Damage inspection and vulnerability analysis of existing buildings with steel moment-resisting frames

The Northridge earthquake caused a number of steel moment-resisting frame (SMRF) buildings to suffer brittle fractures in their beam-to-column welded connections, which raised the concern that similar (undetected) damage may have occurred in other SMRF buildings during past earthquakes in the region. Several issues may arise in decisions to rehabilitate or upgrade older buildings. One is the extent of building to inspect for possible weld fractures. A second is whether fractured connections identified in inspection should be repaired before permitting long-term occupancy. A third is the connection repair cost. This paper proposes an efficient method for selecting connections to be inspected in an existing SMRF for purposes of condition and seismic fragility assessment. The efficiency of this selection method is illustrated by modeling the partial inspection process of two steel frame buildings. Finally, a vulnerability analysis of these buildings is performed as a basis for evaluating repair costs.