Research On The Tendon's Stress Of Unbonded Full Prestressed Simply Supported Beam

With the development of transportation project in our country, the carrying load of the bridge is more and more heavier day by day, so most of the prestressed concrete bridges are damaged in different levels. Meanwhile, other civil construction facilities used prestressed concrete has the same problems as the bridges. So, it's very urgent to detect the damage state of the structure and give a health evaluation. The failure of the prestressed concrete is caused by the tendons failure or concrete failure, or both of them. At present, the detecting techniques for concrete have been perfectly developed and used in existed structures, but for tendons, it is backward. In view of that, the dissertation does the experimental investigation and theoretical research on the effective prestress detecting of the prestressed concrete beams. In the present dissertation, the experiment of two unbonded prestressed simple concrete beams, three bonded beams and the relevant material property test are carried. The dynamic experiment mainly considers the influence to the natural frequency caused by effective prestress and load state. The result indicates that, as the effective prestress growing, the natural frequency of the beam increasing slowly, and in the same effective prestress state, as the load increasing, the natural frequency decreasing obviously. After the cracking of the beam, the natural frequency varies irregularly. Through the finite element modal analyzing by ANSYS software, the natural frequencies and mode shapes of the unbonded prestressed simple concrete beam in different prestress levels are gotten. Then, the analysis result has been compared with the experimental result to prove that the finite element analysis is reliable and the analysis result can be the supplement to the experimental data. Due to the shortage of the existed dynamic analysis methods of prestressed concrete beam, the dissertation deduces a natural frequency mathematical model for straight unbonded full prestressed simple concrete beam, proceeding from the basic theory of structural dynamics. Then, the relation between prestress and the natural frequency is also established by using perturbation to solving the model. Last, through the inverse solution of model, an equation for predicting the effective prestress by the frequency is founded. The result shows that it is feasible to predict the frequency by effective prestress, but to predict the effective prestress by frequency have to do much more work.