SYSTEM IDENTIFICATION OF THE VINCENT THOMAS SUSPENSION BRIDGE USING EARTHQUAKE RECORDS

Abstract eng:
A combination of linear and nonlinear system identification techniques is employed to obtain a reduced-order, multi-input-multi-output (MIMO) dynamic model of the Vincent Thomas Bridge based on the available acceleration measurements of the structure to the 1987 Whittier and 1994 Northridge earthquakes. Results of this study yield measurements of the equivalent linear modal properties (frequencies, mode shapes and non-proportional damping) as well as quantitative measures of the extent and nature of nonlinear interaction forces arising from strong ground shaking. It is shown that, for the particular subset of observations used in the identification procedure, the apparent nonlinearities in the system restoring forces are quite significant, and they contribute substantially to the improved fidelity of the model. Also shown is the potential of the identification technique under discussion to detect slight changes in the structure’s influence coefficients, which may be indicators of damage and degradation in the structure being monitored. Difficulties associated with accurately estimating damping for lightly damped long-span structures from their earthquake response are discussed. The technical issues raised in this paper indicate the need for added spatial resolution in sensor instrumentation to obtain identified mathematical models of structural systems with the broadest range of validity.

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