Coauthored Publications with: Chastre

Journal Article

Pacheco, JN, de Brito J, Chastre C, Evangelista L.  2019.  Probabilistic Conversion of the Compressive Strength of Cubes to Cylinders of Natural and Recycled Aggregate Concrete Specimens. Materials. 12:280., Number 2 AbstractWebsite

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

Ludovico-Marques, M, Chastre C, Vasconcelos G.  2012.  Modelling the compressive mechanical behaviour of granite and sandstone historical building stones. Construction and Building Materials. 28:372-381., Number 1 AbstractWebsite

Building stones, particularly sandstone and granite, are very important in the building elements of Portugal’s historical and cultural heritage. Experimental research, based on uniaxial compressive tests, was carried out on selected representative samples of lithotypes of rocks used in historic built heritage, with a view to evaluating the compressive mechanical behaviour of different building stones. The results showed that porosity plays a central role in the compressive behaviour of granites and sandstones. As porosity can be evaluated in field conditions with non-destructive tests it was decided to derive an analytical model to predict compressive behaviour based on the knowledge of porosity of the building stones. A cubic polynomial function was adopted to describe the pre-peak regime under compression to implement the model. Furthermore, a statistical correlation between mechanical and porosity data had to be defined. Good agreement between experimental and analytical compressive stress–strain diagrams, from which the mechanical properties like compressive strength and modulus of elasticity can be derived, was achieved.

Chastre, C, Silva MAG.  2010.  Monotonic axial behavior and modelling of RC circular columns confined with CFRP, Aug. Engineering Structures. 32:2268-2277., Number 8 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.

Larrinaga, P, Chastre C, Biscaia HC, San-José JT.  2014.  Experimental and Numerical Modelling of Basalt Textile Reinforced Mortar Behavior Under Uniaxial Tensile Stress. Materials & Design. 55(March):66-74. AbstractWebsite

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

Biscaia, HC, Chastre C, Cruz D, Viegas A.  2017.  Prediction of the interfacial performance of CFRP laminates and old timber bonded joints with different strengthening techniques, 1/1/. Composites Part B: Engineering. 108:1-17. 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.

Almeida, G, Melício F, Biscaia H, Chastre C, Fonseca JM.  2016.  In-Plane Displacement and Strain Image Analysis, 24 February 2015. Computer-Aided Civil and Infrastructure Engineering. 31:292-304., Number 4 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.

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.

Marques, PF, Chastre C, Nunes Â.  2013.  Carbonation service life modelling of RC structures for concrete with Portland and blended cements. Cement and Concrete Composites. 37:171-184. Abstractmarques_chastre_et_al._2013.pdfWebsite

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

Biscaia, HC, Chastre C, Silva MAG.  2012.  Double shear tests to evaluate the bond strength between GFRP/concrete elements. Composite Structures. 94:681-694., Number 2 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.

Biscaia, HC, Chastre C, Viegas A.  2015.  A new discrete method to model unidirectional FRP-to-parent material bonded joints subjected to mechanical loads, 3//. Composite Structures. 121:280-295. 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.

Biscaia, HC, Cruz D, Chastre C.  2016.  Analysis of the debonding process of CFRP-to-timber interfaces, 6/15/. Construction and Building Materials. 113:96-112. 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.

Heidari, M, Chastre C, Torabi-Kaveh M, Ludovico-Marques M, Mohseni H.  2017.  Application of fuzzy inference system for determining weathering degree of some monument stones in Iran. Journal of Cultural Heritage. 25:41-55. Abstract

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

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

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

Marques, PF, Chastre C.  2012.  Performance analysis of load–strain models for circular columns confined with FRP composites. Composite Structures. 94:3115-3131., Number 11 Abstractmarques__chastre_2012.pdfWebsite

The use of FRP composites for the confinement of concrete has become an important aspect to consider on strengthening of concrete columns. It is important therefore that accurate modelling tools are available for the design of this system considering, not only the peak values of load and strain, but also the complete stress–strain behaviour. A wide group of authors have proposed several models specific for FRP-confined concrete based either on theoretical assumptions (analysis-oriented-models – AOMs) or on mathematical calibration from testing results (design-oriented-models – DOMs). This article carries out the implementation and analysis of nine existing models for circular concrete columns in view of axially tested reinforced concrete columns confined with CFRP with three different diameters: 150; 250 and 400 mm. The global shape of curves, peak compressive load, stress–strain relation, axial-to-lateral relation and dilation response were studied to conclude which models’ curves were closer to tests. Quantification of errors in face of the testing results was carried out for the most important parameters – ultimate load, strain and lateral stress – as well as for other curve parameters. Some models are accurate in predicting the peak load, though only few can accurately predict the load–strain and dilation behaviour.

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, H, Chastre C, Silva C, Franco N.  2018.  Mechanical Response of Anchored FRP bonded joints: A Nonlinear Analytical Approach. Mechanics of Advanced Materials and Structures. 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.

Yang, Y, Silva MAG, Biscaia H, Chastre C.  2019.  Bond durability of CFRP laminates-to-steel joints subjected to freeze-thaw, 2019/03/15/. Composite Structures. 212:243-258. AbstractWebsite

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

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, Micaelo R, Teixeira J, Chastre C.  2014.  Delamination process analysis of FRP-to-parent material bonded joints with and without anchorage systems using the Distinct Element Method. Composite Structures. 116(September–October):104–119. 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.

Faustino, P, Chastre C.  2015.  Analysis of load–strain models for RC square columns confined with CFRP, June 2015. Composites Part B: Engineering. 74:23-41. 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.

Biscaia, HC, Chastre C, Viegas A, Franco N.  2015.  Numerical modelling of the effects of elevated service temperatures on the debonding process of frp-to-concrete bonded joints. Composites Part B: Engineering. 70:64-79. 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.

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.

Heidari, M, Torabi-Kaveh M, Chastre C, Ludovico-Marques M, Mohseni H, Akefi H.  2017.  Determination of weathering degree of the Persepolis stone under laboratory and natural conditions using fuzzy inference system. Construction and Building Materials. 145:28-41. Abstract

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

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

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

Larrinaga, P, Chastre C, San-José JT, Garmendia L.  2013.  Non-linear analytical model of composites based on basalt textile reinforced mortar under uniaxial tension, 12//. Composites Part B: Engineering. 55:518-527. AbstractWebsite

The recent development of inorganic based composites as low-cost materials in reinforced concrete structural strengthening and precast thin-walled components, requires the creation of models that predict the mechanical behaviour of these materials. Textile Reinforced Mortar (TRM) shows complex stress–strain behaviour in tension derived from the heterogeneity of its constituent materials. This complexity is mainly caused by the formation of several cracks in the inorganic matrix. The multiple cracking leads to a decrease in structural stiffness. Due to the severe conditions of the serviceability limit state in structural elements, the prediction of the stress–strain curve is essential for design and calculation purposes. After checking other models, an empirical nonlinear approach, which is based on the crack control expression included in the Eurocode 2, is proposed in this paper. Following this scope, this paper presents an experimental campaign focused on 31 TRM specimens reinforced with four different reinforcing ratios. The results are analysed and satisfactorily contrasted with the presented non-linear approach.