Effect of Dimension and Detail on the Capacity of Precast Concrete Parking Structure Diaphragms

Floor systems in precast concrete parking structures are intended to provide diaphragm action between elements of the lateral loadresisting system during seismic response. Investigations stemming from recent poor seismic performance of some of these structures have raised significant design issues related to the diaphragm. These issues include the possibility of larger-than-expected lateral forces, questionable strength and ductility in joints at critical locations, and the potential for large drift demand on the gravity system due to excessive diaphragm flexibility. A PCI Daniel P. Jenny Research Fellowship has examined the behavior of precast concrete parking structure diaphragms. In this paper, the results of nonlinear static analyses of topped and pretopped diaphragms are presented. These results reveal the effect of structural dimension and construction details on the diaphragm service level stiffness and ultimate capacity. A companion paper ("Seismic Design Recommendations for Precast Concrete Diaphragms in Long Floor Span Construction," to appear in the next issue of the PCI JOURNAL) will provide seismic design guidelines for long span precast diaphragms. In that paper, the results presented here will be interpreted with respect to expected seismic demands, as established for flexible diaphragm structures in parallel research.