Mutual pounding of adjacent structures during earthquakes

For adjacent structures separated by a small gap, there is a danger of their colliding in the event of a sufficiently large earthquake excitation. This mutual-pounding phenomenon has often caused extensive structural damage in past earthquakes. When retrofitting nuclear-power plants for increased seismic requirements, the size of the existing gap may be found to be too small. This can also arise when existing structures are recalculated with modern analytical procedures which account, e.g. for soil-structure interaction, including the material non-linearities of the soil and of the superstructure. (orig.)