Study On Mechanical Performance Of Long Span Steel-Concrete Composite Continuous Girder Bridges

The steel-concrete composite girder bridge structure gives full play to the good tensile properties of steel and the good compressive properties of concrete,which increases the spanning capacity of the composite bridge.At the same time,it has the advantages of large span-to-depth ratio,less deflection,and high stiffness,and has been widely used in bridge engineering structure.However,this type of bridge also has some problems,especially in the negative moment zone of a continuous steel-concrete composite bridge,the concrete slab will generate tensile stress,which leads to the bridge deck cracking,resulting in the failure of waterproof layer and make the bridge deck pavement vulnerable to damage.The concrete deck is usually under tension,and the bottom flange of the beam is under compression.which generally has short comings in view of durability,loading capacity and service life of the structure.Therefore,based on Harbin Changjiang Road interchange bridge,this article studies the mechanical performance of continuous composite girder bridges,analyze the optimized construction technology and construction influencing factors of the continuous composite girder bridge,and study the engineering measures to improve the force in the negative bending moment zone at the middle support to reduce the risk of cracking of the concrete deck in the negative bending moment zone.Firstly,the mechanical characteristics and related calculation theories of steelconcrete composite girder bridge are summarized and analyzed,and the influence of shear lag and interface shear slip on the bearing capacity is analyzed.Secondly,finite element modeling of steel-concrete composite girder bridge is carried out by using MIDAS Civil software.In the modeling process,considering the influence of construction process,the influence of factors such as support jacking,temperature,concrete creep and shrinkage on the mechanical properties of steel-concrete composite girder bridge is analyzed.The adjustment effect of different jacking heights on the negative bending moment of composite beams is analyzed,and the relationship between the change of bridge internal forces and the jacking displacement of middle support is obtained,which provides a theoretical basis for jacking construction.At the same time,this thesis also analyzes the effect of creep and shrinkage on the long-term performance of composite beams,and also the influence of concrete creep and shrinkage on the jacking effect of middle support is discussed.The results show that reasonable support jacking height can significantly improve the mechanical properties of long-span continuous steel-concrete composite girder Bridges by controlling the concrete cracks in the negative bending moment zone.The concrete bridge decks can retain a certain amount of compressive stress,while the compressive stress at the bottom flange of the steel girder can be reduced.At the end,the influence of temperature variation in high-cold region,on the steelconcrete composite continuous beam structure is analyzed.Based on the long-term data collected by the installed health monitoring system,the overall temperature variation law of the bridge and the monitoring results of temperature gradient along the beam depth are given,and compared with the temperature model given in the design specification to provides a reference for bridge temperature load model in cold region.