Study On Frameless Demolition Technology For Arch Bridge Under Stress Free State

Truss composite arch bridge is a bridge type independently developed in China,which has both the mechanical characteristics of beam bridge and arch bridge.The fracture joint is set at the appropriate position of the upper chord to make the stress of the whole bridge member tend to be uniform.With the construction of climbing pole,the problem of building a bridge with small equipment is solved.Therefore,it has been rapidly promoted in the 1980 s.Due to the weak rigidity of the connecting members and the repeated loading of vehicles,a large number of cracks occur in the bridge body,which endangers the safety of the bridge.In recent years,more and more truss type composite arches have been listed in the list of dangerous bridges and have to be demolished.At present,there is little research on the demolition technology of truss composite arch in China.Therefore,relying on the scientific and technological project of Guizhou Provincial Department of transportation,"Comprehensive solution research on demolition and reconstruction of original arch bridge(2020-123-018)" and Guizhou Huayudong bridge(truss composite arch bridge with main span of 150m)as the engineering background,the following research work were carried out in this dissertation:①Combined with the characteristics of the original bridge site reconstruction using concrete-filled steel tube arch bridge scheme,the "concrete filled steel tube arch support demolition method" is proposed,that is,the concrete-filled steel tube arch is first constructed,then used as the auxiliary support for the demolition of the old bridge,and the temporary buckle is set between the steel tubular arch and the truss composite arch bridge as the temporary support for the demolition of the old bridge.②The detailed demolition scheme design of Huayudong bridge was carried out,and the demolition scheme of bridge deck system and main arch ring was further given;with the help of MIDAS / Civil finite element software,the integrated model of new bridge,sling and old bridge is established,and the stress and displacement changes of new bridge and old bridge arch ring during the demolition process were analyzed in detail.③Because the actual internal force state of the old bridge is difficult to be accurately evaluated,and the process of arch opening is difficult to be accurately simulated by finite element method,there are problems such as high construction risk and large uncertainty in arch ring opening.In view of the above problems,firstly,the sensitivity analysis of common influencing factors of arch ring internal force was carried out,and the factors that have great influence on the safety of arch ring were obtained;secondly,the adjustment scheme of sling was determined to control the internal force of arch crown section,and the internal force state of arch ring before and after arch opening was analyzed in detail;finally,the construction scheme of "Jack assisted release of internal force" was proposed The detailed construction steps were given to further ensure the stability and safety of the arch opening process.④Due to the actual internal force state of the old bridge was difficult to be accurately evaluated,and the process of arch opening was difficult to be accurately simulated by finite element method,there are problems such as high construction risk and large uncertainty in arch ring opening.In view of the above problems,firstly,the sensitivity analysis of common influencing factors of arch ring internal force was carried out,and the factors that have great influence on the safety of arch ring were obtained;secondly,the adjustment scheme of sling was determined to control the internal force of arch crown section,and the internal force state of arch ring before and after arch opening was analyzed in detail;finally,the construction scheme of "Jack assisted release of internal force" is proposed The detailed construction steps are given to further ensure the stability and safety of the arch opening process.