Effect of Reinforcement Type, Diaphragms, and Hollow Core on the Torsional Capacity of HSC Box-Girders under Torsion, Shear, and Bending

Mariwan Mirhaj Mohamed-Salih, Ali Ramadhan Yousif


To date, no research has been conducted on high-strength concrete (HSC) box-girders reinforced with basalt fiber reinforced polymer (BFRP) rebars and steel stirrups under combined actions of torsion, shear, and bending. In this work, rectangular HSC box-girders utilized with BFRP bars as internal longitudinal reinforcement under the combined state of loading are studied exclusively. A steel-reinforced (control) specimen and three other rectangular HSC box-girders made of BFRP bars and steel stirrups were tested under combined torsion, shear, and bending loading. Every specimen was 500 mm wide by 375 mm high, with a constant wall thickness of 120 mm, a total length of 5000 mm. Each contained about 2.5 percent total reinforcement, equally distributed between the longitudinal bars and transverse steel stirrups. The study aims to evaluate the torsional behavior of HSC box-girders considering the effect of longitudinal reinforcement type, provision or elimination of diaphragms, and the method of filling the hollow core. The experimental findings show that replacement of longitudinal steel bars with BFRP bars result in a drop in the ultimate torsional capacity by 15 percent; in addition, while the deflections at comparable loadings were lower in the entirely steel-reinforced specimen, but surprisingly, the final deflections were less in the BFRP-replaced case. When the diaphragms are eliminated, the ultimate capacities drop significantly by about half of that of a comparable specimen with diaphragms. When the hollow cores were left unfilled with Styrofoam, the ultimate capacity decreased by 30 percent with comparable twist angles but lower deflections at failure.


Keywords: box-girder, high-strength concrete, fiber-reinforced polymer bar, torsion, combined loading.

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