Research On Pushover--Capacity Spectrum Analysis Of RC Frame Structure

As have been shown by a serial of massive earthquake, it is very necessary to analyze the elastoplasticity of the building subjected to strong earthquake ground movements. The elastoplastic time-history analysis cannot be wildly used in practical works because of its complicate calculation and uncontrollable, though it has been proved to be the most reliable method in the elastoplastic dynamic analysis of the structure. Because of this, the Push-over analysis is put forward in succession by different researchers in variant countries in order to check the aseismic ability of structure. In its essence, Push-over analysis is a kind of statistic calculation method. In brief, one of simulating lateral inertia forces is put on the analyzing model and is enlarged step by step till the structure gets into a predetermined state. During the procedure, the yielding elements are then relaxed to form plastic hinges and incremental lateral loading until a nonlinear static capacity curve is created. The curve is calculated in terms of lateral top roof displacement and total lateral force at the base of the building. The Push-over analysis can briefly predict the behavior of the structure under the lateral force and find out the appearance sequence and distribution of plastic hinge of the end of members and the weak points of the structure. In this article, the procedure of Push-over analysis has been put into effect, and following factors has mainly researched in Push-over analysis: choosing the calculation model of both structure and element; analyzing the yielding moment and limiting moment of cross section; posing the distribution pattern of lateral force; discussing the influence of high class mode of vibration on the structure. The author also combined the Push-over analysis results with Chinese code in effect to research the following problem: establishing elastic demand spectrum ofdifferent damping and elastoplastic demand spectrum of different ductility, which are based on the code; putting forward a comprehensive method used to estimating structure seismic performance. In this article, the author made a Fortran Language program, analyzed a real case through Push-over and checked its usefulness. The results showed that: (1) the estimating method based on the code is useful and can be practiced. (2) the Push-over analysis program made by author can analyze the behavior of structure and estimate structural performance. (3) More than two distribution patterns of lateral force should be used in analyzing structure in Push-over analysis; the adaptable loading pattern is more reasonable than fixed loading pattern because it takes the structure dynamic properties into account, however, fixed loading pattern could be used in comparatively regular structure. (4) In judging the aseismic ability of structure, it was advisable to combine the capacity curve in term of top roof displacement and base-shear with the displacement of different story and the distribution of plastic hinges.