Coauthored Publications with: Biscaia

Journal Article

Biscaia, H, Cardoso J, Chastre C.  2017.  A Finite Element Based Analysis of Double Strap Bonded Joints with CFRP and Aluminium. Key Engineering Materials. 754:237-240. Abstract
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Biscaia, HC, Chastre C, Silva MAG.  2013.  A smeared crack analysis of reinforced concrete T-beams strengthened with GFRP composites, 11//. Engineering Structures. 56:1346-1361. 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.

Biscaia, HC, Borba IS, Silva C, Chastre C.  2016.  A Nonlinear Analytical model to predict The full-range debonding process of FRP-to-parent material interfaces free of any mechanical anchorage devices, 15 March 2016. Composite Structures. 138:52-63. 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.

Yang, Y, Biscaia H, Silva MAG, Chastre C.  2019.  Monotonic and quasi-static cyclic bond response of CFRP-to-steel joints after salt fog exposure, 2019/07/01/. Composites Part B: Engineering. 168:532-549. AbstractWebsite

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

Biscaia, HC, Micaelo R, Teixeira J, Chastre C.  2014.  Numerical analysis of FRP anchorage zones with variable width, 11//. Composites Part B: Engineering. 67:410-426. 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.

Biscaia, H, Micaelo R, Chastre C, Cardoso J.  2018.  Cyclic loading behaviour of double strap bonded joints with CFRP and aluminium. Key Engineering Materials . 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.

Biscaia, HEC, Silva MG, Chastre C.  2009.  Caracterização Experimental e Modelação Numérica da Ligação GFRP/BETÃO. Mecânica Experimental. :9-18., Number 16 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.

Biscaia, HC, Chastre C, Silva MAG.  2015.  Bond-slip model for FRP-to-concrete bonded joints under external compression, 10//. Composites Part B: Engineering. 80:246-259. 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.

Biscaia, HC, Chastre C, Cruz D, Franco N.  2017.  Flexural Strengthening of Old Timber Floors with Laminated Carbon Fiber-Reinforced Polymers. Journal of Composites for Construction. 21:04016073., Number 1 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.

Silva, MAG, Biscaia H, Chastre C.  2013.  Influence of Temperature Cycles on Bond between GFRP and Concrete. ACI Structural Journal. 110(6):977-988. AbstractWebsite

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

Biscaia, H, Franco N, Nunes R, Chastre C.  2016.  Old suspended timber floors flexurally-strengthened with different structural materials. Key Engineering Materials. 713:78-81. 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.

Biscaia, HC, Chastre C, Silva MAG.  2019.  A Simple Method for the Determination of the Bond-Slip Model of Artificially Aged Joints. Journal of Composites for Construction. 23:04019028., Number 4 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.

Biscaia, HC, Chastre C, Silva MAG.  2013.  Linear and nonlinear analysis of bond-slip models for interfaces between FRP composites and concrete. Composites Part B: Engineering. 45:1554-1568., Number 1 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.

Biscaia, HC, Silva MAG, Chastre C.  2015.  Factors influencing the performance of externally bonded reinforcement systems of GFRP-to-concrete interfaces, 2014/06/29. Materials and Structures. 48(9):2961-2981.: Springer Netherlands 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.

Biscaia, HC, Chastre C, Silva MAG.  2017.  Analytical model with uncoupled adhesion laws for the bond failure prediction of curved FRP-concrete joints subjected to temperature. Theoretical and Applied Fracture Mechanics. 89:63-78. 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.

Biscaia, HC, Chastre C, Silva MAG.  2013.  Modelling GFRP-to-concrete joints with interface finite elements with rupture based on the Mohr-Coulomb criterion, 10//. Construction and Building Materials. 47:261-273. 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.

Biscaia, H, Chastre C, Cruz D, Franco N.  2016.  Flexural Strengthening of Old Timber Floors with Laminated Carbon Fiber Reinforced Polymers. Journal of Composites for Construction. :04016073. 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.

Biscaia, HC, Chastre C, Silva MAG.  2019.  Estimations of the debonding process of aged joints through a new analytical method, 2019/03/01/. Composite Structures. 211:577-595. 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.