Research Into Secondary Moment And Redistribution Of Internal Force About Bonded Post-Tensioned Prestressed Concrete Frame

At first, this thesis analyzes the main causes in theory, which have effects on the redistribution of internal force and modulation of moment for the bonded post-tensioned partially prestressed concrete frame (for short prestressed frame), including the relative height of compressive zone of section (ξ), secondary moment and types of load applying. Then, this thesis analyzes the test of prestressed frame. Then, a method, called curvature-force method, for nonlinear analysis of prestressed frame is put forward. The method, based on the finite element theory, force-method theory, increment method and middle stiffness method, making use of the increment of curvature of the section, works out the increment of load applying and is proved in this thesis. At the same time, plastic hinge, rigid zone, negative stiffness, load relaxing and so on are taken into account. With curvature-force method, this thesis designs the program for nonlinear analysis and simulates the test. The results of nonlinear analysis are good agreement with the ones of test. So the method of nonlinear analysis is proved reliable and practical.At last, with the program, 18 one-storey and one-span prestressed frames are simulated. Some conclusions are reached with the taking into account the ξ, secondary moment and types of load applying: (1) The ξ in the beam affects the ductility of the section and rotary property of the plastic hinge. So total coefficient of the modulation of moment becomes less with the ξ becoming bigger. (2) If secondary moment is taken for one kind of modulation of moment and there are the same ξ, the effect of secondary moment on the modulation of moment becomes bigger with secondary moment becoming bigger. If prestressed frame can not complete full redistribution of internal force, ultimate load may put off and put up because of secondary moment. Total coefficient of modulation of moment also is bigger. (3) Total coefficient of modulation of moment for the frame applied horizontal load and vertical load is bigger than that of the same frame applied vertical load. So, for the design of prestressed frame, the later coefficient may be considered as the parameter of modulation of moment and the moment modulated is the moment caused by the vertical load plus the one by the horizontal load.