Research On The Key Technology Of Walking-type Incremental Launching Construction Of Long Span Steel Box Girder

Steel box girder with incremental launching construction combines the characteristics of light weight,high strength and large span capacity of steel structure with the advantages of short period,automation and less interference to traffic under the bridge of incremental launching construction.It has been more and more popular in the bridge construction of large and medium span or special situations.In recent years,the higher precision of walking-type incremental launching construction has appeared,and it is gradually popularized and applied.At present,the research on the incremental launching construction of concrete bridge has been quite mature,but the results are not all applicable to the incremental launching construction of steel box girder.There are still some deficiencies in the research of steel box girder with incremental launching construction,mainly in the most unfavorable stress situation of steel box girder and the possible support voiding phenomenon.Therefore,this paper will rely on the incremental launching construction of Xiangfu Road steel box girder bridge across Beijing-Hong Kong&Macao Expressway in Changsha.Combined with the problems found in the monitoring of incremental launching construction,based on the existing research results,this paper analyzes and studies the key stress and support voiding of the steel box girder with incremental launching construction.The main tasks are as follows:1.Research on the calculation model suitable for the long-span steel box girder with walking-type incremental launching constructionBased on the project,this paper compares and analyzes the monitoring results and the theoretical results of a long-span steel box girder with walking-type incremental launching construction.There is an obvious support voiding during construction.However,taking block setting measures in the actual construction leads that actual stress differs greatly from theoretical results.It is very unfavorable to the bridge and construction safety.Therefor,a new calculation model of "forced displacement" at the void space is proposed and the reasonable value of the threshold of "forced displacement" is suggested according to three principles.The comparison between the two calculation models shows that the new calculation results are in good agreement with the measured results.Therefore,the calculation model can well simulate the situation of support voiding and steel block setting during construction.2.Theoretical analysis and research on the force of the incremental launching construction of steel box girderBased on the principle of classical analytical method,the force analysis of continuous girder bridge in the process of incremental launching construction under the condition of n unequal span and n equal span is carried out respectively,and the simple calculation formula of the maximum reaction force in the process of incremental launching construction is carried out.Combined with the supporting project,the accuracy of the formula is verified.By simplifying the calculation model and using displacement method,the influence degree and law of length ratio,self-weight load ratio and stiffness ratio parameters on the internal force in the incremental launching construction process are calculated and analyzed.Based on the control of bending moment and reaction force,the best formula of guide beam parameter calculation is obtained and the suggested range is given.This paper introduces the parameter of side main span ratio λ,and discusses the reasonable value of the parameters and parameters of guide beam under the condition of long side span,so as to provide reference for the actual construction and calculation.3.Control and analysis of voiding problem of steel box girder with incremental launching constructionIn view of the support voiding phenomenon in the incremental launching construction of long side span steel box girder,this paper carries out theoretical calculation and analysis,and puts forward the calculation formula of support voiding,and takes the supporting project as an example to calculate.Through the finite element simulation,the incremental launching construction models of different side span and guide beam length are established respectively,the influence of side span and guide beam length on the reaction force of temporary pier support is explored,and the reasonable parameter range is proposed,which can provide technical reference and guidance for similar bridges with incremental launching construction.