Model for lightweight concrete columns confined by either single hoops or interlocking double spirals

This article presents an analytical model to predict the stress-strain rela tionship of spirally confined medium- and high-strength light-weight aggreg ate (HS-LWA) concrete columns. The confinement pressure is assumed to vary along the height and the lateral dimension of the column section. The inter nal force equilibrium, the properties of the materials, and the geometry of the section are used to evaluate the lateral pressure. The model uses a si ngle fractional equation that captures the realistic behavior of the respon se in the ascending and descending portions of the stress-strain curve. The parameters in the model are calibrated using the results of 16 spirally co nfined LWA column specimens tested recently at North Carolina State Univers ity. The column test specimens were from an elliptical cross section and co nfined by single hoops or interlocking double spirals. The analytical model is sensitive to influencing parameters, including the strength of concrete, yield strength of the confining reinforcement, volume tric ratio of the confining reinforcement to the concrete core, spacing of the confining reinforcement cross section of the confined core, and configu ration of the lateral confining reinforcement. The model demonstrates good predictive capability for the behavior of LWA concrete column specimens wit h concrete strengths from 40 to 103 MPa (5.8 to 15 ksi).