Study Of Dynamic Properties Of Unbonded Full Prestressed Concrete Simply-supported Beams

The actual prestressing force in the prestressed concrete structures is one of the most important aspects of the structure health. It's very important to estimate the actual prestressing force in the structure health monitoring and detection. Some specialists attempted to find out some test methods about how to know the prestressing force, as is pointed out in the related literature, nearly none of simple and effective methods have been developed. This article based on the dynamic properties of structures, according to the change of the mode parameters, established the relationship of prestressing force and frequencies, then discussed the nondestructive test methods which used dynamic properties to test the prestressing force.Test of three unbonded prestressed concrete beams were carried out. Prestressing forces were applied to the beams in steps, and the first three frequencies were obtained. The results indicate that in full-prestressed beams, the first two frequencies go up with the prestressing force. According to the change of deflections with different prestressing forces, testifies that the bending stiffness increases with the prestressing force.Based on the test results of 6 beams, this article analyzed the relationship between the prestressing force and frequencies, and then deduced the relationship of prestressing force and the bending stiffness. According to the nonlinear constitutive relationship of concrete, the article discussed the reason to change the stiffness,established a new model of the prestressed beam. An equation of concrete Young's modulus is obtained by the software 1stOpt. Then this article calculated the frequencies of prestressed beams. The results showed that the equation suggested by this article had good precision. According to the comparison, discussed the reason of which to change the stiffness.In this article, finite element dynamic model of unbonded prestressed concrete beams was established by general finite element software ANSYS. According to the problem of dealing with the tendons and the prestressing force in the general analytic model, the stiffness of the beam model was amended. The results shows that, this model can simulate the frequencies of beams well.