The performance of hot-dip galvanized composite beams made of high and higher strength steel in standard fire resistance tests

Abstract

The lower emissivity of hot-dip galvanized steel sections as compared with non-galvanized steel, particularly at temperatures below 500 °C, results in slower heating when exposed to fire, thus enabling fire resistance ratings of R30 for compact cross-sections without additional passive fire protection. Using galvanized high and higher-strength steels allows R30 fire resistance to be achieved in composite beams more efficiently and cost-effectively. These ideas are investigated experimentally and via numerical analyses in this paper.

Large-scale standard fire resistance tests are presented to evaluate the performance of hot-dip galvanized composite beams under thermal and mechanical loads. The tests include a variety of beam geometries and depths, using steel grades S460M and S690QL. Single-symmetrical beams were designed with a reduced top flange thicknesses and compact bottom flanges to optimize overall depth and improve thermal response during fire testing. The temperature-dependent material properties of the S460M and S690QL steels is characterised, including steady state and transient tensile tests on both steels, and the results are compared with those given in DIN EN 1993-1-2. Hot-dip galvanized secondary beams with different connection types were connected in the middle of the beams during the large scale fire resistance tests so as to investigate temperatures experienced by differing connection details. The collected test data are used to validate and verify finite element models for such composite beams when exposed to standard fire exposures, alongside further parametric studies examining elements such as cross sectional geometry of the composite beam, the degree of shear connection, and the overall length of the beams. The outcomes of these studies contribute to the determination of the minimum required degree of stud shear connection for hot-dip galvanized composite beams in standard fire scenarios.