Analysis Of Influence Of Stress Change Of Pavement Structure Due To Structural Change In Bridge-Subgrade Transition Section

In the last two decades,with rapid development of infrastructure construction in China,a large number of roads have been constructed.The bridge-subgrade transition section is the position where bridge and subgrade are connected.The structure includes a sudden change of the flexible foundation and the rigid foundation.The disease could be more severe than the ordinary road sections,which could lead to hidden dangers in traffic safety.Therefore,this paper analyzes the influence stress change of pavement structure due to structural change in bridge-subgrade transition section,which has reference significance for the future design and construction.Firstly,two typical transition sections are considered,which are the transition section between the concrete bridge and subgrade and the one between the steel bridge and the concrete bridge.A literature survey is carried out to find the commonly used structure of each type of transition section.The most commonly used structure of the first transition section is inverted trapezoidal form while the most commonly used structure of the second one is double box one chamber form in terms of steel bridge.These two typical structures are the basis for finite element model.In addition,the common types of diseases in the two typical transition sections are summarized,which are not caused by differential settlement.These are the basis for analysis of relevant mechanical indicators.Then the three-dimensional finite element models of two typical transition sections are established in ABAQUS,the finite element software.After that,for the first transition section,the most unfavorable load position of the tensile stress of asphalt layers is at the junction of the abutment and the embankment,while that of the tensile stress of the slab is at 2m away from the abutment.Moreover,the most unfavorable load position of the compressed strain of the top surface of the subgrade and the compressed stress of asphalt layers are respectively at 8m and 1m away from the abutment.The extreme value of tensile stress of the slab,the compressed strain of the top surface of the subgrade and the compressed stress of AC-20 are more sensitive to the axle load of the vehicle.The extreme value of tensile stress of asphalt layer and the compressed strain of the top surface of the subgrade are more sensitive to the resilient modulus of the embankment of transition section.In addition,the extreme value of tensile stress of the asphalt layer and the slab are sensitive to changes in the elastic modulus of the slab.Different forms of structure have advantages and disadvantages.The measures are proposed to optimize the structure based on these conclusions,including the deployment of reinforcement in the bottom of the concrete slab,making sure that the compactness of the embankment of transition section be above 95% and multi-layer reinforcement of embankment of transition section.In addition,using inverted trapezoidal or trapezoidal structure,and using SBS modified asphalt and fine-grained mixture could be good choices.Moreover,the elastic modulus of the embankment of transition section should be controlled between 120 MPa and 160 MPa,while the grade of the cement for concrete slab should be selected between C20 and C35.The overweight vehicles should also be forbidden to pass through the transition section structure.Finally,for the transition section of the steel bridge,the most unfavorable load position of the maximum principal stress of asphalt layers are respectively at 8m and 10 m away from the bridge’s end.The most unfavorable load position of the shear stress of the asphalt layers along horizontal and vertical of the road are respectively at 8m away from the bridge’s end and at the bridge’s end.Each index is sensitive to the axle load of the vehicle,but not sensitive to the vehicle speed.The extreme value of the maximum principal stress and the shear stress along vertical of the road of the epoxy asphalt layer are more sensitive to the elastic modulus of the epoxy asphalt concrete.In addition,the maximum principal stress of asphalt layers are more sensitive to the distance between the diaphragms,with a minimum value.Structural changes will lead to an increase,up to 40%,in the response of bridge decks within 3.5m from the end of the steel bridge.The measures are proposed to optimize the structure based on these conclusions.The adhesive layer should be added between the steel bridge structural layers,while the distance between the diaphragms should be 3.5m~4.5m.On the other hand,within 3.5m from the end of the steel bridge,steel fiber should be added to asphalt mixture,and a certain amount of gravel should be scattered on the adhesive layer.Constructional reinforcement or steel wire mesh could be welded on the steel deck.Using SBS modified asphalt and fine-grained mixture is a good choice,while angular and wear-resistant gravel should be selected as aggregate.The elastic modulus of epoxy asphalt concrete should be less than 3000 MPa.In addition,the overweight vehicles should also be forbidden to pass through the transition section structure.