Stochastic methods for the seismic analysis of bridges

Stochastic methods for the seismic analysis of bridges are discussed in the present work. Models describing the seismic input by response spectra, power spectral densities and accelerograms are reviewed along with their extensions to spatially varying ground motions. The effect on bridges of the seismic waves spatial variability is studied within the framework of a multiple support response spectrum. A simplified method is suggested to quickly evaluate the sensitivity of bridge structures to small spatial variations. An algorithm is given to find the least favorable solicitation when spatial variability is large and uncertain. A nonlinear response spectrum technique is proposed to account for the ductility capacity in the structure. It is based on equivalent linearization techniques and a modal synthesis that takes advantage of the localized character of nonlinear elements in bridges (plastic hinges, bearings). Results in terms of ductility demand and energy dissipated through hysteretic cycles compare favorably with Monte-Carlo simulations but are far less costly. Eventually, a reliability analysis technique for nonlinear structures subjected to stochastic loading processes is discussed. (author)