Shaking Table-Structure Interaction

摘要

The 20x20 ft shaking table at the Earthquake Engineering Research Center inBerkeley is tested for interaction effects. The tests include three loading configurations: a bare table, a table loaded with a 70 kip mass and a table loaded with a 68 kip single degree-of-freedom structure with a height of 219 inches. The shaking table has 5 degrees of freedom: one horizontal, one vertical and 3 rotational. When loaded with heavy and tall structures, it undergoes pitching (rocking) motion even in the absence of a pitch degree of freedom. It is observed that the interaction effects are negligible for the bare table and the rigid mass case. For the tall and heavy structure the pitching of the seismic simulator was evident when a horizontal signal was used; in addition, a change in frequency component of the horizontal table motion near the structural frequency was observed. Mathematical models are derived for analyzing the table-structure system. Simplified spring-mass-damper models are discussed. Methods for avoiding modeling of the table flexibilities are presented. Interaction effects are studied using response spectra and the equivalent coupled single degree-of-freedom table-structure system. It is concluded that the interaction effects are very similar to those encountered in soil structure interaction studies. The interaction causes a reduction in the structural frequency component of the command signal near the structural frequency and usually, but not always, an increase in damping. The change in the frequency component of the command signal near the structural frequency due to interaction does not significantly affect the ability of the shaking table to produce damaging motions to the test structure.