Research On Detecting The Effective Prestress Of Bridges By Using Blind-hole Method

The effective prestress of prestressed steel is one of the important parameters to assess the performance of prestressed concrete bridge. Due to various factors cause the loss of prestress is uncertain that could cause actual value of effective prestress is differ to design value, therefore effective method to accurately detect the effective Prestress of bridge is need urgently. Most methods in this field of research is drilling concrete on the bottom of beam to test the effective prestress of prestressed concrete bridge. In this paper, new ideas, to take strand as the research object, using blind-hole method to detect the effective prestress of bridge, mainly for the following studies:First of all, in this paper, defined the basic theory of the blind-hole method for flat sheet, through reviewing the relevant literature. Analyzing the impact of drilling on the bottom of prestressed concrete girder for effective stress of strand, obtained change of strand stress cause by drilling concrete very little under the action of weight and prestress.Secondly, using finite element software to establish wire and strand model, obtained stress release value on the edge of hole and stress concentration factor along the longitudinal direction of the model. The results show that stress release value on the edge of hole and stress concentration factor of strand used commonly in road increase with the radius of hole together within a certain range, it first increase with drilling depth but slightly reduce or constant when drilling depth more than 2.67 times of the radius of hole. When the section is different, stress release value on the edge of hole and stress concentration factor is different. When changed tensile load and elastic modulus of strand, calculate and analyze stress release value on the edge of hole and stress concentration factor, it concluded: only stress release value on the edge of hole has positive relationship with tensile load.Finally, test strand by blind-hole method, detect stress release value on the edge of hole under different factors. The relationship between stress release value on the edge of hole and the parameters of drilling depth and radius which the theoretical analysis to identify is consistent with the experimental result. When drilling position closer to the resistance wire of strain gauges, the test operation measure the greater value of stress release and better measuring result. Compared and analyzed the theoretical stress release value, verify the feasibility of blind-hole method to measure existing stress of strand. By derivation and amendment, obtained the calculating method for effective prestress of strand in beam under certain conditions, provided a feasible method for the detection of effective prestress of prestressed concrete beam.