Concrete-Filled Hollow Structural Steel Columns after Exposure to ISO-834 Fire Standard

Abstract

The use of hollow structural steel (HSS) columns filled with concrete has become widespread in the past few decades. The residual strength of a composite column may be used to assess the potential damage caused by fire and help to establish an approach to calculate the structural fire protection for minimum postfire repair. The behavior of 12 concrete-filled HSS columns with or without fire protection after exposure to the ISO-834 fire standard subjected to axial or eccentric loads has been experimentally investigated and the results presented in this paper. Comparisons are made with predicted column strengths using the existing codes such as LRFD-AISC-1994, AIJ-1997, EC4-1996, DL5085/T-1999, and GJB4142-2000. A mechanics model is developed in this paper for concrete-filled HSS columns after exposure to the ISO-834 fire standard, and is a development of the analysis used for ambient condition. The predicted load versus mid-span deflection relationship for the composite columns is in good agreement with test results. Based on the theoretical model, influence of the changing strength of the materials, fire duration time, sectional dimensions, steel ratio, load eccentricity ratio and slenderness ratio on the residual strength index (RSI) is discussed. It was found that, in general, the slenderness ratio, sectional dimensions and the fire duration time have a significant influence on the RSI. However, the steel ratio, the load eccentricity ratio and the strength of the materials have a moderate influence on RSI. Finally, formulas suitable for incorporation into building code, for the calculation of the residual strength of the concrete-filled HSS columns after exposure to ISO-834 fire standard are developed based on the parametric analysis results.