Technology Research On Dismantling Long-span Prestressed Concrete Continuous Girder Bridge And Building New Steel Box Girder Under Running Condition

Highway bridges,urban bridges,national and provincial highway bridges,due to the fact that some of them have reached the service life;the load level has been continuously upgraded,there are quality problems in construction,initial design defects,and the deterioration of bridges in the later operation stage.After reinforcement and repair,the disease degree has been deepened for a period of time,and the structure can no longer be upgraded or improved by other means to meet the existing bearing capacity Capacity requirements;the route from the new planning,cross line river navigation level to improve navigation clearance to improve the bridge needs to be demolished and new,bridge demolition technology research is constantly developing forward,this paper takes the large-span variable height box section prestressed continuous girder bridge as the background,studies the old bridge demolition construction method,operation and traffic health monitoring,new steel box girder construction technology and so on.The concrete continuous box girder is demolished by static force,the side span is located on the river bank and supported by steel pipe support of rotary cast-in-place pile,the middle span is assembled by Bailey piece hanging basket,the hanging basket is hoisted parallel to each cutting beam section,and the main girder is demolished section by section in reverse order.In the process of demolition,the main girder system is constantly changing,and the demolition process is controlled in real time.Midas city carries out theoretical calculation on the stress,deformation and side span support settlement of key sections in the main girder demolition stage,and analyzes and calculates the safety of side span support and lifting hanging basket.In order to adapt to the economic development,in the process of reconstruction and expansion,in order to ensure the traffic operation status of the bridge,the scheme design is to demolish and build a new bridge with a single width,change the road with two-way four lanes,and meet the traffic conditions after the completion of the new construction,then change the traffic and exchange the construction.The bridge structure to be demolished is seriously damaged to ensure the traffic safety.The traffic health monitoring scheme is formulated to monitor the strain,displacement and vibration frequency of the key section of the box girder during the operation.Set early warning value,automatically alarm when the limit is exceeded,and stop the traffic to ensure safety.The original upper structure was removed and the lower structure was retained for reinforcement and reconstruction.The upper structure was newly built steel box girder,the side span support was removed and transformed into new steel box girder,the side span support was spliced by sections,and the large section of the middle span was lifted and closed in parallel.The key point of connection between demolition and new construction is to keep the substructure in use and to remove the support for reconstruction.For the navigable river,under the condition of limited safe operation radius,the key technologies of side span segment hoisting,longitudinal traction block segment positioning and accurate positioning,mid span bridge deck crane cantilever assembly,mid span large segment hoisting and closing,reasonable adjustment of large segment hoisting to ensure the welding quality and how to effectively ensure the smooth and reasonable stress of bridge line are adopted.