Crack formation in FRC structural elements containing conventional reinforcement

It is well known that both crack spacings and crack widths in members with conventional reinforcement can be reduced by adding steel fibers to the concrete mix. This behavior is important not only for predictions of the tensile behavior including tensile stresses due to tension stiffening and fibers, but also for evaluations of the serviceability or ultimate capacity of FRC members containing conventional reinforcement (R/FRC). Since test results for the tensile behavior of R/FRC members are scarce in comparison to those for ordinary reinforced concrete members (RC) or FRC members without rebar, an experimental program was undertaken to better understand the effect of fibers in conjunction with conventional reinforcement.In this research, direct tensile tests were conducted on 12 RC and 48 R/FRC specimens of 1.0 m length. The variables included steel fiber type, fiber volumetric ratio, and reinforcement ratio. From the test results it was observed that cracks were more finely distributed in R/FRC members, and that the average crack spacing decreased until the rebar yielded. After yielding of the rebar, the tensile deformation was dominated by one or two cracks. It was also determined that currently available formulae significantly overestimate the average crack spacing in R/FRC members. Based on the test results, a new crack spacing formula is developed in this paper.