Strengthening Aspects to Improve Serviceability of Open Web Expanded Steel-Concrete Composite Beams in Combined Bending and Torsion

摘要

The performance of open web expanded steel-concrete composite beams under combined bending and torsion was investigated up to failure. Two strengthening techniques were proposed: the first, by adding steel stiffeners only to web sections, and the second by exposing composite beams to external prestressing after supporting the web sections with steel stiffeners. Six specimens were tested divided across the two main groups. Each group included three specimens, which were designated according to the type of strengthening technique used. Load capacity, load-deformation responses, and strain across section depth were monitored. The results showed that the first strengthening technique reduced the deflection under service loads by 14.13% and 11.55% for castellated and cellular specimens, respectively, while the second technique decreased the comparative values by 147.82% and 30.11%, respectively. In terms of the angle of twist, torsional stiffness increased by 27.58% due to the application of steel stiffeners for castellated specimen, while, in the cellular specimens, there was no apparent contribution from adding these stiffeners in terms of improving torsional performance at the early stages of loading. The second technique did show a greater reduction in the angle of twist, by 93.10% and 39.53% for castellated and cellular specimens, respectively.