Seismic demand evaluation for a 4-story steel frame structure damaged in the Northridge earthquake

This paper summarizes results and conclusions from a case study concerned with the prediction of seismic demands and correlation of these demands with connection fractures discovered after the Northridge earthquake. Two adjacent buildings are used for this purpose. One is a 4-story building that experienced many connection fractures in a N-S perimeter frame. The other is a 2-story building that did not exhibit visible connection fractures. The discussion focuses on analytical modeling issues and the interpretation of analytical results obtained from eight series of static (pushover) and dynamic (time history and spectral) analyses. The analytical models are different in each analysis series, ranging from a simple elastic centerline analysis model to inelastic models that incorporate the contributions of the floor slab to the lateral strength and stiffness of moment resisting and simple frames. Two of the models are preliminary attempts to model the post-fracture behavior of one of the frame structures.