Optimization And Reasonableness Of Cable Force Of Composite Girder Cable-stayed Bridge Construction State Study

The cable-stayed bridge with stacked-box girders is a high-precision and high-tech bridge structure,which has been widely used in recent years due to its light weight of the main girder and the time-saving construction period.Compared with ordinary cable-stayed bridges,the structural stress of the cable-stayed bridge with stacked-box girders is more complex,and the precision and technical requirements for the construction process control are higher.In this paper,a certain cable-stayed bridge with stacked-box girders is taken as the research background,and in-depth research is carried out on the optimization of the cable force of the completed bridge,the determination of a reasonable construction state,and the sensitivity analysis and identification of structural parameters.The main research content and results of this paper are as follows:(1)This study investigates the process of obtaining reasonable bridge cable forces for a composite girder cable-stayed bridge using a combined method based on the influence matrix method and the rigid support continuous beam method.The control objectives of the combined method are improved by including the bending moments of the steel main beam and the concrete deck as control targets,which ensures that the obtained bridge cable forces and the corresponding completed bridge state are more consistent with the force system of the composite girder.(2)Considering that the influence matrix method is based on the assumption of structural linearity and employs the linear superposition principle to solve the bridge cable forces without taking into account nonlinear effects,a modified influence matrix method is proposed to reduce the impact of nonlinear effects by reducing the adjustment range of cable forces.The modified method is verified,and the results show that the bridge cable forces obtained by the improved influence matrix method have small errors in controlling the section bending moments of the completed bridge,which are consistent with the target bending moments in the reasonable completed bridge state.Therefore,the modified influence matrix method can be used to guide actual construction.(3)To address the issue of the undefined optimization objectives of cable forces during the construction process of traditional cable-stayed bridges,which are usually selected based on construction experience,this paper proposes an optimization method for cable forces during the construction process based on the zero-stress state method.The calculated cable forces during the construction process are then used in the final calculation to ensure that the obtained completed bridge state is closer to the rational completed bridge state than the conventionally selected cable forces during the construction process.(4)The traditional construction method for the main beam of composite cable-stayed bridges is inefficient and time-consuming.To address this issue,two optimization methods for the main beam construction were proposed.The construction methods were then analyzed using the load-bearing calculation to compare and contrast the stress during the construction process,as well as the stresses and cable forces in the completed bridge.Through this analysis,a most optimal main beam construction method for the composite cable-stayed bridge was determined based on the premise of structural safety and construction efficiency.(5)With regard to the deviation between the parameter values used in theoretical calculations and the actual values of structural parameters in practical construction,sensitivity analysis was performed on the effective parameters determined based on the structural characteristics of a composite girder cable-stayed bridge.The results indicated that the sensitivity of the bridge state was higher for two parameters,namely,the self-weight of the concrete deck and the final tension of the cable.Based on this,a BP neural network was used to identify the self-weight of the concrete deck,and the identification result was compared with the measurement data of the actual bridge.The results demonstrated that the identification effect was good and could be used to guide actual construction.