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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.

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.

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.

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

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

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

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

Stainless steel bonded to concrete: An experimental assessment using the DIC technique, Biscaia, Hugo, Franco Noel, and Chastre Carlos , International Journal of Concrete Structures and Materials, January 30, Volume 12, Number 1, (2018) AbstractWebsite

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

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.

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.

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

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

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.

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.

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.

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.

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.

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

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

Linear and nonlinear analysis of bond-slip models for interfaces between FRP composites and concrete, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Composites Part B: Engineering, Volume 45, Number 1, p.1554-1568, (2013) AbstractWebsite

The paper analyses different analytical and numerical solutions for the debonding process of the FRP-to-concrete interface on shear tests with the FRP plate submitted to a tensile load in one of its ends. From the point of view of the state of the art, two different ways of finding the bond-slip curve from experiments are discussed and analysed. Essentially, three different linear bond-slip models, one exponential model and another power based function are employed in the numerical process. The results are analysed and compared. The differences found in the stress field along the interface, maximum load, maximum slip, ultimate slip, fracture energy and effective bond length are reported. The load-slip behaviour is also presented for the linear and non-linear models herein studied and the influence of the local bond-slip model on the debonding process is discussed. The numerical integration process used on the present study proved to be coherent with the analytical expressions determined for the linear bond-slip models and allowed to verify that maximum load transmittable to the FRP plate is influenced by the square root of the FRP stiffness and fracture energy even when nonlinear bond-slip models are assumed.

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.

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.

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

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

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

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

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.

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

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

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

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

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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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.

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.

Nonlinear numerical analysis of the debonding failure process of FRP-to-concrete interfaces, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Composites Part B: Engineering, Volume 50, p.210-223, (2013) AbstractWebsite

The paper analyses numerical solutions for the process leading to debonding failure of fiber reinforced polymers (FRP)-to-concrete interfaces in shear tests with the FRP plate subjected to a tensile load at one end. Any realistic local nonlinear bond-slip law can be used in the numerical analysis proposed in the present study. However, only a Popovics’ type expression is employed in the numerical process due to its use in different studies found in the literature. Effective bond length (Leff) is discussed and an expression depending on the Popovics’ constant (nP) is proposed to calculate it. Assuming a fracture in pure Mode II, the debonding process is analyzed in detail and distributions of bond stresses and strains in the FRP plate along the interface are presented. The load-displacement behaviour is also presented and the influence of the local bond-slip law on the debonding process is discussed.

Numerical analysis of FRP anchorage zones with variable width, Biscaia, Hugo C., Micaelo Rui, Teixeira João, and Chastre Carlos , Composites Part B: Engineering, 11//, Volume 67, p.410-426, (2014) AbstractWebsite

The use of Fibre Reinforced Polymers (FRP) has recently become widespread in the construction industry. However, some drawbacks related to premature debonding of the FRP composites from the bonded substrates have been identified. One of the solutions proposed is the implementation of mechanical anchorage systems. Although some design guidelines have been developed, the actual knowledge continues to be rather limited. Thus, designers and researchers have not yet achieved any consensus on the efficiency of any particular anchor device in delaying or preventing the premature debonding failure mode that can occur in Externally Bonded Reinforcement (EBR) systems. This paper studies the debonding phenomenon of FRP anchoring systems with a linear variable width, with a numerical analysis based on the Distinct Element Method (DEM). Combined systems with constant and variable width are also discussed. The FRP-to-parent material interfaces are modelled with a rigid-linear softening bond–slip law. The numerical results showed that it is possible to attain the FRP rupture force with a variable width solution. This solution is particularly attractive when the bonded length is shorter than the effective bonded length because the strength of the interface can be highly incremented.

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.

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

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

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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Modelação de vigas de betão armado reforçadas à flexão com materiais compósitos de matriz polimérica, Biscaia, H. C., Chastre C., and Franco N. , JPEE2014 – 5ª Jornadas Portuguesas de Engenharia de Estruturas, Encontro Nacional Betão Estrutural 2014., LNEC, Lisboa., (2014) Abstractartigo_jpee_biscaia_chastre_franco.pdf

Nas últimas décadas, os estudos sobre o desempenho de vigas de betão armado (BA) reforçadas com materiais compósitos de matriz polimérica têm aumentado. Porém, muitas dúvidas e questões persistem, fazendo realçar algumas lacunas sobre o conhecimento adquirido. Um desses aspetos reside na forma de modelar a ligação entre o compósito e o betão. É também sabido que a modelação da abertura de fendas no betão (discreta ou distribuída numa banda) influência o desempenho da ligação entre os materiais colados.
Nesse sentido, apresentam-se, neste trabalho, os resultados numéricos obtidos da modelação numérica não-linear a 3D de vigas de BA sujeitas a flexão de 4 pontos. Os resultados numéricos são confrontados com os experimentais e os diferentes parâmetros que influenciam a ligação analisados e discutidos.

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

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

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

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

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

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

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.

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.

A smeared crack analysis of reinforced concrete T-beams strengthened with GFRP composites, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Engineering Structures, 11//, Volume 56, p.1346-1361, (2013) AbstractWebsite

The strengthening of reinforced concrete structures with laminates of fibre reinforced polymeric (FRP) matrix has received considerable attention, although there still is lack of information on the more adequate modelling of the interface between FRP composites and concrete. An experimental programme is described and was designed to: (i) characterise glass FRP-to-concrete interface by shear tests; (ii) analyse reinforced concrete T-beams with external GFRP plates. Double shear tests were carried out based on 15 cm cubes with GFRP bonded to two opposite faces. The concrete T-beams were 3.0 m long and 0.28 m high and were loaded till rupture in 4-point bending tests. The external reinforcement system showed great strength increment in relation to the non retrofitted T-beam, confirming to be an effective approach to the flexural strengthening of RC beams. The computational analysis was based on a three dimensional smeared crack model. In total, 22 computational analyses were made. Models with and without interface FE associated with Mohr–Coulomb failure criterion for the FRP-to-concrete interface were defined and different strength types of concrete were considered. The rigid interface does not predict the rupture of the T-beam with precision; however, the results obtained for low concrete strengths revealed that rigid interfaces can be assumed when conjugated with the fixed crack approach. Consequently, a slightly stiffer response of the beam is obtained. The maximum bond stresses obtained from Finite Element Analysis (FEA) revealed that the models with rigid interfaces developed lower bond stresses due to the lack of relative displacements between both materials. The effects of assuming either fixed or rotated crack approaches were also compared. The rotated crack conjugated to a fine mesh in the vicinity of the GFRP-to-concrete stress led to a very good estimation of the bond stresses along the interface. The prediction of the T-beam rupture was also estimated with better results when the rotated crack was used in the model. In general, the FEA predicted with very good results the de-bonding of the GFRP-to-concrete interface of T-beams externally bonded with GFRP composites.

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.

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

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

Modelling GFRP-to-concrete joints with interface finite elements with rupture based on the Mohr-Coulomb criterion, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Construction and Building Materials, 10//, Volume 47, p.261-273, (2013) AbstractWebsite

The strengthening of reinforced concrete structures by means of externally bonded fibre reinforced polymers (FRPs) is now routinely considered and applied in the retrofit or strengthening of structures. FRP composites have received a considerable attention from civil engineers in recent years due to the high strength-weight and stiffness/weight ratios when compared to other materials. However, when FRP composites are bonded to a concrete surface, there is a persistent potential problem that the FRP plates may debond prematurely from the concrete. This is a very important issue for the engineers who have to focus on the computational modelling of this phenomenon. Some studies can be found in literature on computational modelling. However, there is very little information about the best modelling of the interface between FRP composites and concrete and this work is intended to help bridge this gap. The computational analysis presented here is based on three-dimensional software which assumes the smeared crack model, and the interface finite elements (FEs) used have a rupture criteria based on the Mohr-Coulomb criterion with tension cut-off. The definition of these FEs was based on double shear tests that were performed specifically for this purpose and they have shown that the debonding phenomenon can be predicted with some accuracy. In total, 10 double shear models were studied and the results were compared with the 21 experimental tests performed. The double shear tests consisted of applying loads to 2 layered GFRP laminates bonded to a 150 mm concrete cube with a bonded area of 150 × 80 mm (length × width). Double shear models with and without a gap interface were considered in order to emphasize the importance of modelling the GFRP-to-concrete interface with interface finite elements. The effect of the concrete strength on the interface performance was also considered. An externally bonded reinforcement (EBR) concrete T-beam strengthened with 2 GFRP layers is presented to illustrate the application of the method. The wet lay-up technique was used for the external reinforcement of a reinforced concrete T-beam and then tested under a four point bending test until rupture. The results are reported and differences between the numerical and the experimental results are discussed.

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

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

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.

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.

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.

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.

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.

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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.

Princípios básicos para a conceção de estruturas de edifícios em zonas sísmicas, Chastre, Carlos, Lúcio Válter, and Tsoukantas Spyros , Estruturas Pré-moldadas no Mundo - Aplicações e Comportamento Estrutural, p.227-248, (2012) Abstract
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Nondestructive testing methodology to assess the conservation of historic stone buildings and monuments, Chastre, Carlos, and Ludovico-Marques Marco , Handbook of Materials Failure Analysis: With Case Studies from the Construction Industries, p.255-294, (2018) Abstract

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

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.

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].

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

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

Torres pré-fabricadas de betão para suporte de turbinas eólicas, Chastre, Carlos, and Lúcio Válter , Estruturas Pré-moldadas no Mundo - Aplicações e Comportamento Estrutural, p.91-106, (2012) Abstract
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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.

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

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

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

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

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

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

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

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

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.

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.

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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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.

Reinforced Concrete Columns Jacketed with FRP Composites and Subjected to Cyclic Horizontal Loads, Chastre, C., and Silva M. G. , International Conference CCC2008 - Challenges for Civil Construction, Porto, (2008) Abstract
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Preface, Chastre, Carlos , 2nd International Conference on Building Materials and Materials Engineering - ICBMM 2018, Volume 278, Lisbon, Portugal, (2019) Abstract

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

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.

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

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

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.

Monotonic axial behavior and modelling of RC circular columns confined with CFRP, Chastre, Carlos, and Silva Manuel A. G. , Engineering Structures, Aug, Volume 32, Number 8, p.2268-2277, (2010) AbstractWebsite

The retrofit of reinforced concrete columns with FRP jackets has received considerable attention in recent years. The advantages of this technique compared to other similar techniques include the high strength-weight and stiffness-weight ratios of FRP (Fibre Reinforced Plastics), the strength and ductility increase of RC columns confined with FRP jackets as well as the fact that FRP external shells prevent or mitigate environmental degradation of the concrete and consequent corrosion of the steel reinforcement. Furthermore, this method also reduces the column transversal deformation and prevents the buckling of longitudinal reinforcement. Twenty five experimental tests were carried out on reinforced concrete columns confined with CFRP composites, and subjected to axial monotonic compression. In order to evaluate the influence of several parameters on the mechanical behavior of the columns, the height of the columns was maintained, while changing other parameters: the diameter of the columns, the type of material (plain or reinforced concrete), the steel hoop spacing of the RC columns and the number of CFRP layers. Predictive equations, based on the experimental analysis, are proposed to estimate the compressive strength of the confined concrete, the maximum axial load and the axial or the lateral failure strain of circular RC columns jacketed with CFRP. A stress-strain model for CFRP confined concrete in compression, which considers the effect of the CFRP and the transversal reinforcement on the confined compressive strength of the column is also proposed. The curves, axial load versus axial or lateral strain of the RC column, are simulated based on the stress-strain model and include the longitudinal reinforcement effect. The results demonstrate that the model and the predictive equations represent very well the axial compression behavior of RC circular columns confined with CFRP. The applicability of this model to a large spectrum of RC column dimensions is its main advantage.

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

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

Potencialidade e Limitações dos Novos Materiais de Reforço de Estruturas, Chastre Rodrigues, C., and Silva M. G. , RILEM – 57th Annual Week 2003 & Seminário NDB, Lisboa, (2003) Abstract
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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.

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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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.

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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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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.

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.

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.

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.

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.

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.

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.

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 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.

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

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