The following is the related contents about the installation and construction of stay cables of the north branch main bridge of Jingzhou Yangtze River Bridge brought by Zhongda Consulting for your reference.

1 general situation of the project

The main bridge of the north branch of Jingzhou Yangtze River Highway Bridge is a prestressed concrete cable-stayed bridge with two towers and double cable planes, with a main span of 511 meters and a side span of 211 meters, and the stay cables are arranged in a fan shape. The stay cables adopt PES7 hot polyethylene cable and PES7 cold-cast upsetting anchor anchorage system. The minimum spacing of stay cables on the bridge deck is 4m and the standard spacing is 8m. There are ***126 stay cables in the south tower of Beicha Bridge, which are divided into eight specifications: PES7-139, 163, 187, 211, 241, 253, 265 and 283. The longest stay cable is 268 meters and the cable weight is 22.5 tons. The South Tower is located in the main channel in the center of the river, and the construction site is narrow. During the installation and construction of stay cables, the cable is pulled from the ship's cable tray to the bridge, and the tower end is hung first, and then the beam end is hung. The main girder construction adopts the symmetrical suspension casting construction technology of hanging basket with 8 meters front fulcrum. (refer to Architectural Chinese Website)

2 Process flow

The installation and construction of stay cables are interspersed in each process of cantilever casting construction of main girder. The solid wire frame represents the main process of cable installation and construction. When the cable is tensioned for the first time, it can simultaneously enter the next cable installation and construction.

3 Construction equipment and layout

The installation and construction of stay cables are mainly divided into cable laying on the bridge, hanging at the tower end, hanging at the beam end, cable tension and conversion, etc. The following facilities are required to complete these works:

Cable pulling system of hoist-cable hanging on the bridge, cable hanging at the tower end and cable hanging at the beam end

Tension system in the tower-cable tension and adjustment

. The winch platform at the top of the tower must be firm and reliable to ensure the safety of equipment and personnel when the winch pulls the cable.

inside the tower: each stay cable currently under construction is provided with a set of tensioning mechanism, including four sets of braces, tension rods, jacks, oil pump trucks, etc. Full scaffolding shall be set up in the cable laying area of the tower, and a movable operating platform shall be set up.

beam end: the tensioning mechanism of the front fulcrum of the hanging basket includes a tension rod, a brace, a jack, an oil pump truck, a pulley block, etc. The welding cage at the front end of the hanging basket is used as an operating platform for cable tensioning and cable force conversion.

Bridge deck: each side main span is equipped with a 11-ton hoist and a 5-ton hoist; Equipped with guide pulleys, rollers for traction and translation of stay cables and guide devices for pulling cables onto the bridge are arranged on both sides of the bridge deck.

under the bridge: one square barge is moored near the steel cofferdam, one horizontal steering cable tray is placed at the bow and stern, and stay cables to be hung are piled on the square barge.

Statistical table of main equipment models and quantities

Note of unit quantity of serial number name

1 Tower crane tower top cable duct position can lift 6 tons

2 floating cranes with a capacity of 131 tons, lifting cables

3 barge ships with a capacity of 1311-411 tons, placing cable trays and stay cables

4 winch platforms with a capacity of 111 tons, 4 hoists with a capacity of 5 tons and 2 hoists with a capacity of 3 tons

. 31 tons, 2 wheels, 4 groups

6 single roller skates, 8 used together with windlass, change direction

7 jack stands, 4 sets in the 8,851-ton top tower, and 4 sets at the 511-ton top beam end

8 oil pump stands, 8 matched with jacks

9 chain block 2111-ton, 5-ton, 2-ton three-model

11 guide device groups, 4 stay cables, guide the bridge, At the side of the bridge

11 rollers, 121 stay cables are dragged and translated on the rollers

12 Elevator platform, 1 personnel and small equipment are transported vertically

4 Installation and construction methods

For short cables less than 6 tons, the tower crane lifts the whole plate to the bridge deck, after the plywood is put on, the tower crane lifts the anchor head of stay cables to the cable conduit position, and the middle winch at the top of the tower pulls the anchor cup into the tower to complete the tower end hanging; For stay cables larger than 6 tons, the bridge deck winch will be used to pull the cable from the cable tray to the bridge, two winches at the top of the tower will pull the anchor head into the cable duct to complete the hanging of the tower end, and the bridge deck 11-ton winch will pull the anchor head of the stay cable at the beam end to the front end of the hanging basket to form the front fulcrum.

4.1 Stay cables are towed to the bridge

After the stay cables enter the site for acceptance, they are lifted by a 31-ton floating crane and put into the cable tray. The steel wire rope of 5t hoist on the bridge deck is bound and connected with the anchor head of stay cable in the cable tray. When the anchor head of the hoist is turned to the horizontal direction through the guide device, the steel wire rope of 11t hoist is connected with the anchor cup of stay cable by the lifting head, so that the connection between 5t hoist and the anchor head is released, and the 11t hoist pulls the stay cable onto the bridge to complete the cable laying. Rollers are set at intervals of 8 meters on the bridge deck to prevent the PE protective layer from being scratched when the stay cables are pulled and translated. The stay cables of the main span are pulled from the side span to the bridge, and the square barge is docked in the direction of the side span of the cofferdam; The stay cables of the side span are pulled from the main span to the bridge, and the square barge is docked in the direction of the main span of the cofferdam.

4.2 hanging at the tower end

Take two cables of the side span as an example. After all the two cables of the side span are towed to the bridge deck, the length of the cables is greater than the length of the poured beam end of the side span, so the anchor head of the tower end is flat at the position near the zero block of the main span. The hoist at the top of the tower lowers the steel wire rope to the bridge deck, which is connected with the stay cable with a splint, and the hoist at the middle of the tower lowers the steel wire rope from the tower, penetrates the cable duct and is connected with the stay cable anchor cup with a lifting head. The tower crane lifts the stay cables at two points near the zero block of the main span, and at the same time, two hoists at the top of the tower lift the stay cables. At this time, the anchor head of the stay cables slowly lifts from the main span to the side span. After a certain height, the tower crane is unhooked, and the cable anchor cup is pulled into the tower by two hoists at the top of the tower, and the large nut of the anchor cup is screwed on to complete the hanging of the tower end.

4.3 hanging four stay cables at the beam end

side main span, the tower end is hung, the hanging basket is erected, the hanging point is anchored, the angle of the front fulcrum tension rod is positioned, and the anchor head of the traction beam end is connected with the hanging basket tensioning mechanism to form the front fulcrum. Taking the side span as an example, the anchor point of stay cable is established at the front end of the side span hanging basket, and the anchor point is fixed with the pulley block. The steel wire rope of the winch with a side span of 11 tons passes through the pulley block and is bound with the anchor head of the stay cable at the beam end. The anchor cup is equipped with a conversion connector and an upper fork head, and the winch pulls the stay cable to connect the upper fork head with the tension connecting rod by a pin shaft to form the front fulcrum of the hanging basket. The jack at the front end of the hanging basket shall be tensioned, and the stay cable shall continue to be pulled until it is close to the first tensioning tonnage. When pulling the cable at the beam end, the main span of the side span shall be symmetrical on the same side. In order to reduce the horizontal traction between the upper fork head and the tension rod, 21 pairs of stay cables were installed and constructed, and the length of the tension rod was extended from 2.4 meters to 3.8 meters.

4.4 Soft Traction

With the cantilever casting of the main girder, the length and weight of stay cables are increasing, and the horizontal traction force of the front fulcrum formed by the stay cables at the beam end is increasing. When the cable is pulled at the end of the cable beam in the last two sections, the maximum traction force of the winch equipment is close to the horizontal traction force of the cable calculated by sag method. Because the concrete in the last two sections of the side span is poured first and then the cable is hung, it is decided to use soft traction for the installation and construction of the cable in the last two sections of the side main span. In fact, soft traction is to use the steel hinge wire harness with variable length as a flexible tension rod to extend the stay cable, so as to reduce the horizontal traction at the beam end. During construction, the stay cables are firstly pulled to the tower end for temporary fixation, and the anchor cup in the tower is connected with long soft traction to relieve the temporary anchorage. When the soft traction reaches the maximum, the soft traction steel hinge wire is anchored, and the beam end winch pulls the cable-stayed anchor head to connect with the tensioning mechanism to form a front fulcrum, and the tower end jack then tensions the traction steel hinge wire harness step by step until the anchor cup enters the tower, and the anchor cup nut is screwed to complete the tower end hanging.

4.5 first tensioning of stay cables

after all four stay cables are hung at the tower end and the beam end, the stay cables shall be tensioned for the first time according to the monitoring instructions, and the first tensioning shall be carried out in the tower or at the beam end. When the sag of the stay cable is not very large, the first tensioning is carried out with the tensioning mechanism in the tower; At the end of the construction, the sag of nearly ten segments of cables is very large, and the first tensioning is carried out by the tensioning mechanism at the beam end. When the beam end is tensioned, the tensioning mechanism of the hanging basket may rotate with the internal torsion of the parallel steel wire of the stay cable, and the rotation of the tensioning mechanism can be restrained and adjusted by applying a torque in the opposite direction to the tensioning mechanism with chain block while the stay cable is tensioned. Four stay cables shall be tensioned synchronously, symmetrically and in stages, and each stage shall be controlled within 1.5 tons, which shall be controlled by reading of oil pressure gauge.

4.6 Second tensioning of stay cables

After the first tensioning, steel bars shall be bound and concrete shall be poured. When half of the concrete is poured, the concrete volume of the main span and the upstream and downstream shall be balanced and symmetrical, and the stay cables shall be tensioned for the second time, and the cable force and elevation shall be adjusted to meet the monitoring requirements. The second tensioning is carried out in the tower. According to the tonnage classification provided by the monitoring instruction, ensure that the four jacks are tensioned synchronously and symmetrically. After the second tensioning meets the requirements, continue to pour the remaining concrete.

4.7 Cable force conversion

After the concrete strength meets the strength of prestressed tensioning, the prestressed tendons in the main girder are tensioned, and the cable force conversion is carried out after tensioning. Cable force conversion is to convert the pulling force of stay cables on the front fulcrum of hanging basket to the prestressed concrete main beam and remove the front fulcrum. Before the cable force conversion, the big nut of the cable anchor cup is not stressed, but the big nut in the brace of the tensioning mechanism is stressed. The anchor cup is pulled outward by the jack for about 1 cm, and the big nut of the anchor cup is screwed up to make it close to the anchor pad of the main beam, and the jack releases pressure and returns oil. At this time, the big nut in the brace of the tensioning mechanism is no longer stressed, but the big nut of the anchor cup is stressed, and the cable force conversion is completed by releasing the conversion connector. Cable force conversion requires four jacks to perform tension conversion synchronously, and the tonnage of tension conversion should not be too large.

4.8 Third tensioning of stay cables

The third tensioning of stay cables is carried out in the tower. Like the first and second tensioning, the four jacks should be tensioned symmetrically step by step. This tensioning should adjust the position of the big nut of the anchor cup at 2/3 of the anchor cup to avoid adding a pad on the anchor cup. After the third tensioning, the hanging basket falls off the frame, the walking hanging basket, and the tensioning mechanism in the tower moves to the lower root cable to carry out the construction of the next section.

5 Conclusion

The author has participated in the installation and construction of stay cables in the south tower of Beicha Bridge, and has several experiences:

(1) The designed tensile strength of the tension rod of the hanging basket at the front fulcrum is at least twice the maximum tonnage of the stay cables, and the tensile strength test should be done before the tensioning mechanism is used, and the use of the tensioning mechanism should be checked regularly, and measures should be taken to ensure that the tension rod is not sheared when used as the front fulcrum. The length of tension rod is suggested to be about 5 meters, and a long tension rod can reduce the horizontal traction of the cable at the beam end.

(2) When pulling stay cables at the beam end and tower end, the performance of each hoist, pulley block, wire rope, anchor point, wire rope and buckle should be carefully checked.

(3) It is emphasized that the tension of stay cables should be synchronized by stages.

(4) In the process of cast-in-place construction of main girder, the following economic and feasible measures can be taken to reduce the vibration of stay cables:

a The gap between stay cables and steel conduit of stay cables is plugged with wedge-shaped wooden plugs.

b cable clamps are installed on the stay cables, and the cable clamps are connected with the bridge deck embedded parts by tensioners and steel ropes.

(5) It is difficult to accurately set out and locate the center coordinates of the anchor pad plate for upsetting the beam end according to the designed theoretical coordinates. To ensure that the stay cable is centered in the steel conduit after the bridge is completed, the damping device should be installed, and the inclination angle of the steel conduit should be constantly corrected during the concrete pouring process.

[6] Anti-fouling, oil-proof, waterproof and fireproof measures shall be taken for the stay cables. Rollers shall be set when the stay cables are dragged and translated. It is forbidden to scratch the PE protective layer by hard dragging. Special slings and fixtures shall be made to ensure that the stay cables are always in a free bending state during lifting.

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