Research On Key Technology Of Demolition Construction Monitoring Of Variable Cross Section Continuous Box Girder Bridge

Bridge demolition,safety is the top priority,in the construction process must do a good job of monitoring work.In this paper,based on a new show bridge(long-span variable cross-section continuous box girder bridge)demolition project,first of all,based on characteristics of bridge structure and site environment put forward the construction scheme of static cutting,floating crane carry crane dismantle,then precise theory to analyze the simulation model based on the scheme,the last in the construction of the whole monitoring,ensure the safety of the bridge.The span of the bridge is large.Temporary support is set in the side span before removal.Then,the bridge deck system and part of the flange plate are removed,and the external prestressing tendons are removed.The mid-span box girder is cut in segments by rope saw,and then removed by floating lifting,and the side span is directly cut out mechanically.Mechanical analysis is carried out on the machinery and tools used in the demolition to ensure that the pull-out resistance and strength checking of the ground anchor meet the requirements and ensure safety.According to David Bell,"dismantling a nonlinear structure and building a precise theoretical analysis model is the key to success." Scientific simulation analysis is the core of monitoring work.When modeling old Bridges,it is necessary to focus on the influence of disease on model parameters.During monitoring,parameters are collected on site,local solid model is established by using FEA,and the diffusion crack model is adopted to calculate stiffness reduction,which is applied in the Civil calculation model.Due to the high risk of bridge demolition,the main girder model and the side-span support model were established by using Midas Civil to simulate the construction stages of new construction,operation,reinforcement and dismantling.The compressive stress of the normal section of the main girder,the principal stress of the inclined section,the deformation and anti-overturning of the main girder,and the strength and deformation of the side-span support in the dismantling stage were analyzed in detail.Accurate grasp of the stress and deformation of the main girder,support in the process of demolition of the general law,to verify the safety of the structure,but also for the construction monitoring stages to create theoretical data.Finally,FEA is used to analyze the hoisting section of box girder in detail,which avoids the previous empirical prediction and improves the safety of construction.On the basis of theoretical analysis,the site monitoring work is implemented.Through real-time collection and analysis of data,and the least square method is used to identify and correct errors.On this basis,the calculation parameters are adjusted,the theoretical model is optimized,and the feedback guidance is given to the next stage of construction.At the same time,the early warning threshold is set to ensure the safe and controllable dismantling process.The results show that the method is feasible,which can provide reference for similar bridge demolition work,and can also be an extended example for the formulation of relevant codes.