| Steel-concrete composite beams have been widely used because of their apparent advantages in force,construction,and economy.They have been continuously developed and innovated.In cable-stayed Bridges,steel-concrete composite beams have lighter dead weight and larger span capacity than concrete beams.Compared with a steel girder,a composite girder has the advantages of significant deck stiffness,easy maintenance,and less noise.Composite beam has excellent advantages in railway,especially in high-speed railway cable-stayed bridges;its mechanical properties and cracking resistance is worth further study.Based on the longitudinal rib of Guangzhou-Shanwei High-speed Railway cross Shenzhen-Shantou West Expressway Bridge with steel-concrete composite girder as the background,finite element simulation analysis and experimental study were carried out on the most unfavorable stress section,and the corresponding calculation theory was derived.The main research contents and results are as follows:(1)ANSYS was used to establish the finite element model of the most unfavorable stress section of the original bridge girder and analyze the stress distribution law of each plate of the concrete and steel girder.The calculation results show that the stress of the concrete and steel structure of the girder of the bridge is in a reasonable range under the condition of maximum joyous bending moment.Under the condition of maximum negative bending moment,the concrete bridge deck is cracked under the condition of maximum negative bending moment,and the steel structure stress is within a reasonable range.(2)To verify the mechanical characteristics of the steel-concrete composite girder beam with longitudinal ribs and the cracking law of the concrete deck under a negative bending moment of the original bridge,four types of test models were designed based on the finite element calculation results of the original bridge.Through the scheme comparison and selection,the model test scheme of steel-concrete composite beam with longitudinal rib on double I-beam is determined,equivalence analysis is carried out,and the corresponding loading scheme and load conditions are determined.(3)According to the designed test model of steel-concrete composite beam with longitudinal rib,the static load model test is carried out.The stress,deformation,and slip data of the test model under the condition of maximum positive and negative bending moments and 2.0 times of positive and negative bending moments were tested and analyzed,respectively.The results show that under the condition of maximum joyous bending moment and overload of 2.0 times,the test model is in the elastic working state.Under the condition of overload of2.0 times,the maximum stress of concrete is-33.87 MPa,and the maximum stress of steel structure is 91.98 MPa.Under the condition of maximum negative bending moment,the maximum stress of steel structure is 345.45 MPa under the condition of 2.0 times overload.(4)In the loading process of negative bending moment,the test model concrete bridge deck cracks at 0.6 times load(loading force 734.53 k N),and the maximum crack width of concrete at 1.0 times and 2.0 times maximum negative bending moment load is 0.12 mm and0.31 mm,respectively.It meets the 0.2mm limit of the "Code for Design of Railway Bridges and Culverts" and "Code for Durability Design of Railway Concrete Structures."(5)The cracking moment formula and the elastic ultimate bearing moment formula of steel-concrete composite beams with longitudinal ribs under negative bending moment are derived.The cracking moment of the test model calculated by the above formula is 0.37 times the maximum negative bending moment load,and the elastic ultimate bearing moment is 2.13 times the maximum negative bending moment load.The concrete crack formula of longitudinal ribbed steel-concrete composite beams considering the thickness of the steel roof and the force ratio of the compound section is presented. |
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