Influence of Diaphragm Behavior on Performance of Precast Parking Garages During Northridge Earthquake

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9416274 Sause Many precast parking garages were heavily damaged in the Northridge earthquake. The gravity load system of many of these structures consisted of double tee floor units supported by inverted tee girders, spandrel girders, and columns with corbels. The lateral load system consisted of a few shearwalls with diaphragms formed by the double tees with reinforced topping slabs. These two systems are usually designed as separate systems. If the diaphragm develops cracks as a result of large in-plane forces and bending moments, significant diaphragm deformation may result and the rigid diaphragm assumption may be inadequate. Yielding of diaphragm reinforcing steel would result in much large diaphragm deformation. The objectives of this project are to: (1) study the influence of diaphragm behavior on the levels of drift experienced by the gravity load systems of precast parking structures during the Northridge earthquake, (2) evaluate whether diaphragm failure contributed to the observed damage in precast parking structures, and (3) propose capacity design concepts for precast diaphragms, if appropriate. A prototype parking structure based on the damaged parking structures will be designed and detailed. The seismic force- deformation behavior of a typical diaphragm of the prototype structure will be studied analytically, using a linear model, and two nonlinear models of different levels of detail and complexity. Unidirectional and bidirectional seismic loads will be considered. The seismic force- deformation behavior of a typical shearwall will also be studied analytically. The results of this analysis will be used to assess the significance of the diaphragm deformation. If appropriate, capacity-based design concepts for diaphragms will be developed using the results of nonlinear dynamic analysis of the prototype structure. The type of construction of precast parking structures damaged in this earthquake is widely used across the country, a nd thus a substantial hazard may exist. The research undertaken in this project will evaluate the role of diaphragm behavior and new capacity-based design concepts will be proposed to avoid inadequate diaphragm behavior in new precast parking structures. This is a Northridge Earthquake project. ***