Buckling of Steel Portal Frames Considering Material Non-Linearity

In this research, an experimental study was carried out to investigate the failure modes of eight frames with IPE cross-sections. The study was conducted by subjecting these frames to two equal concentrated loads (applied directly on columns); however, the resulted data was obtained using load cells to record load increments. Comparison between experimental and theoretical results was tabulated by analyzing the eight portal frames using the following methods: 1- Quasilinear analysis. 2- Non-linear material analysis. 3- Codes AISC ASD, and AISC LRFD. For non-linear material analysis, direct tensile and stub column tests were performed to obtain the secant modulus as a function of plastic energy density. A mathematical formula was designed for this purpose using a special computer program. Moreover, a comparison of "AISC LRFD & AISC ASD" with the experimental results were implemented. Furthermore, the non-linear material model was also applied to these Codes. Linear analysis gives a reasonable approximation to deflections before yield occurs. Calculation of buckling loads for different frames using Euler formula, ASD, and finite element quasilinear analysis are significantly overestimate the experimental results. Whereas, incorporating the non-linear material model into the above mentioned methods of analysis brings the values very close to the experimental results.