Seismic Performance Evaluation of Pre-Northridge Steel Frame Buildings with Brittle Connections

Abstract

As part of the (FEMA/SAC) Phase 2 program, this study focused on performance prediction and evaluation of existing steel SMRF buildings assumed to be built prior to the Northridge Earthquake. Several classes of buildings, which are representative of typical buildings based on year of construction and brittle pre-Northridge connections, were designed in accordance with the 1973, 1985, and 1994 UBC provisions. Then, the frame analysis models were developed including the effects of brittle connections, panel zone deformation, and interior gravity frames. Based on the drift demands and capacities calculated using each set of 20 SAC ground motions representing 2/50 and 50/50 hazard levels, a performance prediction and evaluation procedure based on the reliability framework is presented. Confidence levels that existing buildings will exceed the predefined performance level for different hazard levels are calculated. The pre-Northridge design and construction represented by the old building codes and brittle connections force the buildings to experience large seismic demand and result in a low confidence level in achieving the desired performance levels.