Improvement Of Component-performance-based Seismic Assessment Method And Application In Frame Structures Supported By Stepped Foundation

Performance-based seismic assessment can be divided into the overall structural performance-based seismic assessment and component-performance-based seismic assessment. There are some differences in component-performance-based seismic assessment in different domestic specifications. How to establish a set of convenient and effective component-performance-based seismic assessment method in engineering pracitce is an issue that needs to be addressed urgently. Structural components have a big difference in damage under earthquake action, especially ground columns and step-terrace columns of the upper ground layer of frame structure supported by stepped foundation, it’s too rough to ascertain the structure performance level with overall structural performance index, it’s necessary to ascertain performance of frame structure supported by stepped foundation from component level to strctural level. So component-performance-based seismic assessment method can be good used in frame structure supported by stepped foundation. Displacement indicators are widely used in component performance assessment, and whether these indicators can apply to frame structure supported by stepped foundation remain to be studied.This thesis put forward suggestions for improvement based on the analysis on the existing component-performance-based seismic assessment methods, and establish a set of convenient and effective component-performance-based seismic assessment method, and then compare differences between the improved method and the original method to evaluate the structure performance. Analyse the suitability and the actual assessment effect of material strain, plastic hinge, generalized shear deformation, interstory drift, destructive story drift, and component drift based on material strain in frame structure supported by stepped foundation detailedly using finite element analysis software SAP2000 and Perform-3D to select the better index, then using the index and the improved method to evaluate the actural structure performance. Analytical method used in this thesis is mainly dynamic nonlinear analysis method.Through the study of this thesis, the main conclusions are as follows:①In this thesis, autor learned from each other in order to put forward an assessment method of “weighted average + serious damage limit” based on existing methods, “weighted average”, namely ascertaining the structure performance level with average damage level of the whole structure, “serious damage limit”contains that ascertaining the structure performance level with the highest value of the whole stories’ structural components’ serious damage level’s weighted value and the lowest value of all key components’ performance levels, and take the lowest level of all ascertained structure performance levels as the final structure performance level. Compared with the original method, the component importance is considered, and method to ascertain weak story is added, and unreasonable problem of multiple proportional control in the original method is avoided, also it’s convenient to check the comprehensive damage of beams and columns of a layer in the improved method.②material strain, plastic hinge, and component drift based on material strain are suitable for frame structure supported by stepped foundation. Eneralized shear deformation, interstory drift, and destructive story drift are not suitable for frame structure supported by stepped foundation. On the consideration of only different constaints at the bottom of ground columns and step-terrace columns, usually damage of ground columns is greater than step-terrace columns.③material strain and component drift based on material strain are roughly the same to ascertain the component performance of frame structure supported by stepped foundation, component drift based on material strain is relatively safe in limit. Compared with component drift based on material strain, material strain is better in line with the actual situation and it’s easier to use. Due to differences in norms of China and the United States, chinese component performance levels can’t be obtained from plastic hinge, it is suggested that the plastic hinge can be used as reference indexe. In this thesis, the author recommend material strain can be first selected, if material strain is not directly gotten, component drift based on material strain can be used as index to assess performance of component with the plastic hinge as a reference, while destructive story drift is recommended when ascertaining interstory drift.