An Analysis of Base Isolation Design Issues for Navy Essential Construction.

Base isolation isolation of the columns of building using spring-damper systems was found to offer significant potential for reduction of damage to essential Navy structures. This report review the principles of base isolation and presents site selection criteria. A design procedure for use of isolators on Navy mission essential construction was formulated. A detailed analysis of an isolated structure shows the significance of the isolators nonlinear hysteretic behavior. Linear analysis techniques may underestimate structure displacements by 50 percent, and moments by 15 percent. Vertical acceleration effects which are usually neglected increase moments by about 15 percent. Simplified linear models of isolation, such as required by a response spectra analysis neglect the hysterisis of the isolator. A nonlinear analysis must be used to predict structure displacements. A single-degree-of-freedom SDOF representation of the structure on isolators was found to be highly accurate in predicting displacements, and yet simple enough to include in the design criteria. Use of only linear response techniques is not adequate.