Detection Methods And Experimental Research On Effective Prestress Of PC Bridges With Medium And Small Spans

Nowadays, prestressed concrete (PC) constructions predominate in small and medium span bridges field. Because prestress could improve anti-cracking ability and working performance of constructions, in addition, prestress is one of the most important index which assess reliability of PC construction in service. Nevertheless, there is no mature method to detect effective prestress of PC constructions in service. In usual way, prestress loss was estimated by specifications, each prestress loss factors is independent and nonlinear leading to complication of prestress loss calculation. Or test equipments were embedded in constructions within construction period which has high accuracy but lack of availability and increase project cost on account of installation time restraint. Therefore, research on quick and lossless methods to detect PC constructions in service has engineering significance.First of all, theoretical model about prestress and dynamic stiffness relationship were introduced including fundamental vibration theoretical model, traditional analysis model, Kirchhoff dynamic model, Kim Jeong-Tae theory and Ruige Li theory, compared models above with experimental study on prestress and frequency relationship before, a reasonable theoretical model was selected as the research basis. Meanwhile, effective stiffness modifier formulas about the actual dynamic stiffness and actual static stiffness are summarized which provided some inspiration for subsequent experimental data analysis. In addition, the working principle of magnetic flux sensor was introduced which provided theoretical basis for further research.In accordance with the principle of equivalent stress, the prestressed concrete T beam model adopt a standard T beam scaled-down design, the model design was introduced in detail. Then, the paper introduced the test methods, the arrangement of measuring point, data acquisition and cautions. In order to ensure accuracy of the test data, some force hammer excitation methods were studied and contrasted, effect factors of the frequency test were discussed, a optimal solution was proposed eventually. The finite element model for modal analysis was built, modeling cautions were introduced and the theoretical value of experimental frequency was provided.Experiment used the static stiffness (deflection), dynamic stiffness (frequency) and the magnetic flux test methods, the experimental study on three pieces of prestressed concrete T beams were carried out, the relationship between the static stiffness and prestress and the relationship between the dynamic stiffness and prestress were introduced, and prestress assessment menthods by static stiffness and dynamic stiffness were tried to put forward in PC bridges in service. In addition, the precision and applicability of magnetic flux sensor were determined, a certain reference was provided in the detection and evaluation of the effective prestress.