Study On Stress Performance And Crack Resistance Method Of Negative Moment Region Of Steel-concrete Composite Bridge

The steel-concrete composite beam has the advantages of light weight,high bearing capacity,high stiffness and good seismic performance,and has broad application space in the newly built medium-span bridges and reinforcement projects of old bridges.However,in the application process of composite continuous bridge,the negative bending moment area has the disadvantage of steel beam compression and concrete tension,and the cracking problem of bridge deck should be paid attention to.In view of this,through theoretical derivation and numerical simulation,this thesis studies the mechanical properties of the negative bending moment zone of the composite bridge,the cracking control method of the concrete bridge deck in the negative bending moment zone and the calculation method of the crack width.The main research results are as follows:1.Based on the bending analysis theory of composite bridges,the design methods and related calculation contents of the negative bending moment zone in the codes of China,Britain,Europe and the United States are compared and analyzed.Based on the engineering example of a(40+50+40)m three-span steel-concrete composite continuous beam bridge,the mechanical properties of the negative bending moment zone of the composite bridge are analyzed by numerical simulation.The results show that the calculation results of the crack width in the codes of different countries are quite different,and if the appropriate cracking control measures are not taken during the bridge work,the crack width of the composite bridge is difficult to meet the code requirements.2.The anti-cracking optimization analysis is carried out on the unfavorable stress form of the negative bending moment zone of the composite bridge,and an improved pre-combined composite bridge cracking control method is proposed.In order to analyze the crack resistance effect of the pre-combined method,the stress state of the section in the negative moment area of the conventional prestressed composite bridge and the pre-combined composite bridge was studied,and the calculation formula of the stress at the fulcrum section of the pre-combined composite bridge was deduced.Based on the engineering example,the finite element model is established,and the results of comparison between the improved pre-combined method and other anti-cracking measures in the aspects of bridge deck compressive stress reserve,full bridge deflection,cracking moment and crack width are analyzed.The results show that the finite element calculation results of the pre-combined method are in good agreement with the theoretical calculation values,which can effectively improve the application effect of prestress,and the compressive stress reserve for bridge deck is more than 1.3 times that of other methods.3.The difference between the pre-combined composite beam and the normal composite beam in the arrangement of studs is studied.The influence of different stud layouts on the mechanical properties of composite beams is analyzed.Considering the plastic damage of concrete materials and the connection difference of interface,two steel-concrete composite beam models were designed and established.S1 is a normal composite beam with uniform studs,and S2 is a cluster stud composite beam with pre-combined method.The mechanical properties of the two groups of models were compared from the aspects of load-slip curve,loaddisplacement curve,crack development and bending capacity.The results show that there is no significant difference between the two in bearing capacity and failure mode;there are differences in local slip,but the difference between 4 % and 9 %;the initial cracking positions are different,the cracking position of composite beam S1 concrete is at the maximum negative bending moment,and the cracking position of S2 is above the cluster stud.4.The calculation formula of crack width in negative bending moment zone of steelconcrete composite continuous bridge is studied.Based on the bond-slip theory,considering the stiffness reduction of cracking section in negative moment section,the interface slip effect between steel beam and concrete bridge deck and the bond relationship between different types of reinforcement and concrete,the calculation formula of crack width of composite bridge are modified.