Relative safety of high‐rise and low‐rise steel moment‐resisting frames in Los Angeles

This study assesses the deformation demands posed by high hazard seismic events to some common steel moment frame (SMF) structures in the Los Angeles region. The structures under consideration were SMF structures designed using the 1994 UBC for high seismic risk, both short and tall, similar to many SMF structures in Los Angeles. Lumped plasticity frame models are developed with the most current knowledge of nonlinear modelling techniques and component properties and are subjected to recorded and simulated ground motions. The recorded ground motions are selected and scaled to represent a high hazard seismic event. The simulated ground motions are extracted from a simulation of a magnitude 7·15 rupture of the Puente Hills fault. The frame models are varied to consider brittle pre‐Northridge welds, ductile post‐Northridge welds as well as simplified and detailed modelling techniques. Structural safety is assessed in terms of the number of structures that exceeded a safe inter‐storey drift ratio for each ground motion set. Also, the relative safety of the tall and short SMF, taking into account brittle and ductile welds, is evaluated. Lastly, the differences in demands imposed by the recorded and scaled ground motions on tall SMF structures are compared.