Erection and demolition of catwalk in suspension bridge construction?

The Kaituo Avenue Bridge across the Yihe River has a total length of 495 meters, a bridge width of 45 meters and a bridge area of about 24,583.5 square meters. The main bridge is a self-anchored suspension bridge with parallel double cable planes, with a span combination of 70.5 m+175 m+70.5 m = 316 m, two towers with three spans, and the total height of tower columns is 52.5m m. The main tower+auxiliary tower design (3 # ~ 6 # in turn) is adopted, and the approach bridges on both sides are 29 m+29 m+. The whole bridge is equipped with two main cables, which are galvanized high-strength steel wires with a diameter of 5.4 mm. Each main cable consists of 19 prefabricated parallel steel wires, each main cable contains 127 galvanized high-strength steel wires with a diameter of 5.4 mm, and each main cable consists of 24 13 steel wires. Main cable precast strand adopts hot cast anchor.

The catwalk is lower than the center line of the main cable 1.5m, and the catwalk surface is 4.0m wide. Each catwalk is supported by 8 φ40mm wire ropes, and each handrail adopts 2×φ20mm wire ropes. The handrails on both sides are made of large square-eye steel mesh with a height of1.2m..

2 Catwalk Cable Traction System

2. 1 guide cable

The guide cable is located between the two main towers, and its main function is to pull the other catwalk cables across the main span, bearing only traction and not gravity. The steel wire rope with a diameter of φ28mm is adopted, and the cranes on both sides can rotate back and forth to make the guide rope reciprocate. There are guide ropes on the catwalk upstream and downstream of this bridge.

2.2 Track support cable for catwalk erection

When the guide cable pulls other cables across the mid-span, all the weight is borne by the support cable, which is pulled by the guide cable to stand upright in the air.

2.3 Installation of Guide Cable

The φ28mm guide rope passes through one end of the steel rope head at the top of pier No.4 and enters the 20t winch, and the other end is wound on the bridge deck and temporarily fixed under pier No.5..

The traction speed of the manual stacking guide rope on the bridge deck is consistent with that of the winch, and it should be towed along the bridge axis as far as possible; There must be a certain backward force when the cable winch on the shore pays off the cable, and observe the counterweight while paying off the cable. If the balance weight moves too high, it should be paid off quickly to reduce the balance weight. Otherwise, the pay-off should be slowed down.

When the wire rope end of the guide rope reaches the bottom of the main tower of Pier 5, the winch of Pier 4 stops paying off the rope. At the same time, the guide rope is temporarily fixed at the top of Pier 4. Put the reserved guide index on the pulley at the top of the tower, and then introduce it into the 20t winch through the diverting pulley. When it is wound into a certain linear shape, the tip rope on the iron barge can be released.

Remove the counterweight with a crane, and then introduce the excess wire rope into the pulley, which will be attended by the 20t hoist of the main tower of Pier 4. The crane under the main tower of Pier 5 will lift the guide rope to the calculated line shape.

2.4 Track Support Cable Erection

Remove the rope ends of the two towers of the guide rope, and adjust the length of the guide rope in the crane on both sides of the river so that the guide rope has enough travel to bring the stay rope to the top of the 5# pier. Place the supporting cable tray on the bracket of 3# pier span tray, lead the rope end to the top of the tower, and connect it with the guide rope after passing through the roller. Start the hoist, guide the cable to run to the 5# pier, and tow the temporary load-bearing cable of catwalk to the 5# pier.

3 catwalk erection

3. 1 structure and layout of catwalk

Catwalk is a kind of high-altitude scaffold, which is used for erection, measurement, cable adjustment, cable tightening, cable clamp installation, sling and main cable corrosion protection.

The catwalk consists of catwalk bearing cable, catwalk surface, railing and handrail cable.

Layout of catwalk surface: the catwalk is lower than the center line of the main cable 1.5m, and the catwalk surface is 4.0m wide. Each catwalk is supported by 8 φ40mm wire ropes, and the catwalk load-bearing cables are anchored in the anchor box with adjustable length at the top of the main tower or in front of the cable saddle. The bottom layer of catwalk surface net is welded with large eye steel mesh, and the surface layer is welded with small eye steel mesh. The bottom layer and surface layer are bound and fixed with square battens, and connected with cross channel steel with steel belt bolts. The transverse channel steel is fixed on the catwalk bearing cable with bolts. Each side of the handrail adopts 2×φ20mm steel wire rope; The handrails on both sides are made of large square-eye steel mesh with a height of1.2m. In order to maintain the linearity and wind-resistant stability of the catwalk, horizontal and vertical wind-resistant stay cables are planned. Before the formal construction, wind tunnel model tests of the wind-resistant stability of the catwalk are needed to determine the wind-resistant structure of the catwalk. Cat Lane is divided into three sections: main span, south span and north span.

3.2 Erection of Catwalk Bearing Cable

Manufacture of catwalk load-bearing cable

The load-bearing part of the catwalk is that the catwalk load-bearing cable is divided into three sections along the bridge, one section spans the middle section and the other two sections span the side section. Each catwalk bearing cable adopts φ40mm non-rotating steel core steel wire rope with anchor heads at both ends.

Catwalk load-bearing cable is steel core wire rope. In the process of manufacturing, the wire rope should be pre-stretched to eliminate the inelastic deformation of the wire rope. The pre-tension of wire rope should not be less than 1/2 of the breaking tension of each wire rope, and keep it for 60min, do it twice and record it. Ensure that the steel core will not slide during pre-stretching. The tensioned steel wire rope is well coiled in the natural state, which is convenient for paying off the cable without twisting.

After the catwalk load-bearing cable is cut according to the designed length, the anchor head is poured at its end. The fabrication of the anchor head should meet its stress requirements, and the steel strand is perpendicular to the end face of the anchor head.

3.2.2 Erection of Catwalk Load-bearing Cable

On the erected guide cables and track support cables, a single pulley coupler is installed at the top of pier No.4, and a drum with a brake for winding the main span catwalk load-bearing cable is placed at the bottom of pier No.4, and the end of the catwalk load-bearing cable is pulled out and led to the top of the tower. A 3m short steel wire rope is connected with the rope clamp at a distance of 5m from the end, and the other end is connected with the guide cable through the rope clamp, and the catwalk bearing cable is tied with the track supporting cable.

The guide rope pulls the catwalk load-bearing cable forward, so that the catwalk load-bearing cable is pulled to the 5# pier.

The 5t crane will anchor the 3# pier anchor head of catwalk bearing cable to the anchor box, and then anchor the 6# pier anchor head of catwalk bearing cable to the 6# pier anchor box.

Adjust the sag of the catwalk load-bearing cable according to the measurement results.

Move the track bearing cable at the top of the tower to the top surface where the second catwalk bearing cable needs to be installed, and the guide cable will also move. After preparation, the upstream and downstream are symmetrical, and the above steps are repeated until the remaining catwalk load-bearing cables are completed. Fully adjust the line type of all catwalk load-bearing cables.

The middle span catwalk bearing cable and the side span catwalk bearing cable are symmetrically erected. Pay attention to the operation balance of the left and right side spans and the middle span, minimize the displacement influence on the main tower, and make the main tower bear less horizontal force.

When the main span catwalk load-bearing cable is erected, the pulling and releasing speed of the cable system and the cable releasing system should be consistent and closely related. When there is a fault in the middle, the pulling and releasing system should be stopped completely, and the cable should be released after the fault is handled.

During the erection of catwalk load-bearing cables, the displacement and torsion of the main tower tops on both sides should be observed at any time and controlled within the design allowable range.

3.3 aisle panel

Catwalk surface: Catwalk surface is composed of catwalk surface bed and handrail. The catwalk surface bed consists of large and small steel wire mesh, channel steel beam, steel bar and square wood, which are connected with each other by bolts and screws and fixed on the catwalk bearing cable. The handrail of the railing consists of an upright post installed on the channel steel beam, a φ 16mm steel wire rope passing through the upright post and a steel wire mesh fixed on the steel wire rope of the handrail.

The catwalk panels are prefabricated into rolls in the factory, transported to the construction site and hoisted to the top of the tower. The loose coil slides down the catwalk load-bearing cable, and the guide bolt is installed at the same time. After the first volume is completed, connect the second volume and continue to slide.

In order to make the catwalk panel move in the gentle span of the catwalk load-bearing cable, it is necessary to install the guide cable. When the self-weight can't overcome the friction, use the guide rope to apply force. In order to slide forward safely, the aisle panel must be kept backward. After the catwalk panel slides into place, lock it on the catwalk load-bearing cable.

4-channel demolition

The catwalk demolition work includes: catwalk variable hanging rope, side net, handrail rope, catwalk surface net, catwalk load-bearing cable, catwalk working platform and wind-resistant cable.

The sequence of catwalk removal: wind-resistant cable → railing and railing net → catwalk surface net → catwalk bearing cable → handrail cable → catwalk working platform.

Mechanical equipment: tower crane, pulley block, chain crane, etc.

5 conclusion

Catwalk is an indispensable temporary structure in the construction of modern long-span suspension bridge. Although it is a large-scale temporary structure, it has long service time and frequent operation, and it is a large-scale temporary stress structure. Therefore, it is necessary to standardize and control the design scheme, erection and demolition of the catwalk, and strengthen the safety awareness of the construction team in order to achieve the goal of safe and rapid production.

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