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The performance of a progressive damage model in quantitative hybrid effect prediction of a comprehensive set of different 16 unidirectional interlayer (layer-by-layer) hybrid composites was assessed. Composites, produced by the hand lay-up method, made out of four different commercially available dry unidirectional fabric materials, namely high-modulus carbon, standard carbon, E-glass and basalt, were tested. Tensile tests on single fibres were performed in order to determine their Weibull strength distribution parameters, which were used as inputs of the progressive damage model. Reasonably good agreement between analytical and experimental hybrid effect results was obtained, which allowed to estimate satisfactorily the reference strengths of the unidirectional low strain composite materials. Next, an existing analytical model for the simulation of stress–strain curve of hybrid composites was adapted to contemplate the hybrid effect, which allowed to predict the following properties of unidirectional hybrid combinations: ‘yield’ stress (or pseudo-yield stress), pseudo-ductile strain and strength. It was verified as well that predictions of the three properties referred to were in close agreement with the test results. Finally, damage mode maps were used in the analysis of these properties and, furthermore, of the hybrid effect and the elastic modulus of hybrid combinations.

This work was developed within the scope of the research project “Easyfloor—Development of composite sandwich panels for building floor rehabilitation”, which aims at developing an innovative hybrid sandwich panel as an alternative construction system to conventional floor solutions, mainly for building rehabilitation. The developed hybrid sandwich panel is composed of a top face layer of steel-fibre-reinforced self-compacting concrete (FRC), a core of polyurethane (PUR) closed-cell foam, a bottom face sheet, and lateral webs of glass-fibre-reinforced polymer (GFRP). Full-scale experimental tests on the developed sandwich panels were carried out to characterize their short- and long-term (creep) flexural behaviour. The present work includes a detailed description of the developed panels and the experimental programme carried out and presents and discusses the relevant results. The experimental results showed an almost linear behaviour up to failure. The creep tests were carried out for a period of 180 days, using a creep load equal to 20% of its ultimate loading capacity. An average creep coefficient of 0.27 was obtained for this period. The composed creep model used to simulate the sandwich panel’s creep deflections by considering the individual viscoelastic contributions was able to predict the observed structural response with good accuracy., project “32EasyFloor—Development of composite sandwich panels for rehabilitation of floor buildings”, involving the company ALTO—Perfis Pultrudidos, Lda., ISISE/University of Minho, and CERis/Instituto Superior Técnico, supported by FEDER funds through the Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI)—project no. 3480 (POCI-01-0247-FEDER-003480). This work was also partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020.

In civil engineering there is a need for lightweight structural elements, specifically in applications such as the rehabilitation of degraded floors in existing buildings and modular construction. Metaheuristic search procedures are suitable to tackle optimization problems concerning material efficiency, but their use in real design applications is still limited. This paper presents the preliminary design in terms of structural, thermal, and acoustic performance of a floor system based on steel web core sandwich panels with polyurethane (PUR) foam core and a new genetic algorithm (GA) procedure developed to optimize its mass. The optimization study also addresses the minimization of cost and environmental impact and includes a wide range of practical engineering requirements. The constraints stemming from the building codes are incorporated in a new adaptive penalty function whose formulation and performance are thoroughly investigated. Examples of how to formulate the optimization problem in terms of Eurocode verifications are provided to foster the use of optimization procedures in current design practice. The results are presented in terms of design variables and constraints search histories as well as optimal feasible and unfeasible solutions. General conclusions and specific recommendations are drawn based on the case study presented for the design of sandwich floor panels and steel web core sandwich panels, respectively., This work was developed within the scope of the research project "Lightslab -Desenvolvimento de solucoes inovadoras de lajes de painel sandwich", supported by FEDER funds through the Operational Program for Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI) -project no. 33865 [POCI-01-0247-FEDER-033865]. This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. The first and third authors wish also to acknowledge the grants DFA/BD/8319/2020 and SFRH/BSAB/150266/2019 respectively, provided by Fundacao para a Ciencia e a Tecnologia, IP (FCT), financed by European Social Fund and national funds through the FCT/MCTES.

In the scope of an R&D project a new floor system based on sandwich panel has been developed. The lightweight structural system shall be a competitive solution when compared to traditional rehabilitation technique of degraded timber floors in old buildings. The layout of the sandwich prototypes designed involved the use of steel face sheet and i) steel webs and polyurethane (PUR) foam core system, ii) glass fiber-reinforced polymer (GFRP) webs and PUR foam core system and iii) outer steel webs and balsa wood core. The design of the sandwich panels included an optimization procedure. A multi-objective genetic algorithm (GA) was developed for this purpose as it is a search method well suited for the solution of optimization problems. The multi-objective GA aims at the minimization of the three objective functions, i.e. cost, mass and environmental footprint of the sandwich panel. The definition of the main feature of the algorithm includes consideration about encoding procedure, fitness scaling, selection method and handling of constraints. The boundary conditions are imposed so that the retrieved solutions will represent a feasible solution to the problem. These boundary conditions are the analytical formulation of the serviceability, ultimate limit state and thermal transmittance verifications imposed by the building codes to sandwich panels. The present paper deals with the introduction of all the aspects of the optimization problems providing as an example the optimization of the panel with steel face sheets, webs and PUR foam., This work is part of the research project Lightslab - development of innovative slab solutions using sandwich panels (POCI-01-0247-FEDER-033865), co-funded by the European Regional Development Fund (FEDER), through the "Programa Operacional Competitividade e Internacionalizacao" (POCI) and the Portuguese National Innovation Agency (ANI). The first and second authors acknowledge the grants DFA/BD/8319/2020 and SFRH/BSAB/150266/2019, respectively, provided by FCT, financed by European Social Fund and by national funds through the FCT/MCTES.

This paper presents an experimental work to investigate the effect of fatigue loading and high service temperature on the flexural performance of near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams. The experimental program included 11 beams, where the effect of the strengthening (CFRP) ratio (0.06 % and 0.18 %), fatigue load level (R1 = 0.57 and R2 = 0.38) and applied temperature (20 °C and 70 °C) have been considered. Experimental results on fatigue tests showed that high service temperature resulted in an increase in deflections and reduction in the stiffness of the specimens along the test. Moreover, the application of fatigue cycles with larger amplitude resulted in the failure of the specimens (by steel rupture), whilst specimens submitted to lower fatigue amplitude survived to the fatigue cycles. The NSM CFRP-strengthening helped to postpone the final failure of strengthened RC beams after steel reinforcement rupture during the fatigue test. Besides, damage due to fatigue derived in lower residual yielding and ultimate load in the post-fatigue test This research was supported by the Spanish Ministry of Science and Innovation (MCIN/ AEI) under project PID2020-119015GB-C22, the Generalitat de Catalunya under the grant number 2019FI_B 00054 and mobility grant from Universitat de Girona (MOB 2021)

This paper presents some of the initial results from an ongoing research project which concerns a new NSMR strengthening method, expected to provide high ductility and strengthening effect as well as increased response consistency. A prestress of 1100 MPa activation was applied to the ductile NSMR system and compared to a reference beam. Ductility in this system is provided by a response controlling anchorage system, which interacts with the adhesively bonded NSMR. The proposed adhesive has a low E-modulus which is expected to reduce stress concentration issues of adhesively bonded joints when compared to stiffer epoxy adhesives are used, where IC-debonding seems to be the dominating failure mode. A beam deflection increase of approximately 105% has been observed when using the low E-modulus adhesive compared to the the epoxy adhesive. Change in the failure modes were furthermore observed, where the brittle de-bonding failure modes were mitigated thus extending the yielding regime with approximately 150%.

Significant strengthening of concrete structures can be obtained when using adhesively-bonded carbon fiber-reinforced polymer (CFRP) systems. Challenges related to such strengthening methods are; however, the brittle concrete delamination failure, reduced warning, and the consequent inefficient use of the CFRP. A novel ductile near-surface mounted reinforcement (NSMR) CFRP strengthening system with a high CFRP utilization is introduced in this paper. It is hypothesized that the tailored ductile enclosure wedge (EW) end anchors, in combination with low E-modulus and high elongation adhesive, can provide significant strengthening and ductility control. Five concrete T-beams were strengthened using the novel system with a CFRP rod activation stress of approximately 980 MPa. The beam responses were compared to identical epoxy-bonded NSMR strengthened and un-strengthened beams. The linear elastic response was identical to the epoxy-bonded NSMR strengthened beam. In addition, the average deflection and yielding regimes were improved by 220% and 300% (average values), respectively, with an ultimate capacity comparable to the epoxy-bonded NSMR strengthened beam. Reproducible and predictable strengthening effect seems obtainable, where a good correlation between the results and applied theory was reached. The brittle failure modes were prevented, where concrete compression failure and frontal overload anchor failure were experienced when failure was initiated., The funding source do not wish to be revealed as stated in this section.

This work addresses the durability of structural epoxy adhesives and carbon fibre reinforced polymer (CFRP) laminates typically used in strengthening of existing reinforced concrete structures exposed to natural ageing. The experimental program included four natural (real) outdoor environments inducing ageing mainly caused by carbonation, freeze-thaw attack, elevated temperatures, and airborne chlorides from seawater. Moreover, a control (reference) environment (20 °C of temperature and 55% of relative humidity) and an environment involving water immersion of the materials under controlled temperature (20 °C of temperature) were also included in this investigation. The characterization involved the assessment of the physical, chemical and mechanical properties along a study period of up to two years. Furthermore, comparisons between the natural ageing tests developed in the scope of the present work and accelerated ageing tests existing in the literature were performed. Regarding to the epoxy adhesives, an increase in the glass transition temperature with the time was observed, while the tensile properties decreased, regardless of the outdoor environment. The CFRP laminates were marginally affected by the studied environments. Despite the remarkable dispersion of the results observed in the accelerated ageing tests for the period investigated, this testing protocol yielded higher mechanical degradation than under natural ageing., This work was carried out in scope of the project FRPLongDur POCI-01-0145-FEDER016900 (FCT PTDC/ECM-EST/1282/2014) funded by national funds through the Foundation for Science and Technology (FCT) and co-financed by the European Fund of the Regional Development (FEDER) through the Operational Program for Competitiveness and Internationalization (POCI) and the Lisbon Regional Operational Program and, partially financed by the project POCI-01-0145-FEDER007633, and partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. This work is financed by national funds through. Foundation for Science and Technology, under grant agreement (SFRH/BD/131259/2017) attributed to the first author.

This paper addresses the viscoelastic behaviour of a commercially available cold-curing structural epoxy adhesive, under different preparation, curing and hygrothermal conditions. The main parameters studied were the preparation method (influence of the degassing and the temperature of the initial curing), the creep stress level, and the hygrothermal conditions. Tensile creep tests last up to 2400 hours. Test results revealed that the preparation method has great influence on the tensile properties of the adhesive, particularly on the viscoelastic response where degassing and curing at 20 ºC showed lower creep deformations. Specimens under 98% of relative humidity faced tertiary creep and then rupture. For the adopted levels of creep stress, the adhesive shows a linear creep behaviour, being parameterized using the Burgers and the modified Burgers equations., This work was carried out in scope of the project FRPLongDur POCI-01-0145-FEDER-016900 (FCT PTDC/ECM-EST/1282/2014) funded by national funds through the Foundation for Science and Technology (FCT) and co-financed by the European Fund of the Regional Develop-ment (FEDER) through the Operational Program for Competitiveness and Internationalization (POCI) and the Lisbon Regional Operational Program and, partially financed by the project POCI-01-0145-FEDER-007633. This work was also partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE) , under reference UIDB/04029/2020. The authors also like to thank the S&P Clever Reinforce-ment Iberica Lda.com pany for providing the materials. The first author wishes also to acknowledge the grant SFRH/BD/131259/2017 provided by Fundacao para a Ciencia e a Tecnologia (FCT) , while the fourth author acknowledge his sabbatical grant SFRH/BSAB/150266/2019, provided by FCT, financed by European Social Fund and by national funds through the FCT/MCTES.

The influence of the adhesive type on bond behaviour between concrete and Carbon Fibre Reinforced Polymers (CFRP) laminate strips, in the context of Near Surface Mounted (NSM) strengthening technique, is considered as crucial for an efficient design. Thus, direct pullout tests were carried out to assess the influence of i) type of adhesive ii) CFRP cross-section and (iii) bond length on behaviour of NSM-CFRP system. Two types of stiff adhesives and one type of flexible adhesive were studied. For similar bond lengths, significantly higher maximum pullout force and bond stiffness were observed in the case of stiff adhesives, while noticeably higher slip at maximum force was achieved with the flexible adhesive. Analytical and numerical investigations were carried out in order to determine the local bond stress-slip relationships for both stiff and flexible adhesives. After demonstrating its good predictive performance, the analytical approach was used to design curves of the required anchorage lengths of NSM-CFRP system at ultimate limit state conditions. For the analytically calibrated mechanical parameters of NSM bond-slip law a two-dimensional numerical model of the direct pullout tests was worked out., PTDC/ECMEST/1282/2014; POCI-01-0145-FEDER-016900; POCI-01-0145-FEDER-007633; SFRH/BD/131259/2017; SFRH/BSAB/150266/2019. FEDER funds through the Operational Program for Competitiveness Factors – COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project FRPLongDur POCI-01-0145-FEDER-016900 (FCT PTDC/ECMEST/1282/2014) and partly financed by the project POCI-01-0145-FEDER-007633. The first and second authors acknowledge the grants SFRH/BD/131259/2017 and SFRH/BSAB/150266/2019 provided by FCT, respectively, financed by European Social Fund and by national funds through the FCT/MCTES

An experimental study on the performance of adhesive connection between Glass Fibre Reinforced Polymer (GFRP) plates and Steel Fibre reinforced self-compacting Concrete (FRC) was conducted. Fresh FRC was poured out onto the surface of GFPR plates, to create 40 square specimens (300 by 300 by 45 [mm]). Pull-off tests were performed to evaluate the tensile strength of the adhesive connection when different types of adhesives (four) and surface treatments (three) are used. Furthermore, the effect of five different environmental conditions on the tensile strength of the adhesive connection was also evaluated. After analysing the results and performing a variance analysis (ANOVA), it has been shown that the pull-off behaviour is highly influenced by the type of adhesive and by the environmental action. In spite of that, the dominant failure mode was cohesive failure in the FRC substrate, therefore good bond conditions between both materials were achieved., POCI-01-0247-FEDER-003480; SFRH/BSAB/150266/2019; SIKA, KERAKOLL and MAPEI. project “EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings”, involving the company ALTO – Perfis Pultrudidos, Lda., ISISE/University of Minho and CERis/Instituto Superior Técnico, supported by FEDER funds through the Operational Program for Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI) – project no. 3480 (POCI-01-0247-FEDER-003480). The first author acknowledges the grant SFRH/BSAB/150266/2019 provided by FCT, financed by European Social Fund and by national funds through the FCT/MCTES. Acknowledgments are extended to LEST – Laboratório de Estruturas for their material support. The authors would like to thank SIKA, KERAKOLL and MAPEI companies for suppling the adhesives

In order to overcome the main mechanical drawbacks of GFRP profiles, namely their high deformability and proneness to instability phenomena, several GFRP-concrete hybrid solutions comprising bonded connections with epoxy adhesive have been proposed. Although being able to provide almost full interaction at the GFRP-concrete interface(s) (at least in the short-term), there is very little information about the durability of such connection systems, which raises concerns about the long-term performance of hybrid structural solutions. This paper presents experimental and numerical investigations on the durability of adhesively bonded connections between pultruded GFRP profiles and steel fibre reinforced self-compacting concrete (SFRSCC). GFRP-SFRSCC specimens were first subjected to accelerated ageing, involving thermal and wet-dry cycles, and then subjected to push-out tests. The accelerated ageing did not have significant influence on the strength of the GFRP-SFRSCC connection; however, it had a very deleterious effect on its stiffness. The numerical study included the development of finite element models of the specimens tested. Using bi-linear bond-slip laws, it was possible to simulate the test results with good accuracy. In the final part of the paper, the influence of the interface stiffness reduction on the deformability of a real hybrid structure (the Sao Silvestre footbridge) is analysed. Although the stiffness of the GFRP-SFRSCC interface is considerably reduced by the ageing processes, this results in a very small increase of the overall mid-span deflections of the footbridge.

Preprint, This paper presents design procedures for fibre reinforced polymer (FRP) systems inserted in the cover of concrete elements according to the near-surface mounted (NSM) technique. Such strengthening system depends greatly on their bond strength. Two existing design formulations to estimate the bond strength of NSM FRP systems in concrete are studied. A reliability analysis is conducted with the purpose of making the design formulations consistent with the partial safety factors philosophy, including the Eurocodes. Hence, the necessary probabilistic distributions are calibrated based on a large database of bond tests. The results presented herein show that the existing guidelines can be extended and adopted under the framework of the Eurocodes. However, mainly due to their limitations in addressing individually all the possible failure modes, the variability of the probabilistic distributions found are quite high, leading to high partial coefficients of safety., This work was supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project FRPLongDur POCI-01-0145-FEDER-016900 (PTDC/ECM-EST/1282/2014) and partly financed by the project POCI-010145-FEDER-007633. The first author wishes also to acknowledge the Grant No. SFRH/BD/87443/2012 provided by FCT., info:eu-repo/semantics/publishedVersion

Epoxy adhesives have been extensively used in strengthening of reinforced concrete structures. In spite of that, research on the viscoelastic behaviour of these adhesives and its influence on the mechanical behaviour of strengthened concrete structures is scarce, particularly at the early ages of curing. The main goal of present work is to better understand the tensile creep behaviour of a specific commercial epoxy adhesive both at early ages and at long term. For this purpose, an experimental program comprising tensile creep tests was performed, in which epoxy specimens were subjected to: (i) equal stress levels but loaded at different ages, and; (ii) two different stress levels for a specific loading age. The results obtained have confirmed the viability of the principles of homogeneity and superposition, thus allowing the classification of this epoxy as linear viscoelastic. In addition, analytical simulations with Burgers model were carried out, and its predictive performance was considered insufficient at early ages, particularly upon unloading. In order to surpass some disadvantages of this model, a new framework is proposed to analytically evaluate the creep curing behaviour of this type of viscoelastic epoxy adhesives. The obtained results evidenced the capability of the proposed framework to predict the creep behaviour of an epoxy adhesive since its early ages., This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project FPReDur FCOMP-01-0124-FEDER-028865 (FCT reference PTDC/ECM-EST/2424/2012) and the project VisCoDyn FCOMP-01-0124-FEDER-041751 (FCT reference EXPL/ECM-EST/1323/2013), as well as the project POCI-01-0145-FEDER-007633. The authors also like to thank the S&P Clever Reinforcement Ibérica Lda. company for providing the material tested in ambit of the present work. The first author wishes also to acknowledge the grant SFRH/BD/89768/2012 provided by FCT. The second author wishes also to acknowledge the grant SFRH/BDE/96381/2013 co-funded by CiviTest-Pesquisa de Novos Materiais para a Engenharia Civil, Lda and by FCT., info:eu-repo/semantics/publishedVersion

The paper presents the numerical modelling of a temporary residential floor prototype composed of three jointed composite floor sandwich panels made of glass fiber reinforced polymer (GFRP) skins, a polyurethane foam core (PU) and pultruded U-shaped GFRP profiles working as ribs. Panels are supported on a GFRP pultruded frame structure. A 3D nonlinear finite element model is developed considering geometrical and material nonlinearities and adherent surfaces interaction. The model is coherently validated with experimental results, showing its capability to capture the mechanical performance of a single panel (which includes the possibility of local instability on the GFRP skin), two and three panels working together, and the whole prototype. A series of parametric studies are then conducted using the numerical model developed. Those studies aim to (i) assess the influence that ribs on the panel stiffness and on the shear stresses distribution through the sandwich panel’s components, (ii) the flexibility of the designed connections between jointed panels and frame structure, and (iii) the influence of geometry in the modular housing., This work is part of the research project ClickHouse – Development of a prefabricated emergency house prototype made of composites materials, involving the company ALTO – Perfis Pultrudidos, Lda., CERis/Instituto Superior Técnico and ISISE/University of Minho, supported by FEDER funds through the Operational Program for Competitiveness Factors – COMPETE and the Portuguese National Agency of Innovation (ADI) – project no. 38967. Special thanks are given to company ALTO – Perfis Pultrudidos, Lda., who manufactured all the elements (GFRP profiles and sandwich panels) involved in the research. The numerical model was performed in collaboration with the Department of Construction Engineering of the Universitat Politècnica de València.

Freshwater is an increasingly scarce resource. Its use in the production of concrete is one important contributor to its fast depletion. Alternatively, the use of seawater for reinforced concrete production, combined with the use of glass fibre reinforced polymers (GFRP) as reinforcement, may represent an interesting solution to increase concrete sustainability. The objective of this paper is to explore this promising solution through the development of concrete compositions with seawater. Additionally, it is also an objective to assess the bond behaviour between GFRP rods and concrete, in a design perspective. The influence of concrete age, rod diameter and anchorage length were also investigated. An analytical model capable of determining the local bond stress-slip laws was used. Results demonstrated that the use of seawater had no relevant effects on neither concrete mechanical properties nor bond behaviour., The study presented in this paper is a part of the research project “NEXT-SEA: Next Generation Monitoring of Coastal Systems in a Scenario of Global Change”, financed by CCDRN and FEDER funds in the scope of the Next-sea project (NORTE-01-0145-FEDER-000032). The authors acknowledge all the companies that have been involved supporting and contributing for the development of this study, mainly: S&P Clever Reinforcement Ibérica Lda., Burgoparaíso – Unipessoal Lda., Secil, Sika Portugal – Produtos Construção e Indústria S.A. The first and the last authors wishes also to acknowledge the grants SFRH/BD/131913/2017 and SFRH/BSAB/150266/2019, respectively, provided by FCT, financed by European Social Fund and by national funds through the FCT/MCTES.

The use of mechanical anchorage systems can delay or avoid premature failure of reinforced concrete (RC) structures with externally-bonded fiber-reinforced polymer (EB-FRP) laminates. This work reports the results of an experimental program aimed at studying the bond behavior of a metallic anchorage plate, typically used for pre-stressed EB-FRP systems. The overall experimental program comprised 17 concrete prisms with carbon fiber reinforced polymer (CFRP) laminates externally bonded to the concrete with mechanical anchorage at the end and where different levels of normal stress were applied. Direct shear tests were carried out using two configurations: (i) the steady-state tests, where the laminate was pulled out from the block with increasing force and constant temperature (20 ºC, 60 ºC and 80 ºC); (ii) and the transient tests, where the laminate was pulled out with constant force (0.36%, 0.45% and 0.54% of strain) and the temperature was gradually increased. Experimental results showed that the ultimate capacity of the mechanical anchorage can decrease by 44-59% depending on the temperature and level of normal stress., This work was supported by FEDER funds through the Operational Program for Competitiveness Factors – COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project FRPLongDur POCI-01-0145- FEDER-016900 (FCT PTDC/ECM-EST/1282/2014) and partly financed by the project POCI544 01-0145-FEDER-007633. The first author wishes also to acknowledge the grant SFRH/BD/98309/2013 provided by FCT. The second author acknowledges the Spanish Government (Ministerio de Educación, Cultura y Deporte) for the grant José Castillejo ref. CAS16/00288. Finally, the authors also like to thank all the companies that have been involved supporting and contributing for the development of this study, mainly: the S&P Clever Reinforcement Ibérica Lda. company for providing the laminates, the epoxy adhesive and metallic anchorage plates; the Hilti Portugal-Produtos e Serviços, Lda. company for providing the chemical bond agent to fix the anchor bolts; and the Tecnipor-Gomes & Taveira Lda company for producing the concrete blocks.

Over the last two decades, the use of fibre reinforced polymer (FRP) materials for strengthening existing reinforced concrete (RC) structures has been constantly increasing, and nowadays it is considered state-of-the-art and is frequently used by the construction industry. Typically, these composite materials are externally bonded (EBR technique) or near-surface-mounted (NSM technique) on the elements to be retrofitted. Although substantial research has been performed and design rules have been established, most studies focused on the short-term structural performance of the strengthened elements without considering their long-term behaviour. The FRPLongDur R&D project aims at studying the long-term structural behaviour and durability performance of RC elements strengthened in flexure with Carbon FRP (CFRP) laminates according to the EBR and NSM techniques, under various real environmental exposure and loading conditions (carbonation, moisture, chlorides, thermal and freeze-thaw cycles, initial FRP pre-strain level and sustained loading). For this purpose, several prototypes have been installed in different sites of Portugal, each one being representative of the above listed environments under investigation, currently considered as the most critical exposure conditions. Additionally, test specimens of the materials involved – CFRP laminate, epoxy adhesive and concrete – and bond specimens have been prepared and installed near the other prototypes in order to evaluate their own durability. The present paper presents the initial insights on the ongoing FRPLongDur project., PTDC/ECM-EST/1282/2014; SFRH/BD/131259/2017, info:eu-repo/semantics/publishedVersion

In the past two decades, the use of Fiber Reinforced Polymer (FRP) bars in reinforced concrete structures has been increasing, replacing conventional steel reinforcement, especially in areas with adverse environmental conditions. This paper presents a literature review on the bond behavior of FRP bars to concrete, which includes studies on their (i) instantaneous and (ii) long-term (durability) properties. This work also included a database created from the collection of experimental data in the existing literature, with results from a total of 1002 pullout tests, intended to clarify the most relevant parameters that influence the bond of FRP bar to concrete. The analysis conducted on the database yielded the conclusion that FRP bar exhibits a good performance as reinforcement in concrete structures. Moreover, the collected data allowed the development of FRP bar to concrete bond (durability) long-term predictions considering the type of exposure environment., The study presented in this paper is a part of the research project “EcOffShorBE – Eco Offshore Built Environment”, financed by FEDER funds in the scope of the EcOffShorBE project (NORTE-01-0247-FEDER-037417). This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. The first and second authors wish also to acknowledge the grants no. DFA/BD/6484/2020 and SFRH/BSAB/150266/2019, respectively, provided by FCT.

Several reinforcing strategies have recently been developed to overcome glass brittleness and numerical simulations are essential to investigate the structural behaviour of such hybrid systems. Based on previous experimental results from monotonic quasi-static tests, this paper presents a numerical study about the flexural behaviour of glass beams reinforced with glass fibre reinforced polymer (GFRP) laminates bonded with two different adhesives: polyurethane and epoxy. The main objective of this study is to evaluate the efficiency of different constitutive models to simulate the non-linear behaviour of glass, considering the following factors: initial stiffness, cracking load, post-cracking stiffness, crack pattern and progressive failure. The glass is simulated using smeared crack (SCM) and damaged plasticity (DPM) models with static and dynamic numerical approaches. Particular attention is paid to the influence of the several parameters that influence the structural behaviour of glass (e.g. threshold angle), as well as to the interfaces between all the materials involved (e.g. thickness of the adhesive layer). In relation to static numerical approaches, dynamic numerical approaches require more computational effort and their dynamic effects may influence the structural responses obtained; however, they also show to be able to capture all the stages of cracking in greater detail, because stability during cracking formation is guaranteed even at smaller loading stages. Since DPM models do not allow considering a maximum absolute damage factor of 1.0, the smeared crack models simulate better the non-linear behaviour of glass., The first and third authors wish also to acknowledge the grants SFRH/BD/122428/2016 and SFRH/BSAB/150266/2019, respectively, provided by Fundação para a Ciência e a Tecnologia, IP (FCT), financed by European Social Fund and by national funds through the FCT/MCTES.

This work investigates the quasi-static, low-cycle and fatigue behavior of hybrid glass/ultra-high modulus carbon (GC) and low modulus/ /high modulus carbon (CC) fiber composites. These pseudo-ductile unidirectional interlayer hybrids are a new type of composites whose potential is not yet fully understood, particularly under cyclic/fatigue loading. Different test methods (digital image correlation, video extensometer and thermal camera) were used to record the evolution of the strain, damage and temperature during loading. The results of quasi-static loading shown pseudo-ductile responses with multiple fractures for all the series. The CC specimens exhibited higher initial elastic modulus, ‘yield’ stress and strength, while the GC specimens showed the highest pseudo-ductile strain. Much higher capacity of CC to resist to fatigue loading was observed. In the GC specimens significant damage was accumulated during fatigue loading, when the damage evolution of multiple fractures in different layers developed to delamination between the glass and carbon layers., The authors acknowledge the assistance provided by the technical team of the structural engineering Experimental platform (GIS-ENAC at the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland) for the use of testing equipment, and the support of S&P Clever Reinforcement, that provided the raw materials (E-glass, standard and high modulus carbon sheets and the epoxy adhesive). The first author acknowledge the STSM grant provided by COST Action CA18120 (CERTBOND), supported by COST (European Cooperation in Science and Technology). The second author acknowledge his sabbatical grant SFRH/BSAB/150266/2019, provided by Fundação para a Ciência e a Tecnologia, IP (FCT), financed by European Social Fund and by national funds through the FCT/MCTES and also the financial support by the EPFL/Section of Civil engineering. This work is also part of the research project ‘EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings’, involving the company ALTO – Perfis Pultrudidos, Lda., CERis/Instituto Superior Técnico and ISISE/University of Minho, supported by FEDER funds through the Operational Program for Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI) – Project No. 3480 (POCI-01-0247-FEDER 003480).

This paper presents the effectiveness of soft computing algorithms in analyzing the bond behavior of fiber reinforced polymer (FRP) systems inserted in the cover of concrete elements, commonly known as the near-surface mounted (NSM) technique. It focuses on the use of Data Mining (DM) algorithms as an alternative to the existing guidelines’ models to predict the bond strength of NSM FRP systems. To ease and spread the use of DM algorithms, a web-based tool is presented. This tool was developed to allow an easy use of the DM prediction models presented in this work, where the user simply provides the values of the input variables, the same as those used by the guidelines, in order to get the predictions. The results presented herein show that the DM based models are robust and more accurate than the guidelines’ models and can be considered as a relevant alternative to those analytical methods., This work was supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project CutInDur PTDC/ECM/112396/2009 (Ref. PTDC/ECM/112396/2009) and partly financed by the project POCI-01-0145-FEDER-007633. The first author wishes also to acknowledge the Grant No. SFRH/BD/87443/2012 provided by FCT.

This paper presents a tension stiffening model for Fiber Reinforced Concrete (FRC) tensile member reinforced by hybrid glass fiber reinforced polymer (GFRP) and steel bars. The model is developed through an explicit analytical bond formulation by considering a four-linear bond shear stress-slip relationship to simulate the bond behavior between reinforcing bars and surrounding FRC. The model is also capable of simulating both the fiber reinforcement contribution and the yielding stage of steel bar at cracked section. Additionally, a FE Model is carried out using a multi-directional smeared crack approach for modeling cracking process in FRC, and adopting interface finite elements to simulate the bond behavior between reinforcements and FRC, whose constitutive model was defined from the aforementioned bond law. Both the analytical and numerical approaches showed a good agreement with some recent experimental results on tension-stiffening in the literature. Finally, an extensive parametric study is performed by using the analytical model, and the influence of the involved parameters on the tension-stiffening and cracking behavior of hybrid GFRP/steel FRC tensile member is investigated., QREN project n. 30367 – UrbanCrete, Portuguese Foundation for Science and Technology (FCT) - SFRH/BD/77409/2011

With the aim of characterising a commercially available epoxy adhesive used for fibre-reinforced polymers strengthening applications, when submitted to different environmental conditions, mainly thermal (TC), freeze-thaw (FT), and wet-dry (WD) cycles and immersion in pure (PW) and water with chlorides (CW) for periods of exposure that lasted up to 16 months, an experimental program was carried out. Several methodologies were used in its characterization, mainly the scanning electron microscope (SEM), dynamic mechanical analysis (DMA), standard tensile tests (STT) coupled with digital image correlation (DIC). In general the results revealed that the chemical composition was not affected by the environmental conditions. Nevertheless, it was verified through DMA and STT that the modulus of elasticity and tensile strength of the epoxy adhesive increased in the TC, while the specimens submitted to PW and CW faced a high degradation in terms of its mechanical properties. Eventually, the glass transition temperature (Tg) was not affected by the environmental conditions, apart from the specimens subjected to TC and FT, presenting a higher and lower Tg, respectively, when compared with the reference specimens., This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project FPReDur PTDC/ECM-EST/2424/2012. The first and second authors wishes also to acknowledge the grants SFRH/BD/89768/2012 and SFRH/BD/80338/2011, respectively, provided by FCT.

This work presents the results of an experimental and numerical investigation on the flexural behaviour of reinforced concrete (RC) slabs strengthened by carbon fibre reinforced polymers (CFRP) laminates applied according to the near surface mounted (NSM) technique, using stiff and flexible adhesives. Two study variables were analysed: i) the adhesive type and ii) the existence or not of pre-cracking on the slabs. The results show a clear dependence of slab’s flexural performance on the adhesive type: the use of flexible adhesive yields to 80% of the maximum load achieved with stiff adhesives. The existence of pre-damage did not affect the structural behaviour of the slabs. CFRP rupture was observed with the use of stiff adhesives while CFRP debonding has occurred with the flexible one. Finally, a higher ductility was observed when using flexible adhesive. A numerical model was worked out and calibrated to simulate the flexural behaviour of the tested slabs. The numerical simulations showed a very good agreement with the experiments. Besides the very good predictive performance in terms of load-displacement behaviour, the numerical model also correctly reproduced the failure modes obtained in the experiments and the differences in the bonding mechanisms of slabs strengthened with the stiff and flexible adhesives. It was demonstrated that the proposed numerical model can be used in engineering practice for the analysis and design of NSM CFPR strengthening systems for existing RC structures., FEDER funds through the Operational Program for Competitiveness Factors – COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project FRPLongDur POCI-01-0145-FEDER-016900 (FCT PTDC/ECMEST/1282/2014) and partly financed by the project POCI-01-0145-FEDER-007633. The first and third authors acknowledge the grants SFRH/BD/131259/2017 and SFRH/BSAB/150266/2019 provided by FCT, respectively, financed by European Social Fund and by national funds through the FCT/MCTES

The main goal of the work herein presented is to propose an accurate three-dimensional finite element model to predict the compressive behaviour of hybrid FRP-confined concrete. This was achieved through the modification of the concrete damaged plasticity model (CDPM) available in ABAQUS software, since the original CDPM has shortcomings that make it unusable to predict the compressive behaviour of confined concrete. It was demonstrated that, by turning the yield function and the flow rule dependents on the confining pressure, it is possible to use the model referred to and obtain accurate results. An analytical model was used to obtain the input parameters needed to calibrate the CDPM. A specific user subroutine was developed to modify the original CDPM. Hybrid FRP properties were calibrated as well, using an appropriate analytical model. Plasticity was assumed in the hybrid combinations for which pseudo-ductile tensile responses occurred. The performance of the proposed CDPM was validated using both experimental results and analytical predictions. It was concluded that, by using the developed 3D finite element model for hybrid FRP-confined concrete in compression, a very good agreement between experimental, analytical and numerical compressive stress-strain and lateral strain-axial strain curves is reached., The authors wish to thank to FCT - Portuguese Foundation for Science and Technology and to the Doctoral Program Eco-Construction and Rehabilitation for supporting the PhD grant (PD/BD/52660/2014). Acknowledgements are extended to the following programs that partially supported the study herein presented: European Funds for Regional Development (FEDER) through the Operational Program for Competitiveness Factors (COMPETE), Operational Program for Competitiveness and Internationalization (POCI), and again FCT through both FRPLongDur POCI-01-0145-FEDER-016900 (FCT reference PTDC/ECM-EST/1282/2014) and POCI-01-0145-FEDER-007633 projects. Last but not least, the authors also acknowledge the support of both S&P Clever Reinforcement Ibérica Lda and Dalla Betta Group Company.

An experimental campaign was carried out to assess shear creep behaviour of a rigid low-density closed-cell polyisocyanurate (PIR) foam. Two service temperature values were considered, 20 ºC and 30 ºC, and the applied stresses ranged between 20% and 60% of the corresponding shear strength. The results showed that a stress amplitude of 30% was enough to cause nonlinear creep response. Furthermore, creep deformations were slightly smaller in the tests at 30 ºC, a fact that matched the viscoelastic response of the PIR foam obtained from DMA testing. Finally, creep prediction curves were calibrated through an analytical approach based on the Findley’s power law., This work is part of the research project “EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings”, involving the company ALTO – Perfis Pultrudidos, Lda., CERis/Instituto Superior Técnico and ISISE/University of Minho, supported by FEDER funds through the Operational Program for Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI) - project no. 3480 (POCI-01-0247-FEDER-003480). The second author acknowledge the grant SFRH/BSAB/150266/2019 provided by FCT, financed by European Social Fund and by national funds through the FCT/MCTES. Acknowledgments are extended to LEST – Laboratório de Estruturas for their material support. The contribution of the Department of Mechanical Engineering of the University of Minho is also gratefully acknowledged in the person of Engineer Pedro Ribeiro. Lastly, the authors would like to thank SIKA Company for suppling the adhesive.

The externally bonded reinforcement (EBR) technique is one of the most widely used strategies for the flexural strengthening of reinforced concrete (RC) with fibre reinforced polymer (FRP) materials. The EBR technique offers several structural advantages when the FRP material is prestressed. The development of high shear stresses at the ends of the prestressed FRP material can cause premature FRP peeling-off failure. This premature failure can be delayed or even avoided with the use of special end-anchorage systems, like the mechanical anchorage (MA) system and the gradient anchorage (GA) system. This paper presents an experimental and a numerical study on RC slabs strengthened in flexure with prestressed carbon FRP (CFRP) laminate strips, namely: (i) one reference slab; (ii) one slab strengthened with nonprestressed externally bonded CFRP (EB-CFRP) laminate; (iii, iv) and two slabs strengthened with prestressed EB-CFRP laminates using the MA and GA systems. The performance of these simulations was compared with results of the slabs experimentally tested up to failure. Subsequently, these models were used on a parametric study that intended to investigate the influence of different parameters affecting the behaviour of the slabs strengthened with prestressed EB-CFRP laminates., FCT -Fundação para a Ciência e a Tecnologia(POCI-01-0145-FEDER-007633), info:eu-repo/semantics/publishedVersion

This paper addresses the durability of bond between concrete and carbon fibre reinforced polymer (CFRP) strips installed according to the near-surface mounted (NSM) technique (NSM CFRP-concrete systems) under the effects of two main groups of environmental conditions: (i) laboratory-based ageing conditions; (ii) real outdoor ageing conditions. The bond degradation was evaluated by carrying out direct pullout tests on aged specimens that were previously subjected to distinct environmental conditions for different periods of exposure. Moreover, the degradation of the mechanical properties of the involved materials was investigated. The digital image correlation (DIC) method was used to document the evolution of the deformation fields at the surface over the whole region of interest consisting of concrete and epoxy adhesive at the ligament region. This information supported the discussion about the evolution of the bond resistant mechanism developed in NSM CFRP-concrete specimens during testing, as well as the assessment of the bond quality of the system. In general, the results obtained from the durability tests conducted have shown that the different exposure environments, which may be considered as quite severe, did not result in significant damage on NSM CFRP-concrete system. The maximum decrease of about 12% on bond strength was obtained for real outdoor environments. Conversely, a maximum increase of 8% on bond strength was obtained on the specimens exposed to the temperature cycles between –15 °C and +60 °C. DIC allowed to document the stress transfer mechanisms established between the CFRP and the concrete substrate, revealing the crack patterns and the influence widths of the CFRP reinforcement strips, which were shown to be important for avoiding group effect when using multiple parallel strengthening CFRP strips., FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the projects CutInDur FCOMP-01-0124-FEDER-014811 (PTDC/ECM/112396/2009), FRPLongDur POCI-01-0145-FEDER-016900 (PTDC/ECM-EST/1282/2014) and partly financed by the project POCI-01-0145-FEDER-007633. The authors also like to thank all the companies that have been involved supporting and contributing for the development of this study, mainly: S&P Clever Reinforcement Ibérica Lda., Artecanter - Indústria de Transformação de Granitos, Lda., Vialam – Indústrias Metalúrgicas e Metalomecânicas, Lda., info:eu-repo/semantics/publishedVersion

Within the civil engineering field, the use of the Finite Element Method has acquired a significant importance, since numerical simulations have been employed in a broad field, which encloses the design, analysis and prediction of the structural behaviour of constructions and infrastructures. Nevertheless, these mathematical simulations can only be useful if all the mechanical properties of the materials, boundary conditions and damages are properly modelled. Therefore, it is required not only experimental data (static and/or dynamic tests) to provide references parameters, but also robust calibration methods able to model damage or other special structural conditions. The present paper addresses the model calibration of a footbridge bridge tested with static loads and ambient vibrations. Damage assessment was also carried out based on a hybrid numerical procedure, which combines discrete damage functions with sets of piecewise linear damage functions. Results from the model calibration shows that the model reproduces with good accuracy the experimental behaviour of the bridge.

The Externally Bonded Reinforcement (EBR) technique using Carbon Fiber-Reinforced Polymers (CFRP) has been commonly used to strengthen concrete structures in flexure. The use of prestressed CFRP material offers several advantages well-reported in the literature. Regardless of such as benefits, several studies on different topics are missing. The present work intends to contribute to the knowledge of two commercially available systems that differ on the type of anchorage: (i) the Mechanical Anchorage (MA), and (ii) the Gradient Anchorage (GA). For that purpose, an experimental program was carried out with twelve slabs monotonically tested under displacement control up to failure by using a four-point bending test configuration. The effect of type of anchorage system (MA and GA), prestrain level (0 and 0.4%), width (50 mm and 80 mm) and thickness (1.2 mm and 1.4 mm) of the CFRP laminate, and the surface preparation (grinded and sandblasted) on the flexural response were the main studied parameters. Better performance was observed for the slabs: (i) with prestressed laminates, (ii) for the MA system, and (iii) with sandblasted surface preparation., This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project FRPreDur - PTDC/ECM-EST/2424/2012. The authors also like to thank all the companies that have been involved supporting and contributing for the development of this study, mainly: S&P Clever Reinforcement Iberica Lda, S&P Clever Reinforcement Company (Switzerland), Tecnipor - Gomes & Taveira Lda., Via lam - Industrias Metalurgicas e Metalomecanicas, Lda., Hilti Portugal-Produtos e Servicos, Lda. The first and second authors wish also to acknowledge the grants SFRH/BD/98309/2013 and SFRH/BD/94850/2013, respectively, provided by FCT.

This paper presents the results of an experimental research on bond and flexural behavior of concrete elements strengthened with carbon fiber reinforced polymer (CFRP) laminate strips under fatigue loading conditions, applied according to the near-surface mounted (NSM) strengthening technique. Long-term performance of the NSM system could be compromised by fatigue loading, which may result in deterioration and weakening of individual components (steel, FRP, concrete), or loss of bond performance and composite action. Hence, an experimental program composed of direct pullout tests and slab specimens was carried out to evaluate the influence of the stress level and amplitude of cycles imposed to the specimens. In bond fatigue tests, debonding failure occurred for a maximum stress level corresponding to 60% of the ultimate bond load obtained from monotonic loading. The fatigue loading imposed on the slabs did not yield to its failure. Consequently, the load carrying capacity obtained from post-fatigue tests of strengthened slabs was not significantly affected by this action., This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project CutInDur PTDC/ECM/112396/2009. The authors also like to thank all the companies that have been involved supporting and contributing for the development of this study, mainly: S&P Clever Reinforcement Iberica Lda., Casais - Engenharia & Construcao S.A., Artecanter - Industria de Transformacao de Granitos, Lda., Tecnipor - Gomes & Taveira Lda., Vialam - Industrias Metalurgicas e Metalomecanicas, Lda., Hilti Portugal-Produtos e Servicos, Lda., Novo Modelo Europa, S.A., Sika Portugal - Produtos Construcao e Industria, and S.A., Cachapuz - Equipamentos para Pesagem, Lda. The first and second authors wishes also to acknowledge the Grants SFRH/BD/80338/2011 and SFRH/BD/89768/2012, respectively, provided by FCT.

Manuscript version, The present paper explores a new modular floor prototype to be used in emergency houses. The prototype is composed of a frame structure made of glass-fibre-reinforced polymer tubular pultruded profiles, a slab made of sandwich panels with a polyurethane foam core and glass-fibre-reinforced polymer skins, and a tailored connection system that provides integrity between assembled components. A series of experimental tests are carried out including flexural tests on a single panel, on two and three connected panels, and on the assembled floor prototype. The behaviour of the panels is analysed when they are not considered part of the glass-fibre-reinforced polymer framed structure, namely the failure mechanisms and the efficiency of the proposed connection system between the panels. The performance of the floor prototype to support typical load conditions of residential houses is also assessed. Additionally, an analytical model was used to deeper study the behaviour of the developed sandwich panels, connection system and the modular floor prototype., SFRH/BSAB/114302/2016; ADI - project no. 38967, info:eu-repo/semantics/publishedVersion

The use of Carbon Fibre-Reinforced Polymer (CFRP) laminates as Externally Bonded Reinforcement (EBR) has been widely used to strengthen concrete structures in flexure. In some strengthening applications special end-anchorage systems are required at the end of the FRP element in order to transfer the high shear stresses, typically developed between the FRP reinforcement and the concrete substrate, so as to avoid a premature FRP peeling-off failure. A typical anchorage system is the mechanical anchorage, where the laminate is transversely compressed through an anchorage plate, which is fixed to concrete with prestressed screws. The influence of laminate width and compressive stresses created by the anchorage system still requires better understanding. This paper aims at studying the experimental overall bond response of concrete elements strengthened with mechanically anchored EBR CFRP systems. For this purpose, 6 concrete blocks of 200x500x800 mm3 were strengthened with CFRP laminates of different widths using EBR technique; afterwards they were mechanically anchored to the concrete with different levels of transverse compression, and finally they were tested under a pull-out configuration until failure. The results of the investigation show the influence of the width of the laminate, the level of confinement on the bond strength and capacity of the system., This work was supported by FEDER funds through the Operational Program for Competitiveness Factors – COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project FRPLongDur POCI-01-0145-FEDER-016900 (FCT PTDC/ECMEST/1282/2014) and partly financed by the project POCI-01-0145-FEDER-007633. The first author acknowledges the Spanish Government (Ministerio de Educación, Cultura y Deporte) for the grant José Castillejo ref. CAS16/00288. The second author wish also to acknowledge the grant SFRH/BD/98309/2013 provided by FCT. Finally, the authors also like to thank the S&P Clever Reinforcement Ibérica Lda. company for providing the materials, info:eu-repo/semantics/publishedVersion

An experimental study on the tensile stress–strain curves of interlayer (layer-by-layer) unidirectional hybrid FRP composites was conducted aiming at evaluating the corresponding hybrid effect and pseudo-ductility of this innovative solution. Different combinations of the following dry unidirectional fabric materials, also varying the number of layers, were adopted in tests: high-modulus carbon, standard carbon, E-glass, and basalt. The composites were produced layer-by-layer by hand lay-up method, using an epoxy-based resin as matrix. The results have shown a strain increase at failure of both standard carbon and high-modulus carbon fibres with the volume decrease of these materials in hybrid combinations. It was also concluded that combining high-modulus carbon with E-glass, high-modulus carbon with basalt, or high-modulus carbon with standard carbon can lead to very good pseudo-ductile tensile behaviour. Finally, it should be highlighted that an existing analytical model in the literature was satisfactorily adopted to predict the tensile response of these hybrid composites., S&P Clever Reinforcement Ibérica Lda. PTDC/ECM-EST/1282/2014, info:eu-repo/semantics/publishedVersion

Throughout this paper, a new system for connecting composite sandwich wall panels is proposed. The relevant structural components are investigated with the aim of utilizing these panels as insulated wall elements in building applications or prefabricated modular systems. The adopted sandwich wall panels are composed of hand-layup Glass Fiber Reinforced Polymer (GFRP) outer skins and low density closed polyurethane (PU) foam core. The sandwich wall panels present an overall geometry of 2880×960×64 mm3. One challenge of the proposed new system that was examined included joining the panels in the longitudinal direction (along their height) and transversally connecting (along their width) to other structural elements, similar to beams at the bottom and top. The structural performance of the sandwich wall panels was experimentally tested and thereafter analytically assessed in two cases: (i) single wall panels; (ii) two jointed wall panels. Outward localized GFRP wrinkling, followed by global buckling was observed as the dominant failure mode in both cases. Further, the capability of the proposed connection system to increase the axial load capacity of the jointed panels was evaluated. The study illustrates that axial capacity of two jointed sandwich wall panels compared to the single sandwich wall panel, increased substantially from 91% to 152% depending on the failure modes., This work is part of the research project ClickHouse - Development of a prefabricated 595 emergency house prototype made of composites materials, involving the company ALTO – 596 Perfis Pultrudidos, Lda., CERis/Instituto Superior Técnico and ISISE/University of Minho, supported by FEDER funds through the Operational Program for Competitiveness Factors – 598 COMPETE and the Portuguese National Agency of Innovation (ADI) - project no. 38967. 599 Special thanks are given to company ALTO who manufactured all the elements (GFRP 600 profiles and sandwich panels) involved in this work. ClickHouse - FEDER / COMPETE / ADI - project no. 38967., info:eu-repo/semantics/publishedVersion