Base mat uplift effects on the seismic response of a rectangular nuclear building

This contribution presents results of a seismic analysis of a rectangular building subjected to an earthquake in its weak direction with special regard to nonlinear base mat uplift effects. A nuclear power plant switchgear building, is assumed to be located in the Upper Rhine Graben, which belongs to the highest German earthquake zones. The peak ground acceleration based is 0.3 g. A linear earthquake analysis predicted that more than 50% of the area of the base mat would uplift off the supporting soil. For the state of maximum uplift conditions, a static analysis of the building subjected to the gravity loads of the lifted-off building parts would lead to high shear and tensile forces in the concrete walls, which would require an extreme amount of reinforcement. A nonlinear earthquake analysis was performed considering the nonlinear relationship - overturning moment vs. base rotation - in order to give an adequate estimate of the amount of base mat uplift and internal forces in the walls. Nonlinearities due to the decreasing contact area between base mat and soil were considered taking also into account the time-dependency of the vertical load component due to vertical vibrations. (orig./HP)