Study On Behavior Mechanism Of Prestress In Post-tensioned Prestressed Concrete Strctrue

With the great development of prestressed concrete structure in our country, there are still some defects in the method for analysis of behavior mechanism of prestress. Today, equivalent load method is widely used in analyzing and calculating the prestress in prestressed concrete structure. In equivalent load method a series of equivalent load which has the same function with the prestress is substituted for prestress. However, because of the complexity of the force system, treating the effect of prestress as a group of constant external load is questionable. Some difficult problems in the field on the effects of prestress which is the key factor were studied in the paper. The study is divided into two facets: the effect of prestressed reinforcement on the concrete structure in basic beam and the whole effect of prestress in frame structure. The main work has been done as follow in the paper is:1. Based on the mechanism of prestressing equivalent loads, separate sheaf-beam model and the equivalent load of various form of prestressed reinforcement is analysised. And what's more, secondary moment in hyperstatic structure is deduced.2. On the base of the separate sheaf-beam model, analysis method of second-order elasticity is used in analysis of unbonded prestressed concrete. The classical second-order differential calculating method is introduced. Method for nonlinear compressed bar and second-order elastic iterative theory is presented and some formulas are deduced. In addition, with the Visual Basic Software, a program for second-order elastic iterative calculation is compiled. In the end, the calculative results of some sample beam by these methods are compared.3. Considering the axial deformation, a series of problems including the transfer of prestress in frame structure, the effect on the compressive force by the lateral restraints, the effect on the compressive force by the restraints ofsecondary beam and secondary internal force in frame structure. The theoretic formulas about the loss in prestress and secondary moment produced by lateral restraints are deduced. To analyze the effect on the compressive force by the restraints of secondary beam, Plane and space finite element analysis of a sample prestressed frame structure is presented by ANSYS software. 4. The theory and method of nonlinear finite element simulation of prestressed concrete structure is introduced. The process of construction of a prestressed frame structure is simulated. Method and Proposals are presented for practical applications.The research work in the paper includes theoretic analysis and practical calculation. The two second-order elasticity simplified computational methods about unbonded prestressed concrete and the theoretic analysis of the effect on the compressive force by the lateral restraints is a new study. It is significant in improving design theory and instructing engineering practice.