Question

What is the cause of severe damages to elevated highway structures in the time of earthquakes?

Answer 1

When the ground shakes, highwy structures respond to the accelerations transmitted from the ground through the structure's foundation. The inertia of the structure (it wants to stay at rest) can cause shearing of the structure which can concentrate stresses on the weak walls or joints in the structure resulting in failure or perhaps total collapse. The type of shaking and the frequency of shaking depends on the structure. Tall structures tend to amplify the motions of longer period motions when compared with small structures. Each structure has a resonance frequency that is characteristic of the building. Predicting the precise behavior of buildings is complicated, a rule of thumb is that the period of resonance is about equal to 0.1 times the number of stories in the structure.