Numerical and experimental studies of cold-formed steel floor systems made of hollow flange section joists in fire

Fire performance of load-bearing LSF floors made of hollow flange section joists was investigated. Full scale fire tests were performed to determine the reliable fire-resistance rating of the LSF floor systems made of hollow flange sections (LiteSteel Beam). The test results proved the superior fire performance of LSF floors made of hollow flange section joists. Elevated temperature mechanical property tests were then performed. Suitable predictive equations were proposed for the elastic modulus and yield strength reduction factors and stress-strain models of hollow flange sections.

Thereafter, thermal and structural finite element models of LSF floors subjected to fire on one side were developed and were validated using the full scale test results. An extensive finite element analysis based study was then conducted to investigate the effects of joist dimensions such as web depths and thicknesses, types of wall configuration, joist section profiles, service holes in the LSF floor joists and elevated temperature mechanical properties on the fire performance of LSF floors. It was also shown that the commonly used critical temperature method based on the average temperature was appropriate in determining the FRR of LSF floors.

The accuracy of the currently available effective width based design rules were verified to predict the structural capacity of hollow flange section joists subjected to non-uniform temperature distributions. New direct strength method based design rules were then proposed to determine the FRR of LSF floors made of hollow flange section joists.