Application Of Neural Network Combined With Genetic Algorithm In Stressless Closure Control Of Steel Truss Arch Bridge

Arch bridge has always been the longest bridge type in China's bridge construction.With the development of the arch bridge towards long and large,there are still many problems to be solved in the aspects of arch bridge theory,design,construction,and operation.In steel truss arch bridges,cable slings are generally used for hanging construction.As the key component of this construction method,the optimization of the cable force value has been favored by many scholars and experts.At present,there are few researches on the calculation and optimization of cable forces for the arch bridges constructed by the hanging cables hanging cables.Taking the Xiangxi Yangtze River Bridge under construction as an example,based on the goal of an unstressed closure,this paper carried out an optimized analysis and analysis of the construction control cable force for large-span steel box truss arch bridges.The main contents are:1.In order to make the linear shape of the cantilever assembled steel truss arch bridge coincide with the bare arch linear shape of the primary landing frame,a linear control method based on the unstressed state method is proposed.The core of this method is to control the stress-free assembly of arch rib segments.It is clear that the goal of the non-stressed closure of the closure section is to control the geometric dimensions of the closure opening so that it meets the requirements of the unstressed length and the stress-free curvature of the closure section.To achieve this goal,the cable force is optimally controlled.Based on the commonly used cable lifting cable-stayed buckle hanging method for arch bridges,the optimization calculation of the cable force is introduced.According to the cable optimization experience of the cable-stayed bridge,an optimization method for the buckle cable force in the construction of the arch bridge is proposed.2.Based on the Xiangxi Yangtze River Bridge project,a space finite element model integrating the main arch,the buckle tower,and the anchor cable was established.The complete construction steps were established using Midas civil finite element analysis.The cable force optimization can be converted into the minimization problem solving.The global optimization solution can be effectively obtained by using the genetic algorithm,but a large number of finite element analysis calculations are needed.The BP neural network can establish the nonlinear mapping relationship between the cable force value(input)and the structural response change(output).This capability provides a powerful calculation method for the genetic algorithm to solve the cable force optimization problem.According to MATLAB,neural network and genetic algorithm have been compiled to optimize the cable force calculation program.Under the constraint conditions such as the displacement deviation of the expected the final closure and the allowable value of the deduction position of the deduction tower,this program uses the neural network to automatically establish the mapping relationship between the cable force and the final closure displacement.Finally,the genetic algorithm is used to find the optimal cable force that satisfies the expected displacement of the final closure.3.The optimal cable force value is substituted into the finite element model for simulation analysis during the construction phase,and the arch line shape after closing is obtained,and the line shape is compared with the bare arch line pattern of a drop frame.The results show that the arched line shape obtained by the optimization method of this paper is in good agreement with the bare arch line shape of the primary landing frame.This shows that the cable force optimization method used in this paper is reasonable and effective,not only provides a scientific method for the construction control of the bridge,but also this method is expected to be widely applied to the cable force optimization analysis of the cantilever assembled bridge.4.Based on the results of the cable force calculation based on the calculation of the unstressed closure,the calculation of the stress-free cable length is performed,and the unstressed state of the arch rib segment is constant during the construction process.Therefore,it is ensured that the arch ribs after closing the closure are in line with the naked arch pattern of the primary landing frame after the buckle anchors are removed.