Seismic Capacity and Performance of Waffle‐Flat Plate Structures Under Near‐Fault Ground Motions: Bidirectional Shake Table Tests

ABSTRACT A reinforced concrete waffle‐flat plate structure was subjected to a sequence of bidirectional near‐fault ground motions on a shake table until collapse. The test specimen was designed under current building codes and assigned a region of moderate seismicity. The ground motions were scaled in amplitude to represent very frequent, frequent, design, and very rare earthquakes at the site. Under these levels of seismic action the structure did not exceed the limit states established by the second generation (2G) of Eurocode 8, although collapse occurred under a seismic action slightly less severe than expected due to the accumulation of damage caused by previous tests. A large amount of energy was dissipated through torsion of the transverse beams by means of a brittle internal mechanism that was not intended to occur. Damage concentrated at the exterior plate‐to‐column connection (torsion failure of the transverse beams), which dissipated 63% of the total input energy and 93% of the energy that contributes to damage (i.e., input energy minus energy dissipated by inherent damping). In comparison with the plate, the columns dissipated a very small amount of energy (less than 7%). The total energy input on the structure until collapse under near‐fault bidirectional seismic actions was close to that obtained in previous studies with a similar specimen under unidirectional or under bidirectional far‐field ground motions. Finally, the behavior factor obtained from the capacity curve —estimated using the experimental base shear vs. top displacement relationship (1.55) — was very close to the behavior factor ( q = 1.6) prescribed by the 2G of Eurocode 8 for torsionally flexible WFP systems for use in force‐based seismic design methods.