Vibration control of structures during urban earthquakes

This paper addresses the problem of protecting structures from urban earthquakes. Urban (near field) earthquakes are responsible for generating a variety of ground motions. Some of these ground motions induce large displacements which result from rapid long period pulses-a type of excitation that can be detrimental to flexible structures. Herein a case study is presented for the response of a base-isolated structure located in Los Angeles, CA. The structure is subjected to two different records which have been recorded only 24 km apart during the Northridge earthquake; and it is shown that a protective isolation system that is beneficial to the structure when subjected to one ground motion is detrimental to the structure when subjected to the other. The alternative solution of controlling the response of flexible structures with controllable fluid dampers is investigated and preliminary results are presented