In the last three decades, glass fiber-reinforced polymer (GFRP) has gained wide acceptance as an alternative reinforcement to avoid the potential of corrosion and related deterioration of reinforced concrete infrastructure. Recent experimental results for concrete columns reinforced entirely with GFRP bars have demonstrated their effectiveness in resisting lateral loads induced by wind or earthquakes. However, in most of the research studies carried out so far, the columns were tested under reversed cyclic loading, while subjected to low to moderate levels of axial load that would be rather representative of columns located in the top stories of multi-story buildings. This has been the main impetus to investigate FRP-reinforced columns under high levels of axial load with different ratios of longitudinal reinforcement. To that end, a finite element model (FEM) that considers the material and geometric nonlinearity and the bond behavior of GFRP bars was developed and validated against the available experimental results. Twenty-one specimens encompassing wide levels of axial load and longitudinal reinforcement ratios were studied. Results are presented in terms of strength, stiffness, and deformation capacity as affected by axial load. The moment-axial load interaction diagrams for the simulated specimens are also discussed. The paper concludes by proposing the most appropriate performance design levels for GFRP-reinforced columns. Quantification of the seismic response parameters within this study is aimed at facilitating the adoption of GFRP bars in North American codes as internal reinforcement for earthquake-resisting systems.

Service life of existing post-tensioned concrete members is significantly impacted by the corrosion of its unbonded steel tendons. This deterioration, commonly initiated by the penetration of chloride ions from deicing salts or grouts, is exacerbated by increases in live and superimposed dead loads. There is a need to develop more durable and improved design alternatives with enhanced serviceability, ductility, and strength performances. This study focuses on the serviceability performance of hybrid beams prestressed using a combination of bonded and unbonded steel and carbon fiber-reinforced polymer (CFRP) tendons. Eighteen beams were tested to failure under third-point loading with emphasis on the tendon materials’ (that is, CFRP and steel) performance. Results show that hybrid beams, using CFRP as the unbonded element, are very robust prestressing systems that may achieve extended service life due to their corrosion resistance, while maintaining comparable service performance when compared to hybrid steel beams.

To study the hysteretic behavior of concrete-filled square carbon fiber-reinforced polymer (CFRP) steel tubular (S-CF-CFRP-ST) beam-columns under different influence factors, 12 specimens were designed, and the failure mode, middle section lateral force-deflection (P-Δ) curve, middle section bending moment-curvature (M-ϕ) curve, and middle section deflection-deformation (Δ−Δ′) curve were studied. Using the axial compression ratio and longitudinal CFRP reinforcement coefficient as influencing factors, the effects of the axial compression ratio and longitudinal CFRP reinforcement coefficient on the P-Δ skeleton curve, M-ϕ skeleton curve, strength and stiffness degradation, ductility, cumulative energy consumption, and other indexes were studied. The P-Δ curve and deformation mode of the specimens were simulated by ABAQUS, and the effects of the axial compression ratio, slenderness ratio, and other main parameters on the hysteretic performance of the members were studied. The test results show that CFRP has good lateral restraint and longitudinal reinforcement effect on concrete-filled steel tubular (CFST) columns, and the local buckling of CFST is delayed. The P-Δ curve and M-ϕ curve of all specimens are full. In addition, the steel tube and CFRP have good synergy in both longitudinal and transverse directions. The change of the axial compression ratio and longitudinal CFRP reinforcement coefficient has no significant effect on the strength degradation. The increase of the axial compression ratio and longitudinal CFRP reinforcement coefficient can improve the flexural capacity and stiffness of the specimens, and slow down the stiffness degradation, but reduce the ductility and cumulative energy consumption of the specimens. The finite element software ABAQUS is used to simulate the P-Δ curve and deformation mode of the specimens. It is found that the simulation results are in good agreement with the experimental results. Based on the model analysis of the main parameters, it is found that the increase of steel yield strength and CFRP layers can improve the bearing capacity of the specimens, and the axial compression ratio has the most significant effect on the specimens.

This paper presents a method to quantify shear-transfer mechanisms from large-scale reinforced concrete deep beam experiments. The framework uses the Two-Parameter Kinematic Theory in conjunction with basic constitutive relationships to backcalculate the shear-carrying mechanisms in deep beams using only detailed experimental data and member properties. The input to the method is the experimentally obtained displacement field data and critical crack information, including crack widths, crack slips, and member properties; the output of the method is the applied load on the member. The framework is applied to five previously conducted large-scale deep-beam experiments and the assessed loads are compared to the measured applied loads. The results indicate that experimental data including detailed crack geometry, crack widths, and slips can be used to assess the applied load on deep beams. The framework provides a foundation upon which direct crack-based assessment methods can be further developed.

It is noted that the concrete compression zone of reinforced concrete (RC) slabs in the failure section under pure bending is unlike that of beams. The ratio b/x—section width b to the concrete compression zone height x—is great enough, leading to strain constraint in the direction of size b, and to the appearance of the plane strain instead of the plane stress taking place in the beams. The due increase of concrete compressive strength under the plane strain conditions is shown. The method of experimental determination of the concrete compressive ultimate stress fcu in the RC bending slabs is stated, and the experimental results are given, showing the considerable stress fcu increment with an increase of the b/x. The decrease of crack openings and deflections of the slabs with an enhanced b/x is noted. A relationship is offered for taking into account the b/x influence on the concrete compressive strength of the RC elements under bending.