The Analysis Of The Cumulated Damage Of Steel Frame Structures Under Earthquakes And The Experiment Study

Steel frame structure will be in nonlinear state under strong earthquake, some local damage appear and its mechanics character degradation of stiffness and strength. This degradation has the effect on the structure dynamic character (eg. Degradation of its frequency) and on seismic performance. So how to evaluate the structures' mechanics characters under several earthquakes became very important for analysis of structural dynamic under earthquakes. To get the purpose, it must establish the accumulated damage index of every storey under earthquakes, then using the damage index to establish the degraded stiffness and the degraded strength. From this point, based on damage mechanic, the paper built a restoring force model, which take the effects of cumulated damage into account, and checked the model by using experiment, and finally offered the help to fix the damaged structures caused by earthquakes and to evaluate the ability of aseismatic of structures.This thesis is included 7 chapters.Chapter 1, states the reality of today's cumulated damage research on structures. The review on the model of evaluating structural earthquake damage is made and deficiency in its point out, and present research work connected with subject in this paper.Chapter 2, based on damage mechanic, using the double variables for damage index, the writer builds a restoring force model, which take the effects of cumulated damage into account for steel member of shear type, and gives the establish method of the parameters. This model takes the degradation of stiffness and strength.Chapter 3, used the proposed restoring force model and the structural dynamics theory, the paper set up the stiffness matrix that takes the effects of cumulated damage into account. Therefore, the stiffness matrix lays the foundation for the analysis of elasto-plastic structural responses of steel frames including the effects of cumulated damage under multi-timed earthquakes. A computer program SFADA is given according to the theory and methods developed in this paper to analyze the elasto-plastic structural responses of steel frames of shear type including the effects of cumulated damage. The paper used an example that calculated by both program SFADA and program SAP2000. By comparison of the results of two programs, the correctness of the analysis of elasto-plastic structural responses of steel frames is proved.Chapter 4, introduces the shaking table test of steel frame, which includes the model of the tests, cases of tests and the processed data, which proves out the proposed damage model.Chapter 5, by comparison of results from a specially designated shaking table test and the theoretical computation by SFADA tells correctness of the theory and reliability of the program developed in this paper.Chapter 6, based on the achievements of today's research on seismic damage performance-based design of reinforced concrete structures, the seismic damage performance-based design approaches of steel frame structures are presented.Chapter 7, gives the main conclusion and the prospect.