Analytical models for stress–strain behaviour of UHPC confined with spiral stirrups

Abstract

The axial stress–strain models of confined ultra-high performance concrete (UHPC) were important key inputs for analytical programs to predict the full-range loading deformation of confined UHPC. The concrete columns confined with stirrups under axial compression tended to be a failure in shear-compression failure. However, the existing models for evaluating the axial stress–strain models of confined UHPC did not consider the shear-compression failure. In this paper, an experiment on the axial stress–strain behaviour of confined UHPC was presented. The specimens consisted of 75 UHPC with compressive strength up to 155.45 MPa were confined by spiral stirrups. According to test results, a theoretical model for axial stress–strain curves of confined UHPC by considering the shear-compression mechanism of UHPC was developed. In the proposed models, the real lateral stress of stirrups was adopted to calculate the lateral confinement of stirrups, rather than assumed that the stirrups reached the yield strength. In addition, the effects of dowel action of stirrups and longitudinal reinforcement were considered. Furthermore, the prediction models for the compression behaviour indicators of confined UHPC included peak stress, peak strain, initial tangent modulus, residual stress, and residual strain were proposed. By comparing with existing models, the proposed analytical models of axial stress–strain curves of confined UHPC had high accuracy and high stability.