Abstract
Many aftershocks were observed in the Pacific coast of Tohoku Earthquake. In view of this fact, aftershocks should be paid attention, although it is ignored in the conventional design method. In this paper, the effect of aftershocks to buildings is discussed focusing attention on the energy input especially. From the cumulative energy spectrum, it is elucidated that aftershocks recorded this time has enough energy to bring certain degree of damage. P-Δ effect degrades the strength of the buildings virtually. Therefore, the building damaged after main shock can be brought significant incremental deformation by small energy of aftershocks.
