Study On The Temperature Effect Of Super Long-Span Rail Cable-Stayed Bridge With Unequal Tower And Composite Girder

With the rapid development of China’s urban transportation network,the number of bridges has increased significantly.Due to the limitations of space navigation requirements,exhibition line restrictions,foundation conditions and terrain,it is inconvenient and economical to use cable-stayed bridges of equal height of traditional bridge towers,and the appropriate span combination of cable-stayed bridges of high and low towers can adapt to the terrain.The cable-stayed bridge with steel-concrete composite beam as main beam has the advantages of small structural dead load,large rigidity,beautiful and novel shape,etc.,and its application is more and more widely.The bridge structure in the natural environment will be affected by the effect of temperature,and its effect accounts for a large part of the live load,which has a greater impact on the limit state of the bearing capacity of the bridge.Most scholars at home and abroad have concentrated on studying the temperature effect of double-tower cable-stayed bridges with equal height,while the temperature effect of this kind of asymmetric high-tower and low-tower cable-stayed bridges is less studied.Based on the world’s largest span-track cable-stayed bridge,Chongqing Nanjimen track cable-stayed bridge with unequal tower and composite beam,this paper analyzes the sunshine temperature field of the separated steel box composite girder and the high-low tower cable-stayed bridge under the bridge state Temperature effect,and further discussed the effect of auxiliary pier on the temperature effect of high and low tower cable-stayed bridge.The main research contents and conclusions are as follows:(1)The characteristics of composite beams,cable-stayed bridges with high and low towers and the current research status of temperature effects at home and abroad are described,and the characteristics of temperature loads,the heat transfer between the bridge structure and the outside world,the heat conduction theory,the finite element method of temperature field The theoretical calculation method of temperature effect provides the theoretical basis for the subsequent research.(2)Based on the COMSOL heat transfer module,a three-dimensional finite element model of the cross section of the split steel box composite beam was established,and the temperature field of the split steel box composite beam for five consecutive days was analyzed and calculated.analysis.The results show that at 14:00,the vertical temperature difference in the concrete slab reaches a maximum of 19.9℃;due to the thermal insulation effect of the steel box,there is an obvious lateral temperature difference between the concrete slab between the steel box and the concrete slab above the steel box can reach a maximum of 9℃.(3)The finite element model of high and low tower composite beam cable-stayed bridge was established through Midas/Civil,and the temperature effects,temperature gradients and temperature difference of cable and tower beam after the completion of the bridge were analyzed respectively.The influence of the vertical displacement of the main girder of the cable-stayed bridge,the stress of the main girder and the cable force.The results show that: under the action of temperature,there is a clear difference in the structural response of the two sides of the high and low tower,and the extreme value of the stress of the main beam of the low tower is generally greater than that of the high tower.(4)It is revealed that the number of auxiliary piers is set for the high-low tower cable-stayed bridge.The vertical displacement of the main beam,the stress of the lower edge of the steel main beam and the concrete slab under the effect of the system temperature rise,the positive temperature difference of the temperature gradient,the positive temperature difference between the cable and the tower beam The variation law of the edge stress,and further analyzed the effect of different positions of an auxiliary pier on the side of the high tower on the temperature effect of the high and low tower cable-stayed bridge.The results show that the auxiliary pier can significantly reduce the vertical displacement of the main beam under the temperature of one side span of the auxiliary pier,but at the same time it will lead to the increase of the mid-span displacement;the number of auxiliary pier settings affects the lower edge of the steel beam and the concrete under the temperature The influence of the upper edge stress on the plate is mainly on the side span of the side where the auxiliary pier is provided;the position of the auxiliary pier is mainly changed to change the position where the structure response extreme occurs.The results of this research can provide a basis for the design of high and low tower cable-stayed bridges,and provide a positive reference for future theoretical research on this type of bridge.