Dynamic Distortions in Structures Subjected to Sudden Earth Shock

An inspection of earthquake records indicates that the ground may have practically harmonic motion for several successive swings after the initial shock. The amplitude and perhaps the period of the motion is then changed, sometimes quite radically. Some engineers feel that it is scarcely possible, under these conditions, for a structure with a period of vibration very close to that of the ground to attain critical distortions because of insufficient time for the amplitude to build up. This paper contains the results of model experiments on a single-mass system and a theoretical analysis of the behavior of an elevated water tank, all subjected to a sudden shock followed by harmonic vibrations.