Response of extended structures to incoherent ground motions
by Dimitrios Pachakis
M.Phil. Civil Engineering
xi, 124 leaves : ill. (some col.) ; 30 cm
This thesis deals with two specific topics arising in the seismic analysis of extended structures, such as bridges and pipelines. They deserve special treatment compared to buildings and other point structures because they are subjected to spatially variable ground motions....[ Read more ]
This thesis deals with two specific topics arising in the seismic analysis of extended structures, such as bridges and pipelines. They deserve special treatment compared to buildings and other point structures because they are subjected to spatially variable ground motions.
The first part investigates the differences in the amplitudes and phases of simulated spatially variable ground motions by four different methods and the effect of the incoherence on them. It is found that even though all of the can reproduce fairly well the prescribed spectral and cross spectral density functions, they do not perform equally well in terms of the generated amplitudes, phases and computational efficiency. A thorough investigation is done to determine the patterns of amplitude variability in frequency and space and it is found that the parameters of the coherency affect the spatial correlation of the amplitudes in low frequencies.
In the second part, a recently proposed computationally efficient method for the calculation of reliability integrals is applied to a five-span bridge subject to incoherent earthquake ground motion. The uncertainties in the soil, the excitation and the structure are taken into account as well as the effect of flexible supports, in the calculation of the first passage probability for a certain response quantity. It is shown that the method can be applied easily to serviceability limit-state problems where the response can be calculated in the frequentcy domain and provide a framework for sensitivity analysis. Moreover, the influence of the uncertainty in the various soil-foundation-structure system parameters on the total reliabilit is investigated. It is found that structural and soil model uncertainties can change the failure probabilities significantly. Considering those uncertainties in reliability calculations gives a more robust estimate