Research On The Widening Mechanical Behavior And Test Of Existing Box Girder Bridge Under Traffic Load

This article describes the connection type and construction method of concrete stitch in bridge widening. The traffic restriction, segmental casting of concrete stitching, provision of fixture construction, provision of temporary bracing, layered casting, provision of I-beam assist measures under continuous traffic load is discussed by numerical simulation and experimental argumentation. Study the deformation of concrete stitch under traffic loads in different construction technology and judge their effectiveness. It concludes with recommendations on the design of bridge widening.The main contents are as follows:(1) The development of bidge widening engineering and technology, research results of its widening design and construction was discussed and analysed. The principles of bridge widening reconstruction was summarized, and problems need to be solved and methods were proposed.(2) This chapter introduces two commonly used concrete constitutive model in Abaqus calculation detailed, including concrete smeared cracking model and concrete damage plasticity model and its based theory. The theory mainly related to model stress cracking-strain calculations, uniaxial stress-strain calculations, fracture surface behavior, yield criterion, flow rule, hysteretic rules. Concrete damage plasticity model was used in bearing capacity calculation of segmental model test, and prepare for the subsequent derivation of constitutive relation of concretestitch failure criterion.(3) Midas Civil model of old bridge was established to determining the most disadvantageous position of the vehicle load, thus to arrange the longitudinal load distribution in Abaqus model of old bridge. Calculate the span deflection in widening side of the old bridge under four kinds of traffic organization schemes as the basis for selected traffic control program during construction times. Bridge widening construction under traffic load will cause the vertical deflection difference and contraflexural curvature on both sides of the concrete dect stitch, the contraflexural curvature will cause early concrete cracking if it exceed the.threshold curvature. The deflection difference on both sides of the concrete dect stitch as an important indicator in order to assess the effectiveness of different widening construction technology. Old and new brige models was established to research the measures to mitigate the concrete stitch deflection difference,which include segmental casting of concrete stitching, provision of fixture construction, provision of temporary bracing and their different combinations.(4) The boundary conditions and load peak force of test will determined by numerical simulation results. It ensures the concrete stitch deflection difference, shear forces and bending moments would transferred equivalent with concrete age between entire and section bridge model. Collected the vertical vibration acceleration and the dynamic deflection of the Yueqing Bay viaduct tipical bridge span under normal traffic load. Compare the measured and calculated deflection values in the side of old bridge widening stitch, then perform model amended and develop loading system by rain-flow counting method to statistics traffic frequency. Test model design, production, installation, measuring points and formulate loading scheme to prepare for the model tests.(5) Three full scale sections test to study the widening structure of prefabricated small box girder bridge under traffic load, which include NON, DOL and SR. The key issues of each specimens like shear transfer, apparent mass, carrying capacity, damage failure mode and residual deformation characteristics would studied by reciprocating cyclic loading and monotonic destruction loading. The research shows:the slope of curve in SR was significantly greater than the first two groups test, which indicate a slight vibration under the vehicle load will have an impac to concrete strength development; the ultimate bearing capacity in SR is greater than the NON, DOL group too, it indicates reduced stitch deflection difference by lateral connection would increase the ultimate strength of concrete. It must be taken measures to minimize its slight vibration, in design and construction.