação, assim como na realização de testes em modelos experimentais à escala, tendo por objetivo avaliar o comportamento da estrutura antes e após a reabilitação. O património arquitetónico construído constitui uma parte importante da história da civilização humana e é um fator determinante da nossa identidade coletiva que importa preservar para as gerações futuras. Com a sua intervenção na conservação, reabilitação, valorização e divulgação do património construído, os autores deste livro estão a cumprir um importante papel na nossa sociedade, preservando um legado que nos foi deixado pelos nossos antepassados.

Reliability analysis: the next step towards recycled aggregates concrete affirmation, Pacheco, João, de Brito Jorge, Chastre Carlos, and Evangelista Luís , Construction projects: improvement strategies, quality management and potential challenges, p.1-54, (2017) Abstract

TThis chapter concerns the need to evaluate the reliability of structural elements produced with recycled aggregates concrete (RAC) in order to address some designers’ scepticism towards the use of this eco-friendly material. The current knowledge on RAC’s behaviour demonstrates its viability for structural purposes. However, of the investigations performed so far very few are related to a fundamental aspect towards RAC world-wide application as a structural material: structural codes have a probabilistic basis.After briefly presenting the state-of-the-art knowledge on the material properties and structural behaviour of RAC, the limitations of the current knowledge are debated. Afterwards, an introduction to structural codification is presented, as well as the fundamentals of reliability analysis. Examples of code verifications are contextualized with their underlying assumptions and the information necessary for code calibration is discussed. The role of reliability in the calibration of structural codes is shown, common techniques for reliability calculations are briefly explained, and relevant references in the area are cited for the readers’ perusal.Having established how structural codes are calibrated, the state-of-the-art on the probabilistic and statistical knowledge of RAC properties is reviewed. The implications of the very reduced number of studies on this area are discussed and the need to conduct further studies is emphasized.Afterwards, investigations that used reliability analysis to calibrate partial safety factors applicable to RAC are reviewed. The methodology of each investigation is presented, the experimental tests that led to the definition of the probabilistic information of the RAC’s parameters are described and the need to have a wide range of data coming from different RAC compositions and aggregate sources is debated.This chapter finishes by contextualizing the current knowledge on RAC properties with the necessary information for code calibration procedures. The relevance of a code proposal towards RAC affirmation as a structural material is highlighted, as well as the requirements of such code. Suggestions for future studies are made.

2016
Lateral cyclic behaviour of RC columns confined with carbon fibres, Faustino, Pedro, Frade Pedro, and Chastre Carlos , Structures, February 2016, Volume 5, p.196-206, (2016) AbstractWebsite

Reinforced concrete (RC) columns with various strengthening systems and different conditions were tested to cyclic lateral and axial loading for the purpose of performance assessment. Tests included confinement strengthening with carbon-fiber-reinforced polymer (CFRP) sheets, longitudinal strengthening with CFRP laminates and confining CFRP jacket, longitudinal strengthening with stainless steel bars and confining CFRP jacket, tested column until reinforcing steel failure, repair and CFRP confining jacket, and longitudinal strengthening with stainless steel bars. The analysis of the tests results as to load-displacement relationship and energy dissipation led to the conclusion that the use of external longitudinal strengthening with CFRP confinement is effective for performance retrofitting and upgrading, and viable in terms of execution. The load capacity increase due to strengthening reached 36–46% with good ductile behaviour. Nonlinear numerical modelling was carried out using two approaches which represent reasonably well the global performance of the studied columns for the prediction of the ascending load-displacement relationship and the peak load values in each cycle.

Analysis of the debonding process of CFRP-to-timber interfaces, Biscaia, Hugo C., Cruz David, and Chastre Carlos , Construction and Building Materials, 6/15/, Volume 113, p.96-112, (2016) AbstractWebsite

The use of Fiber Reinforced Polymers (FRP) in the strengthening of timber structures is quite recent and few studies have discussed the debonding between these materials. The analysis of the Mode II debonding process between FRP composites and timber elements may be of great importance because this mode is predominant in the case, for instance, of the bending of beams. Knowing the appropriate bond-slip model to use on the estimation of the performance of FRP-to-timber interfaces is greatly relevant. Under such circumstances, a detailed knowledge of all the states that CFRP-to-timber interfaces are subjected to is important as well. The current work gives answers to these aspects proposing an analytical solution based on a tri-linear bond-slip model that is capable of describing precisely the full-range debonding behavior of FRP-to-timber interfaces. Thus, the purpose of this study is to contribute to existing knowledge with an analytical solution capable of describing the full-range debonding process between a FRP composite and a substrate. The analytical solutions herein proposed are also compared with the results obtained from several experiments based on single-lap shear tests. Comparisons at different load levels and different bonded lengths are presented. The slips, strains in the CFRP composite and bond stress distributions within the bonded interface are emphasized in the text. The complete load-slip response of CFRP-to-timber interface is also analyzed. Each state of the debonding process is described and each one is identified in the load-slip curve.

Análise experimental de vigas de betão armado reforçadas à flexão com compósitos de FRP, Chastre, Carlos, Biscaia Hugo, Monteiro António, and Franco Noel , TEST&E 2016 - 1º Congresso de Ensaios e Experimentação em Engenharia Civil, 4-6 July 2016, IST, Lisbon, Portugal, p.8, (2016) Abstractteste2016_-_01066_-_chastre.pdf

O reforço das estruturas de betão armado com compósitos de FRP tem tido um incremento considerável nos últimos anos devido às características de durabilidade e das elevadas relações resistência-peso e rigidez-peso dos compósitos de FRP comparativamente com outros materiais de reforço. A fim de analisar o comportamento de diferentes soluções de reforço estrutural de vigas de betão armado (BA) com compósitos de FRP foi realizado um programa experimental que incluiu o ensaio de vigas de BA reforçadas com as seguintes técnicas de reforço: EBR (Externally-Bonded Reinforcement), NSM (Near Surface Mounted) e pela técnica CREatE (continuous reinforcement embedded at ends). As vigas de BA ensaiadas tinham seção em T, com um vão de 3,0 m e uma altura de 0,3 m e foram solicitadas em flexão em 4 pontos e testadas até a rotura. A técnica CREatE provou ser a mais eficaz das três alternativas testadas mobilizando a totalidade do CFRP e apresentando a maior capacidade resistente e a ductilidade mais elevada.

Análise experimental do comportamento à flexão de vigas de betão armado reforçadas com armaduras pós-instaladas de aço inoxidável, Franco, Noel, Chastre Carlos, and Biscaia Hugo , TEST&E 2016 - 1º Congresso de Ensaios e Experimentação em Engenharia Civil, 4-6 July 2016, IST, Lisbon, Portugal, p.8, (2016) Abstractteste2016_-_01067_-_noel.pdf

A procura de soluções de reforço mais eficientes que permitam aumentar a capacidade resistente de elementos estruturais sujeitos a flexão levou ao desenvolvimento de um sistema inovador de aplicação de armaduras de reforço coladas pelo exterior. Neste artigo descrevem-se os ensaios experimentais realizados e analisam-se os resultados obtidos com vigas de betão armado reforçadas com armaduras pós-instaladas de aço inoxidável com diferentes técnicas: Externally Bonded Reinforcement (EBR), Near Surface Mounted (NSM) e com o novo sistema de reforço desenvolvido - Continuous Reinforcement Embedded at Ends (CREatE). As vigas ensaiadas monotonicamente até à rotura em flexão de quatro pontos têm seção transversal em T e um vão livre de três metros. No novo sistema de reforço as armaduras são ancoradas por aderência no interior do elemento estrutural, o que associado à utilização de armaduras em aço inoxidável, possibilita aumentos de resistência e ductilidade consideráveis face às técnicas tradicionais de colagem pelo exterior.

Avaliação experimental de diferentes ligações coladas, Biscaia, Hugo, Chastre Carlos, Cruz David, Franco Noel, and Nunes Ricardo , TEST&E 2016 - 1º Congresso de Ensaios e Experimentação em Engenharia Civil, 4-6 July 2016, IST, Lisbon, Portugal, p.8, (2016) Abstractteste2016_-_01050_-_biscaia.pdf

A utilização de materiais compósitos de matriz polimérica (Fiber Reinforced Polymers - FRP) como armadura de reforço de diferentes elementos estruturas de várias naturezas (e.g. betão armado, aço, madeira ou alvenaria) tem vindo a suscitar o interesse da comunidade científica internacional. Inicialmente, a simples colagem pelo exterior dos compósitos de FRP aos elementos estruturais permitiu identificar um fenómeno de descolamento prematuro do compósito para níveis de extensão muito aquém dos seus limites de rotura. Com base na experimentação, algumas teorias têm surgido no sentido de explicar o fenómeno do descolamento prematuro dos FRPs. Por outro lado, outras técnicas de reforço têm sido propostas com o objetivo de adiar ou simplesmente eliminar esse fenómeno. Neste trabalho, são analisadas diferentes ligações coladas entre laminados de CFRP e outros materiais tais como, o betão armado, o aço e a madeira. Duas técnicas de reforço por colagem vulgarmente citadas na literatura internacional foram utilizadas: Externally Bonded Reinforcement (EBR) e Near Surface Mounted (NSM). Os resultados experimentais permitiram constatar que o desempenho local das ligações estudadas é distinto, tendo-se observado que as relações entre a tensão de aderência e o deslocamento relativo entre superfícies é: (i) na ligação CFRP/betão do tipo não linear e caracteriza-se por, após atingir-se uma tensão de aderência máxima, o descolamento ocorre quando a tensão de aderência tende para zero; (ii) na ligação CFRP/aço o desempenho é do tipo bi-linear, i.e. com um troço inicial retilíneo até atingir-se uma tensão de pico seguindo-se um troço linear descendente até tensão de aderência nula; e (iii) na ligação CFRP/madeira o desempenho é do tipo tri-linear, i.e. similar à ligação CFRP/aço mas com um troço constante a seguir ao troço linear descendente e que se esgota para um deslocamento relativo último.

Reforço à flexão de pavimentos antigos de madeira com recurso a laminados de fibras de carbono, Biscaia, Hugo, Chastre Carlos, Cruz David, Franco Noel, and Nunes Ricardo , TEST&E 2016 - 1º Congresso de Ensaios e Experimentação em Engenharia Civil, 4-6 July 2016, IST, Lisbon, Portugal, p.8, (2016) Abstractteste2016_-_01049_-_biscaia.pdf

O dimensionamento de vigas de madeira aos Estados Limites de Utilização (ELUt) tem limites muito apertados tanto para ações de curto prazo como para ações de longo prazo. Uma solução eficiente para este problema passa por aumentar as seções transversais das vigas. Porém, este tipo de solução não só acarreta um aumento de custos como também altera profundamente arquitetura original do edifício abrindo, por conseguinte, uma oportunidade para encontrar outras soluções mais eficientes. Neste sentido, o uso de armaduras de reforço em vigas de madeira pode ser considerado como uma solução promissora uma vez que as estruturas, novas ou velhas, manteriam o aspeto estético original sem introduzir nos elementos reforçados, um aumento significativo do seu peso próprio, melhorando o seu desempenho face a ações de curto e longo prazo. O presente estudo é dedicado à análise de vigas de madeira antigas reforçadas à flexão com materiais compósitos de fibras de carbono, vulgarmente designados na literatura internacional por Carbon Fiber Reinforced Polymers (CFRP). Neste trabalho, foram reforçados e ensaiados à flexão pavimentos antigos de madeira tendo-se analisado os respetivos desempenhos aquando da utilização de uma técnica de reforço por colagem tradicional (Externally Bonded Reinforcement - EBR) e aquando da utilização de uma técnica de reforço por colagem inovadora (Continous Reinforcement Embedded at Ends - CREatE). Os ensaios experimentais permitiram verificar que a técnica de colagem inovadora CREatE confere aos pavimentos de madeira uma maior rigidez e resistência face à técnica tradicional conseguindo se mobilizar a totalidade do compósito de CFRP.

Novo sistema de reforço à flexão de vigas de betão armado com armaduras de aço inoxidável aplicadas pelo exterior, Franco, Noel, Chastre Carlos, and Biscaia Hugo , II Encontro Luso-Brasileiro de Degradação de Estruturas de Betão, 27-29 September, LNEC, Lisbon, Portugal, p.12p., (2016) Abstractdegrada_2016_-_noel_franco_-_ext-abstract.pdf

O reforço à flexão de vigas de betão armado tem apresentado uma evolução com tendência para soluções onde são utilizadas armaduras à base de materiais compósitos de fibras de Carbono, Vidro, Basalto ou Aramida, aplicadas com as técnicas Externally Bonded Reinforcement (EBR) ou Near Surface Mounted (NSM). No entanto, o comportamento elástico-linear destes materiais e as roturas tendencialmente frágeis das soluções condicionam a sua utilização em estruturas onde se pretende alguma ductilidade. Por conseguinte, procurou-se desenvolver um sistema de reforço estrutural alternativo e inovador em que os materiais de reforço aplicados, conjuntamente com a solução de reforço, conseguissem minimizar ou eliminar os riscos de roturas prematuras e ao mesmo tempo aumentassem a ductilidade dos elementos reforçados. Neste trabalho, apresenta-se em pormenor este novo sistema de reforço à flexão de vigas de betão armado com armaduras de aço inoxidável ancoradas internamente por aderência. Neste sistema de reforço as armaduras são contínuas e pós-instaladas pelo exterior, ficando as extremidades ancoradas por aderência no interior do elemento estrutural. Apresentam-se e discutem-se os resultados dos ensaios realizados para avaliar o desempenho das vigas de betão armado reforçadas com esta nova técnica. Os modos de rotura observados são também motivo de análise mais detalhada. Evidenciam-se alguns benefícios na utilização deste sistema de reforço inovador, nomeadamente ao nível da capacidade resistente última das vigas de betão armado e fazem-se algumas recomendações para a sua aplicação e utilização na reabilitação de elementos estruturais degradados.

Novo sistema de reforço estrutural de vigas de betão armado com compósitos de FRP ancorados internamente por aderência, Chastre, Carlos, Monteiro António, Biscaia Hugo, and Franco Noel , II Encontro Luso-Brasileiro de Degradação de Estruturas de Betão, 27-29 September, LNEC, Lisbon, Portugal, p.12p., (2016) Abstractdegrada_2016_-_carlos_chastre_-_ext-abstract.pdf

A reabilitação de estruturas de betão armado com compósitos de FRP tem tido uma grande aceitação em especial devido às excelentes características de durabilidade dos materiais compósitos, ao seu baixo peso e às suas elevadas prestações mecânicas. Contudo, o comportamento elástico-linear dos compósitos de FRP e a sua forma de aplicação pode originar roturas prematuras, quer na técnica de reforço EBR (Externally Bonded Reinforcement), em que o compósito é colado externamente, quer na técnica NSM (Near Surface Mounted) em que o compósito é inserido na zona do recobrimento. No sentido de minimizar o risco de roturas prematuras e ao mesmo tempo aumentar a ductilidade dos elementos reforçados, desenvolveu-se um novo sistema de reforço estrutural em que as armaduras são ancoradas internamente por aderência. A fim de validar o novo sistema de reforço estrutural com compósitos de FRP foi realizado um programa experimental que incluiu o ensaio de vigas de betão armado (BA) reforçadas com as seguintes técnicas de reforço: EBR, NSM e pela nova técnica CREatE (continuous reinforcement embedded at ends). Neste artigo descrevem-se os ensaios experimentais realizados e analisam-se os resultados obtidos. As vigas de BA ensaiadas tinham seção em T, com um vão de 3,0 m e uma altura de 0,3 m e foram solicitadas em flexão em 4 pontos e testadas até a rotura. A técnica CREatE provou ser a mais eficaz das três alternativas testadas mobilizando a totalidade do CFRP e apresentando a maior capacidade resistente e a ductilidade mais elevada.

In-Plane Displacement and Strain Image Analysis, Almeida, Graça, Melício Fernando, Biscaia Hugo, Chastre Carlos, and Fonseca José Manuel , Computer-Aided Civil and Infrastructure Engineering, 24 February 2015, Volume 31, Number 4, p.292-304, (2016) AbstractWebsite

Measurements in civil engineering load tests usually require considerable time and complex procedures. Therefore, measurements are usually constrained by the number of sensors resulting in a restricted monitored area. Image processing analysis is an alternative way that enables the measurement of the complete area of interest with a simple and effective setup. In this article photo sequences taken during load displacement tests were captured by a digital camera and processed with image correlation algorithms. Three different image processing algorithms were used with real images taken from tests using specimens of PVC and Plexiglas. The data obtained from the image processing algorithms were also compared with the data from physical sensors. A complete displacement and strain map were obtained. Results show that the accuracy of the measurements obtained by photogrammetry is equivalent to that from the physical sensors but with much less equipment and fewer setup requirements.

Experimental Analysis of Column To Column Connections for Precast Concrete Truss, Souza, Sueli, Lúcio Válter, Chastre Carlos, Souza Luiz, and Martins David , fib Symposium 2016. Performance-based approaches for concrete structures, 21 – 23 November, Cape Town, South Africa, p.10p, (2016) Abstract

The wind energy production is a growing industry and the energy produced is renewable and environmentally cleaner than most of the other systems. The towers to support the wind energy generators may be built with precast concrete elements that are competitive in comparison to other structural systems. The evolution of the technology for wind energy production shows a clear need for larger wind turbines and longer blades and, consequently, taller towers, where precast concrete solutions are competitive. Truss precast concrete towers is a solution that complies with the demands of the present and future wind energy production. The research on the execution and structural behaviour of the connections between the tower elements is an important issue. This communication presents the experimental analysis of column to column connections for precast concrete towers. The tests included connections with commercial threaded bars welded to the rebars and connections with grouted corrugated steel sleeves. Thick joints (50 mm) filled with fibre reinforced grout and thin joints (3 mm) filled with epoxy resin were tested and analysed.

Flexural strengthening of columns with CFRP composites and stainless steel: Cyclic behavior, Faustino, Pedro, and Chastre Carlos , Journal of Structural Engineering, 21 September 201, Volume 142, Number 2, p.04015136, (2016) AbstractWebsite

This study presents the testing, completion, and analysis of different external strengthening systems applied to rectangular reinforced concrete columns with rounded corners. The experimental study included confinement strengthening with carbon-fiberreinforcedpolymer (CFRP) sheets, longitudinal strengthening with CFRP laminates and confining CFRP jacket, longitudinal strengtheningwith stainless steel bars and confining CFRP jacket, tested column until reinforcing steel failure, repair and CFRP confining jacket,and longitudinal strengthening with stainless steel bars. The analysis of the experimental results included lateral load-displacement relationship, energy dissipation, ductility, and curvature damage assessment classifications. It was concluded that the use of externallongitudinal strengthening combined with CFRP confinement is effective for enhancing performance and is viable in terms of execution. The load capacity increase due to strengthening reached 36–46% with good ductile behavior (failure was reached at 4.4% drift ratio). Despite some differences between CFRP laminates and stainless steel, all columns presented moderate degrees of damage between 1 and 2% drift ratio and minor damage degree until 1% drift ratio.

fib Bulletin 78. Precast-concrete buildings in seismic areas, Tsoukantas, Spyros, Toniolo Giandomenico, Pampanin Stefano, Ghosh S. K., Sennour Larbi, D’Arcy Thomas, Sthaladipti Saha, Menegotto Marco, Özden Şevket, Lúcio Válter, Chastre Carlos, Dritsos Stefanos, Psycharis Ioannis, Topintzis Tryfon, Kremmyda Georgia, Fernández-Ordóñez David, de Chefdebien André, Hughes Simon, and Rajala Lasse , fib bulletin, 2016, Number fib Bulletin 78, Lausanne, p.273, (2016) Abstractfib_bulletin78.jpgWebsite

This document has a broad scope and is not focussed on design issues. Precast construction under seismic conditions is treated as a whole. The main principles of seismic design of different structural systems, their behavior and their construction techniques are presented through rules, construction steps and sequences, procedures, and details that should lead to precast structures built in seismic areas complying with the fundamental performance requirements of collapse prevention and life safety in major earthquakes and limited damage in more frequent earthquakes.The content of this document is largely limited to conventional precast construction and, although some information is provided on the well-known “PRESSS technology” (jointed ductile dry connections), this latter solution is not treated in detail in this document.The general overview, contained in this document, of alternative structural systems and connection solutions available to achieve desired performance levels, intends to provide engineers, architects, clients, and end-users (in general) with a better appreciation of the wide range of applications that modern precast concrete technology can have in various types of construction from industrial to commercial as well as residential. Lastly, the emphasis on practical aspects, from conceptual design to connection detailing, aims to help engineers to move away from the habit of blindly following prescriptive codes in their design, but instead go back to basic principles, in order to achieve a more robust understanding, and thus control, of the seismic behaviour of the structural system as a whole, as well as of its components and individual connections.

Lifetime modelling of chloride induced corrosion in reinforced concrete structures with concrete with portland and blended cements, Faustino, Pedro, Chastre Carlos, Nunes Ângela, and Brás Ana , Structure and Infrastructure Engineering, 2016, Volume 12, Number 9, p.1013-1023, (2016) AbstractWebsite

This article discusses mathematical modelling of the long-term performance of concrete with different supplementary cementitious materials in a maritime environment. The research was carried out in the light of the national Portuguese application of the CEN standards with mandatory requirements for a performance-based design approach. Laboratory investigations were performed on concrete compositions based on CEM I and CEM II/B-L in which the cement was partially replaced by either 0% (reference composition) or 50% of low calcium fly ash (FA). Concrete compositions were made with the objective to achieve service lives of 50 and 100 years with regard to steel corrosion. Test results of compressive strength, chloride potential diffusion and electrical resistivity are reported for different curing ages of 28, 90, 180 and 365 days. Chloride diffusion results were used for the implementation of modelling equations in order to estimate the design lifetime regarding reinforcing steel corrosion. A performance-based approach using a probabilistic method was carried out and the results obtained are compared with the requirements according to the Portuguese prescriptive approach. The modelling results show that FA blended compositions have better performance compared to those with Portland cements, especially if curing ages beyond 28 days are considered.

Análise do desempenho da técnica CREatE para reforço à flexão de vigas de betão armado com armaduras de aço inoxidável, Franco, Noel, Chastre Carlos, and Biscaia Hugo , Encontro Nacional Betão Estrutural 2016, 2-4 November 201, FCTUC, Coimbra, Portugal, p.10, (2016) Abstractbe_2016_paper_74_noel__franco.pdf

Neste artigo apresentam-se as principais características da técnica de reforço Continuous Reinforcement Embedded at Ends (CREatE), os procedimentos de aplicação e as vantagens e limitações da sua utilização. Apresentam-se também os resultados dos ensaios realizados para avaliar o desempenho desta técnica no reforço à flexão de vigas de betão armado com secção transversal em T, reforçadas com armaduras pós-instaladas de aço inoxidável, coladas pelo exterior ou inseridas na zona de recobrimento. As vigas reforçadas com a técnica CREatE e ensaiadas à flexão em quatro prontos apresentaram elevados acréscimos de resistência e ductilidade quando comparadas com as vigas reforçadas com as técnicas tradicionais - Externally-Bonded Reinforcement (EBR) e Near Surface Mounted (NSM). As vigas reforçadas com a técnica CREatE foram sujeitas a carregamentos monotónicos ou cíclicos, tendo-se constatado que as roturas prematuras que estão associadas às técnicas tradicionais anteriormente referidas nunca foram observadas nas vigas reforças com esta técnica. Desenvolveu-se um modelo numérico simples, e com boa precisão, para modelar o desempenho das vigas de betão armado, sendo os resultados apresentados e discutidos.

Ligações em superfícies curvas entre compósitos de FRP e betão sujeitas a temperaturas elevadas, Biscaia, Hugo, Chastre Carlos, Silva Manuel, and Franco Noel , Encontro Nacional Betão Estrutural 2016, 2-4 November 201, FCTUC, Coimbra, Portugal, p.13, (2016) Abstractbe_2016_paper_109_biscaia.pdf

O reforço estrutural com materiais de matriz polimérica reforçada com fibras (FRP) em diferentes tipos de elementos estruturais, e.g. pilares, vigas, lajes ou arcos, tem sido objecto de vários estudos. No entanto, os estudos sobre a avaliação da aderência entre ligações coladas em superfícies curvas são muito limitados, não se conhecendo trabalhos, quer analíticos ou numéricos, que se debrucem ainda sobre o efeito da temperatura neste tipo de ligações coladas. Todavia, os trabalhos disponíveis na literatura indicam, de forma unânime, que o descolamento do FRP da superfície curva exige a interacção entre os modos de fractura I e II. Neste sentido, o presente estudo propõe o desenvolvimento de uma solução analítica simples para simular ligações CFRP/betão com superfícies curvas de raio constante e que assumem ambas, isoladamente ou simulataneamente, as acções: (i) aplicação de uma força ao FRP; e (ii) uma a variação de temperatura. Dependendo dos coeficientes de dilatação térmica linear dos materiais colados e para níveis de temperatura não muito superiores à temperatura de transição vítrea (Tg) do FRP, o efeito da temperatura pode ser, do ponto de vista da resistência da ligação, prejudicial ou benéfico, ou seja, pode diminir ou aumentar a capacidade resistente da ligação. Diferentes critérios de rotura são adoptados e diferentes situações, e.g. raio da curva ou diferentes níveis de temperaturas, são abordadas. A solução analítica pressupõe que a lei de aderência relativamente ao modo II de fractura depende da temperatura e é representada por um exponencial, enquanto que para o modo I se assume uma lei de aderência do tipo linear com rotura frágil e cuja influência da temperatura é feita de acordo com os mesmos pressupostos da lei exponencial.

Modelo analítico não linear para analisar as ligações CFRP/betão, Biscaia, Hugo, Chastre Carlos, Franco Noel, and Cardoso João , Encontro Nacional Betão Estrutural 2016, 2-4 November 201, FCTUC, Coimbra, Portugal, p.9, (2016) Abstractbe_2016_paper_108_biscaia.pdf

Desde que o reforço estrutural começou a utilizar materiais de matriz polimérica reforçada com fibras (FRP) que o fenómeno do descolamento prematuro dos compósitos de FRP da superfície colada tem merecido especial atenção de vários autores. O conhecimento do processo de descolamento completo da ligação CFRP/betão ganhou assim, algum destaque nos últimos anos. Na generalidade, as ligações CFRP/betão têm sido analisadas com recurso métodos analíticos e numéricos sendo que, nos primeiros, se tem vindo a adoptar leis de aderência muito simplificadas das observadas experimentalmente. Apesar das simplificações adoptas nas análises analíticas, as expressões obtidas são muito importantes já que têm grande potencial em serem adoptadas pelos códigos ou normas nacionais e/ou interncionais. Por outro lado, e apesar de adoptarem leis de aderência mais refinadas, as análises numéricas permitem apenas a obtenção de expressões empíricas que podem não contemplar a generalidade dos casos estudados. Neste sentido, este trabalho apresenta um conjunto de soluções analíticas com base numa lei de aderência exponencial capaz de representar todas as não-linearidades envolvidas no descolamento da ligação CFRP/betão. Os resultados analíticos são confrontados com ensaios experimentais em que a técnica de colagem EBR foi utilizada. Contudo, o modelo analítico proposto pode ser também utilizado quando a técnica Near Surface Mounted (NSM) é adoptada. Adicionalmente, são apresentadas soluções analíticas para o caso em que o deslocamento relativo entre o CFRP e o betão é restringido por, e.g., um dispositivo de amarração mecânica instalado na extremidade oposta à aplicação de carga.

A Nonlinear Analytical model to predict The full-range debonding process of FRP-to-parent material interfaces free of any mechanical anchorage devices, Biscaia, Hugo C., Borba Isabel S., Silva Cinderela, and Chastre Carlos , Composite Structures, 15 March 2016, Volume 138, p.52-63, (2016) AbstractWebsite

Ever since Fibre Reinforced Polymers (FRP) began to be used in the repair or strengthening of structural elements, the premature debonding of the FRP composite from the substrate has been an important drawback that have been motive of several studies. The importance of knowing and describing the full-range behaviour of FRP-to-parent material interfaces rigorously is therefore urgent. However, at present, there are no analytical solutions that describe the full-range behaviour of such interfaces that help us to understand the full debonding phenomena of FRP-to-parent material interfaces free of any mechanical anchorage devices. Therefore, the aim of this study is to contribute the advances of that knowledge through an analytical solution by means of an exponential bond-slip model that is known to represent the nonlinearities involved in the debonding process of the FRP composite from the substrate. Analytical solutions for the slips, strains in the FRP composite, bond stress distributions along the bonded interface and stresses in the substrate are presented. A full-range load-slip analysis is also discussed.

Durability Assessment of Consolidation Effect on Sandstone Monuments, Ludovico-Marques, Marco, and Chastre Carlos , 41th IAHS Word Congress of Housing. Sustainability and Innovation for the Future, 13-16 September , Albufeira, Portugal, p.10p, (2016) Abstract41_iahs_2016_-_marco_marques_-_ext-abstract_durability_assessment_of_consolidation_effect_on_sandstone_monuments_ludovico_marques__chastre.pdf

The façades of St. Leonard’s church and the castle in Atouguia da Baleia village in western region of Portugal are monuments built in Middle Ages. Significant stone degradation patterns are visible, being the alveolization an outstanding case study.The more porous type of sandstones similar to the variety found in the vernacular architecture of Atouguia da Baleia was treated with ethyl silicates. In order to allow the study of the durability of these conservation treatments, accelerated artificial ageing salt crystallization tests were carried out and an automatic ageing chamber was developed.Physical and mechanical behaviour was assessed on consolidated specimens before and after accelerated artificial ageing salt crystallization tests. The authors propose a prediction of the durability of these consolidation treatments by means of the salt crystallization ageing results.

Experimental Analysis of Reinforced Concrete Beams Strengthened with Innovative Techniques, Chastre, Carlos, Biscaia Hugo, Franco Noel, and Monteiro António , 41th IAHS Word Congress of Housing. Sustainability and Innovation for the Future, 13-16 September , Albufeira, Portugal, p.10, (2016) Abstract41_iahs_2016_-_carlos_chastre-ext-abstract.pdf

The strengthening of reinforced concrete structures with FRP materials has received a considerable increment in recent years due to their durability characteristics, high strength-weight and stiffness-weight ratios of FRP compared to other materials.An experimental program was conducted in order to analyse the behaviour of different structural solutions to strengthen reinforced concrete beams with carbon FRP composites: EBR (Externally-Bonded Reinforcement), NSM (Near Surface Mounted) reinforcement and an innovative technique externally-bonded using continuous reinforcement embedded at ends (CREatE). The RC beams had a 3m span by 0.3m height and were tested until rupture in a 4-point bending test system.The CREatE technique has proved to be the most effective of the three alternatives tested, with the full utilisation of the CFRP and the highest strength, combined with the highest ductility.

A New Bonding Technique for the Rehabilitation of Old Timber Floors with CFRP Composites, Biscaia, Hugo, Chastre Carlos, Cruz David, and Franco Noel , 41th IAHS Word Congress of Housing. Sustainability and Innovation for the Future, 13-16 September , Albufeira, Portugal, p.10, (2016) Abstract41_iahs_2016_-_hugo_biscaia_-_ext-abstract.pdf

Despite the number of applications with Carbon Fiber Reinforced Polymers (CFRP) have been grown in civil constructions, the studies available in the literature dedicated to the strengthening of old timber beams are very rare. This paper analyses the bending behaviour of old suspended timber floors flexurally-strengthened with CFRP laminates. A new bonding technique developed by the authors is presented which mainly consists on the embedding of both CFRP ends into the core of the timber beams. Differences between the traditional strengthening, i.e. Externally Bonded Reinforcement (EBR), and the new bonding technique are reported. A timber pavement without any CFRP laminate bonded to its soffit was also considered and the results were used as reference values for comparison with the strengthened specimens. The results revealed that the CFRP laminate used for the flexurally-strengthened of the specimen according to the EBR technique reached only 27.2% of the rupture strain of the CFRP laminate whereas the new bonding technique was capable to prevent the premature debonding of the CFRP from the timber substrate and the rupture of the CFRP laminate was observed. Furthermore, the strain distributions in the CFRP laminates and the bond stresses within the CFRP-to-timber interfaces were affected when the new technique was used. For the sake of better understanding the rupture modes observed, a numerical approach was developed which allowed us to conclude that, until the collapse of the beams, the timber never reached its yielding point and the collapse were mainly due to the poor quality of the timber (e.g. quantity of knot, cracks and irregular geometries) and the low shear capacity of the beams.

Avaliação dos Portais da Igreja de São Leonardo na Atouguia da Baleia Utilizando Testes Não Destrutivos, Chastre, Carlos, and Ludovico-Marques Marco , 10º Congresso de Mecânica Experimental (CNME 2016), 12-14 October 20, LNEC, Lisbon, Portugal, p.12, (2016) Abstractcnme2016_paper_51_chastre.pdf

Neste artigo é apresentado um resumo das intervenções de conservação realizadas no século passado na Igreja de São Leonardo, bem como um resumo dos estudos realizados na última década. Em seguida mostra-se o padrão de degradação que ocorre nos portais de arenito da igreja e é analisada a evolução da alveolização que ocorreu nos portais de arenito ao longo dos últimos sessenta a setenta anos. No final, a inspeção visual dos portais de arenito é comparada com um levantamento realizado através de varrimento por laser tridimensional.

Reforço de Vigas de Betão Armado com Armaduras Pós-Instaladas de Aço ou de FRP, Chastre, Carlos, Biscaia Hugo, and Franco Noel , 10º Congresso de Mecânica Experimental (CNME 2016), 12-14 October 20, LNEC, Lisbon, Portugal, p.12, (2016) Abstractcnme2016_paper_45_chastre.pdf

Apresentam-se e analisam-se um conjunto de ensaios realizados em vigas de betão armado reforçadas com armaduras pós-instaladas de aço ou de FRP, incluindo os referentes a uma nova técnica (CREatE) desenvolvida na FCT NOVA, tendo-se concluído que a técnica CREatE possibilita aumentos de resistência e ductilidade consideráveis face às técnicas tradicionais.

Damage Effect on Concrete Columns Confined with Carbon Composites, Faustino, Pedro, and Chastre Carlos , ACI Structural Journal, Volume 113, Number 4, (2016) AbstractWebsite

Five experimental cyclic tests were carried out on reinforced concrete rectangular columns with rounded corners, different condition (new and damaged) and different strengthening systems: that included confinement through carbon fiber (CFRP) jackets, anchor dowels, high strength repair mortar and external longitudinal stainless steel bars. Lateral load - displacement relationship, energy dissipation, ductility and curvature results were analyzed together with two different damage assessment classifications. The overall evaluation concludes that the use of external confinement with CFRP on RC columns is viable and of effective performance enhancement alone and combined with other techniques. Damaged columns that were retrofitted showed an increased load capacity up to 20% along with good ductile behavior within the limits of the US, European, Canadian and Japanese codes, with minor/moderate degree of damage at 1% drift ratio and moderate degree of damage at 2% drift ratio.

Effect of Artificial Accelerated Salt Weathering on Physical and Mechanical Behavior of Sandstone Samples from Surface Reservoirs, Ludovico-Marques, Marco, and Chastre Carlos , Handbook of Materials Failure Analysis With Case Studies from the Oil and Gas Industry, p.215-233, (2016) Abstract

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Experimental evaluation of bonding between CFRP laminates and different structural materials, Biscaia, Hugo, Chastre Carlos, Borba Isabel, Silva Cinderela, and Cruz David , Journal of Composites for Construction, Volume 20, Number 3, p.04015070, (2016) AbstractWebsite

This study presents an analysis of Carbon Fiber Reinforced Polymers (CFRP)-to-parent material interfaces based on 40 single-lap shear tests intended to highlight the strength of the interfaces under fracture mode II. Three different substrates are analyzed: timber;concrete and steel, using the same CFRP laminates and adhesive agent. The Externally Bonded Reinforcement (EBR) technique was used throughout the study. The results show that the CFRP-to-timber interfaces had the highest strength but also showed that these interfaces need a longer bonded length in order to reach maximum strength, i.e., CFRP-to-timber interfaces had the longest effective bond length. The local non-linear bond-slip curve of CFRP-to-concrete can be approximated to exponential curves, whereas the CFRP-to-timber or steel interfaces showed tri-linear and bi-linear bond-slip relations, respectively. Also, the CFRP-to-timber interfaces revealed the highest fracture energy.

Flexural Strengthening of Old Timber Floors with Laminated Carbon Fiber Reinforced Polymers, Biscaia, Hugo, Chastre Carlos, Cruz David, and Franco Noel , Journal of Composites for Construction, p.04016073, (2016) AbstractWebsite

A set of three old suspended timber floors were flexurally-strengthened with Carbon Fiber Reinforced Polymers (CFRP) strips in order to investigate the effectiveness of externally bonding FRP to their soffits. The specimens were from an old building and 740 mm-wide bands were transferred to the laboratory in order to be tested in a 4-point bending test. One specimen was tested with no strengthening system and the results obtained were used as reference values for comparison with the specimens those were externally bonded and reinforced (EBR) with CFRP strips. Two similar EBR systems were studied: (i) keeping both ends of the CFRP strips free of any restriction (traditional technique); and (ii) embedding both ends of the CFRP strips into the timber, thus providing a bonding anchorage of the strips (new technique). The installation of the new strengthening system comprises the opening of holes in the timber and the creation of a transition curve between the holes and the timber surface. This transition curve allows a smooth transition of the CFRP laminate between the hole and the timber surface, thus avoiding stress concentrations in this area. After the opening of the holes, the resin is applied inside the hole and on the beam surface, and then the CFRP laminate is mounted. The load-carrying capacity of the specimens, the rupture modes, the strains and bond stress distributions within the CFRP-to-timber interface are presented. A nonlinear numerical simulation of the specimens based on the mid-span cross-sectional equilibrium is also presented. The results showed that the use of the new strengthening system enhances the performance of the specimens when compared with the traditional strengthening system.

Influence of external compressive stresses on the performance of GFRP-to-concrete interfaces subjected to aggressive environments: An experimental analysis, Biscaia, Hugo, Silva Manuel A. G., and Chastre Carlos , Journal of Composites for Construction , Volume 20, Issue 2, p.04015044, (2016) AbstractWebsite

Despite the fact that FRP composites are a reliable structural material with reasonable durability performance, the environment to which the strengthened structure is exposed can make the strengthening system vulnerable. In this study, the effectiveness of Externally Bonded Reinforcement (EBR) systems when external compressive stresses are applied to glass (G) FRP-to-concrete interfaces in several aggressive environments is analysed. The compressive stress imposed on the GFRP-to-concrete interface intends to simulate, for instance, the effect produced by a mechanical anchorage system applied to the EBR system. The design and the region to set those mechanical anchorage systems are not yet well understood and are mostly applied without really knowing how they will behave. This work shows an exhaustive experimental programme based on several double shear tests subjected to salt fog cycles, dry/wet cycles and two distinct temperature cycles: from -10ºC to +30ºC and +7.5ºC to +47.5ºC. The Mohr-Coulomb failure criterion was found to provide a good representation of the performance of the GFRP-to-concrete interface, and changes of cohesion and internal friction angle of those interfaces during the hours of exposure to the aggressive environments are reported.

Old suspended timber floors flexurally-strengthened with different structural materials, Biscaia, Hugo, Franco Noel, Nunes Ricardo, and Chastre Carlos , Key Engineering Materials, Volume 713, p.78-81, (2016) Abstract

The design of timber beams has strict limits when it comes to the Serviceability Limit States (SLS) either in short-term or in long-term deflections. In order to face this aspect efficiently, the increase of the cross section of the beams might be considered as a solution. However, the prohibitive increase of the costs associated to this solution or the change of the initial architecturedesign of the building, opens the opportunity to find new and more efficient solutions. In that way, the use of additional reinforcements to the timber beams may be seen as a promising solution because either new or old structures would keep always their original aesthetical aspect with no significant self-weight increase and improving their behaviour to short and long-term actions.Therefore, the current study is dedicated to the analysis of composite timber beams where Fiber Reinforcement Polymers (FRP), steel or stainless steel are used to improve the stiffness, strength and deflection behaviour of old suspended timber floors. An experimental program was conducted where old suspended timber floors reinforced with CFRP strips were subjected to 4-point bending tests. A simplify nonlinear numerical model was developed to simulate the bending behaviour of the specimens and several other cases with other reinforcement configurations and different structural materials were assumed. The numerical analysis herein presented also takes into account both Ultimate and Serviceability Limit States of the reinforced specimens.

Old suspended timber floors flexurally-strengthened with different structural materials, Biscaia, Hugo, Franco Noel, Nunes Ricardo, and Chastre Carlos , 15th International Conference on Fracture and Damage Mechanics, Alicante, Spain, (2016) Abstract

The design of timber beams has strict limits when it comes to the Serviceability Limit States (SLS) either in short-term or in long-term deflections. In order to face this aspect efficiently, the increase of the cross section of the beams might be considered as a solution. However, the prohibitive increase of the costs associated to this solution or the change of the initial architecturedesign of the building, opens the opportunity to find new and more efficient solutions. In that way, the use of additional reinforcements to the timber beams may be seen as a promising solution because either new or old structures would keep always their original aesthetical aspect with no significant self-weight increase and improving their behaviour to short and long-term actions.Therefore, the current study is dedicated to the analysis of composite timber beams where Fiber Reinforcement Polymers (FRP), steel or stainless steel are used to improve the stiffness, strength and deflection behaviour of old suspended timber floors. An experimental program was conducted where old suspended timber floors reinforced with CFRP strips were subjected to 4-point bending tests. A simplify nonlinear numerical model was developed to simulate the bending behaviour of the specimens and several other cases with other reinforcement configurations and different structural materials were assumed. The numerical analysis herein presented also takes into account both Ultimate and Serviceability Limit States of the reinforced specimens.

2015
Analysis of load–strain models for RC square columns confined with CFRP, Faustino, Pedro, and Chastre Carlos , Composites Part B: Engineering, June 2015, Volume 74, p.23-41, (2015) AbstractWebsite

This article presents the comparison between 6 theoretical models of axially confined concrete columns with the experimental results of 7 tested columns of different authors. This study analysed the accuracy of 6 different confinement models for square columns taking into account the results of experimental tests on 7 RC columns confined with CFRP sheets with different dimensions and carried out by different authors. The profile of curves, the peak/failure values, the stress–strain and axial–to–lateral relations were studied to conclude which models show the best correlation with the experimental test results. Quantification of this deviation was carried out for key parameters. Some models predicted peak values with reasonable accuracy – Manfredi & Realfonzo, Campione & Miraglia, Lam & Teng, Pellegrino & Modena – although for the whole load–strain behaviour only the model of Faustino, Chastre & Paula seemed to be reasonably accurate in most cases.

A new discrete method to model unidirectional FRP-to-parent material bonded joints subjected to mechanical loads, Biscaia, Hugo C., Chastre Carlos, and Viegas André , Composite Structures, 3//, Volume 121, p.280-295, (2015) AbstractWebsite

Nowadays fiber reinforced polymer (FRP) composites play an important role in the strengthening of structures. Different methods can be used to apply these materials: the externally bonded reinforcement (EBR), and the near surface mounted (NSM) using strips and NSM rods. There are only a few studies comparing these methods or presenting an efficient model to simulate these strengthening techniques. This study looks mainly at the analysis of the interface between FRP-to-parent material bonded joints. The paper examines, through a new discrete model based on axial and shear springs, the performance of FRP-to-parent material bonded joints for EBR or NSM techniques using strips or composite rods. In order to implement the model a routine in MATLAB was developed and several bond–slip curves were assumed. The results revealed that load–slip curves or bond stresses, strains or slippages along the bonded length obtained from several bond–slip curves are similar to the analytical and other numerical solutions found in literature. In what concerns the adhesion between two different materials, and assuming the same bond characteristics for the three fiber strengthening techniques, the NSM system using FRP strips had the highest maximum load transmitted to the FRP strip combined with the lowest effective bond length. The results obtained from the proposed model were also very accurate with that obtained from an analytical solution found in literature that simulates the debonding phenomenon of FRP-to-concrete interfaces between to adjacent cracks.

Comportamento Dinâmico de Torres Treliçadas em Concreto Armado para Turbinas Eólicas Offshore, Souza, Luiz A. S., Chastre Carlos, LUCIO Válter J. G., and Souza Sueli T. M. , Congresso de Métodos Numéricos em Engenharia, 29 de Junho a 2 , Lisboa, Portugal, p.18, (2015) Abstractsouza2015chlusu.pdf

A demanda de energia, faz com que o homem esteja sempre a procura de novas soluções para a sua produção. Uma opção é a energia eólica, por se tratar de uma energia limpa, renovável e inesgotável. Para se evitar a ocupação das terras férteis, é natural a busca de soluções no mar. Portanto, neste trabalho é estudado o comportamento estrutural dinâmico de uma torre treliçada em concreto armado pós-tensionado por tirantes externos idealizada para uso offshore com a finalidade de suporte para turbinas eólicas de eixo horizontal. A torre está sujeita às ações gravitacionais, aerodinâmicas e hidrodinâmicas. Para considerar estas ações desenvolveu-se um código computacional específico usando a linguagem MATLAB. É proposto um modelo simplificado para análise bi-dimensional, utilizando-se elementos de pórtico plano com a finalidade de contornar as dificuldades de uma análise tridimensional. Embora específico para este tipo de torre, o codigo permite variar geometrias, carregamentos e alterações do nível do mar. Nas cargas aerodinâmicas élevado em conta o espectro de Von Karman. As cargas hidrodinâmicas são avaliadas pela equação de Morison. As cargas nodais equivalentes são determinadas por integração ao longo do elemento estrutural de acordo com o proposto por Souza. Os tirantes pós-tensionados são monitorados para não sofrerem esforços de compressão. A análise é realizada no domínio do tempo utilizando-se o algoritmo de integração de Newmark.. Através dos procedimentos adotados foi possível obter resultados para as freqüências, deslocamentose esforços, que se mostraram coerentes com os obtidos por modelos tri dimensionais mais complexos. O código desenvolvido permitiu a análise de forma simples, eficiente e confiável de torres treliçadas de concreto armado.

Modelo simplificado para análise do comportamento dinâmico de torres treliçadas em concreto armado para turbinas eólicas offshore, Souza, Luiz A. S., Chastre Carlos, LUCIO Válter J. G., and Souza Sueli T. M. , CILAMCE 2015 - XXXVI Ibero-Latin American Congress on Computational Methods in Engineering, 22-25 Nov, Rio de Janeiro, Brasil, p.16p, (2015) Abstractsouza2015chlusu-cilamce2015paper327.pdf

Este trabalho apresenta o desenvolvimento de um software para análise de torres treliçadas em concreto armado, pós-tensionada por tirantes externos, com a finalidade de suporte para turbinas eólicas de eixo horizontal, em ambiente offshore. A torre está sujeita às ações gravitacionais, aerodinâmicas, hidrodinâmicas. Desenvolveu-se um código computacional, em linguagem MATLAB, específico para este tipo de torre. As dificuldades de uma análise tridimensional mais complexa foram reduzidas propondo-se um modelo simplificado bi-dimensional utilizando-se elementos de pórtico plano. As cargas de vento são variadas segundo o espectro de von Karman. Para as ondas marítimas e correntes são implementados o espectro de Pierson-Moskowitz e o de JONSWAP. As cargas hidrodinâmicas são avaliadas pela equação de Morison. Estas cargas são integradas ao longo dos elementos estruturais e transformadas em cargas nodais equivalentes, de acordo com o proposto por Souza. A análise é realizada no domínio do tempo com algoritmo de Newmark. Este software, por ser específico para este tipo de torre, possui facilidades na introdução de dados e na modelagem da estrutura. Com estas estratégias o modelo apresentou bons resultados para a avaliação de cargas, cálculo de freqüências naturais, resposta de deslocamentos, esforços e reações.

Factors influencing the performance of externally bonded reinforcement systems of GFRP-to-concrete interfaces, Biscaia, Hugo C., Silva Manuel A. G., and Chastre Carlos , Materials and Structures, 2014/06/29, Volume 48, Issue 9, p.2961-2981, (2015) AbstractWebsite

Fibre reinforced polymer (FRP) composites may prematurely debond from the surface of concrete, i.e. before its elastic resistance is exhausted. This is a very common situation and can be aggravated if additional factors are not taken into account. These factors include the type of surface preparation, the exposure to aggressive environmental action, the tensile concrete strength or fatigue and creep loading to which the structural element may be subject. An experimental programme based on double shear tests was undertaken to analyse the influence of some of these factors on the performance of the interface between composite glass fibres (GFRP) and concrete. The results allowed the determination and comparison of maximum loads transmitted to the GFRP plates and maximum bond stresses obtained considering various surface treatments and aging conditions. Bond–slip curves were also determined. The experimental results are compared with those obtained from a numerical analysis.

Visão Integrada da Reabilitação, Faria, Paulina, and Chastre Carlos , Paredes 2015. Reabilitação e Inovação., 18 de Junho 2015, Lisboa, p.1-20, (2015) Abstractpaulina_faria_e_carlos_chastre_-_visao_integrada_da_reabilitacao.pdf

A reabilitação de um edifício tem muitas vezes de ser analisada e efetuada tendo em conta os edifícios vizinhos e a envolvente. No caso particular da reabilitação de um edifício, à partida devem considerar-se, de forma integrada, todos os requisitos que não são cumpridos face aos padrões atuais. Com base nessa análise, e tendo em conta muitas vezes condicionantes vários, que vão desde estéticos, técnicos, culturais a económicos, e que dependem em larga medida das tipologias construtivas, a intervenção tem de ser cuidadosamente concebida, preparada e executada. Apresentam-se sinteticamente as tipologias construtivas mais correntes, o contexto legislativo português da construção e específico da reabilitação. Efetua-se uma análise à legislação vigente, detalhando com maior detalhe o Regime Especial da Reabilitação Urbana, que possibilita dispensas de cumprimentos regulamentares mas apenas relativos a aspetos construtivos. Por esse motivo apresenta-se também uma síntese de aspetos relativos à segurança estrutural na reabilitação de edifícios com tipologias correntes. Pretende-se, através desta síntese, contribuir para uma visão mais integrada da reabilitação.

Bond-slip model for FRP-to-concrete bonded joints under external compression, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Composites Part B: Engineering, 10//, Volume 80, p.246-259, (2015) AbstractWebsite

The influence of compressive stresses exerted on FRP-concrete joints created by external strengthening of structural members on the performance of the system requires better understanding especially when mechanical devices are used to anchor the externally bonded reinforcement (EBR). The numerical modelling of those systems is a tool that permits insight into the performance of the corresponding interfaces and was used in the present study, essentially directed to analyse the effectiveness of EBR systems under compressive stresses normal to the composite surface applied to GFRP-to-concrete interfaces. The compressive stresses imposed on the GFRP-to-concrete interface model the effect produced by a mechanical anchorage system applied to the EBR system. An experimental program is described on which double-lap shear tests were performed that created normal stresses externally applied on the GFRP plates. A corresponding bond-slip model is proposed and the results of its introduction in the numerical analysis based in an available 3D finite element code are displayed, showing satisfactory agreement with the experimental data. The results also showed that lateral compressive stresses tend to increase the maximum bond stress of the interface and also originate a residual bond stress which has significant influence on the interface strength. Also, the strength of the interface increases with the increase of the bonded length which have consequences on the definition of the effective bond length.

Numerical modelling of the effects of elevated service temperatures on the debonding process of frp-to-concrete bonded joints, Biscaia, Hugo C., Chastre Carlos, Viegas André, and Franco Noel , Composites Part B: Engineering, Volume 70, p.64-79, (2015) AbstractWebsite

There are many issues concerning the performance behaviour of FRP-to-concrete interfaces at elevated service temperatures (EST). At EST, i.e. slightly above the glass transition temperature (Tg), some properties associated with the FRP composites, such as the stiffness, strength or the bond characteristics, degrade. This is a crucial issue and there are only a few studies that take into account such effects on FRP-to-concrete interfaces at EST. This paper examines, through a numerical analysis, the performance of FRP-to-concrete bonded joints at EST using a new discrete model based on truss elements and shear springs. The External Bonded Reinforcement (EBR) systems subjected to EST are analyzed. The numerical discrete model was implemented in a MATLAB routine and the bond-slip curves of the interfaces at EST were obtained from a model found in literature. The numerical results revealed that the interface at EST behaves similarly to one with two equal mechanical loads applied at both ends of the FRP plate. The load-slip curves or bond stresses, strains or slippages along the bonded length obtained from several bond-slip curves at different temperatures were obtained. Two different single-lap shear tests were simulated at steady-state (steady temperature followed by load increase) and transient state (steady load followed by temperature increase). Regarding the influence of the temperature on the adhesion between the FRP and concrete, the results showed that an increase in the temperature at an earlier situation, i.e. during a period where temperature had no influence in the concrete deformations, leads to an increase in the effective bond length of the interface affecting the initial strength of the interface.

2014
Precast concrete wind tower structures. Historic development, current development and future potential, Lúcio, Válter, and Chastre Carlos , CPI - Concrete Plant International, 3, June 2014, Number 3, p.110-115, (2014) Abstractcpi_03-2014_p144-149.pdfWebsite

The wind energy production is a growing industry and the energy produced is renewable and environmentally cleaner than most of the energy production systems. The supports of the wind energy generators may be built with precast concrete elements. The precast solutions for these structures are competitive in comparison to other structural systems. The evolution of the technology for wind energy production shows a clear need for larger wind turbines and longer blades and, consequently, taller towers. The experience also shows that precast concrete solutions increase their competitiveness as the tower height increases. Offshore wind farms have some advantages in relation to onshore ones, which explains recent investments in this area. Also in this case, the durability of concrete in the sea when compared to steel, gives advantages to precast concrete in relation to other structural solutions. This paper shows the evolution of the supports of the wind energy generators and the advantages of the use of precast concrete towers.

An experimental study of GFRP-to-concrete interfaces submitted to humidity cycles, Biscaia, Hugo C., Silva Manuel A. G., and Chastre Carlos , Composite Structures, 4//, Volume 110, Issue April, p.354-368, (2014) AbstractWebsite

Systems externally reinforced by bonded fibre reinforced polymers (FRP) are widely used in the retrofitting and strengthening of reinforced concrete (RC) structures. A drawback of the usage of this technique lies on the uncertainty of the long term behaviour of those reinforcements. Researchers have paid heed to this aspect and a number of tests and alternative techniques have recently been described. An experimental programme developed to supplement work of the authors recently published and which focused on specimens not submitted to aggressive environments is described. The specimens used have the same geometry as in the previous paper, but they were exposed to salt fog cycles and dry/wet cycles with salt water for periods of 3000 h, 5000 h and 10,000 h. The interface of the glass fiber polymeric composite (GFRP)-to-concrete was characterized after the systems underwent such aggressive conditions. The GFRP wrap comprised of two layers and wet lay-up technique was used on its preparation and application. The cohesion and friction angle for GFRP-to-concrete interfaces were measured tat selected stages of ageing process and envelope failure laws were obtained based on the Mohr–Coulomb failure criterion. Changes of 27% in cohesion and 8% in the friction angle were found due to the attack of the interface and consequences of the changes are examined.

fib Bulletin 74. Planning and design handbook on precast building structures, Acker, Arnold Van, Chastre Carlos, Crisp Barry, Fernandez David, Lúcio Válter, Elliott Kim S., Hughes Simon, Jones George, Karutz Holger, Klein-Holte Ronald, Maas Stef, Menegotto Marco, Tsoukantas Spyros, and van der Zee Pieter , fib bulletin, 2014, Number fib Bulletin 74, Lausanne, p.313, (2014) AbstractWebsite

In 1994 fib Commission 6: Prefabrication edited a successful Planning and Design Handbook that ran to approximately 45,000 copies and was published in Spanish and German.Nearly 20 years later Bulletin 74 brings that first publication up to date. It offers a synthesis of the latest structural design knowledge about precast building structures against the background of 21st century technological innovations in materials, production and construction. With it, we hope to help architects and engineers achieve a full understanding of precast concrete building structures, the possibilities they offer and their specific design philosophy. It was principally written for non-seismic structures.

The handbook contains eleven chapters, each dealing with a specific aspect of precast building structures.
The first chapter of the handbook highlights best practice opportunities that will enable architects, design engineers and contractors to work together towards finding efficient solutions, which is something unique to precast concrete buildings.
The second chapter offers basic design recommendations that take into account the possibilities, restrictions and advantages of precast concrete, along with its detailing, manufacture, transport, erection and serviceability stages.
Chapter three describes the precast solutions for the most common types of buildings such as offices, sports stadiums, residential buildings, hotels, industrial warehouses and car parks. Different application possibilities are explored to teach us which types of precast units are commonly used in all those situations.
Chapter four covers the basic design principles and systems related to stability. Precast concrete structures should be designed according to a specific stability concept, unlike cast in-situ structures.
Chapter five discusses structural connections.
Chapters six to nine address the four most commonly used systems or subsystems of precast concrete in buildings, namely, portal and skeletal structures, wall-frame structures, floor and roof structures and architectural concrete facades.
In chapter ten the design and detailing of a number of specific construction details in precast elements are discussed, for example, supports, corbels, openings and cutouts in the units, special features related to the detailing of the reinforcement, and so forth.
Chapter eleven gives guidelines for the fire design of precast concrete structures. The handbook concludes with a list of references to good literature on precast concrete construction.

Materiais e tecnologias de reforço de estruturas de betão - potencialidade e limitações, Chastre, Carlos , REHABEND 2014 - Congresso Latinoamericano "Patología de la construcción, Tecnología de la rehabilitacíon y gestión del patrimonio"., 2014, Santander, (2014) Abstractcarlos_chastre__-_rehabend2014_-_santander.pdf

O desenvolvimento da engenharia de estruturas tem tido grandes avanços nas últimas décadas, baseados em novos meios de cálculo e na investigação em novos materiais e tecnologias a eles associadas. Por sua vez, as atividades de reparação e reforço têm vindo a incrementar devido ao envelhecimento e à degradação das estruturas de betão, o que consequentemente tem dado origem ao aparecimento de novos materiais e tecnologias de reparação e reforço de estruturas. A utilização destes novos materiais na construção tem vindo a substituir outros materiais e técnicas existentes, requerendo, no entanto, mais estudos sobre o seu real comportamento quer em termos de caracteristicas mecânicas quer em termos de durabilidade.

Assessing the behaviour of RC beams subject to significant gravity loads under cyclic loads, Gião, Rita, Lúcio Válter, and Chastre Carlos , Engineering Structures, 2//, Volume 59, Number 2, p.512-521, (2014) AbstractGiao et al 2014.pdfWebsite

Gravity loads can affect a reinforced concrete structure’s response to seismic actions, however, traditional procedures for testing the beam behaviour do not take this effect into consideration. An experimental campaign was carried out in order to assess the influence of the gravity load on RC beam connection to the column subjected to cyclic loading. The experiments included the imposition of a conventional quasi-static test protocol based on the imposition of a reverse cyclic displacement history and of an alternative cyclic test procedure starting from the gravity load effects. The test results are presented, compared and analysed in this paper. The imposition of a cyclic test procedure that included the gravity loads effects on the RC beam ends reproduces the demands on the beams’ critical zones more realistically than the traditional procedure. The consideration of the vertical load effects in the test procedure led to an accumulation of negative (hogging) deformation. This phenomenon is sustained with the behaviour of a portal frame system under cyclic loads subject to a significant level of the vertical load, leading to the formation of unidirectional plastic hinges. In addition, the hysteretic behaviour of the RC beam ends tested was simulated numerically using the nonlinear structural analysis software – OpenSees. The beam–column model simulates the global element behaviour very well, as there is a reasonable approximation to the hysteretic loops obtained experimentally.

Surveying of Sandstone Monuments: New and Traditional Methodologies to Assess Viability of Conservation Actions, Chastre, C., Ludovico-Marques M., Saumell J., Guerrero M., and Delgado M. , 40th IAHS Word Congress of Housing. Sustainable Housing Construction., 16-19 December 2, Funchal, Portugal, p.ID 307 (10p), (2014) Abstract40_iahs_chastre_-_ext.abstract.pdf

Sandstone building stones are important in the building elements of Portuguese monuments, particularly in the western and southern regions. Alveolization due to salt crystallization was the most important degradation pattern found in the old sandstone façades of St. Leonardo’s Church, a Portuguese monument built in Atouguia da Baleia village in the Middle Age. Its sandstone façades have a widespread distribution of deep and large alveolization patterns mainly on portals and vaults that appeared as a result of the past and present vicinity of seashore. In this paper a summary of conservation interventions carried out in the past century in St. Leonardo’s Church is presented, as well as a summary of the studies carried out in the last decade. Then the degradation patterns on the sandstone walls of St. Leonard’s Church are shown and finally the evolution of the alveolization occurred on the sandstone walls over the last sixty to seventy years is analysed. Visual inspection of sandstone walls is compared with a survey performed by laser scanning, which seems to be a powerful technology to carry out 3D geometric modelling of the building elements of stone monuments and also the 3D mapping of stone degradation patterns.

Conservation of sandstone monuments: a new approach in consolidation treatments, Ludovico-Marques, M., and Chastre C. , 40th IAHS Word Congress of Housing. Sustainable Housing Construction., 16-19 December, Funchal, Portugal, p.ID 211 (10p), (2014) Abstract40_iahs_ludovico-marques_-_ext.abstract.pdf

Sandstones are very important in the building elements of world’s historical and cultural heritage. The façades of St. Leonard’s church in Atouguia da Baleia village in western region of Portugal are an outstanding example of the effect of alveolization on going for several centuries. In Middle ages there was an harbour and a sodium chloride rich environment near this church was responsible for this significant stone degradation pattern.
A new approach of consolidating products application on stone walls façades based on Karsten pipe using total head to allow full absorption of stone was followed.
Experimental research, based on physical and mechanical tests, was carried out on selected representative samples of a variety of sandstones on monuments treated with ethyl silicates in order to assess the effectiveness and harmfulness of these treatments.
The comparison of results between traditional immersion applications and Karsten pipe’s based procedure on stone monument indicate the potential viability of this new approach when difficult conditions of consolidating products’ absorption occurs on stone monuments.

Effect of consolidation treatments on mechanical behaviour of sandstone, Ludovico-Marques, Marco, and Chastre Carlos , Construction and Building Materials, 11/15/, Volume 70, p.473-482, (2014) AbstractWebsite

Experimental research was carried out about into ethyl silicate applications on sandstone samples. Consolidation was assessed by drilling strength, impregnation depth and also monotonic and cyclic uniaxial compressive tests in order to evaluate the compressive mechanical behaviour of treated sandstone. The stress–strain compression diagrams showed a significant increase in the values of mechanical parameters after consolidation treatments. The difference in compressive strength values between monotonic and cyclic compression disappears after the consolidation treatments. An equation of consolidation effect was obtained from an analytical model by means of compressive behaviour assessed by stress–strain diagrams. These sandstone samples have values of porosity similar to the more weathered variety of sandstone found in facades of monuments in the village of Atouguia da Baleia, in the western region of Portugal. The most important degradation pattern found on sandstone building stones is alveolization caused by salt crystallization since the Middle Ages.