Mechanical Behavior And Analysis Of Steel-concrete Composite Widened T-Girder Bridges

Currently,an increasing number of highway bridges are being refined and widened.Materials and structures used to widen and refine bridges are also complex and diverse.Under some specific conditions,there are several advantages of using the steel-concrete composite to widen old bridges.In the published widened bridges research,the overall mechanical behavior andanalysis of widened bridges are lacking.Whether the widened bridges can and work normally and improve structural resistance and what the best connection is between old and new girders to improve mechanic behaviors for the widened steel-concrete composite bridges have not been answered yet.The exact definition of the suitable girder calculation method for steel-concrete composite widened bridges is limited and there is not reference for determining the number of girders used.In addition,shrinkage and creep are also unavoidable problems for the widen bridges and the effects of them on the mechanical behaviors are necessary to be evaluated.In this paper,a single composite girder was used to widen the old bridge.Based on the load test,the possibility of widened composite bridges to achieve required resistance was determined.The mechanical behaviors of structures with different connection methods are also determined by the finite element analysis(FEM).By the comparison of theoretical results and FEM results,the suitable girder calculation method was proposed.Additionally,the algebraic method was utilized to evaluate shrinkage and creep in bridges and their effects on mechanical behaviors of superstructures.The main research contents are presented as follows:(1)The load test of the steel-concrete composite girder with the loading efficiency as the verification standard was conducted,indicating that the overall widened structure is worked well after the load test and it follows the general rules of structural behaviors and has a large strength reserve.Base on the comparison of the moment and deflection for pinned and rigid connections in widened bridges,the lateral load distribution for the rigid connection is more even.The exterior girders of old bridges are now becoming the interior girders in new bridges,therefore,more moment and shear are existing in the girders indicating that the design and calculation need to be reevaluated.(2)The theoretical calculations of the rigid beam method,modified rigid beam method and the rigid-connected beam method were conducted and compared with FEM to solve the mentioned problems.The modified rigid method was determined to be suitable for widened bridges transverse girder calculation.Under the premise of the end beam existing in composite and old structures,the lateral girder distribution factors(GDFs)are not affected by the number of beams,however,the existence of the end beam has a significant influence on GDFs.(3)Combining the mechanism of shrinkage and creep and the calculation method,the algebraic method was utilized in steel-concrete composite widened bridges to propose the moment and force equations that offsetting shrinkage and creep.Based on the FEM analysis,total four load cases with different connections and stitching time,were conducted to calculate effects of shrinkage and creep on new and old bridges superstructures.