147 publications from this institution
Results from nonlinear finite element analyses of fibre reinforced polymer (FRP)-strengthened concrete beams and slabs are presented. The direct shear test, a basic application that provides insight into FRP-concrete interfacial behaviour, is also considered. The motivation for this work is the fact that, although there is a large amount of experimental data available on the FRP strengthening of concrete structures, a full understanding of the various load–deformation behaviours and debonding phenomenon is still lacking. The numerical models presented in this paper adopt a displacement-controlled solution and are capable of simulating FRP-strengthened beams either in shear or in flexure, as well as slabs strengthened using either passive or prestressed FRP laminates. Results of the different applications are presented and compared with published test data, and a very good agreement in terms of the ultimate load carrying capacities, load–deflection behaviour and modes of failure, is obtained.
The use of a recently introduced "near surface embedded" (NSE) technique for fabric reinforced cementitious matrix (FRCM) system is shown to be a viable alternative to the conventionally used externally bonded FRCM counterpart with the potential to mitigate FRCM/concrete debonding. This paper presents a study on the interaction of FRCM and stirrups for RC beams strengthened in shear using the NSE-FRCM system. The experimental program involved eight (8) rectangular RC beams with and without internal shear reinforcement. Two test variables were considered; namely, fabric type (carbon, glass and polyparaphenylene benzobisoxazole) and internal shear reinforcement within the critical shear span (with and without stirrups). The experimental results revealed that the NSE-FRCM can successfully be used to enhance the shear capacity of the strengthened beams. Carbon FRCM was the most effective of all the fabric types. Moreover, an interaction between the stirrups and the NSE-FRCM system has been observed. The percentage gain in the shear strength was reduced from 69% to 38% due to the presence of stirrups within the critical shear span. Moreover, the NSE-FRCM strengthening has reduced the strain in the stirrups owing to the load sharing between the stirrups and the strengthening system.
Abstract Concrete bridge piers reinforced with conventional steel bars experience large permanent (residual) deformation that may lead to uneconomical repair or demotion of bridges due to their non-functionality post strong seismic event. Thus, sufficiently ductile materials are required to reinforce concrete bridge piers in the plastic hinge zone in order to limit their permanent damage and deformation post-earthquake event. Previous studies showed that partial replacement of conventional steel reinforcement bars with superelastic shape memory alloy (SMA) bars in the plastic hinge zone of concrete bridge piers has the capacity to limit the residual deformation owing to the superior self-centering properties of SMA bars. In this study, the efficacy of hybrid SMA/steel reinforcement for hollow section concrete bridge piers under combined reverse cyclic and constant axial loading is numerically investigated for the first time. The responses of the piers were evaluated in terms of different performance indices including hysteretic characteristics, residual deformation, energy dissipation capacity, and self-centering capacity. A sensitivity analysis was used to explore the main effects of key design parameters and their interactions on each performance index at four damage states, namely, complete, extensive, moderate, and slight damage states. The results of this study demonstrate the effectiveness of hybrid SMA/steel reinforcement for enhancing the seismic behavior of hollow section concrete bridge piers.
The objective of this research work is to simulate the interfacial shear response of fibre-reinforced polymer/concrete joints using a micromechanics-based concrete approach. The M4 version of the microplane concrete theory is coded in FORTRAN and implemented as a parallel user-defined subroutine into the commercial finite element software package ADINA. This article first focuses on three-dimensional nonlinear micromechanics-based finite element analyses. Then, validations are carried out using experimental results of 40 fibre-reinforced polymer/concrete joints. The objective is to assess the accuracy of the microplane approach to represent the interfacial shear behaviour of the fibre-reinforced polymer/concrete joints as an alternative to implementing interface elements. At the end of this article, numerical comparisons are presented between the predictions using a phenomenological concrete constitutive law adopted in the software package (with a smeared crack model) and the micromechanics-based analysis (microplane theory) to simulate the concrete behaviour.
A finite element model is developed for analyzing the interfacial behaviour for fibre-reinforced polymer (FRP) laminates externally bonded to concrete prisms and subjected to direct shear. The element sizes of the FRP, adhesive, and concrete at the interface were chosen to be very small (0.25–0.5 mm) so that the debonding behaviour could be properly captured. The behaviour at the interface between the FRP composite and the concrete is modelled using truss elements connecting the FRP laminate to the concrete block. The truss elements incorporate a nonlinear bond stress-slip relationship controlled by several parameters related to the characteristics of the FRP composite, adhesive, and concrete. Results are given in terms of the load capacity of the joint and the stress and strain distributions in the FRP, at the interface, and in the concrete. In addition, the transfer lengths, as well as the force transfer between the FRP laminate and the concrete block, are investigated. Comparisons between the finite element results and available experimental data are presented.Key words: nonlinear finite element analysis, FRP-to-concrete bonded joints, interface elements, debonding, interfacial behaviour, transfer lengths.
Recently, seawater has emerged as viable mixing water for concrete, especially in the case of non-reinforced concrete applications or with the use of non-corrosive reinforcement. Previous studies concerning seawater-mixed concrete mostly revealed an initial slight increase in its strength performance (i.e., till Day 14 following mixing), followed by a strength reduction of 7–15% (i.e., after 28 days or longer) as compared to the conventional freshwater-mixed concrete. With an attempt to explain such observations, this paper aims at comparing the microstructure of freshwater-and seawater-mixed cement pastes. Scanning electron microscopy was utilized to observe the microstructure of freshwater and seawater pastes at Days 3 and 28 following mixing. At Day 3, seawater paste was observed to have more densified microstructure as compared to that of the freshwater counterpart, resulting in relatively higher strength performance. At Day 28, the microstructure was almost similar for the two cement pastes. However, seawater paste was observed to have salt impurities as a result of seawater ions, which possibly cause a slightly lower strength performance as compared to the freshwater paste.
This paper presents an experimental study on the efficacy of a recently introduced hybrid “near surface embedded/ externally bonded” NSE/EB fabric reinforced cementitious matrix (FRCM). Seven medium scale RC beams, deficient in shear, were constructed and tested under three-point loading. Six beams were strengthened using hybrid NSE/EB-FRCM technique and one beam was left un-strengthened as a reference. Two main test variables were considered; viz., strengthening configuration: full versus intermittent strengthening configuration and FRCM type: glass FRCM versus polyparaphenylene benzobisoxazole (PBO). The test results revealed that the hybrid NSE/EB-FRCM strengthening technique is effective in enhancing the shear capacity of the strengthened beams. The strengthened specimens showed an average of 67% higher shear capacity relative to the reference specimen. With regard to the FRCM type, G-FRCM strengthened specimens showed an average of 73% enhancement in the shear capacity, which was 12% higher than the value for PBO-FRCM counterpart. Moreover, the strengthened beams showed higher deflection at the ultimate load than that of the reference specimen. Furthermore, the hybrid NSE/EB-FRCM technique has shown to be a promising alternative to the conventionally used externally bonded FRCM system with the potential to reduce the debonding of FRCM from the concrete substrate.
The structural performance of corrosion-damaged reinforced concrete (RC) beams repaired with fabric-reinforced cementitious matrix (FRCM) was investigated. Eleven RC beams were constructed and tested in flexure under four-point load configuration. Nine beams were subjected to an accelerated corrosion process for 70 days to obtain an average mass loss of 13% in the tensile steel reinforcing bars while two other beams were tested as controls. One corroded beam was repaired with carbon fiber-reinforced polymer (CFRP) before testing for comparison. The test parameters included the number of fabric plies (1–4), the FRCM repair scheme (end-anchored and continuous U-wrapped strips), and FRCM materials [carbon and polyparaphenylene benzobisoxazole (PBO)]. Test results showed that corrosion slightly reduced the yield and ultimate strengths of the beams. The use of FRCM increased the ultimate capacity of corroded beams between 5 and 52% and their yield strength between 6 and 22% of those of the uncorroded virgin beam. Beams repaired with U-wrapped FRCM strips showed higher capacity and higher ductility than those repaired with the end-anchored bottom strips having a similar number of layers. A high gain in the flexural capacity and a low ductility index were reported for specimens with a high amount of FRCM layers. A new factor was incorporated in the design equations of the ACI 549.4R-13 to account for the FRCM scheme.
This paper presents a comprehensive experimental work to study the interaction between the internal and external shear reinforcement for strengthened reinforced concrete (RC) deep beams.For this purpose, a total of twelve medium-scale RC deep beams have been designed, fabricated, and loaded monotonically till a completed failure.Four beams were kept unstrengthened to act as reference beams, while others have been strengthened using hybrid carbon-glass Fiber-reinforced polymer (FRP) strips.All beams have been designed to be shear deficient in one side, which will be called herein as a critical shear span (CSS).The study included three test parameters: strengthening technique (externally bonded and near-surface mounted), number of internal and external shear reinforcement (two and three) in the CSS, and the alignment of the internal and external shear reinforcement (aligned and unaligned) to each other.The results revealed that the near-surface mounted (NSM) technique could be able to mitigate the premature debonding mode of failure which was dominant with the beams strengthened by the externally bonded (EB) counterpart.The NSM technique could be able to increase the shear capacity of the strengthened beams up to 45% compared to the corresponding technique.The results also showed that the unaligned configuration of the internal and external shear reinforcement was better than the aligned one for both NSM and EB techniques.
