Analysis For Residual Bearing Capacity Assessment Method Of In-Service Prestressed Concrete Girder Bridges

Prestressed concrete structure has been widely used in the world of bridge structures, because of its making full use of high-strength material strength and improving the structure mechanical properties in the use phase. Since the reform and opening up, China’s bridge construction is enter a high-speed development period. Especially the prestressed concrete structures have already dominated in medium and small span bridges. Composition of materials in prestressed bridge will gradually occur under the influence of aging in the climate, environment and other natural factors. The increasing role of heavy vehicles makes the mechanical properties of the bridge components continue to decay. In addition to the difference between early bridge design specifications and new loads, all of these cause the carrying capacity of built prestressed concrete bridge fell and reducing the durability issues. Such problems will affect the normal use of the structure, or even a serious threat to bridge safety. Therefore, in-service inspection of prestressed concrete bridge technology to conduct research for a true understanding of prestressed bridge in the normal operating stage performance, which provide a theoretical basis and practical reference for the safe operation, maintenance and conservation of prestressed bridge structures.This paper based on the related topics of western transportation construction projects, whose name is technology of fast capacity evaluation for western existing small span bridges (200731881232), aimed at small and medium span prestressed girder bridges in service, according to the small load deflection of a single point or multi-point test results, calculating the actual bending stiffness in whole or in segments of the longitudinal of multi-girder bridges. Building a cross stiffness network to reflect the actual distribution of vertical and horizontal stiffness to intuitive full-bridge damaged area and determine the degree of injury profiles. Ultimately based on the actual structure residual stiffness of the bridges to complete the whole calculation of load capacity, promote the carrying capacity of prestressed bridges value detection process.In this paper the main research work completed as below:1. After comparative study of the common short-term deflection methods of bridges such as linear bilinear method, effective moment method, curvature integral method, PPC advise method and highway bridge design standard method, it presents the standard formula in china to analysis the flexural stiffness of bridge structure. Also after analysis of the common calculation of effective prestress based on sensitivity analysis, modeling analysis, static analysis, dynamic analysis and the relative detection such as direct method, SSRHT method, shape memory alloy technology, acoustic emission technology and the statics principle testing technology, recommended prestressed cable tension tester detection in effective prestressed of service bridges.2. Present the opinion that bending stiffness of prestressed beam bridge affected by the tensile force, according to the indoor real beam model and ANSYS simulation analysis to establish the numerical relationships between effective prestress and bending stiffness. Put forward general correction formula for the bending stiffness based on the standard formula in china of short-term deflection and take which as a basis for the calculation of actual bending stiffness. Put forward the bending stiffness fitting equation with its specific section type, section size, span calculations, and the location of the external load, according which proposed the real bridge stiffness calculation method based on small and medium span prestressed girder bridge standard drawings.3. Based on the traditional static load test performance parameters, use commonly transverse distribution coefficient method as analytical tools, proposed two methods, which are the stiffness decomposition based on the absolute deflection without considering the influence from calibration coefficients and the stiffness decomposition based on the deflection ratio with considering the influence from calibration coefficients. By verifying we know that both of two methods consistent with the distribution of lateral rigidity of existing bridges, suggested to use the stiffness decomposition based on the absolute deflection for the longitudinal stiffness calculation.4. According to the finite element theory, deduce the longitudinal stiffness of sub-solving equations with any bridges and can select subsection quantity according to the importance of the bridge and the actual defect. Put forward the longitudinal stiffness of sub-solving equations of simple-supported bridges, simplify stiffness formula and its coefficient table, with which to solve the prestressed girder bridge stiffness vertical distribution and reflect the actual structure of the longitudinal extent of damage and the damage distribution.5. According to the specification of the carrying capacity method of prestressed concrete bridge, increase the uncracked tensile zone of concrete contribution to the stiffness of the cross section. Introducing a concept with area on behalf of prestressed to reflect current average of the working performance of the structure, and combined with structural stiffness and the measured effective prestress to calculate the residual carrying capacity. Increased the concept of away pressure degrees and bearing degrees to reflect the effective and carrying capacity reserve level of the actual structure.6. Based on C++builder6.0and easy language environment to compiled capacity assessment software of in-service medium and small span prestressed girder according to analysis a13m PC hollow slab to get its actual horizontal and vertical cross stiffness and residual load capacity3D drawing. The results quantitative description the bridge operating performance in the current phase and verify the validity of the method.