Seismic Evaluation of Old RC Waffle Flat-Plate Systems

Abstract eng:
In moderate-seismicity southern European countries it is very common to use reinforced concrete waffle flat-plate structures for sustaining both vertical and lateral earthquake loads. In the case of Spain, many of these structures were designed during the seventies, eighties and nineties according to earlier seismic codes which required relatively small lateral strength and did not contain any provision for attaining ductility. Past earthquakes have raised serious concerns about the safety of these structures in the case of a severe earthquake. In this paper, a numerical investigation is carried out to evaluate the seismic demands on old RC waffle plate systems located in southern Spain, in a moderate-to-high seismicity region. A prototype building, designed according to Spanish codes from the 1970´s to 1990´s and current construction practices, was analysed with SAP2000 by using a non-linear static method. The frame model was equipped with user defined hinges based on testing. The low gravity shear ratio and the consideration of punching reinforcement (a usual Spanish practice even when it was not deemed necessary from calculation) leads to a strong column/weak slab behaviour.

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