[Hot News Everyday] The first push construction steel box girder of Beijing Xiongyang Expressway was successfully erected

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On December 3, with the smooth operation of the jacking equipment, the steel box girder with a total length of 77.5 meters and a weight of 3868 tons was accurately positioned on the main span pier like a steel dragon. The launching erection of steel box girders of Changyang Flyover over Fangshan Metro Line and National Highway 107 of Beijing Xiongyang Expressway (Beijing Section) Project was successfully completed.

What are the difficulties faced by the construction of the traffic trunk lines crossing two operations? The reporter learned from the construction company, China Railway Third Engineering Group Co., Ltd. that the intersection angle between the route of Beijing Xiongyang Expressway and the subway Fangshan Line is about 78 degrees. The viaduct is used to cross the subway Fangshan Line and the national highway 107. The span is (38+61+39), a total of 138 meters. The beam is arranged in two pieces, left and right. The beam is 2.625 meters high. It is an ultra wide variable cross-section curved steel beam, and the widest part of a single piece is 34.326 meters. The multi-point and multi platform walking pushing system is used to synchronously push the two steel box girders from small mileage to large mileage section by section, and the circular operation makes the steel box girders reach the design position, with the pushing area equal to the size of 7 tennis courts.

Zhang Qingnan, deputy project manager of China Railway Third Bureau, said: "The push construction method has simple equipment, stable construction, low noise, and does not need to interrupt traffic, which can minimize the impact on the safety of subway and national road traffic operation." It is understood that the peak traffic flow of the existing national road 107 is about 1000 vehicles/hour, The operation frequency of Fangshan Metro Line is as high as one train every 5 minutes. Under such heavy traffic pressure, if conventional cast-in-place concrete beam construction is adopted, not only the construction cost is high, but also the safety risk is great. Even so, the jacking construction is technically quite difficult because of the complicated traffic diversion and reconstruction work, multiple temporary piers in the middle of the span as auxiliary supports, the heavy weight of the steel box girder, and the need to adjust the height and line type of the temporary piers for many times during the jacking, so the project is also listed as a difficult and high-risk project along the whole line.

How can a giant weighing thousands of tons be safely pushed into place? Zhang Qingnan told the reporter: "This operation is not easy. Except that the steel box girder is pushed to the edge of Fangshan Line in the early stage for daytime construction, the rest of the jacking and beam falling must be carried out in the skylight point of the subway at night." During the construction, temporary buttresses need to be arranged on both sides of the existing expressway first, and the fabricated beam body needs to be spliced on the site, welded into a whole before launching, In the process, the requirements for linear control and beam falling accuracy are very high. "The left and right steel beams are pushed at the same time, and then the transverse beam adjustment and beam fall of 2m height will be carried out after they are in place. A good set of combined boxing requires not only high cooperation, but also stability and accuracy, which is a severe test for us," said Zhang Qingnan.

In order to ensure the smooth construction, the project technicians and the rear research team use the finite element modeling software madis to establish models for the left and right steel beams of the launching section, and determine and calculate the stress and deformation values of each working condition according to the construction process to meet the design requirements. At the same time, the coordinates of the motion track of the steel beam are taken every 0.1 meters forward, and the launching track of the steel beam is simulated before construction, repeatedly deduced, and the linear deviation warning value is formulated. At the construction site, 48 600 ton walking jacks are used to control the displacement in the transverse, longitudinal and vertical directions in three dimensions, and the precision of precise adjustment and positioning is ≤ 1mm. In order to ensure the synchronism of walking jacks during pushing and correct deviation in real time, multiple control cabinets are arranged on the site and connected by optical fiber network cables to form a local area network. All pushing equipment is remotely controlled through the big data of the main control cabinet, so that each movement unit can run on the established mathematical mode and move forward according to the preset track, It provides strong technical support and guarantee for the successful launching and beam falling in place.

It is reported that the Jingxiong Expressway is the most convenient rapid transit corridor connecting Beijing and Xiong'an, and the most convenient expressway channel connecting the central urban area of Beijing and Daxing International Airport to Xiong'an New Area.

(Courtesy of China Railway Third Engineering Group Co., Ltd.)

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