Key Technology Of Pulling Construction Control For Steel Box Girder Of Upper-span Railway In Short Window Period

The first span of the viaduct of Fengxin Express Line in Zunyi City is a simply supported steel box girder bridge with a length of 50 m and a width of 31 m.It is constructed by multi-point towing on the busy Sichuan-Guizhou railway.In this paper,the drag construction of the bridge span was analyzed and studied as the engineering background,the specific contents were as follows:Towing construction of steel box girder of upper span railway.Bridge propulsion method is one of the commonly used construction methods in bridge construction.According to the propulsion system,it is mainly divided into propulsion method,towing method,jacking method and clamping method,in which propulsion method and jacking method are more common,but the integral towing construction of steel box girder is relatively rare.The cross-railway transportation on the bridge is busy,and the window time of each drag is short.Along the direction of the bridge,there are still two rigid frame bridges that cross the railway under the bridge,which need to be strengthened and protected.In addition,it is located in the mountain area and the construction space is narrow,which makes the towing construction of the bridge span more difficult.To ensure that the beam moves along the established towing route,prevent the large lateral deviation of the beam in the towing,and ensure the safety of the bridge structure in the towing construction,reliable and accurate theoretical calculation and strict control measures are needed.In this paper,the finite element analysis model of the whole process of towing construction of the bridge is established by using Midas software,and the bridge structure,force pier and auxiliary pier and support system are simulated and analyzed in detail.Towing construction control and monitoring.The synchronization of multi-point Jack,the deflection of main beam axis,the stress of main beam and auxiliary pier,the inclination and displacement of permanent pier,the settlement of auxiliary pier and railway frame bridge,the deflection and temperature of main beam and steel guide beam are monitored in real time.By setting the early warning value,the stress safety of the system construction is monitored at any time,and combined with theoretical calculation and analysis,the safety of main beam structure,permanent pier and auxiliary pier,railway and its lower frame bridge are ensured.At the same time,the effect of deviation correction is also tested,which greatly improves the speed and accuracy of deviation correction in the process of dragging.There are many items that need to be controlled and monitored in this bridge,the strain observation points are arranged in many places,and some of the observation points need to be observed for a long time.Benxi steel box girder bridge is sensitive to temperature changes,and other parameters are modified by monitoring the environment and the surface temperature of the main girder.Analysis and optimization of the results.Through the analysis of the theoretical early warning value and the measured value,this paper made a detailed calculation and comparative analysis of the problems that may occur in the towing construction process control of the bridge and put forward a specific optimization scheme.The results showed that the control method was appropriate,and the optimization scheme was reasonable and effective,and provided reference for the design,construction and monitoring of similar bridges.