Study On Internal Force Redistribution And Moment Modification In Prestressed Concrete Frame

Recently, prestressed frames are widely used in Chinese civil engineering. But the usual elastic design method of prestressed frames are incoordination with the obvious nonlinear character appeared in the course of loading. In order to solve the problem, acoording to the moment modification standard of reinforced frame structures and the experimental results of prestressed continuous beams, some country'codes adopt moment modification design method to consider the nonlinear character of prestressed hyperstatic structures in the course of loading. But these moment modification standards only fit for prestressed continuous beams, in order to use these standards to prestressed frames, there are more questions to be solved. Because the structural and load style of prestressed frames are more complex than prestressed continuous beams. This thesis regards bonded post-tentioned partially prestressed frames as research objects. After a large number of experiment researches and nonlinear finite element analysises, the rules of plastic internal force redistribution are discovered, then some useful suggest to the moment modification of prestressed frames are presented in this thesis.The main research work finished in this thesis is as following:①The long-span prestressed primary beam structure programme and secondary beam structure programme in prestressed primary-secondary beam system are introduced in this thesis. The three methods to solve the construction problem of top-side beam-column joint of long-span prestressed frames are introduced, they are the method to place prestressed bar in top columns, hinged-rigid support method and strong beam & weak column method. The secondary moment, plastic internal force redistribution and moment modification are discussed in this thesis.②Experiment researches to ten full size prestressed frames are finished in this thesis, the important rules to the plastic internal force redistribution by some influencing factors are discovered, these influencing factors include the relative height of equivalent compression zoneξ, partial presstressing ratioλ, secondary moment M_sec, horizontal load, the axial pressure ratio of column, the reinforcement of sections.③Based on two stage (stretching stage & loading stage) analysis of prestressed frames, Nonlinear finite element analysis program to prestressed frames is developed in this thesis. From the stress-strain curve of reinforcement bar and concrete, layered finite element model and arc-length control method are adopted to analysis prestressed frames...