This study focuses on the evaluation of the surface deformation height of ribbed type of GFRP rebars. The bond behaviour of ribbed type of GFRP rebar is investigated in terms of the effective deformation height and bond rigidity, both experimentally and numerically. Pullout tests on ribbed type GFRP rebars embedded in concrete have been conducted to obtain an accurate bond stress-slip law and also to closely observe the state of the surface of pulled-out rebars at failure, in order to categorise accurately the mode of failure. In the pullout tests, the high temperature regime is particularly considered. In addition, finite element (FE) simulations of the specimens subjected to pullout tests are developed. From the FE analyses and the experiments, the effective surface deformation height and bond rigidity of the GFRP rebar with ribs was determined. The numerical results were substantiated by the experimental findings and good agreement was observed. Moreover, adding milled glass fibres in the surface deformations could not increase the effective surface deformation height and bond rigidity of the rebar; however, it seems to improve the bond strength because increasing the proportion of milled glass fibres improves the connections between the core and rib section.
Background: While improved student engagement has been highlighted as an essential goal and a major outcome of Problem and Project-Based learning (PBL), little empirical evidence has been provided regarding types and forms of student engagement. Material and method: The study explored forms of student engagement in PBL settings, drawing on empirical data of observations and group interviews with 23 project teams (116 students) in four different PBL undergraduate civil engineering courses at Qatar University. Results: The study identified four patterns of student engagement in a PBL setting. Participants reported significant indicators of the first two patterns - engagement as autonomy and as connection. Regarding the other two indicators, namely relational and emotional engagement, they reported positive yet slightly fewer indicators. Three factors were identified that influenced student engagement in a project teams, namely PBL types and its appropriateness to the nature of the course, students' prior experiences with PBL, and team dynamics. Conclusions: These results facilitate the establishment of an institutional framework supporting a progressive approach to embracing PBL. In this framework PBL implementation begins with diverse practices at the course level and has systemic change as its ultimate goal. This framework particularly aims to support an institutionalized approach to transition to PBL in a socio-cultural context (e.g., a non-western context) where instructors are as the primary and authoritative source of knowledge. The overall outcome of the study supports management of change from a lecture-based mode to PBL in a non-western context.
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.
Although there is a large amount of experimental data available on the fiber-reinforced polymer (FRP) strengthening of concrete structures, a full understanding of the various debonding phenomena is somewhat lacking. As a contribution to fill this need, two-dimensional and three-dimensional (3D) nonlinear displacement-controlled finite-element (FE) models are developed to investigate the flexural and FRP/concrete interfacial responses of FRP-strengthened reinforced concrete beams. Interface elements are used to simulate the FRP/concrete interfacial behavior before and after cracking. The analysis is carried out using two different relations for the interface; namely, nonlinear and bilinear bond–slip laws. The results predicted using these two laws are compared to those based on the full-bond assumption. The FE models are capable of simulating the various failure modes, including debonding of the FRP, either at the plate end or at intermediate cracks. The 3D model is created to accommodate cases of FRP-strengthened reinforced concrete beams utilizing FRP anchorage systems. In addition, the models successfully represent the actual interfacial behavior at the vicinities of cracks including the stress/slip concentrations and fluctuations. Results are presented in terms of the ultimate load carrying capacities, failure modes and deformational characteristics. Special emphasis is placed on the FRP/concrete interfacial behavior and cracking of the concrete. The numerical results are compared to available experimental data for 25 specimens categorized in six series, and they show a very good agreement.
Given the increasing global concern of freshwater scarcity, the use of seawater in concrete mixtures appears to be a way forward towards achieving sustainable concrete, especially in the case of non-reinforced concrete applications or with the use of non-corrosive reinforcement. This paper reports on the results of an experimental study to compare the freshwater-and seawater-mixed concretes in terms of their strength, shrinkage and permeability performance. The experimental program included the following: (i) compressive strength test (at 3, 7, 28, and 56-day ages); (ii) concrete shrinkage test (at Days 4, 7, 14, 21, 28, and 56 following mixing); and (iii) permeability tests (rapid chloride permeability and water absorption at Days 28 and 56 following mixing). As for the study results, seawater concrete showed a slightly higher early-age (i.e., till Day 7) strength performance than that of freshwater-mixed counterpart, followed by a strength performance that is 7–10% inferior to the freshwater concrete after 28 days or later. Also, the shrinkage of seawater concrete was slightly higher than that of freshwater concrete, with a difference of 5% reported after 56 days following mixing. Finally, the permeability performance of hardened concrete in seawater and freshwater mixtures was similar.
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.
Fabric-reinforced cementitious matrix (FRCM) composites represent a new technique for strengthening concrete and masonry structures. Various studies confirm the efficiency of FRCM systems in terms of ultimate capacity gain, compatibility with the parent material, and viability in corrosive environments and under elevated temperatures. An appealing use of FRCM composites is to strengthen concrete bridges. Vehicular traffic imposes cycles of loading and unloading on the structure that can lead to fatigue failure, but the fatigue life of FRCM materials is yet to be investigated. This study examined fatigue performance of FRCM-strengthened reinforced concrete beams. Twelve concrete beams reinforced with carbon fabric were tested, including four benchmark beams subject to monotonic loading. The effects of fiber architecture and reinforcement ratio were accounted for by using two types of fabrics. Inspection of the fractured sections indicated that fatigue failure in the steel reinforcement was the predominant cause of failure. Analysis of applied stress range versus number of cycles to failure suggested that FRCM systems enhance fatigue life by controlling crack propagation in concrete.
This paper reports on the feasibility of using fabric-reinforced cementitious matrix (FRCM) systems to rehabilitate corrosion-damaged reinforced concrete (RC) beams.Seven large-scale RC beams were constructed and tested to failure under four-point load configuration.Six beams were subjected to an accelerated corrosion process for 70 days to obtain an estimated mass loss of 10% in the tensile steel reinforcing bars.One virgin beam and one corroded unrepaired beam were used as benchmarks for comparison purpose.The other five corroded beams were repaired before applying the FRCM system.The test parameters included the number of fabric plies (1, 2, and 4) and the strengthening schemes (endanchored bottom flexural strips and fully U-wrapped flexural strips).Test results showed that corrosion insignificantly reduced the yield and the ultimate strength of the specimen.However, the corroded specimen failed to meet the provisions of the ACI 318 code for crack width criteria.The use of FRCM increased the ultimate capacity of corroded beams between 6% and 46% and their yield strength up to 20% in comparison with those of the control virgin beam.The specimens repaired with U-wrapped FRCM strips showed higher capacity and higher ductility than those repaired with the end-anchored bottom strips having similar number of layers.A higher gain in the flexural capacity and a lower ductility index were reported for specimens with higher amount of FRCM layers.
This paper presents an analytical study to verify the ACI 549-4R-16 code for experimentally tested Reinforced Concrete (RC) beams, which were strengthened to enhance the flexural capacity using Fiber-Reinforced Cementitious Mortars (FRCM).Twelve RC beam specimens having 2500 mm length, 150 mm width, and 260 mm depth were prepared with two different reinforcement ratios (ρ_s^D12=0.72% and ρ_ s^D16=1.27%),and were then strengthened with two different FRCM systems, namely carbon and polyparaphenylene-benzobisoxazole (PBO) FRCM systems.Two RC beams were tested as control specimens.Six beams were externally reinforced using single, double and triple layers of carbon FRCM system, while the remaining four beams were repaired with one and two layers of PBO FRCM system.The strengthened RC beams were tested in flexural under four-point monotonic loading.The experimental results revealed that a reasonable gain in flexural strength was achieved for both FRCM systems, with up to 78% increase in flexural capacity for carbon FRCM systems and up to 27.5% for PBO FRCM system over that of their control specimens.Further, the results obtained from the theoretical approach using the ACI 549 code conform well with the experimental loadcarrying capacities.Moreover, the values obtained for experimental to theoretical ratio are quite close to 1.00 which somewhat shows satisfactory computational results.
Abstract The field of reinforced concrete (RC) strengthening continues to evolve as the construction industry seeks cost‐effective and sustainable alternatives to structural replacement. This study, therefore, aimed to comprehensively investigate the pioneering application of steel‐reinforced grout (SRG) for strengthening large‐scale, 3.5‐meter‐long continuous RC beams. The main purpose was to explore the complex interplay among SRG density, the number of SRG layers, and the steel reinforcement ratio, and to assess their collective impact on the structural performance of the strengthened beams. Extensive experimental testing was carried out on 10 large‐scale RC continuous beams, including two pristine beams serving as references. The experimental findings demonstrated significant enhancements in the load‐carrying capacity of the strengthened beams, achieving increases ranging from 24% to 104% compared to the corresponding reference beams. Although a reduction in ductility was observed, this emphasized the need to optimize the balance between strength and deformation in the strengthened members. The use of low‐density SRG proved remarkably effective, providing superior bonding and higher efficiency, while high‐density SRG exhibited slightly lower performance due to reduced matrix penetration. Additionally, the number of SRG layers was found to play a crucial role in boosting the load capacity, with more pronounced effects in beams with lower steel reinforcement ratios. To complement the experimental investigation, two theoretical models based on the SRG effective strain were developed and validated against the experimental results. The close agreement between the models and the experimental data underscores their potential as practical tools for the design and optimization of SRG‐strengthened beams, thereby contributing critical insights for engineering applications.
This paper presents the efficacy of a new technique of fabric reinforced cementitious matrix (FRCM) for the strengthening of shear deficient reinforced concrete (RC) beams. This technique involves embedding the FRCM composites in the concrete cover and is referred to as “near surface embedded” FRCM (NSE-FRCM) technique. Five (5) medium scale rectangular RC beams of width × depth × length of 150 × 330 × 2100 mm were constructed and tested under displacement controlled with three-point loading. One beam was kept unstrengthen as a control specimen whereas the other four beams were strengthened with different types and configurations of the NSE-FRCM system. The test parameters were: (a) geometric configuration (intermittent strips of NSE-FRCM versus full NSE-FRCM plate), and (b) fabric types (carbon versus glass fabrics). The test results indicated that the NSE-FRCM technique can successfully be used to significantly enhance the shear capacity of the strengthened beams. The strengthened specimens exhibited an average enhancement in the shear capacity of 62% over the unstrengthen beam. The full NSE-FRCM plate showed higher enhancement in the shear strength compared to that for the intermittent NSE-FRCM configuration. Moreover, the specimens strengthened with carbon FRCM showed higher shear capacity compared to that with glass FRCM counterparts.
