Research On Cable Force Optimization And Cable Adjustment Of Cable-stayed Bridge With Single Tower And Curved Hybrid Girder

with the continuous development of high-strength materials and the continuous improvement of structural analysis methods,the hybrid-girder cable-stayed bridge has been used in the same structural type due to its light weight of the main span steel box girder structure,superior force performance,and fast construction speed.The cable-stayed bridge shows its superiority.Based on the actual engineering background of Shanghai Yunzaobang Bridge,this paper adopts a single-tower double-cable-plane mixed-beam cable-stayed bridge with a span layout of 132+65m=197m,a main span of 132m steel box girder,and a 65m side span of prestressed concrete.Box girder,with a 2m steel-concrete joint transition in the middle.The side span is located on a horizontal curve element with a radius of 251m,and the main span is located on a vertical curve with a radius of 1200m.According to the structural characteristics,the structural status of different cable force optimization methods and the application of cable force adjustment methods in construction tensioning are compared.The research content is as follows:(1)The bridge professional software MIDAS/Civil is used to establish the spatial finite element model of a single-tower curved hybrid cable-stayed bridge,and the minimum bending energy method and zero displacement method are used to optimize the cable force of the bridge.A comprehensive comparison of the bridge structure states(cable force,internal force,line type)after optimization of different cable forces was carried out.The comparative analysis showed that the force and structure of the single-tower curved hybrid-girder cable-stayed bridge tower girder after the minimum bending energy method was used to optimize the cable force The line type is reasonable,but the overall cable force distribution is uneven and further optimization is needed on this basis.(2)The minimum bending energy method is further optimized by adjusting the local stiffness of the structure.After the optimization,the cable force distribution of the bridge is more uniform.At the same time,the internal force and line type of the bridge structure under the action of the design cable force are compared.The results show that the internal force and line type of the optimized bridge structure are more reasonable.Among them,the maximum bending moment value of the side span,the steel-concrete joint section and the main span is more reasonable.Compared with the designed bridge state,it is reduced by 46.0%,86.2%,75.5%respectively;the displacement of the main girder and the displacement of the top of the main tower are reduced,thereby reducing the pre-camber of the bridge structure and reducing the difficulty of construction control.It proves the effectiveness of using the re-optimized minimum bending energy method to optimize the cable force.(3)The analysis of different initial tension cable forces shows that 65%of the bridge cable force is used as the initial tension cable force,which can make the reaction force of the temporary pier and the side span support relatively small and reduce the difficulty of detachment.At the same time,it can ensure that the displacement of the side and mid-span main girder is small after system conversion.(4)Three construction cable force adjustment methods,namely forward installation iteration method,reverse disassembly-forward installation method,and stress-free state method are used to analyze the second round of cable force adjustment,and the second round of tension cable force and bridge cable force are obtained.The results show that the convergence rate of cable force adjustment by the unstressed state method is better than that of the forward-fitting iterative method.From the perspective of the accuracy of the bridge cable force error,the forward installation iteration method is better than the unstressed state method.A comprehensive comparison shows that the method of unstressed state is the best for cable force adjustment,followed by the iterative method of forward installation,and the method of inverted disassembly-forward installation is the worst.(5)Based on the influence matrix of the construction stage,MATLAB software is used to calculate the theoretical cable adjustment value of the whole bridge,and the local cable adjustment is proposed.Through the finite element software for three local adjustments,the full bridge cable force can theoretically be adjusted to the target cable force,and the full bridge cable force error can be controlled within-4.7%to 4.6%.