Study On Local Stress Mechanism Of Connection In Widening Box Girder Bridge And High Toughness Joint Concrete

To improve the traffic capacity of existing highway bridges,widening and rebuilding of bridges are often more advantageous than demolition and reconstruction.However,it is found that the stress state of the widening joint is complex and is easy to crack and the tensile and deformation properties of traditional concrete materials are poor.Therefore,it is of theoretical and practical significance to study local stress mechanism of the connection in widening bridge and to research the materials of widening joint for improving the performance of longitudinal joints.In order to study the local mechanical properties of joints and compare the performances of basic magnesium sulfate cement concrete and common cement concrete as joint materials,this paper mainly carries out the following works: 1.The plate-shell calculation models of widened box girder bridge are established by MIDAS to analyze the influence of wet joint width,roof thickness and web slope on the longitudinal effective working width of the connecting plate of widened box girder bridge,and the lateral calculation model of the connecting plate is established by referring to the calculation theory of continuous unidirectional plate or hinged cantilever plate in bridge deck.2.Two sets of widened box girder models are tested under various load conditions to study the mechanical properties of basic magnesium sulfate cement concrete and ordinary Portland cement concrete as joint materials.At the same time,the finite element models of the elastic stage of widened box girder segment are established by ANSYS,the calculation results are compared with the test results and the calculation models are revised,and then the influence of foundation settlement of the new bridge on the transverse force of the widening joint is analyzed by the finite element models.The main conclusions are as follows:(1)When rigid joints or articulated joints are used for widening bridges,the effective longitudinal working width of connection plate between box girders can be calculated safely according to the empirical formulas.And the longitudinal effective working width of the connecting plate is most affected by the thickness of the roof,the effective working width increases about 30% with the increase of the thickness of the plate by 0.1m.(2)The root shear force of cantilever after widening with articulated connection and the mid-span bending moment of the connecting plate after widening with rigid connection are both larger than those calculated by the empirical formulas,which can be multiplied by a correction factor of 1.4 on the basis of the calculation of continuous unidirectional plate and articulated cantilever plate.Other internal force of the connecting plate can be calculated safely according to the calculation theory of continuous unidirectional slab and articulated cantilever slab in bridge deck.(3)Under the same working conditions,the stress state of the widening joints made of basic magnesium sulfate cement concrete is basically the same with that made of common cement concrete,and the transverse stresses of the two widening joints are close to each other.When the concentrated load acts on the middle of the widening joint,the ultimate bearing capacity of basic magnesium sulfate cement concrete joint is about 1.45 times of that of common cement concrete joint.When the load acts symmetrically on the middle part of the inner flange plate of box girder,the ultimate bearing capacity of basic magnesium sulfate cement concrete joint is about 1.04 times of that of common cement concrete joint.(4)The settlement of the new bridge foundation will produce larger transverse internal force in the widening joint and the inner flange plate of the new and old bridges.The upper edge of the inner flange plate of old bridge and the widening joint near the old bridge are tensioned while the lower edge of which are compressed,and the upper edge of the inner flange plate of new bridge and the widening joint near the new bridge are compressed while the lower edge of which are tensioned.