Evaluating Steel Frames Beyond Alignment Charts’ Assumptions by Nonlinear Finite Element Analysis

Determining the load at which a column buckles is crucial for designing steel structures. In this study, an assessment of buckling loads and, consequently, the effective length factors of columns in frames that do not comply with the alignment charts’ assumptions is conducted using a nonlinear geometric finite element analysis, unlike the common method in technical literature, which obtains the buckling force using stability solutions. The reasons that the alignment charts’ solution does not satisfy frames with specific conditions are the assumptions underlying their derivation, such as idealized boundary conditions (BCs), stiffness distributions, frame interaction, and stability assumptions. Thus, for frames with different conditions, the buckling equation due to the assumed beam‐column models varies, needing to be modified for each special case. By using the custom‐made code writing provided for this research, one can solve for the buckling loads with minimal computational expense. Moreover, using the finite element method (FEM) to solve buckling loads is straightforward, user‐friendly, and helpful in many engineering topics, such as in this research. Four cases presented here demonstrate that the nonlinear FEM yields accurate results in all cases. At the end of each case, a comparison is made between the values obtained by this paper’s method, those obtained from the alignment charts, and other technical literature’s proposals. As a result, it is concluded which cases are in a more critical state.