Lateral response of ultra-high performance concrete columns confined with high-strength spiral stirrups

The lateral confinement of stirrups can effectively restrain the unstable lateral expansion of confined concrete and improve the load capacity and the ductility of concrete. The lateral response of stirrups affects the effective confinements on confined concrete and the dilation of core concrete. However, the lateral response of confined concrete has not received enough attention. In this paper, the lateral responses of 24 ultra-high performance concrete (UHPC) and ultra-high fiber-reinforced performance concrete (UHPFRC) columns confined with high strength stirrups were obtained by experiments. The investigated parameters included concrete strength, stirrups volumetric ratio, and steel fibers contents. The axial stress-lateral strain curves and lateral strain-axial strain responses of specimens were presented to understand the dilation of concrete. The results showed that high strength concrete and high steel fibers contents decreased the dilation of concrete, when stirrups volumetric ratio increased from 1.0 to 2.0%, the dilation of concrete increased by 1.45~2.09 times. Furthermore, the lateral strain-axial strain response prediction models were developed by introducing the effects of steel fibers, which were suitable for predicting the lateral strain-axial strain of confined concrete.