Study On The Subgrade Diseases In Permafrost Of Qinghai-Tibet

"Research on construction technology of large-section steel box girder" relies on mawei bridge of fuzhou city,fujian province located at the mouth of minjiang river and its wiring project,aiming at the technical problems faced by manufacturing technology,transportation stability,overall hoisting and accurate installation of large-section variable section continuous steel box girder.Through engineering investigation,theoretical analysis,field test and other methods,the following results are formed:The manufacturing technology of steel box girder is based on manufacturing linear control,manufacturing dimension control and non-stress analysis.The pre-camber is calculated by simulating the construction condition and considering the bridge alignment.The large section steel box girder is strictly controlled according to the linear parameters of the tire frame and the blanking parameters.Manufacturing dimension is controlled by pretreatment of steel plate,blanking of parts,manufacturing of plate unit and manufacturing process.Based on the non-stress state method,the non-stress linear shape of the main girder is analyzed and determined.According to the analysis results,the welding position of the main girder is set at zero bending moment in the construction site,so that the elastic curve between the girder section and the steel-mixing section of the large section steel box girder always keeps continuous and reaches the ideal linear state and internal force state.The construction water area is affected by both tidal current and runoff,and the tidal range and flow rate vary greatly.The steel box girder across the middle and large sections is the last girder section connected by the main body of the bridge across the river section,and is the key construction period node.Through the installation of the operation from the appropriate operation time selection,process close connection,full task in the period of time,the whole process of security measures deployment system research,to ensure the safety,quality,construction period is fully controllable.Small section of the steel box girder hoisting using hanging basket into using continuous bridge crane jack integral lifting technology,on the installation of steel box girder lifting point location,strengthening methods,form a complete set of hanger and hook the selection and design of the system research,jack speed of synchronization and make sure the safety of small section steel box girder hoisting and controllability.The positioning and adjustment of large section steel box girder are studied by computer to precisely control the adjustment of vertical translation,inclination Angle and rotation Angle around the axis of three sets of oil cylinders respectively,so as to realize the accurate closure of steel box girder installation on site.Through the linear shape and stress monitoring of longkou,the safety of the whole hoisting process can be effectively guaranteed,and the raw materials of scientific research data can beprovided for future engineering design.Through the reasonable selection of cutting technology,process sequence,welding technology and anticorrosion technology of the joints of large section steel box girder,the construction quality of the joints after accurate positioning of steel box girder can be effectively guaranteed.In this paper,the key technical problems such as the manufacturing of 90 m long section steel box girder,the overall transportation stability,the overall hoisting,the installation and positioning of 1200 tons of large-section steel box girder are systematically studied,and the research results play a demonstration and guidance role for the construction of large-section variable section steel box girder bridge under the domestic shallow river environment.