Fire Resistance Design of Concrete-Filled Steel Tube Stub Columns

This paper introduces simplified design methods for calculating the load bearing capacity of axially loaded concrete-filled carbon steel tubular (CFST) stub columns and concrete-filled stainless steel tubular (CFSST) stub columns. Refined finite element (FE) models are developed for capturing the fire performance of CFST and CFSST stub columns under ISO 834 fire. The accuracy of proposed FE models is validated by comparing with existing test data. By using the new developed FE models, the design equations suggested in Eurocode 4 for calculating the axial load bearing capacity of CFST and CFSST stub column in fire are evaluated. It is found that the Eurocode 4 generally provide an unsafe prediction due to the influence of unsuitable consideration on thermal expansion and adopted material strength values. In order to improve the equations in Eurocode 4, correction factors kc and ks for the concrete core and steel tube are defined and calibrated based on comprehensive parametric analysis, and refined equations for predicting the axial load bearing capacity of CFST and CFSST stub columns in fire are suggested. Finally, a design example based on the proposed simplified design methods is demonstrated in this paper.