Development of improved modal pushover analysis and its application for seismic assessment of bridge structures

Abstract

This thesis presents nonlinear static procedures for seismic assessment of cable-stayed bridges, especially by improved modal pushover analysis. To enhance the procedure’s accuracy, the key feature of the improved modal pushover analysis, which is the approximate elastic deformed shape, is improved to reduce the maximum error rates. Applying improved modal pushover analysis with other conventional nonlinear static procedures on multi-span continuous bridges, these procedures’ applicability and trouble spots have been studied. Moreover, the applicability of the improved modal pushover analysis has been verified by applying it to numerous multi-span continuous bridges with several earthquake motions. In addition, the relationship between overall result error rates and approximate elastic deformed shape error has been researched, and it is verified that to secure the procedures’ accuracy, the assumption of the procedure, maintaining a deformed shape after system yielding, should be valid. The assumption is valid when the structure’s shape is relatively regular and the stiffness ratio of pier and deck does not have a certain value. NSPs were also applied on cable-stayed bridges with a number of earthquake motions. The single-mode pushover analysis methods could not produce reasonable results at relatively stiffer sections of the system, such as the tower of a cable-stayed bridge. Multi-mode pushover analysis methods show reliable results with every part of cable-stayed bridges. However, when the introduced reliability indexes, approximate elastic deformed shape error index and earthquake property index have large values, these methods tend to underestimate structures’ deformation.