Collapse Behavior of Steel Columns as Part of Steel Frame Buildings: Experiments and Numerical Models

Earthquake-induced collapse risk assessment of steel frame buildings requires the use of deterioration models that simulate instabilities that cause strength and stiffness deterioration of structural steel components. In the case of steel columns in addition to cyclic deterioration in flexural strength, such models should capture the axial load – bending interaction, the axial contraction as well as the axial strength deterioration after the formation of local buckling within the column cross-section. Based on the available literature, experimental data that characterizes the hysteretic behavior of steel columns at large deformations is scarce. Therefore, the validation and further refinement of new or available steel column deterioration models becomes challenging. This paper discusses the main findings of an extensive experimental program that characterized the hysteretic behavior of wide-flange and hollow structural steel (HSS) columns. The effect of various types of lateral loading protocols on the hysteretic behavior of steel columns was examined with nominally identical specimens. It is shown that a primary failure mode observed in steel columns is the axial shortening. The amount of axial shortening can be considerably different in end columns compared to that observed in interior columns within the same story of a steel moment-resisting frame (MRF). Symmetric loading protocols that are typically used for experimental testing of structural components provide insufficient information for modeling the cyclic deterioration in flexural strength and stiffness of steel columns near collapse. A fiberbased deterioration model is developed for HSS columns that is able to simulate the cyclic hardening prior to the formation of local buckling and the steel column post-buckling behavior including axial shortening. The proposed model is validated with steel column test data that became available from the experimental program.