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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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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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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.

Análise do desempenho à flexão de vigas de betão armado reforçadas com armaduras de aço inoxidável, Franco, N., Chastre C., and Biscaia H. C. , JPEE2014 – 5ª Jornadas Portuguesas de Engenharia de Estruturas, Encontro Nacional Betão Estrutural 2014., LNEC, Lisboa., (2014) Abstractartigo_jpee_2014_franco_chastre_biscaia.pdf

Apresentam-se neste artigo os resultados dos ensaios realizados à escala real de um conjunto de vigas de betão armado com secção em T, levados a cabo para avaliar o desempenho das armaduras de aço inoxidável no reforço à flexão de vigas de betão armado com armaduras pós-instaladas aplicadas com as técnicas de reforço EBR (Externally Bonded Reinforcement), NSM (Near Surface Mounted) e EBR com ancoragens metálicas nas extremidades. Os ensaios realizados demonstraram que as técnicas de reforço utilizadas permitem aumentar a rigidez à flexão em regime elástico. Porém, a viga reforçada através da técnica EBR teve uma rotura prematura antes de atingir o valor da carga de cedência da viga não reforçada. Já as vigas reforçadas com as técnicas NSM e EBR com ancoragens mecânicas superaram o valor da carga de cedência da viga de referência, e as ancoragens mecânicas proporcionaram bastante ductilidade à viga reforçada com esta técnica.

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.

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.

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.

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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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.

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.

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.

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.

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) AbstractWebsite

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.

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.

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.

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.

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.

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.

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The Behaviour of GFRP Reinforced Concrete Columns Under Monotonic and Cyclic Axial Compression, Chastre Rodrigues, C., and Silva M. G. , CCC2001, Composites in Construction, Porto, p.245-250, (2001) Abstractchastre_rodrigues2001si_-_ccc2001.pdf

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The behaviour of RC columns retrofitted with FRP or polymeric concrete under axial compression and cyclic horizontal loads, Chastre Rodrigues, C., and Silva M. A. G. , 9th International Conference on Inspection, Appraisal, Repairs and Maintenance of Structures, Oct 20-21, Fuzhou, PEOPLES R CHINA, p.393-400, (2005) Abstract

The seismic retrofit of reinforced concrete columns with FRP jackets has received a considerable increment in recent years due the high strength-weight and stiffness-weight ratios of FRP compared to other materials. The FRP outer shell also contributes to prevent or delay environmental degradation of the concrete and corrosion of the steel reinforcement. An experimental program conducted in order to analyze the behavior of reinforced concrete columns jacketed with FRP composites or repaired with polymeric concrete and subjected to axial compression and cyclic horizontal loads is described. The dimensions of the cylindrical columns were 1500 mm height by 250 mm diameter. The influence of various parameters on the response, including the type of confining material and the number of FRP layers, is reported. The results of the tests are shown and interpreted.

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.

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.

Bond GFRP-Concrete under environmental exposure, Biscaia, H., Silva M. G., and Chastre C. , 15th International Conference on Composite Structures ICCS 15, Porto, (2009) Abstractbiscaia2009sich_-_iccs15.pdf

Fiber reinforced polymers (FRP) are often used to strengthen RC structures.
Despite intense research, durability of reinforced concrete (RC) retrofitted with FRP remains insufficiently known. Long time behavior of the bond laminate-concrete, in flexural strengthening, under environmental action is not well known, conditioning Codes and engineers. An experimental program that subjected RC beams, externally reinforced with Glass FRP (GFRP) strips, to temperature and salt water cycles, for up to 10000h is reported.
At selected intermediate times, the RC beams were loaded to failure in bending. Rupture took place, normally, by tensile failure of concrete at a short distance from the interface with GFRP. The results showed that freeze-thaw cycles were the most severe of the environmental
conditions. The study also generated also non-linear bond-slip relationships from the experimental data. Numerical modeling has been undertaken, based on a commercial code.
The model is based on smeared cracking. Parameters needed for the characterization, namely cohesion and friction angle, were obtained from shear tests conceived for the effect.

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.

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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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Caracterização Experimental e Modelação Numérica da Ligação GFRP/BETÃO, Biscaia, H. E. C., Silva M. G., and Chastre C. , Mecânica Experimental, Number 16, p.9-18, (2009) Abstractbiscaia2009sich.pdfWebsite

Analisa-se e caracteriza-se por via experimental a ligação entre elementos de betão armado e materiais compósitos, nomeadamente com base nas fibras de vidro. Fabricaram-se vigas de betão armado que foram exteriormente reforçadas com GFRP. Os resultados obtidos experimentalmente foram comparados com os resultados conseguidos por intermédio de modelação computacional, recorrendo-se ao programa de cálculo ATENA 2D. Para melhor modelação de elementos de interface, foram realizados ensaios de corte tendo-se obtido valores que permitiram caracterizar a lei de rotura de Mohr-Coulomb. Os parâmetros estudados foram a evolução das forças máximas absorvidas pelo reforço; as tensões de aderência máximas; a distribuição das tensões de aderência.

Caracterização Experimental e Modelação Numérica da Ligação GFRP/Betão, Biscaia, H., Silva M. G., and Chastre C. , 7º Congresso de Mecânica Experimental, Vila Real, (2008) Abstract
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Carbonation service life modelling of RC structures for concrete with Portland and blended cements, Marques, Pedro Faustino, Chastre Carlos, and Nunes Ângela , Cement and Concrete Composites, Volume 37, p.171-184, (2013) Abstractmarques_chastre_et_al._2013.pdfWebsite

The presented work aims at studying the modelling of long term performance of concrete compositions with different proportions of clinker as regards the diffusion of CO2 in concrete – carbonation. The replacing constituents of clinker that will be part of the binder in each concrete composition are limestone filler and low calcium fly ash (FA). The used percentage of FA by weight of binder was of 50%. Concrete compositions were made following standard prescribed requirements to attain service lives of 50 and 100 years as regards concrete performance against reinforcing steel corrosion. Test results of compressive strength and carbonation depth are reported at different curing ages of 28, 90, 180 and 365 days. Carbonation results were used for the implementation of modelling equations in order to estimate the design service life regarding reinforcing steel corrosion. Two performance-based methods were used: safety factor method and probabilistic method, and their results compared with the traditional prescriptive approach. At the age of 28 days the composition with OPC is the only one that reaches the target periods of 50 or 100 years. For the probabilistic method, different curing age results were analysed. For the tested results at 90, 180 and 365 days of age the reliability of some of the compositions with blended cements is within the minimum required, although still far from the higher performance of concrete with OPC.

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.

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.

Comportamento às acções cíclicas de pilares de betão armado reforçados com materiais compósitos, Chastre Rodrigues, C. , Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, Lisboa, (2005) Abstract

This thesis deals with the analysis of the behaviour of retrofitting reinforced concrete circular columns with FRP materials which were subjected either to axial cyclic compression or axial compression and alternated cyclic horizontal loads. The choice of this topic derived from the need to investigate the behaviour of the strengthening of reinforced concrete columns to seismic actions, especially with new materials such as carbon and glass fibres or polymeric mortars. Another reason for such choice is linked to the strong seismicity of the Portuguese territory.
It has been verified that confined concrete columns with FRP jackets have their resistance and ductility highly increased as these considerably reduce the columns transversal deformation, thus preventing the buckling of longitudinal reinforcement. There has been an increasing use of FRP composites in the strengthening of structures, mainly with GFRP (Glass Fibre Reinforced Plastics) or CFRP (Carbon Fibre Reinforced Plastics). This is due to their attractive characteristics such as high resistance to corrosion, lowratio for weight/strength, moldability, easy application and the fact that there is no need of support structures.
Forty-five experimental tests were carried out, dealing with retrofitting reinforced concrete columns with axial monotonic or cyclic compression reinforced with FRP composites. The column height of 750 mm was maintained in order to evaluate the influence of several parameters in its behaviour: the column geometry (change in its diameter), the type of column (plain or reinforced concrete), transversal reinforcement ratio of concrete columns, the type of external confinement with FRP (C or GFRP), the number of FRP layers and the type of axial loading (monotonic or cyclic).
Twelve additional experimental tests were conducted in order to analyse the behaviour of reinforced concrete columns jacketed with FRP composites and subjected to axial cyclic compression and alternated cyclic horizontal loads. The columns’ dimension was maintained (1500 mm height by 250 mm diameter) and the models were subjected to a series of cyclic and alternated loadings. This enabled the study of the various parameters’ influence in their behaviour such as the type of FRP confinement, the number of FRP layers, the level of axial loading, the jacket’s height or the strengthening of the plastic hinge by replacing the cover concrete with polymeric mortar.
Based on the numerical models presented and experimental analysis carried out, models were proposed and developed to simulate the behaviour of columns jacketed with FRP composites.

Comportamento da Ligação Aço-Resina-Betão em Elementos Estruturais, Chastre Rodrigues, C. , Departamento de Engenharia Civil, Instituto Superior Técnico, 1993, Volume MSc, Lisboa, (1993) Abstract1993_-_msc-_ist_-_carlos_chastre_-_comportamento_da_ligacao_aco-resina-betao_em_elementos_estruturais.pdf

The present work studies the behaviour of bonded steel plates to reinforced concrete elements, which can be used in the strengthening of concrete structural elements. Metallic expansion bolts can be added.The objective of this dissertation is to investigate the behaviour to monotonic actions and particularly to cyclic loading of steel-epoxy-concrete connection with expansion bolts. This cyclic action is of particular interest due to the strong seismicity of the Portuguese territory.The research is mainly based in experimental analysis. The caracterization of the materials was carried out. Six models of the steel-epoxy connection were tested with monotonic loading. Twenty six models of steel-epoxy-concrete bond were submitted either to monotonic or to cyclic actions.Besides the type of action, other parameters were studied in the steel-epoxy-concrete connection models.These were the bond geometry area, the type of concrete, the type of epoxy and connection - with or without metallic expansion bolts.A parametric study with a numerical model of finite elements, as well as a global analysis of the experimental tests of the steel-epoxy-concrete connection was carried out.

Comportamento da Ligação CFRP-Resina–Betão Sujeita a Acções Cíclicas, Marques, J. L., Fong P., Macedo P., Chastre Rodrigues C., and Lúcio V. , Betão Estrutural 2004, Porto, (2004) Abstractmarques2004fomachlu_-_be2004.pdf

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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.

Compression behaviour of short columns made from cement-bonded particle board, Faria, Gonçalo, Chastre Carlos, Lúcio Válter, and Nunes Ângela , Construction and Building Materials, 3//, Volume 40, p.60-69, (2013) AbstractWebsite

Cement bonded particle board (CBPB) is a composite material produced in plates consisting mainly of wood and cement, and may contain additives. This material is currently used in cladding, raised floors, dropped ceilings, prefabricated houses, office containers and various supplies to the building industry such as kitchens, bathrooms and furniture. It is composed of a type of wood Pinus pinaster and/or Pinus pinea, Portland cement type II, sodium silicate and aluminium sulphate. CBPB has been the subject of several studies with the purpose of enabling the use of other types of wood or even vegetable biomass, as the chemical compounds from wood (extractives and sugars) tend to inhibit of cement hydration. A study on the behaviour of short CBPB elements under compression was carried out in the Department of Civil Engineering of Universidade NOVA de Lisboa with the aim of enabling its use in structural elements. The study was supported by VIROC, the company which produces CBPB in Portugal. This paper presents and analyses the most significant results of a campaign of axial compression tests performed on 111 specimens of different heights and cross sections. The behaviour of CBPB specimens of varying slenderness was subjected to a more detailed analysis.

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.

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.

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.

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].

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.

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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.

Degradação da aderência entre compósitos de GFRP e betão devido a condições ambientais severas, Silva, M. A. G., Biscaia H. C., and Chastre C. , Betão Estrutural 2012, Porto, (2012) Abstractsilva2012bich_-_be2012_-_feup.pdf

A degradação da ligação entre compósitos de matriz polimérica reforçada por fibras (FRP) e o betão é uma das principais causas de possível rotura das vigas e lajes de betão armado reforçadas
externamente por compósitos de FRP. Desde há mais de 10 anos que se estuda, por isso, na UNL o
comportamento dessa ligação, integrado em programa mais alargado de estudo da durabilidade deste tipo de reforço, especialmente quando sujeito a condições ambientais severas que se simulam por processos artificialmente acelerados no laboratório. Em particular a degradação da aderência e o possível descolamento precoce do reforço têm sido modelados física e computacionalmente com principal incidência no uso de fibras de vidro (GFRP) e resina epoxídica. Nesta comunicação mostram-se resultados obtidos em termos de capacidade de carga, força transmitida ao reforço e tensões de aderência após envelhecimentos de pequenas vigas de betão armado (BA) por ciclos de nevoeiro salino, ciclos seco/molhado em solução salina, ciclos de temperatura entre +7,5ºC e +47,5ºC e gelo-degelo de -10ºC a +30ºC. Faz-se recomendação quanto à extensão máxima para diferentes envelhecimentos. Apresenta-se comparação entre resultados de modelação numérica e experimental.

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.

Delamination process analysis of FRP-to-parent material bonded joints with and without anchorage systems using the Distinct Element Method, Biscaia, Hugo C., Micaelo Rui, Teixeira João, and Chastre Carlos , Composite Structures, Volume 116, Issue September–October, p.104–119, (2014) AbstractWebsite

This study looks at the analysis of the interface between Fiber Reinforced Polymer (FRP)-to-parent material bonded interfaces. The performance of FRP-to-parent material bonded joints for the Externally Bonded Reinforcement (EBR) technique is numerically modelled with the PFC2D software which is based on the Distinct Element Method (DEM). It is believed that this represents the first time the DEM has been used to simulate the delamination process of FRP-to-parent material bonded joints. In order to validate the analysis performed with the DEM, a Pull-out test with no slip constrains was modelled and different linear bond-slip laws were assumed. The numerical results revealed that the DEM is capable of estimating with good accuracy the exact solutions of bond stresses, strains or slippages along the bonded length for linear bond-slip laws. The bi-linear law available in PFC2D was then compared to the numerical results obtained from other another code developed by the author. The delamination process of Pull-out tests with slip constrain at one of the free ends of the FRP plate is also described and analyzed. The results obtained from the DEM revealed that the delamination process ends with stiffness equal to the axial stiffness of the FRP plate. This evidence highlights the need to design mechanical anchor devices capable of preventing premature debonding which is known to occur on EBR systems.

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.

Design model for square RC columns under compression confined with CFRP, Faustino, Pedro, Chastre Carlos, and Paula Raquel , Composites Part B: Engineering, Volume 57, Issue February, p.187-198, (2014) Abstractfaustino_chastre_et_al._2014.pdfWebsite

The enhancement of the mechanical behaviour of reinforced concrete (RC) columns with regard to axial compression is an up-to-date concern, namely if the strengthening of existing structures is to be considered. In view of this, external confinement with FRP systems has been tested in order to become a feasible technique, since it seems to have important advantages over other systems such as its high strength and stiffness in relation to weight and its improvement of strength and ductility while confining RC columns. Square columns confined with FRP show a more complex interpretation of their behaviour, when compared to circular columns. Accordingly, the present work includes the analysis of two experimental programs regarding axial compression on CFRP confined RC columns: one on circular and square specimens with different corner radii; the other on square specimens with side lengths ranging from medium to large. Based on this, modelling equations are proposed to predict maximum axial load, axial strain and lateral strain, as well as the entire behaviour until failure with curves of axial load-axial strain and axial load-lateral strain. The modelling results show that the analytical curves are in general agreement with the presented experimental curves for a wide range of dimensions.

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.

Development of an injectable grout for concrete repair and strengthening, Bras, Ana, Gião Rita, Lúcio Válter, and Chastre Carlos , Cement and Concrete Composites, (2013) AbstractWebsite

This paper deals with the coupled effect of temperature and silica fume addition on rheological, mechanical behaviour and porosity of grouts based on CEMI 42.5R, proportioned with a polycarboxylate-based high range water reducer. Preliminary tests were conducted to focus on the grout best able to fill a fibrous network since the goal of this study was to develop an optimized grout able to be injected in a mat of steel fibers for concrete strengthening. The grout composition was developed based on criteria for fresh state and hardened state properties. For a CEMI 42.5R based grout different high range water reducer dosages (0, 0.2%, 0.4%, 0.5%, 0.7%) and silica fume (SF) dosages (0, 2%, 4%) were tested (as replacement of cement by mass). Rheological measurements were used to investigate the effect of polycarboxylates (PCE) and SF dosage on grout properties, particularly its workability loss, as the mix was to be injected in a matrix of steel fibers for concrete jacketing. The workability behaviour was characterized by the rheological parameters yield stress and plastic viscosity (for different grout temperatures and resting times), as well as the procedures of mini slump cone and funnel flow time. Then, further development focused only on the best grout compositions. The cement substitution by 2% of SF exhibited the best overall behaviour and was considered as the most promising compared to the others compositions tested. Concerning the fresh state analysis, a significant workability loss was detected if grout temperature increased above 35°C. Below this temperature the grout presented a self-levelling behaviour and a life time equal to 45 minutes. In the hardened state, silica fumes increased not only the grout’s porosity but also the grout’s compressive strength at later ages, since the pozzolanic contribution to the compressive strength does not occur until 28 days and beyond.

Displacement Estimation of a RC beam test based on TSS algorithm, Almeida, G., Biscaia H., Chastre C., Fonseca J., and Melício F. , CISTI'2010 - 5ª Conferencia Ibérica de Sistemas y Tecnologías de Información, Santiago de Compostela, (2010) Abstract

The traditional methodology used in civil engineering measurements requires a lot of equipment and a very complex procedure especially if the number of target points increase. Since the beginning of the current century, several studies have been conducted in the area of photogrametry using digital image
correlation associated with block motion algorithms to estimate displacements in reinforced concrete (RC) beams during a load test. Using image processing techniques it is possible to measure the whole area of interest and not only a few points of the tests materials. In this paper, block-matching algorithms are used in order to compare the results from photogrametry techniques and the data obtained with linear voltage displacement transducer (LVDT) sensors during the load tests of RC beams, which are very common to find in civil engineering laboratories.

Displacement measurements with ARPS in T-beams load tests, Almeida, G., Melicio F., Chastre C., and Fonseca J. , Volume 349 AICT, p.286-293, (2011) Abstract

The measurement of deformations, displacements, strain fields and surface defects in many material tests in Civil Engineering is a very important issue. However, these measurements require complex and expensive equipment and the calibration process is difficult and time consuming. Image processing could be a major improvement, because a simple camera makes the data acquisition and the analysis of the entire area of the material under study without requiring any other equipment like in the traditional method. Digital image correlation (DIC) is a method that examines consecutive images, taken during the deformation period, and detects the movements based on a mathematical correlation algorithm. In this paper, block-matching algorithms are used in order to compare the results from image processing and the data obtained with linear voltage displacement transducer (LVDT) sensors during laboratorial load tests of T-beams. © 2011 IFIP International Federation for Information Processing.

Double shear tests to evaluate the bond strength between GFRP/concrete elements, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Composite Structures, Volume 94, Number 2, p.681-694, (2012) AbstractWebsite

Externally bonded reinforced systems have been widely used in civil engineering. However, the problems associated with bond between structural elements are not yet fully solved. As a consequence, many researchers have been proposing tests and techniques to standardize procedures and reach better agreement for design purposes. In the present paper, an experimental program is described that was developed to characterize the glass FRP/concrete interface by double shear tests made on 15 cm side cubes with GFRP bonded on two opposite faces. The GFRP wrap had two layers applied by the wet lay-up technique and three classes of concrete were considered. With the support of the experimental program, cohesion and friction angle for GFRP–concrete interfaces were found leading to different envelope failure laws, based on the Mohr–Coulomb failure criterion for each concrete class, capable of predicting GFRP debonding. Results are discussed.

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.

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.

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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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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.

Effect of salt crystallization ageing on the compressive behavior of sandstone blocks in historical buildings, Ludovico-Marques, Marco, and Chastre Carlos , Engineering Failure Analysis, 12//, Volume 26, p.247-257, (2012) AbstractWebsite

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 buildings in the village of Atouguia da Baleia. Because weathering progressively increases porosity in stones, experimental research was conducted on the most porous variety of sandstone, which is similar to the type of stones found in the façades of ancient buildings in that village. An automatic salt crystallization accelerated ageing chamber was developed. Monotonic and cyclic uniaxial compressive tests were carried out on samples after sodium chloride crystallization ageing tests had been performed, in order to assess the compressive mechanical behavior of sandstone during accelerated ageing. The results of stress–strain compression diagrams showed a clear decreasing trend in the values of mechanical parameters during the salt crystallization ageing progress. The difference in compressive strength values between monotonic and cyclic compression also decreases with as salt crystallization ageing progresses. A predictive equation that correlates the compressive strength of sandstones with salt crystallization ageing cycles is proposed.

Encamisamento de Pilares de Betão Armado com FRP: Efeitos nas Relações Constitutivas e na Ductilidade, Silva, M. G., and Chastre Rodrigues C. , VI Congresso de Mecânica Aplicada e Computacional, Aveiro, (2000) Abstract
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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.

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.

Estruturas pré-moldadas no mundo, Chastre, Carlos, and Lúcio Válter , Estruturas Pré-moldadas no Mundo - Aplicações e Comportamento Estrutural, p.1-6, (2012) Abstract
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Estruturas Pré-Moldadas no Mundo. Aplicações e Comportamento Estrutural, Chastre, Carlos, Lúcio Válter, Acker Arnold Van, Crisp Barry, Gutstein Daniela, Saraiva Filipe, Doniak Íria, Krohn Jason, Viegas José Barros, Ferreira Marcelo, Menegotto Marco, el Debs Mounir, Hughes Simon, Tsoukantas Spyros, and Pampanin Stefano , 2012, Brasil, p.320, (2012) AbstractWebsite

A indústria do betão pré fabricado é, por tradição, inovadora, precursora de novas tecnologias e de novos materiais.O processo produtivo de estruturas com elementos pré-fabricados difere significativamente do das estruturas betonadas em obra pelo facto de uma parte, ou a totalidade, dos elementos da estrutura serem produzidos em fábrica, em condições de produção melhoradas em relação às condições da obra, e serem posteriormente transportados para a obra, onde são, finalmente ligados entre si. A produção em fábrica é efectuada em ambiente protegido do Sol e da chuva, com operários fixos e com formação profissional para desenvolverem tarefas com procedimentos normalizados. Consequentemente, os elementos executados em fábrica possuem melhor qualidade, sob vários aspectos, do que as estruturas executadas em obra.Este livro divide-se em duas grandes áreas, numa primeira abordam-se algumas aplicações de estruturas pré-moldadas no mundo e numa segunda parte descreve-se o seu comportamento estrutural face a diferentes acções. Nos primeiros capítulos relata-se a experiência da pré-fabricação em três países de diferentes continentes: o Brasil, Portugal e a Austrália e revelam-se novas oportunidades que poderão surgir para a indústria da pré-fabricação. Nos capítulos seguintes dá-se um especial enfoque à investigação do comportamento das ligações (rígidas e semi-rígidas). Aborda-se o projecto de estruturas de betão pré-fabricado às acções acidentais. E por fim, dedicam-se os últimos capítulos ao comportamento das estruturas pré-fabricadas face às acções sísmicas. Nesta área, o bom desempenho das estruturas e grande parte do conhecimento e da tecnologia actual advém da resposta dada pelos engenheiros, investigadores e construtores aos fenómenos naturais que afectam as nossas construções, como comprova o desempenho das ligações dúcteis resistentes a momentos em edifícios pré fabricados de betão no verdadeiro teste sísmico que foram os sismos de Christchurch de 2010 e 2011.

Estudo do comportamento à compressão de compósitos de madeira e cimento, Faria, G., Lúcio V., Chastre C., and Nunes A. , Encontro Nacional Betão Estrutural 2010, Lisboa, (2010) Abstract
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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.

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.

Experimental and Numerical Modelling of Basalt Textile Reinforced Mortar Behavior Under Uniaxial Tensile Stress, Larrinaga, Pello, Chastre Carlos, Biscaia Hugo C., and San-José José T. , Materials & Design, Volume 55, Issue March, p.66-74, (2014) AbstractWebsite

During the last years several projects and studies have improved the knowledge about Textile Reinforced Mortar (TRM) technology. TRM has already been used in strengthening masonry and reinforced concrete structural elements such as walls, arches, columns and beams. This material is presented as a real alternative to the use of fibre-reinforced polymers (FRP) in situations where these composites have presented some drawbacks or their use is banned. Textile Reinforced Mortar show a complex mechanical behaviour derived from the heterogeneity of the constituent materials. This paper aims to deepen the knowledge of this composite material in terms of tensile behaviour. Following this scope, this paper presents an experimental campaign focused on thirty one TRM specimens reinforced with four different reinforcing ratios. The results are analysed and contrasted with two distinct models. i) the Aveston-Cooper-Kelly theory (ACK) which is based on a tri-linear analytical approach; and ii) a nonlinear numerical simulation with a 3D Finite Element code. The Finite Element Analysis (FEA) of the TRM tensile tests also showed no significant dependence on the basalt-to-mortar interface, i.e., the choice of a bond-slip curve in order to reproduce the bond stresses and slippages along the interface is irrelevant and it can be simply considered as rigid interface.

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.

Experimental Investigation of CFRP Reinforced Concrete Columns under Uniaxial Cyclic Compression, Chastre Rodrigues, C., and Silva M. G. , FRPRCS-5, 5th International Conference on Fibre Reinforced Plastics for Reinforced Concrete Structures, Cambridge, UK, p.784-792, (2001) Abstractchastre_rodrigues2001si_-_frprcs-5.pdf

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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.

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.

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Factores que influenciam o desempenho da ligação GFRP/betão, Lucas, D., Biscaia H. C., Silva M. A. G., and Chastre C. , Betão Estrutural 2012, Porto, (2012) Abstractlucas2012bisich_-_be2012.pdf

Os compósitos de FRP podem descolar prematuramente da superfíce de betão, isto é, antes de esgotada a sua resistência elástica. Esta situação é mais provável se não forem tidos em conta factores como o tipo de preparação da superfície, a exposição a acção ambiental severa, e a resistência do próprio betão. Com o objectivo de analisar a influência de parte destes factores no desempenho da ligação compósito de fibra de vidro (GFRP) e betão, empreendeu-se uma campanha experimental baseada em ensaios de corte duplo. Os resultados permitiram determinar e comparar as forças máximas transmitidas ao GFRP e tensões de aderência máxima para diferentes tratamentos de superfície e condições de envelhecimento. Foram também determinadas aproximações para curvas de tensão de aderência vs. deslizamento (bond-slip). Os resultados obtidos são contrastados com resultados obtidos por modelação numérica.

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.

fib Bulletin 63. Design of precast concrete structures against accidental actions, Acker, Arnold Van, Chastre Carlos, Cholewicky Andrzej, Crisp Barry, Lúcio Válter, Elliott Kim S., Engström Björn, Gasperi Antonello, Suikka Arto, Tsoukantas Spyros, Vambersky Jan, and Vantomme John , fib bulletin, Number 63, Lausanne, p.78, (2012) AbstractWebsite

Since the 1980’s, several buildings throughout the world have been subject to gas explosions, impact by cars or airplanes, or car bomb attacks. In many cases the effect of the impact or explosion has been the failure of a critical structural member at the perimeter of the building. After the failure, the load supported by that member could not be redistributed and part or all of the structure has collapsed in a progressive manner. The phenomenon that occurs when local failure is not confined to the area of initial distress, and spreads horizontally and/or vertically through the structure, is termed progressive collapse.

Progressive collapse is a relatively rare event, as it requires both an accidental action to cause local damage and a structure that lacks adequate continuity, ductility, and redundancy to prevent the spread of damage. It is technically very difficult and economically prohibitive to design buildings for absolute safety. However it is possible to construct precast concrete buildings that afford an acceptable degree of safety with regard to accidental actions.

A structure is normally designed to respond properly, without damage, under normal load conditions, but local and/or global damages cannot be avoided under the effect of an unexpected, but moderate degree of accidental overload. Properly designed and constructed structures usually possess reasonable probability not to collapse catastrophically under such loads, depending on different factors, for example: the type of loading; the degree and the location of accidental loading in regard to the structure and its structural members; the type of structural system, the construction technology, and the spans between structural vertical members, etc.

No structure can be expected to be totally resistant to actions arising from an unexpected and extreme cause, but it should not be damaged to an extent that is disproportionate to the original cause.

The aim of fib Bulletin 63 is to summarize the present knowledge on the subject and to provide guidance for the design of precast structures against progressive collapse. This is addressed in terms of (a) the classification of the actions, (b) their effect on the structural types, (c) the strategies to cope with such actions, (d) the design methods and (e) some typical detailing, all supplemented with illustrations from around the world, and some model calculations.

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.

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.

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.

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 Behaviour of RC T-Beams Strengthened with Different FRP Materials, Carvalho, Tiago, Chastre Carlos, Biscaia Hugo, and Paula Raquel , The Third International fib Congress and Exhibition "Think Globally, Build Locally", , Washington DC, (2010) Abstract

The strengthening of reinforced concrete structures with FRP materials has received a
considerable increment in recent years due to the high strength-weight and stiffness-weight
ratios of FRP compared to other materials.
An experimental programme was conducted in order to analyse the behaviour of different
structural solutions to strengthen reinforced concrete beams with FRP composites (EBR
GFRP, EBR CFRP, NSRM-CFRP) and is described. The RC T beams had a 3m span by 0.3m
height and were tested until rupture in a 4-point bending test system.
The NSMR technique has proved to be the most effective of the three alternatives tested, as it
obtained high strength, combined with high ductility. Nevertheless, all the systems show
great strength increment in relation to the non retrofitted T-beams, proving to be effective
approaches to the flexural strengthening of RC beams.

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.

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.

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.

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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.

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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.

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.

Influence of Temperature Cycles on Bond between GFRP and Concrete, Silva, Manuel A. G., Biscaia Hugo, and Chastre Carlos , ACI Structural Journal, Volume 110, Issue 6, p.977-988, (2013) AbstractWebsite

Reinforced concrete (RC) beams externally strengthened with glass fiber-reinforced polymer (GFRP) strips bonded to the soffit may see their load-carrying capacity reduced due to environmental conditions—especially due to the deterioration of bond between the adhesively bonded laminates and concrete, causing premature failure.
More research has been published on the detachment of the laminate progressing from the anchorage zone than on failure induced by the formation of flexural or shear-flexural cracks in the midspan followed by fiber-reinforced polymer (FRP) separation and failure designated as intermediate crack (IC) debonding. An experimental program to study degradation of the GFRP laminate beam specimens after accelerated temperature cycles, namely: 1) freezing-and-thawing type; and 2) cycles of the same amplitude (40°C [104°F]) and an upper limit approximately 70% of the glass vitreous transition temperature of the resin, Tg, is described.
Effects on the bond stress and ultimate capacity are reported. Substantial differences between shear and bending-induced failure and a decrease of bond stresses and engagement of the laminates on the structural response are analyzed.

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.

Influência do Confinamento nos Modelos de Cálculo de Pilares Reforçados com CFRP ou GFRP, Chastre Rodrigues, C., Paula A. R., and Silva M. G. , Betão Estrutural 2000, Porto, (2000) Abstractchastre_rodrigues2000pasi_-_be2000_-_feup.pdf

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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.

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.

Ligação Pilar - Fundação com Armaduras Salientes do Pilar, em Estruturas Pré-Fabricadas, Reguengo, R., Lúcio V., and Chastre C. , 2º Congresso Nacional de Pré-Fabricação em Betão, Lisboa, (2008) Abstractreguengo2008luch_-_2_cnp_-_lnec.pdf

A ligação pilar-fundação tem um papel fundamental no comportamento das estruturas pré-fabricadas, em particular, na presença de acções horizontais, como a acção dos sismos e do vento, que introduzem esforços elevados na base dos pilares. Um dos sistemas de ligação pilar-fundação usados em estruturas pré-fabricadas consiste em deixar na extremidade inferior dos pilares armaduras salientes que são introduzidas em negativos executados nas fundações. Estes negativos são posteriormente injectados com grout para garantir a ligação. No presente trabalho foram estudadas diferentes soluções de negativos para ligação das armaduras do pilar à fundação, tendo sido realizados ensaios monotónicos para analisar o seu comportamento. Nesta comunicação apresentam-se e discutem-se os resultados obtidos da análise experimental efectuada.

Ligação Pilar - Fundação em Estruturas Pré-Fabricadas. Estudo experimental, Reguengo, R., Lúcio V., and Chastre C. , Seminário SILE’08, Lisboa, (2008) Abstract
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Ligação pilar – fundação com armaduras salientes do pilar, em estruturas pré-fabricadas – Ensaios monotónicos e ensaios cíclicos, Reguengo, R., Lúcio V., and Chastre C. , Betão Estrutural 2008, Guimarães, (2008) Abstractreguengo2008luch_-_be2008.pdf

A ligação pilar-fundação tem um papel fundamental no comportamento das estruturas pré-fabricadas,
em particular, na presença de acções horizontais, como a acção dos sismos e do vento. Um dos sistemas de ligação pilar-fundação usados em estruturas pré-fabricadas consiste em deixar na extremidade inferior dos pilares armaduras salientes que são introduzidas em negativos executados nas fundações, sejam elas sapatas ou maciços de encabeçamento de estacas. Estes negativos são posteriormente injectados com “grout” para garantir a ligação. Foram estudados diferentes soluções de negativos para ligação das armaduras do pilar na fundação. Foram realizados ensaios monotónicos e cíclicos, para analisar não só o comportamento às acções estáticas mas também para a acção sísmica. No presente trabalho apresentam-se os resultados obtidos com a análise experimental efectuada. O estudo realizado permite apresentar recomendações para projecto e quais os tipos de ligações com melhor desempenho.

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.

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.