Stainless steel compression members exposed to fire

The fire resistance of austenitic stainless steels is known to be better than that of conventional carbon structural steels. The aim of this study was to find out whether any austenitic stainless steels are available for use in buildings as load-bearing structures without fire protection. This is a critical issue, as aesthetic considerations often undergird the use of stainless steels in buildings. Eliminating the fire protection of structures would result in lower construction costs, a shorter construction period, more effective interior space utilisation, a better working environment and more aesthetic building design. As part of the project transient-state tests were carried out at Helsinki University of Technology at the Laboratory of Steel Structures. The fire resistance tests were performed at VTT Building Technology at the Laboratory of Fire Technology. Concentric compression tests were performed for rectangular 40 x 40 x 4 hollow sections cold-formed from austenitic stainless steel of type Polarit 725 (conforming to material number EN 1.4301 and AISI 304). The behaviour of the butt-welded joint at elevated temperatures was also considered. A simple calculation method is proposed for determining the flexural buckling strength of structures exposed to fire. The simple calculation method is valid when the modified slenderness is below 1.1 at normal temperature. The same formulae are used to determine the ultimate buckling load at elevated temperatures as at normal temperature, but in the former the mechanical properties (modulus of elasticity and yield strength) are reduced. The temperature is assumed to be uniformly distributed throughout the cross-section and along the column. The possibilities of using austenitic stainless steels in load-bearing structures without fire protection seem quite realistic when the parametric fire exposure is adapted or the fire resistance time is 30 minutes or less according to the ISO 834 standard fire-temperature curve. The class requirement of 30 minutes in a standard fire exposure might cause overestimation in normal temperature design. One of the most workable applications of stainless steel might be the load-bearing structures of balconies.