Crawler cranes are smooth walking and flexible moving, and crawler-type equipment has higher applicability in the soft base sections. Crawler cranes erect girders with better foundation requirements than automobile cranes, giving full play to the characteristics of crawler stress dispersion and saving erection construction costs. In this case area, the bridge dispersion construction project can give full play to the characteristics of the crawler crane.
1 Project overview
The starting and finishing mileage is K37+394～K54+000 with a total length of 16.606km, and the project is located in the flood plain area of Jianghan River and Lake, where the terrain is flat and the ground is less undulating, and the vegetation is developed in the area, and the fish ponds, irrigation canals and ditches are more developed. The soft soil along the route is widely distributed.
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 has been completed and has reached the bearing strength; the matting and bearing have been accepted and their indexes such as elevation, flatness, and levelness meet the requirements.
· The strength of the girders has met the erection needs and reached the design requirements, and the quality of the girders has been accepted to meet the requirements of the design documents and construction specifications.
· Before the installation of the beam slab, the beam transportation lane shall be repaired smoothly to ensure the transportation of the beam slab.
·Measurement and sampling, the location of the beam slab must be strictly determined before construction, and the centerline of the beam slab, the end line of the beam slab, the plane position, and elevation of the permanent support and temporary support shall be reviewed and verified before erection.
· In order to ensure the safe operation of the crawler crane, the foundation must be processed before the crawler crane is hoisted. The foundation of the crawler crane is firstly compacted by replacing the slag with slag, and the upper part of the slag is paved with steel plates and crawler cranes.
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, the deviation between the center of gravity line of the girders and the longitudinal centerline of the vehicle shall not exceed 10mm, the girders shall be placed according to the designed pivot point, and the girders shall not be partially lifted or partially placed, and when putting down the girders, they shall be supported before loosening the hook. The speed of the vehicle shall not exceed 5km/h, and a person shall be responsible for directing the vehicle before and after the beam delivery.
2.3 Beam erection
The crawler crane shall arrange the order of lifting bridge span in the actual situation of the girder frame, but the same span lifting shall be carried out from one side to the other (or middle first, then to both sides). The hoisting speed and synchronous rotation are strictly controlled during installation, and one division number, two observers, one safety officer and two drivers are set on site to implement the task of rectifying the girder erection. Lifting, longitudinal movement, lowering, lateral movement and positioning of prefabricated girders need to be uniformly commanded, coordinated and properly carried out according to the predetermined construction sequence.
· Beam lifting: When the beam is first lifted, a trial lifting should be carried out first. When test lifting, first suspend the beam after lifting it about 10-20cm away from the supporting surface and then make a detailed check on the action of each main stressing part, and after confirming that the stressing is good, then lift it at normal speed.
· Turning: Turn the main crane first, and the deputy crane will follow the main crane under the command of the director, and try to synchronize the two cranes to turn the body.
· Beam dropping: first drop the beam at normal speed, observe whether the beam is balanced or not, drop the beam to about 50cm from the support, drop the beam slowly, stop dropping the beam after about 10cm from the erection height, confirm the position of the beam, and then put it into position slowly.
3 Features of crawler crane girder erection
In this project, two 80T crawler cranes are used for erecting 25m box girders and one 80T crawler crane is used for erecting 13m hollow slab girders. There are 248 pieces of 25m box girders and 840 pieces of 13m hollow slabs erected by crawler crane, which are scattered all over the Jiangbei project line. The crawler crane used in this project has a maximum lifting capacity of 80T, a main boom length of 13-58m, a travel speed of 0.9km/h, a lifting speed of 70m/min and a maximum slewing speed of 2r/min. The crawler crane is flexible in travel, safe in erecting girders and has a small ground pressure, which makes it suitable for scattered bridges and flat terrain areas. The crawler crane has wider crawler belt, smooth walking, and the crawler belt can disperse the self weight of the crawler crane and the load of the girder plate when erecting, so the lifting is smooth and the safety performance is high, which is more effective in the area with flat terrain and soft foundation.