Smooth walking and flexible movement are features of crawler cranes, making them highly suitable for soft base sections. Girders are erected by crawler cranes, which have more stringent foundation requirements compared to automobile cranes.
The characteristics of crawler cranes, such as stress dispersion and cost-saving in erection construction, are fully utilized. In this case area, the characteristics of the crawler crane can be fully utilized for the bridge dispersion construction project.
1 Project overview
The project spanned the total length of 16.606km, with the starting and finishing mileage being K37+394～K54+000. The project is situated in the flood plain area of Jianghan River and Lake, characterized by flat terrain, minimal undulations in the ground, developed vegetation, and a significant presence of fish ponds, irrigation canals, and ditches. The route is extensively populated with widely distributed soft soil.
2 Crawler crane girder erection construction
The crawler crane is mainly divided into the following procedures: construction preparation → beam transportation → beam erection → crane shifting and other operation cycles.
2.1 Construction preparation
· The bridge pier construction has been successfully completed, reaching the required bearing strength. The matting and bearing have also been approved, with their elevation, flatness, and levelness meeting the necessary standards.
· The girders have demonstrated the necessary strength for erection and have met all design requirements. The quality of the girders has been thoroughly inspected and confirmed to comply with the design documents and construction specifications.
· Before proceeding with the installation of the beam slab, it is essential to ensure the smooth repair of the beam transportation lane, guaranteeing unobstructed transportation of the beam slab.
· Precise measurement and sampling are crucial steps prior to construction to accurately determine the location of the beam slab. We must thoroughly review and verify the centerline and end line of the beam slab, as well as the plane position and elevation of both permanent and temporary supports before commencing the erection process.
· To ensure the safe operation of the crawler crane, proper foundation preparation is necessary before hoisting it. The initial step involves compacting the foundation by replacing the slag with appropriate materials. Subsequently, steel plates are laid on top of the compacted foundation to serve as a stable base for the crawler crane.
2.2 Beam transportation
The girders are loaded onto trailers by gantry cranes at the precast yard and transferred to the bridge by trailers. During the transportation process, it must be ensured that the girders are smooth and safe, the quality of the girders must not be damaged by overturning during the transportation process, and the speed of the trailer must not be greater than 5 km/h.
· Hoisting beam: When the beam is first hoisted, it should be hoisted for a trial period. When test lifting, suspend the beam after lifting it about 2-3cm away from the supporting surface, and make a detailed check on the action of the main stress parts, and only after confirming that the stress is good, remove the support pad and continue lifting.
· The lifting, longitudinal movement, lowering, lateral movement and positioning of precast beams shall be unified and coordinated, and shall be carried out properly according to the scheduled construction sequence.
· When loading the girders, it is important to ensure that the deviation between the center of gravity line of the girders and the longitudinal centerline of the vehicle does not exceed 10mm. Place the girders according to the designed pivot point and avoid partially lifting or placing them. When putting down the girders, make sure to support them before loosening the hook. The speed of the vehicle must not exceed 5km/h, and someone should be responsible for directing the vehicle before and after delivering the beams.
2.3 Beam erection
The crawler crane will arrange the order of lifting the bridge span based on the actual situation of the girder frame. However, it will perform the lifting of the same span from one side to the other (or middle first, then to both sides). During installation, strict control will be maintained over the hoisting speed and synchronous rotation. On-site, there will be one division number, two observers, one safety officer, and two drivers assigned to implement the task of rectifying the girder erection.
To ensure proper execution, the lifting, longitudinal movement, lowering, lateral movement, and positioning of prefabricated girders must be uniformly commanded, coordinated, and carried out according to the predetermined construction sequence.
When lifting the beam, it is necessary to conduct a trial lift initially. During the trial lift, the beam should be suspended approximately 10-20cm away from the supporting surface, after which a detailed check of each main stressing part’s action is conducted. Once it is confirmed that the stressing is satisfactory, the beam can be lifted at normal speed.
For turning, the main crane should be turned first, with the deputy crane following the main crane under the director’s command. Efforts should be made to synchronize the two cranes in turning the body.
When dropping the beam, it should be done at a normal speed, while observing its balance. The beam is dropped to about 50cm from the support, then gradually lowered. The dropping process should be stopped when the beam is approximately 10cm from the desired erection height. At this point, the position of the beam is confirmed, and it is then slowly put into its final position.
3 Features of crawler crane girder erection
In this project, we utilize two 80T crawler cranes for erecting 25m box girders, and one 80T crawler crane for erecting 13m hollow slab girders. The crawler cranes successfully erect a total of 248 pieces of 25m box girders and 840 pieces of 13m hollow slabs, which are scattered throughout the Jiangbei project line.
The crawler crane employed in this project boasts impressive specifications, including a maximum lifting capacity of 80T, a main boom length ranging from 13m to 58m, a travel speed of 0.9km/h, a lifting speed of 70m/min, and a maximum slewing speed of 2r/min.
This crawler crane demonstrates remarkable flexibility during travel, ensures safety during rafter erection, and exerts minimal ground pressure. As a result, it proves particularly suitable for scattered bridges and areas with flat terrain.
With its wider crawler belt and smooth walking capability, the crawler crane effectively disperses its own weight and the load of the girder plate during erection. This results in smooth lifting operations and enhanced safety performance, particularly in flat terrain areas with soft foundations.