Crawler cranes

How does Crawler cranes work, step by step?

1. 1

   Step 1: Establish whether the project can house the machine

   Before a crawler is selected the team checks the things that most often rule it out: is there a clear area big enough to assemble it, can the delivery vehicles reach that area, is there room to lay down the boom sections, and will the ground carry both the crane and the assembly crane. On open infrastructure, industrial and energy projects the answer is usually yes. On a constrained city centre plot it is usually no, and the project ends up with a tower crane or a large mobile instead. Establishing this early avoids designing a lifting strategy around a machine that cannot get in.

2. 2

   Step 2: Design the working platform and the travel route

   The crawler platform is a designed structure, not a layer of stone. The temporary works designer specifies the build-up, the formation it sits on, any reinforcement beneath it, the gradients the machine can climb and cross, and the stand-off from every excavation, basement, culvert and buried service the route passes. Because the crane travels, the whole route is designed and not only the working positions. The platform is certified in writing before the crane arrives, inspected while the works run, and repaired and re-certified when track traffic ruts it - platform failure under tracked plant is a recurring cause of serious incidents.

3. 3

   Step 3: Deliver and assemble under a lifting plan

   The crane arrives on many vehicles over a planned sequence of days, and is built up by the supplier's specialist erection crew with an assist crane. Boom and jib sections, counterweight, track frames and any superlift are placed under a lifting plan of their own. The project provides the laydown, the ground, the exclusion, the traffic management for the deliveries and the time. Weather governs the operation, and the erection plan carries the criteria for stopping. Getting this into the programme honestly is important, because a crawler assembly compressed into an optimistic window is a bad start.

4. 4

   Step 4: Configure the crane for the work it will do

   A crawler is set up in a configuration - boom length, jib arrangement, counterweight and any superlift - that is chosen for the lifts it will actually perform. Changing that configuration later is a planned operation, not a quick adjustment, so the appointed person looks across the whole campaign of lifts and picks an arrangement that covers them. Where a project has a small number of exceptional lifts and a great deal of routine ones, it is often cheaper to configure for the routine work and bring in a separate machine for the exceptions.

5. 5

   Step 5: Lift, and travel with the load where the plan allows it

   In service the crane works like any other, with trained slingers and signallers and lifts planned by the appointed person. Its distinguishing capability is that it can pick a load and track with it to another position, which suits erecting long runs of steel, walking precast units along a viaduct or feeding a piling operation. Travelling with a load is planned in its own right: the route, the gradients, the ground condition and the load position are all covered, and the platform along that route is the same certified structure as at the standing positions.

6. 6

   Step 6: Keep the platform and the machine under inspection

   A long crawler campaign is a maintenance regime as much as a lifting operation. The platform is walked and inspected on a set frequency and after heavy rain, ruts and soft spots are repaired, and drainage is kept working so water does not sit under the tracks. The machine itself is subject to daily checks, periodic inspections and thorough examinations by competent people. Where the crane stands close to an excavation that is being deepened as the project proceeds, the stand-off is re-checked against the current geometry rather than the geometry at the time the platform was built.

7. 7

   Step 7: Dismantle and reinstate

   Dismantling needs the same assembly area, the same assist crane and the same planning as erection, and the area has to be protected in the logistics plan so it is not built over in the meantime. Once the crane leaves, the platform is broken out or incorporated as the design allows, the formation is inspected, and any ground disturbed by the works is reinstated. On projects where the platform sits over the permanent works, the removal sequence is agreed at design stage rather than left to the end.