Strengthening of concrete with mixed confinement materials - Steel hoops and FRP composites

This paper presents the results of an experimental and analytical study on the behavior of rectangular concrete specimens externally wrapped with fiber reinforced polymer (FRP) composites and internally reinforced with steel hoops, subjected to pure compression. Axial load and strain were recorded to evaluate stress-strain behavior, ultimate strength and corresponding strain of the tested specimens with varying confinement type (one material versus two materials) and confining pressure. The test results showed that the compressive response of concrete confined with both FRP-wrap and steel hoops was quite different from that of concrete confined by either FRP or steel hoops separately, and the need of experimental as well as analytical study to account for the effect of the mixed reinforcements was recognized based on the comparisons between the test results and predictions by the four existing analytical models considered in this study.