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Seismic demands in precast concrete diaphragms

  • Author(s): Schoettler, Matthew John
  • et al.
Abstract

Existing methods of analyzing lateral force demands on structures during seismic events do not fully contemplate the amplification caused by diaphragm flexibility. Moreover, commonly used code provisions do not conservatively anticipate floor demands generated in shear wall buildings. In buildings with floors that act as rigid diaphragms, elastic response necessitates the accurate estimation of design forces, which is currently not provided with an equivalent lateral force analysis. In long span structures with perimeter walls, diaphragm flexibility may result in amplified floor demands. This amplification was addressed while investigating elastic diaphragm demands in precast concrete buildings. Modal response spectrum analysis formulated the basis of the elastic design. A modified version of the modal first mode reduced method proposed by Rodríguez et al. (2002) was extended to shear wall buildings with diaphragm flexibility. This method conservatively estimates the design forces necessary for elastic diaphragm response at the design earthquake hazard. Diaphragm demands were assessed in a large scope analytical with the proposed design method. Results show this method sufficiently bounds demands for rigid floor systems or for systems whose flexibility is included. An experimental program supported the analytical study providing in-plane diaphragm stiffness characteristics of a precast concrete building. A complete structural system was tested at 54% scale with unique diaphragm systems on each of its three floors. Hybrid rocking walls minimized residual drift and allowed customized nonlinear wall behavior at different hazards. Extensive testing and abundant instrumentation generated valuable information regarding the seismic performance of precast concrete systems. These results provided the necessary mechanism for analytical model validation and insight on precast concrete diaphragm behavior

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