Comparison of roles of FRP sheets, stirrups, and steel fibers in confining bond critical regions

Based on experimental data of tension lap splices confined with fiber reinforced polymer (FRP) sheets in normal and high strength concrete (HSC) specimens, a new FRP confinement parameter, K-tr,K-f, was recommended. It accounts for the increase in bond strength due to the presence of FRP sheets. In this paper, a correlation is presented between the confining effects of FRP flexible sheets, transverse reinforcement, and steel fibers to improve the bond capacity and ductility of the mode of failure of tension lap splices. The correlation is based on research programs conducted at the American University of Beirut in recent years using identical specimens except for the confinement method used: FRP sheets, transverse steel stirrups, or steel fibers. Other variables included the amount of confinement provided and concrete strength. Analysis of test results indicated that an equivalent improvement in bond strength of tension lap splices in normal and high strength concrete specimens is provided by an amount of FRP sheets corresponding to a K-tr,K-f value of 2.5, or an amount of transverse reinforcement corresponding to K-tr of 1.0d(b). For HSC specimens, an amount of steel fibers corresponding to a volume fraction of 1% would provide an equivalent improvement in bond strength.