Natural Frequency Analysis Of Prestressed Beam

In21th century, prestressing technique has been widely used in various fields of civil engineering. However, during the operation of the prestressed concrete structure, the prestressed concrete structure will inevitably suffer damages because of a variety of adverse factors. The residual prestress force of the in-service concrete structure has crucial effects on the performance of the structure in future, and therefore the detection of the prestress attracts increasing the attentions of people. Predicting the loss of prestress using dynamic characteristics of structure, a nondestructive detection method, is becoming the new trend of development. However, contradictory views on the relationship between the residual prestress force and the frequencies of the prestressed concrete structure occur. Some people think the frequency of the structure increases with the increase of the prestress. By contrast, some other people insist that the frequency of the structure reduces with the increase of prestress. Even, some others hold that the prestress force has little effect on the frequency of the structure. Based on these contradictory views, the thesis aims to investigate the relationship between the residual prestress force and the frequencies of the prestressed concrete structure and also find the factors which might has some effects on this relationship using theoretical, numerical and experimental methods. Specifically, the thesis contains the following three parts:First of all, the relationship between the residual prestress force and the frequencies of the prestressed concrete structure is achieved theoretically, find that some factors which affects this relationship.Secondly, numerical simulation of the previous dynamic test experiment is performed using the commercial finite element software. The numerical results are in good agreement with the experimental. Also, it is convinced that many experiments can be simulated using commercial finite element software.Finally, parametric analysis on the beam size, ratio of steel in structure and the position of the steel using finite element analysis method is carried out to investigate their effects on the relationship. It is found that the ratio of steel in structure is the main factor which affects this relationship, which improves the method of predicting the loss of the prestress in structure by dynamic characteristics.