Seismic analysis of a bridge structure on liquefiable deposits using a spatially varying ground motion

• Main Author: Ramos, Danniel Jerome B.
• Format: text
• Language: English
• Published: Animo Repository 2015
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/4966
• Institution: De La Salle University

Current design procedures for horizontal structures involve the use of identical seismic records applied simultaneously at the structure. But a number of studies show that such procedures are not always the best case to employ, especially for extended structures such as bridges and pipelines. Hence a spatially varying ground motion is then utilized to overcome the problem. While these researches tackle its main components of wave passage and dispersion, and local soil medium, it has failed to include the potential of liquefaction it its analyses. Using local and generated artificial records, the paper aims to incorporate the phenomenon of liquefaction through the use of non-linear P-y curves based on actual soil characteristics. Spatial variation via multi-support excitation was applied at a straight 726.5 m section of the LRT-Line 1, which was modeled along with its foundation. The same structure is also subjected to an identical support motion modeled with a fixed base using local records. Results from dynamic analyses indicated that spatial variation and non-linear soil structure interaction modeling creates a non-uniform response it can be both beneficial and deleterious to select sections and seismic directions. It generally tends to decrease the demands for columns at the longitudinal direction primarily due to the movement restrictions imposed by the deck, which in turn created larger demands in it. The resulting forces at the deck suggest the possibility of pounding. Responses at the transversal direction tend to be dependent on higher mode shapes, especially for non-uniform motions. Inertial forces due to the inclusion of the piles and pseudo-static displacement levied by spatial variation tend to dominate the response in the combined cases. It was overall found out that the coupled behavior leads to generally unpredictable increases at certain points, thus the conclusions presented may not reflect to other bridge types. The applications of the study should be taken as a case-to-case basis and proper engineering judgment should be exercised.