ABSTRACT
In fire, the outer steel tube is used as a sacrificial layer shielding off either the inner concrete core in case of CFST column or the concrete-infill and inner steel tube in case of CFDST column. Although the CFDST may be an improved column system over the CFST, the main drawback of the CFDST system is that the inner steel tube is still susceptible to rapid temperature increase due to heat conduction through the concrete
1 INTRODUCTION
Performance-based research on fire protection to steel columns has been carried out in the past, including the use of concrete cover, concrete encasing, gypsum wallboard and water filling (Lie 1992). All these measures are to reduce the maximum temperature attained by the column in fire within a critical period of time specified in the building regulations. The main function of the insulation materials used in all these fire protection systems is to protect the structural members from fire attack and, in most cases when there is no fire, the insulation materials themselves may never be used throughout the entire life span of the structural members they protect. A common feature to all these fire protection systems is that the materials, installation and maintenance costs for these systems are relatively high.
