The Study Of Seismic Demand Estimation Method Of Reinforced Concrete Structures

Performance-based seismic engineering (PBSE) is a very important research project in the field of international earthquake engineering, and estimating the maximum response of structures under seismic action accurately and efficiently is the key point of PBSE exactly. Focused on the structural seismic demand estimation method, this dissertation involves the following work:1. The estimation precision and the application range of the ordinary Pushover Analysis Method are discussed in detail. Using some recommendable idea of Model Pushover Analysis and Adaptive Pushover Analysis for reference, two kinds of Modified Pushover Analysis Method (MPAM) are proposed based on ordinary pushover analysis procedures. Considering the structural vibration characteristics after yielding, MPAMâ… correct the lateral loading pattern and the shape vector according to the yielding mode during Pushover Analysis procedures, hence the estimation error of floor displacement and the inter-story drift is reduced significantly. Compared to MPAMâ… , MPAMâ…¡consider the effect of Hmodal combination H, its estimation precision is Improved further more. For the frame damaged with integral mode , the estimation error of MPAMâ…¡is about 5%, For the frame damaged with local mode , the estimation error of MPAMâ…¡is about 10%.2. Based on 30 sets of two-component acceleration records of near-fault earthquake, the mean acceleration response spectrums are calculated in horizontal and vertical direction, the results shows that, compared to the far-fault earthquake, the near-fault earthquake really have much higher vertical effect. Using each set of near-fault acceleration records, a set of dynamic time-history analyses is carried out to determine the displacement responses of 6 story and 10 story frames, the results show that the vertical effect of near-fault earthquake will remarkably amplify the floor displacement and the inter-story drift demands of frame structures. Therefore, considering the vertical effect of near-fault earthquake properly, the modified pushover analysis procedures are proposed in this paper. According to the modified pushover method, the vertical seismic force should be loaded on every lumped mass of multi-degree-of-freedom structures at first, after that the pushover analysis in horizontal direction could be carried out as ordinary. To evaluate the accuracy of the modified and unmodified method, the floor displacement and the story drift demands of six story and ten story frames are estimated using 4 kinds of Pushover Analysis Methods, and compared with the results obtained from the dynamic time-history analysis.3. On the basis of the basic assumptions of pushover theory, the approximate relationship for converting the energy between the MDOF system structure and its equivalent SDOF system is deduced, and an approximate method is suggested to estimate the deformation energy and hysteretic energy of multi-degree-of-freedom system. In light of the idea of seismic damage evaluation of concrete members, a simplified approach is proposed to evaluate the overall seismic performance of concrete structures. The simplified approach synthetically considers the influences of maximum deformation and energy dissipation of structures, and evaluates the overall seismic performance of structures according to structural damage index calculated by Park-Ang damage model. The numerical example indicates that the results of simplified method are very close to the results obtained from time-history analysis, and are safe to some extent.4. The uncertainty generation of earthquake demand parameters caused by a series of basic uncertain factors is analyzed. At the same time, the Hadvantages H and limitations of FOSM method, Tornado Diagram method and Mathematical Statistics method are discussed for the purpose of sensitivity analysis. Illustrated by the case of a frame structure, the sensitivity of four kinds of earthquake demand parameters to a series of basic uncertain factors are estimated using three kinds of methods mentioned above, and the basic uncertain factors are arranged in important order. The result shows that the uncertainty of earthquake demand parameters is most sensitive to the intensity and the profile of ground motion.5. A new seismic random model is proposed, and the model parameters are determined according to different site classifications and design earthquake effects specified in current seismic code. In terms of the new seismic random model, the probabilistic distribution of structural elastic and elastic-plastic displacement demand is deduced based on reliability theory, and the elastic and elastic-plastic displacement spectrum are established. Integrating the theory in this paper and the pushover analysis procedure, the simplified methods for random seismic response analysis and the probabilistic seismic demand analysis are suggested, moreover on the basis of the SDOF and MDOF system case ,the numerical verification are carried out for validating the accuracy of simplified methods. The calculating results of simplified method are very close to which of the numerical method, while the working amount of simplified method is much less than which of the numerical method.