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Abstract Fiber-reinforced polymer (FRP) bars offer a promising alternative to conventional steel reinforcement in reinforced concrete (RC) structures, primarily due to their corrosion resistance. However, their intrinsic linear elastic behavior may limit their applications to non-seismic zones or regions with limited seismic activity. To extend their applications in seismic zones such as Seismic Design Category D, a novel approach involving a hybrid-RC (HRC) cross-section is proposed. This approach entails placing FRP bars on the cross-section exterior for corrosion resistance, while steel bars on the inner side of the cross-section to ensure ductility and energy dissipation. This paper presents a methodology for designing HRC cross-sections and evaluates their ductility and energy dissipation capabilities. The discussion encompasses various design aspects of an HRC section including strength reduction factor, minimum reinforcement ratio, reinforcement strain, concrete shear strength, and the impact of confinement on ductility and energy dissipation. Additionally, an illustrative example of a HRC section demonstrates the practicality of the proposed design methodology in practical applications. 

Abstract The current provisions for development length in the ACI 440.11 code disregard the confinement effect provided by stirrups on the bond strength of longitudinal bars and require splice lengths that pose implementation challenges. Given the significant improvement in GFRP material properties, this study investigated the bond strength of sand-coated GFRP bars and proposed a new factor to include the effect of stirrup confinement on the bond-strength provisions. The experimental program involved 16 GFRP-reinforced concrete (RC) beams having a width of 300 mm, and depth 440 mm, consisting of two repetitions for every configuration, subjected to four-point loading. The test parameters comprised lap-splice length and stirrup spacing in the lap-spliced zone. Out of 16 GFRP-RC beams, two beams were reinforced with two M16 (No. 5) continuous bars and six with varying lap-splice lengths [i.e., 40, 60, and 80 bar diameters (d_b)] without confining stirrups. To evaluate the effect of confining stirrups, eight beams were reinforced with two M16 (No. 5) lap-spliced longitudinal bars (i.e., 40 and 60 d_b) and M13 (No. 4) stirrups spaced at 100 mm (4 in.) and 200 mm (8 in.) center-to-center. Based on experimental results, stirrup confinement clearly increased the bond strength, reduced longitudinal bar slippage, and increased splitting stress. The beams with a splice length of 60 d_band stirrups on 100 mm (4 in.) centers achieved 57% higher capacity than those with the same lap-splice length but without stirrups. Further, the ACI 440.11 equation overestimated the bond strength of sand-coated GFRP bars but yielded conservative results with closely spaced stirrups. CSA S6:25 predicted bond-strength values that were close to the experimental results compared to CSA S6:19, and CSA S806:12. 

Abstract The current code provisions in ACI 440.11 are based on the flexural theory that applies to slender members and may not represent the actual structural behavior when the shear span-to-reinforcement depth ratio is less than 2.5 (i.e., deep members). The Strut-and-tie method (STM) can be a better approach to design deep members; however, this chapter is not included in the code. Research has shown that STM models used for steel-reinforced concrete (RC) give satisfactory results when applied to glass fiber-reinforced polymer-reinforced (GFRP)-RC members with a/d less than 2.5. Therefore, this study is carried out to provide insights into the use of STM for GFRP-RC deep members based on the available literature and to highlight the necessity for the inclusion of a new chapter addressing the use of STM in the ACI 440.11 Code. It includes a design example to show the implications of ACI 440.11 code provisions when applied to GFRP-RC deep members (i.e., isolated footings) and compares it when designed as per STM provided in ACI 318-19. It was observed that current code provisions in ACI 440.11 required more concrete thickness (i.e.,h = 1.12 m) leading to implementation challenges. However, the required dimensions decreased (i.e.,h = 0.91 m) when the design was carried out as per STM. Due to the novelty of GFRP reinforcement, current code provisions may limit its extensive use in RC buildings, particularly in footings given the water table issues and excavation costs. Therefore, it is necessary to adopt innovative methods such as STM to design GFRP-RC deep members if allowed by the code.