Dr. Mohammed Ettouney
Frequency Domain Analysis of Long-Span Bridges Subjected to Non-Uniform Seismic Motion
Non-uniform seismic motion affects the seismic behavior of long-span bridges. Three main reasons for this non-uniformity have been identified. They are local soil conditions, wave passage and incoherency effects. Other effects, such as extended source and attenuation, are relatively small. The importance of non-uniform seismic motions, especially for sensitive and important structures, has lead to the development of several methods of analysis. These methods can be subdivided into two general categories, deterministic and stochastic. Due to the inherent uncertainty of the non-uniform seismic motions, deterministic methods, mainly time integration methods, can be computationally inefficient. Stochastic methods have been based mainly on modal analysis methods. The input / output are either described in terms of power spectral density or response spectra. This paper presents a direct frequency domain method that is based on formulating the whole soil-structure problem. The use of this direct frequency domain method for solving non-uniform seismic support motions is shown. The application of the proposed method to a simple two-dimensional (2D) bridge and a long span suspension bridge is presented. It is observed that non-uniform support motions may result in a large shifting of resonant frequencies of the structure. Also, large redistribution of bridge responses and internal forces were observed when using non-uniform seismic motions when compared with the uniform seismic motions case.
November, 30 2001
3:00 PM EST
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