| The prestressed concrete continuous beam and concrete-filled steel tube arch composite bridge has been widely used in the field of high-speed railway bridge due to its advantages of large structural stiffness,high bearing capacity and beautiful shape.The joint of beam and arch is the key area of continuous beam and concrete-filled steel tube arch composite bridge,and its basic mechanical properties are directly related to the safety of the bridge.According to the investigation of the service status of continuous beam-concrete filled steel tube arch composite bridge,the concrete cracking phenomenon at the arch foot of the bridge built in the past is common,which is extremely detrimental to the structural safety and durability.Aiming at the above problems,this paper takes a long-span prestressed concrete continuous girderconcrete-filled steel tube arch composite bridge-Liuxi River Bridge(span combination of90m+180m+90m,span ratio of 1:5),which is under construction on the freight car outer loop line in the northeast of Guangzhou Railway Hub,as the project support.The causes,control measures and reasonable construction form of arch foot cracking of continuous beamconcrete-filled steel tube arch composite bridge are studied.The specific work completed is as follows:(1)The Ansys nonlinear solid finite element analysis model of the arch foot is established based on the most adverse internal forces of the arch foot obtained from the whole bridge rod system model of the Liuxi River Bridge.The influence of hydration heat of the core concrete on the temperature field of the arch foot and the stress of the outer concrete is studied,and the correctness of the calculation results of the model is verified by the test data of the real bridge.At the same time,the main factors affecting arch foot cracking were studied.The results show that the hydration heat of the core concrete is the main reason for the cracking of the concrete outside the arch foot,and the decrease of the concrete entering temperature and the addition of steel tube rib and prestress are beneficial to reduce the crack of the arch foot.(2)Based on the existing concrete-filled steel tube arch foot structure and the key influencing factors of cracking,a new concrete-filled steel tube and slab-ribbed composite arch foot structure composed of steel tube,shear connectors and ribs was proposed,and its basic mechanical properties and crack resistance characteristics were studied experimentally.The results show that the composite arch foot of concrete-filled steel tube and slab-ribbed has high bearing capacity and good crack resistance.In the process of loading,vertical cracks appear along the length of the steel tube in the arch foot.With the increase of the load,the cracks continue to develop downward.Increasing the number and thickness of the slab ribs and the thickness of the steel tube has a significant effect on reducing the tensile strain of the arch foot of the concrete filled steel tube,and can effectively reduce the crack risk of the arch foot of the concrete filled steel tube.(3)The Ansys nonlinear finite element calculation model of concrete-filled steel tube and slab-ribbed composite arch foot is established,and the correctness of the model is verified by the test results.Based on the verified finite element model,the effects of concrete strength,steel strength and outer concrete thickness on the cracking and axial compression performance of arch foot are further studied.The results show that the concrete strength and steel strength have little effect on the tensile stress of the arch foot of concrete-filled steel tube and slabribbed composite,and the tensile stress of the arch foot can be effectively reduced and the crack resistance of the arch foot can be improved by increasing the thickness of the concrete. |
