Removal of yield stress limitation for composite tubular columns

Abstract

The AISC Load and Resistance Factor Design (LRFD) Specification for composite columns is primarily based on a 1979 Structural Stability Research Council (SSRC) paper. It restricts the yield stress to 55 ksi. It is the purpose of this paper to examine the 55 ksi yield stress limitation in view of the performance characteristics of composite tubular columns. Concrete that is confined by the continuous shell provided by steel tubes are shown to be capable of sustaining substantially higher strains than 0.0018 before either material fails. The potential benefits for composite structures may be significant. The scope of the work did not allow for the development of a new composite column strength model. However, the conservatism of the current criteria point to a significant need for further studies of this problem. In particular, a strength model that incorporates concrete confinement effects will be most useful.