Effect of Prestressing Ratio on Concrete-Filled FRP Rectangular Tube Beams Tested in Flexure
Presented By: Asmaa Ahmed
Affiliation: Universite de Sherbrooke
Description: This paper presents the results of an extensive test program that was aimed at investigating the flexural behavior of rectangular concrete-filled glass fiber-reinforced-polymer (GFRP) tube (CFFT) beams posttensioned (PT) with unbonded steel tendons. The tests intend to simulate a number of design parameters, which are mainly governed by flexural loading. All beams were tested under four-point bending over a simply supported span of 3,000 mm [1229 in.]. Four full-size beams with an identical rectangular cross-sectional of 305 mm × 406 mm [12.0 in. × 16.0 in.] were constructed. The effect of increasing the number of tendons from (2 to 3) and concrete strength from (40 to 65 MPa) [5.80 and 9.43 ksi] was investigated. Besides, a proposed design equation as an extension to AASHTO (2012) equation based on a regression analysis of the test results herein to predicate the flexural capacity is established. The test results show that the cracking loads and post-cracking stiffness can be improved by increasing the number of strands. However, increasing the number of strands shows a slight effect on the ultimate capacity. The flexural capacities of PT CFFTs can be enhanced by increasing the concrete compressive strength without affecting their overall ductility. The proposed model successfully predicts the ultimate moment capacity of the tested beams and other results from the literature with an average of 1.08±0.16 and a COV of 14.5%. However, due to the limited test results in the present study and, in the literature, additional tests on the flexural behavior of PT rectangular CFFT beams are needed to further validate the accuracy of the model
Flexural Design of Masonry Walls Reinforced with FRP Bars Based on Full-Scale Structural Tests
Presented By: Nancy Torres
Affiliation: Escuela Colombiana de Ingenieria
Description: This article presents a protocol for the flexural design of masonry walls reinforced with FRP bars. The proposed design methodology is based on the results of a research program on the behavior of masonry walls reinforced with FRP bars subjected to out-of-plane (flexural) loads. The research program included testing of full-scale masonry walls with different thicknesses, widths, and amounts and types of FRP reinforcement. The research program also included testing of full-scale masonry wall specimens to evaluate the effect of i) different bar lap splice lengths, ii) FRP bar diameter; iii) position of the FRP; iv) masonry strength and v) masonry material. Forty-seven masonry walls, 2.19 m high, were subjected to out-of-plane loads, tested under quasi-static loading cycles. The test specimens included walls constructed using concrete and clay masonry units, reinforced with Glass FRP (GFRP) in different configurations. All the FRP-reinforced masonry walls showed a bilinear moment-deflection curve with one steep slope up to cracking of masonry and a decrease in stiffness after cracking. After failure occurred and as the out-of-plane load was progressively removed, the walls returned to a position close to the initial vertical position. Based on these results, it can be concluded that the design approach to calculate flexural strengths of walls reinforced with FRP bars provided good agreement with the experimental results.
Behavior of Circular Concrete-Filled FRP Tube Columns under Lateral Impact Loading: Numerical Study
Presented By: Maha Abdallah
Affiliation: Universite de Sherbrooke
Description: Several studies have shown the superiority of concrete filled FRP tubes (CFFTs) over conventional reinforced concrete columns. These observations indicated that CFFT columns exhibit much better static structural performance (in terms of ductility and load carrying capacity). However, up to date, very few studies have considered the behavior of CFFT columns under dynamic impact loading. This paper presents a numerical study to investigate the impact resistance of columns strengthened with glass FRP tubes. LS-DYNA finite element software is used to investigate CFFT and RC columns subject to lateral impact loading induced by a 221 kg pendulum. The columns are 1800 mm with the fixed support at the base and 152 mm internal diameter. The models are designed to simulate the destructive effects of a vehicle collision into bridge piers. The impact forces, and deformation states is analyzed. The impact behavior of CFFT columns is also compared with the conventional RC columns counterparts. The numerical results showed that the CFFT columns had higher dynamic impact load and less lateral deflection compared with the RC counterparts. The impact resistance of the CFTT columns was enhanced with an increase in the FRP tube thickness.
Nonlinear Behavior of Continuous RC Beams Strengthened with Near Surface Mounted FRP Bars
Presented By: Majid Kadhim
Affiliation: University of Babylon
Description: One of the successful techniques utilizing fiber reinforced polymer (FRP) reinforcement in concrete retrofit is by embedding bars or strips in pre-cut grooves, forming what is collectively known as near surface mounted (NSM). While great deal of research and attention has been devoted to evaluating NSM-FRP in retrofitting statically determinate members (e.g., simply supported beams), limited work is given to indeterminate structures. In this study, a three-dimensional finite element (FE) model is developed to evaluate the behavior of continuous reinforced concrete (RC) beams strengthened in the negative and positive moment regions with NSM-FRP bars. The model included robust features such as concrete damage plasticity (CDP), FRP failure, slipping and debonding of FRP bars. A recent experimental study conducted on 6 m-long two-span continuous beams was used as a baseline to validate the numerical results. The model was able to accurately predict the beam load-deflection and load-strain responses, for different FRP reinforcement ratios and lengths, with a maximum 8% deviation for the loads at steel yielding and at ultimate. Failures observed in tests, namely, concrete cover separation, cracking and crushing, and FRP bar debonding from adhesive, at both the hogging and sagging regions, were also reasonably simulated. The model will be used next in examining behavioral aspects in detail, evaluating effects of multiple geometric and material parameters, and assisting in developing design recommendations for NSM FRP-strengthened continuous RC beams.
Ultimate and Fatigue Responses of Sand-Coated GFRP-Reinforced, UHPC-Filled, Field-Cast Deck Joints in Slab-On-Girder Bridges
Presented By: Imad Eldin Khalafalla
Affiliation: Ryerson University
Description: This paper investigates the use of glass fiber reinforced polymer (GFRP) bars to reinforce the jointed precast bridge deck slabs built integrally with steel I-girders. In addition to a cast-in-place slab, a three full-size, GFRP-reinforced, precast concrete deck slabs were erected to perform static and fatigue tests using the footprint of the Canadian Highway Bridge Design Code (CHBDC) truck wheel loading. Each slab had 200 mm thickness, 2500 mm width normal to traffic and 3500 mm length in the direction of traffic and supported over braced twin-steel girder system. The closure strip between connected precast slabs has a width of 125 mm with vertical shear key, filled with ultra-high-performance concrete (UHPC). Sand-coated GFRP bars in the precast slab project into the closure strip with a headed end to provide a 100 mm embedment length. A static test and two types of fatigue tests were performed, namely: (i) accelerated variable amplitude cyclic loading and (ii) constant amplitude cyclic loading, followed by loading the slab monotonically to failure. Test results demonstrated excellent fatigue performance of the developed closure strip details. The ultimate load carrying capacity of the jointed deck slab was far greater than the CHBDC design value. While the failure in un-jointed (cast-in-place) slab was purely punching shear, the failure mode in the jointed precast slabs was punching shear failure without complete cone-shape peroration through, and near, the UHPC closure strip. This may attribute to the fact that the UHPC joint diverted the load distribution pattern towards a flexural mode close to failure.