Estimation of lateral stress of stirrups at peak stress and residual stress of confined concrete at stirrups fractured in confined concrete under axial compression

The lateral stress of stirrups at the peak stress of confined concrete was closely related to the load-bearing capacity and deformability of concrete columns, while the fracture of stirrups affected the axial deformability of concrete columns after the peak stress of confined concrete. In this paper, 156 circular concrete columns confined with spiral stirrups and 141 square concrete columns confined with mesh stirrups were tested under axial compression. The effects of the compressive strength of unconfined concrete, the volumetric ratio and the yield strength of stirrups on the lateral stress of stirrups at peak stress and the residual stress of confined concrete at stirrups fractured were analyzed. Furthermore, the prediction models for evaluating the lateral strain of stirrups at the peak stress of confined concrete were established by considering the effects of the volumetric ratio and type of stirrups and the compressive strength of concrete, which had high prediction performance. In addition, the method for judging whether stirrups fractured or not was developed, which was suitable for evaluating the stirrups with and without yield platform. The prediction model for evaluating the residual stress of confined concrete at stirrups fractured was proposed.