A few days ago, the lower beam of the No. 4 cable tower of the Beijiang Bridge of Qinghua Expressway invested by Guangdong Communications Group and constructed by China Railway Bridge Bureau was successfully poured, marking that the main tower of the bridge has entered the construction stage of the upper tower.
The main bridge of the Beijiang Bridge is 1,440 meters, and the main span is 360 meters of double-cable-faced concrete four-tower cable-stayed bridge, which is the key control project of the Qinghua Expressway Project. Among them, the total height of the No. 4 tower is 147.584 meters, which is divided into 26 pouring sections, considering that the stressed structure has high requirements for design strength, the concrete with the number C55 is used, and polypropylene fiber is mixed at the same time.
The lower beam of the No. 4 cable tower is designed as a rectangular section, with 92 bundles of prestressed steel strands, the outer contour is 8 meters high, 8 meters wide, and 35 meters long, and the interior is divided into 3 chambers, 6 meters high and 6 meters wide. The entire lower beam is poured in two times, this is the second pouring, and the pouring height is 4.5 meters. The concrete pouring of the tower and the lower beam has a large amount and a large cross-section, and the temperature control requirements for large-volume concrete are high, and the layered distribution pouring requirements for concrete are high.
The construction of the lower beam under the main tower of the Bac Giang Bridge is carried out synchronously with the tower column, and the method of erecting cast-in-place supports is used for construction. During the construction of the tower column, BIM technology is used to simulate the construction, and the rebar installation adopts the positioning of the slotted tooth plate to ensure that the one-time pass rate of the rebar reaches more than 95%; The lower beam support adopts a combination of double-layer standard and special-shaped Bailey sheets to meet the needs of the special shape structure of the beam and the construction load of 1550 tons; The prestressed steel strand is tied with special equipment, and each bundle is numbered sequentially to avoid the steel strand being knotted inside the pipeline; The intelligent tensile grouting method is adopted for prestressed construction, which effectively guarantees the quality and safety of the project.
For the temperature control and crack resistance of large-volume concrete, the project department boldly carried out technological innovation, optimized the construction plan, and summarized excellent process construction methods to escort the rapid, safe and high-quality construction of the bridge. The anti-cracking performance of large-volume concrete was improved by setting basalt fiber anti-crack mesh on the tower column to resist the temperature shrinkage tensile stress. After the pouring is completed, through the continuous monitoring of the internal temperature of the concrete, the demoulding time is adjusted to reduce the surface cracks caused by the temperature difference between the concrete and the environment after demoulding.
Before the support is erected, the joint testing unit of the project department calculates and analyzes the vertical cumulative deformation of the beam under the main tower according to the construction drawings, and sets the pre-lifting amount and precamber of the main tower beam with reference to the calculation results. At the same time, through the monitoring of the stress and temperature of the lower beam by the embedded concrete strain sensor and the temperature sensor, the stress and temperature changes of the lower beam are always paid attention to during the pouring process and after the pouring is completed. In addition, a foundation settlement control point is embedded on the top surface of the beam for subsequent monitoring of the lower beam settlement by the surveyor.
In order to meet the demand for concrete pouring and control the temperature of concrete into the mold, the project department also formulated a summer construction plan, and effectively controlled the concrete temperature by enabling the cooling unit of the mixing plant, the spray system on the surface of the powder tank to cool the powder, the sand and gravel in the silo to cool down, and the concrete transport vehicle spray cooling.
Affected by the flood season, short-term heavy rainfall occurs frequently in Qingyuan. In order to do a good job in construction early warning, the project department entrusted the Qingyuan Meteorological Service Center to accurately forecast the weather conditions in the area around the Beijiang Bridge, so that the project department can plan the on-site construction as a whole, ensure that the corresponding preventive measures are taken in time during the flood season, and ensure the construction and production.
Guangzhou Traffic Radio, correspondents Zhou Shun, Tan Xiaofeng, Chen Xinqiao's report.