Combined torsion and flexural behavior of FRP strengthened members

Abstract

The study presents an analytical and experimental investigation on the combined torsion and flexural behavior of bare and fiber-reinforced polymer (FRP) strengthened RC members. A refined model, COMBINED-SMM-FRP, is proposed to simulate the pre-crack, post-crack, and post-peak response of bare and FRP-strengthened members subjected to a constant torsion to flexure ratio, where each of the membrane elements is subjected to different boundary conditions and responses. The model predictions are compared with experimental results from the literature covering different FRP types, FRP spacing, wrapping methods, and torsion-to-flexure ratios. Consistent agreement is obtained, and the model can be used to predict the behaviour of bare and FRP-strengthened RC beams. In addition to the analytical model, an experimental program is presented to examine whether externally bonded FRPs can fully suppress premature concrete cover spalling under torsional action. Specimens were strengthened by externally bonded FRP and tested under the combined action of torsion and flexure. The provision of externally bonded FRP is observed to substantially enhance both the cracking and ultimate capacity of members that are susceptible to premature concrete cover spalling. However, it was found that FRPs did not fully suppress premature cover spalling. By incorporating a limit for the spalling of cover, the proposed model can also be used to explore the behavior of RC members with a thick concrete cover where premature spalling occurs.