Research On Lateral Load Patterns Of Pushover Analysis With Consideration Of Effects Of Higher Modes

As a simplified method for evaluating the seismic performance of structure, Static elastic-plastic analysis(Pushover analysis) has been widely used. Pushover method can be used to guide the structure design as well as assess the earthquake-resistant capability of existing structures, and work out a reinforcement scheme. However, the traditional Pushover method with fixed horizontal load pattern cannot consider the influence of higher modes, which limits its application in the seismic performance evaluation of high-rise buildings or irregular structures. In recent years, the number of structure that are greatly influenced by higher modes are increasing, Pushover analysis based on the traditional lateral force pattern will lead to distortion of structural seismic response results. On the other hand, the improved Pushover horizontal load pattern with high calculation precision is complex in concept and calculation, and is hard to implement. Therefore, it is important to put forward a kind of load pattern that is able to consider the effect of higher modes as well as convenient to implement. To this end, the following work has been made:(1) Structure finite element analysis model is set up in Perform – 3D software by using the fiber model method, and take a frame structure experiment as an example. The rationality of the established model is showed by comparing the skeleton curve from experiment with base shear- vertex displacement curve from Pushover analysis.(2) According to the current Chinese structure design codes, 7 concrete-filled steel tubular frame structures and 6 concrete-filled steel tubular frame shear wall structures that have regular flat facade layout are designed. Select 15~21 natural earthquake waves for each structure, carry out separately nonlinear dynamic time history analysis and Pushover analysis under three kinds of conventional horizontal loading pattern for these 13 structures by using nonlinear analysis software Perform- 3 D. Explore the distribution law of story shear and story drift along the height of structure under these two analysis methods, and study the effects of higher mode with the height of structure ascending.(3)Explore the difference level of structural seismic response using nonlinear dynamic time history analysis and Pushover analysis. With story shear and story drift as parameters, compare the results from Pushover analysis under three kinds of lateral force pattern with the average value from nonlinear dynamic time history analysis under multiple earthquake waves. On this basis, the performance of 7 frame structure under strong earthquakes was evaluated using the idea of performance-based design and displacement-based seismic evaluation method.(4)With story drift as study index, the results of nonlinear dynamic time history analysis under multiple earthquake waves as criterion, adopt the method of multiple linear regression fitting to fit Pushover analysis results of three kinds of conventional lateral force pattern, the combination coefficient of different load pattern are obtained. Study the relation between combination coefficient of a certain load pattern and basic period of structure with regard to two kinds of structure forms separately, employ curve fitting method to get the quantitative relation between them, so that to obtain a combinatorial mode of three kinds of conventional lateral load pattern, which can take the effect of higher mode into consideration, and its rationality has been verified.