Energy capacity and seismic performance of RC waffle‐flat plate structures under two components of far‐field ground motions: Shake table tests

The bidirectional response of a portion of a reinforced concrete (RC) waffle-flat plate (WFP) structure subjected to far-field ground motions is studied through shake table tests. The test specimen is a scaled portion of a prototype structure designed under current building codes and located in a region of moderate seismicity of the Mediterranean area. The specimen was subjected to a sequence of tests of increasing acceleration amplitude that respectively represented very frequent, frequent, design, and very rare earthquakes at the site. The test structure performed well (basically in the elastic domain) under very frequent and frequent earthquakes, approached the boundary between the performance levels of life safety and near collapse under the design earthquake, and collapsed under the very rare earthquake. Damage concentrated at column bases and at the transverse beams of the exterior plate-to-column connection. Columns dissipated about 10% of the total energy that contributes to damage, and the rest was dissipated by the exterior plate-column connection. The total energy input on the structure until collapse under the bidirectional seismic action was very close to the value obtained in previous studies on a similar specimen tested under unidirectional ground motions. The capacity curve estimated from the experimental base shear vs top displacement relationship suggests it is best to use a behavior factor of at most q = 2 when designing WFP structures with the reduced-spectrum force-based approach.