Numerical simulation on seismic collapse of thin-walled steel moment frames considering post local buckling behavior

• A fiber element have been developed to simulate post local buckling behavior.
• Hysteretic stress–strain model with a negative slope was developed.
• Cyclic loading significantly increased strength degradation of thin-walled sections.
• Collapse behavior of a steel moment frame under earthquakes was simulated.

Steel moment frame buildings face severe collapse potentials when subjected to earthquakes beyond the design level. Reliable numerical modeling of steel moment frames is significant to assess the critical parameters affecting collapse behavior. A fiber-element model is presented to evaluate post-local buckling behavior for steel structures. A constitutive relationship was defined for material properties taking into account of post-local buckling degradation in strength and stiffness. The model is compared with quasi-static test databases related to H-shaped steel, circular and rectangular hollow steel section (HSS) members. Three parameters, including strength, associated deflection and post-peak degradation were reasonably simulated. Significant strength degradation was triggered by the local buckling in the thin-walled HSS beam–columns. The numerical model well presented the collapse of a steel moment frame tested by E-Defense shaking table. The results show that the thin-walled square HSS column components induced low-ductile collapse behavior due to the prior local buckling at the bottom storey. The proposed fiber-element model provides a simple alternative method for predicting deterioration and collapse of steel frames under extreme earthquakes.