Study On Stress And Deformation Of Surrounding Rock Of Large Section Shallow Buried Large Bias Tunnel With Variable Slope Surface

Steel box basket tied arch bridge has the characteristics of strong bearing capacity,light weight,large span,good seismic resistance and beautiful shape.In recent years,it has been more and more used in long-span bridges and is deeply loved by designers.With the rapid development of long-span tied arch bridge,the determination and optimization of cable force of sling has become the focus of attention in the engineering field.How to determine the most reasonable sling force is particularly important.This paper is based on a through steel box tied basket arch bridge across Fujiang bridge.The bridge adopts a new radial sling and uses Midas civil modeling and analysis method to study the determination and optimization of the cable force of the sling for the first time.The main work and research results are as follows:（1）Relying on a long-span steel box basket tied arch bridge,Midas civil is used to establish the whole bridge model.The rigid support continuous beam method,zero displacement method,internal force balance method and minimum bending energy method are mainly used to calculate the internal force of the completed bridge sling.Under the action of the sling force obtained by the rigid supported continuous beam method,the displacement of the arch rib reaches 46 cm,and the bending moment of the arch foot is too large.Therefore,the rigid supported continuous beam method can not meet the stress target state of this bridge,which is different from that of other arch bridges.The difference between the zero displacement method and the internal force balance method is too large,which is easy to lead to uneven stress and fracture of the sling.The sling force obtained by the minimum bending energy method is relatively uniform,and the bending moment and displacement of the whole bridge also meet the requirements.The sling internal force obtained by this method is selected as the initial cable force of the completed bridge.（2）The unknown load factor method and equal frequency method are used to optimize the initial cable force,which mainly considers the requirements of small force on the short sling and large force on the long sling of the bridge.After comparing the cable force,bending moment and displacement obtained by the two methods,the internal force of the sling obtained by the unknown load factor method with uniform cable force distribution and small bending moment and displacement is finally selected as the design cable force.（3）In the calculation of the sling tensioning sequence in the construction process,this paper simulates three different tensioning sequences.After comparing the arch rib bending moment,tie beam bending moment,arch rib displacement and tie beam displacement under the three schemes,the second scheme with the least impact on the arch rib and tie beam is finally selected,which is tensioned symmetrically from the middle of the span to the arch foot.After determining the tensioning sequence,the positive installation iterative method and reverse disassembly method are used to calculate the initial tensioning force of the sling.The calculation process shows that the positive installation iterative method has higher accuracy,better stress of the whole bridge,and smaller initial tensioning force of the sling,which is convenient for on-site operation.In this paper,through theoretical calculation and finite element simulation calculation,the internal force of the sling of a long-span steel box tied basket arch bridge is determined and optimized,and the cable tension in the construction process is studied.The research results of the radial sling provide a certain reference value for the same type of basket arch bridge in the future.