Fire resistance and stability of non-uniformly heated steel plate girders with slender section

The results of experimental tests and computer simulations pertaining to the bearing capacity of unevenly heated girders made of slender thin walled class 4 sections are presented in this paper. It has been shown, that for the analyzed group of elements the value of lateral-torsional buckling coefficient depends on the initial load level applied to the considered element and the cross section bearing capacity reduction level under fire conditions. It has been determined as well that the influence of steel grade used on the value of buckling coefficient is negligible. Based on the research conducted, a new proposal for calculation of the lateral-torsional buckling coefficient for considered group of elements has been prepared. A simplified method to determine the bearing capacity of non-uniformly heated class 4 sections is proposed in this paper as well. It has been shown that both proposed methods exhibit sufficient convergence of results with the results of computer simulations, and satisfy appropriate acceptance criteria as well.