Finite-Element Model for Confined Concrete Columns

Abstract

The ductility of concrete structures is an issue that is continually being addressed as higher strength concretes are produced, better numerical models have become available, and seismic mechanics become better understood. For high strength concrete columns in axial compression, there are some questions as to the ability of the ties to provide similar levels of confinement as currently exist in normal strength concrete columns having similar tie arrangements. The ratio of the confining stress to the concrete strength is lower for high strength concrete. In many of the empirically based models used for the design of high strength concrete columns, it is taken that the ties are at yield at the peak load. In this paper, a finite-element model is developed to investigate the response of concentrically loaded columns with concrete strengths up to 100 MPa. Numerical examples are presented where it is shown that: (1) for confined high strength concrete columns, the tie steel is not at yield at the peak load; and (2) tension strains at the cover-core interface of high strength concrete columns are large enough to account for the early cover spalling that has been observed experimentally.