Axial Impact Behavior of FRP-Confined Concrete Stub Columns with Square and Circular Cross Section

Abstract

Fiber-reinforced polymer (FRP) wrapping has been shown to be very effective in enhancing the static loading capacity of reinforced concrete columns. However, the impact performance of FRP-confined square concrete columns is still an unexplored field of study. This paper reports experimental results of relatively large-scale FRP-confined square and circular concrete columns subjected to axial impact, using a large-capacity drop-hammer machine. The main parameters include type of FRP, number of FRP layers, and the corner-rounding radius ratio. The results indicate that the failure modes of square columns are strongly influenced by the corner-rounding radius ratio. As expected, the rupture locations of FRP are all in the corner region, where the strain distribution usually shows stress concentration. It is revealed that the actual rupture strain of FRP under impact is significantly lower than that under static load. Columns wrapped in glass FRP (GFRP) and basalt FRP (BFRP) performed better under impact loading than did columns wrapped with carbon FRP (CFRP). Compared with static loading results, the axial stress–strain response under impact exhibits a more complex behavior. Based on the experimental results, an equation is proposed for predicting the FRP confinement effect on concrete for circular and square cross-section columns under impact.