Plastic analysis of steel structures under the effect of non-homogenous temperature

This study aims for two main goals. The first is to develop models for thenon-homogenous temperature distributions result in fire conditions. These models of fire are based on previous experimental studies and theoretical suggestions for the expected distributions of temperature. The second is to calculate the ultimate strength of the common steel cross-section. Interaction curves of this cross-section are presented for different assumed temperaturedistribution models. The critical temperature at which the structure collapses in fire conditions is also calculated from the resulted curves.In this study, incremental steps for the used numerical integration isconsidered and series of iterations are carried out based on an assumed locations and orientations of the neutral axis till the equilibrium conditions for the formulation of the plastic hinge are satisfied. Perfect plastic behavior of thesteel cross-sections is considered using stress-strain relationship which assumes linear relationship in the elastic zone and perfect plastic without strain hardening in the plastic zone. The non-linear effects of the elevated temperature on the used structural materials are also taken into consideration in this work.A FORTRAN computer program is written and developed to carry out the required analysis. The program can handle general loading conditions in thepresence of the non-homogeneity of the temperature gradients on the cross-section. Two different cross-sections are tested at five different assumed linear temperature distributions and five different positions of the wall and slab which give non-linear temperature distributions. The effect of the position of partitionson the temperature distributions is very important so, it affects significantly the ultimate strength of the cross section in fire. Two structures are taken as realapplications examples in which the ,pritical temperatures are calculated.