Yes / This paper presents test results of eccentrically loaded concrete columns reinforced with steel-fibre-reinforced polymer (FRP) composite bars (SFCBs) subjected to chloride corrosion. The first stage of the experimental work explored the tensile and compressive tests of various reinforcements (SFCBs with different cross section, steel and FRP bars) used in the large reinforced concrete (RC) columns after chloride corrosion with or without sustained stresses. The results showed that the tensile and compressive stress-strain relationships of SFCBs are characterised by stable secondary (post-yield) stiffness. The second stage of the testing investigated the structural performance of RC columns with various amounts and types of reinforcements, slenderness ratio, applied load eccentricity and chloride corrosion rate. The results showed that the effect of reinforcements on eccentric compression behaviour is significant. The deformation and crack width of SFCB RC columns, respectively, decreased by 12.2%~52.6% and 8.5%~71.0%, while the load capacity improved by 0.9%~18.8%, when compared with the corresponding FRP RC columns having the same eccentricity and reinforcement ratio. The use of SFCBs as the reinforcement of RC columns, especially with high reinforcement ratio or SFCBs having high area ratio of inner steel to SFCB, is beneficial to reduce the deflection and crack width as well as improve the bearing capacity utilization coefficients under serviceability limit state.

Yes / To investigate the bending behavior of Steel-FRP Composite Bars (SFCBs) reinforced Reactive Powder Concrete (RPC) frame beams, both experimental and theoretical study were conducted on five concrete frame beams with different reinforcement ratio, types of concrete and reinforcement. The results indicate that the bending behavior of SFCBs-RPC frame beams progresses through three distinct stages: from loading to the cracking of tensile RPC, from cracking to the yielding of tensile SFCBs, and from yielding to failure. Compared with steel-reinforced RPC frames, the load of SFCBs-RPC frame beam continues to increase with the increase of deformation after the yielding of SFCBs, demonstrating good bearing capacity and ductility. Furthermore, the deformation and crack width of RPC frame beams are obviously lower than those of ordinary concrete frame beams, indicating the excellent deformation control and crack resistance ability of RPC beams. In addition, formulae for flexural stiffness at each stage were derived using the effective moment of inertia method. Taking the design code of reinforced concrete structure for reference and the tensile contribution of steel fibers and the mechanical performance of SFCBs into consideration, and the formulae for crack width of SFCBs-RPC flexural beam were developed. Formulae for the bearing capacity of SFCBs-RPC frame beams were also proposed on the base of simplified materials constitutive models and reasonable basic assumptions. The values predicted by these proposed formulae aligned well with the results tested. The research provides a theoretical support for the design and application of SFCBs-RPC frame beams.

Yes / This study investigates the bending performance of ultra-high-performance concrete (UHPC) beams reinforced with non-prestressed steel-FRP composite bars (SFCBs) and prestressed fiber-reinforced polymer (FRP) bars. The finite element software ABAQUS was used to simulate the strain behaviors of materials, applying a real strain model for concrete and equivalent plastic strain models for reinforcements. Six beams with different concrete types and reinforcements (prestressed or non-prestressed) were simulated and analyzed. These simulations yielded results that closely aligned with the results tested. Based on the validated FE models, a parametric analysis was conducted to examine the effects of mechanical properties of concrete, mechanical property of non-prestressed reinforcement, and the reinforcement ratio of prestressed FRP bars and non-prestressed SFCB on the bending performance of SFCBs reinforced UHPC beams prestressed with FRP bars. The results indicate that, as the concrete strength increases from C35 to UHPC140, both the bearing capacity and ultimate deflection of flexural beams exhibit a gradual increase. Notably, employing UHPC100 as the matrix results in specimens achieving the highest ductility, deformation, and energy absorption. When non-prestressed FRP bars are replaced by SFCBs, the ultimate load of the beams decreases by 8%, but energy absorption increases by 34%. With an increase in the steel ratio of SFCBs, the ductility, deformation, and energy absorption also gradually increase. Moreover, increasing the reinforcement ratio of both prestressed FRP and non-prestressed SFCBs results in an increase in bearing capacity, but a decrease in ultimate deflection, ductility, deformation, and energy absorption capacity. This research can provide valuable technical references for the analysis and design of UHPC beams reinforced with SFCBs and prestressed FRP bars. / Financial support from the National Natural Science Foundation of China (52378201),the High-End Foreign Experts Project of Ministry of Science and Technology, China (G2022014054L), the Jiangsu Construction System Science and Technology Project (2023ZD104 and 2023ZD105), the Nantong Jianghai Talents Project (226), the Science and Technology Project of Yangzhou Construction System (202309 and 202312) and the Research Project of Jiangsu Civil Engineering and Architecture Society (the Second Half of 2022).