Fe simulation of space steel frames in fire with warping effect

Most structural fire resistance analyses are confined to 2-D frames. To gain a more in-depth understanding of the response of a steel frame at elevated temperatures, 3-D simulations are necessary. This paper outlines the formulation of a two-noded 3-D beam-column to study the response of a steel frame in fire. The program is capable of small-strain large deformation analysis. Warping effect, a significant phenomenon in thin-walled members, is considered in the formulation. Degradation of steel mechanical properties at elevated temperatures is also considered, while thermal gradient is considered by slicing a cross-section into discrete segments. Creep can be either implicitly or explicitly taken into account. Several widely-used beam-to-column connections are approximated as zero-length semi-rigid springs. Their nonlinear moment-rotation relationships at elevated temperature are incorporated into the program. Unloading of both material stress-strain curve and moment-rotation characteristics of a connection are accounted for. The Newton-Raphson method is employed for nonlinear solving procedure. At the latter part of this paper, the program is verified against benchmark tests. All of them demonstrate the accuracy and reliability of the program.