Model Identification and Seismic Analysis of Meloland Road Overcrossing

Abstract

This report presents the results of research directed toward model identification and seismic analysis of the MRO. This research has been implemented to meet the requirements of Tasks 4 and 5 of the UNR-D&M research program (Sec. 1.1.3) and also to provide a basis for developing improved bridge modeling procedures as required under the D & M research program on SBOs (Sec. 1.1.4). The scope of this research effort consisted of our development of a finite element model of the MRO whose parameters were estimated through the application of state-of-the-art system identification methods to the MRO's recorded motions from the Imperial Valley Earthquake. These estimated model parameters were also checked for consistency with an overall range of model parameter values computed using established engineering procedures. This model was then used in a series of parametric dynamic analyses of the seismic response of the MRO which enabled us to evaluate the effects of uncertainties in the various model parameters on the demand forces and moments in the structural members and the foundation springs. Maximum foundation spring forces and moments obtained from these analyses were used as input to nonlinear static analyses of the MRO's pile foundations in order to compute the demand forces and moments within the piles. The demand forces and moments within the MRO's structural and pile elements were then compared against the capacities of these elements. These analysis results have been interpreted to assess the seismic performance and design of the MRO, and also to provide an important basis for our development of improved modeling and seismic evaluation procedures for short bridge overcrossing structures. The above efforts have focused on the modeling and analysis of the MRO's translational and rotational response to transverse horizontal input motions; i.e., the bridge's response to vertical and longitudinal input motions was not included in this research. This focus on the MRO's response to transverse horizontal input motions was adopted because: (a) this response will lead to more severe earthquake-induced internal forces and moments, particularly in the central pier which is the element of an SBO that is typically most vulnerable to seismic excitation; and (b) our past evaluations of the MRO's recorded motions have shown that its response to transverse horizontal input motions is strongly affected by SSI, whereas SSI has only a negligible effect of the MRO's response to vertical and longitudinal input motions (Werner, et. al., 1987).

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