Diaphragm damage was observed in several precast concrete parking structures following the 1994 Northridge earthquake. In order to reduce the likelihood of damage in future earthquakes, the design provisions for chord reinforcement in diaphragms were modified in the 1997 Uniform Building Code, and new provisions for selecting web reinforcement were introduced in the 1999 AC! Building Code. This paper focuses on recent changes to the AC! Building Code and summarizes the results of a series of analyses of idealized buildings to demonstrate that diaphragms proportioned in accordance with earlier codes may be vulnerable to seismic damage. A diverse set of factors, including the orientation of precast members and the stressstrain characteristics of welded wire fabric, contributed to the observed damage in precast concrete parking structures.
