A workshop for haul trucks gets sized from the truck, and the truck is the wrong unit of measurement.
The truck decides the door and the floor. The component decides the span, the height and the crane — and the component is usually the largest thing that ever comes off the machine and has to be lifted clear of it. A dump body raised for service is a truck problem. A rear axle assembly hanging from a crane above the chassis is a building problem.
1. Start from the component that has to be lifted over the truck
The design question is not "how big is the truck" but "what comes off it, and where does it go".
An engine or a transmission typically has to be lifted out and set down beside the machine. A rear axle or a final drive has to be lowered, moved sideways and put on a stand. A radiator or a hoist cylinder may be longer than the truck is wide. Each of those has a weight, a shape and a required position, and those three numbers set the crane and the clear space around the bay.
The practical consequence is that the useful clear height is measured to the hook, not to the roof, and the useful width is measured between the columns that the component has to pass, not between the walls.
2. Clear span: why one column in the wrong place ruins the bay
A maintenance bay wants to be column-free across the vehicle and the laydown area beside it.
A typical haul truck with its body raised occupies in the order of 10 m (33 ft) of length and 6 m (20 ft) of width, and a bay that lets a crane work on both sides needs perhaps 20 to 24 m (65 to 80 ft) of clear width. Put a column line down the middle and the bay becomes two narrow strips, each of which is too tight for the crane to swing a component.
That puts pressure on the roof structure: a 24 m clear span is a different frame from a 12 m one, deeper rafters, heavier columns, more substantial foundations. It is worth paying for, because the alternative is a workshop that cannot do the one job it was built for.
Where the site cannot afford a single clear span, the honest answer is a crane that runs on a runway along one side and reaches across, rather than a central column line. The reach is a crane selection question, and it is cheaper to buy reach than to buy a column in the wrong place.
3. The floor is an interface, not a slab
A haul truck workshop floor carries more than a truck.
It carries the truck's wheel loads, which are concentrated and large. It carries the outriggers of a mobile crane working inside the bay. It carries the stands and jigs that components sit on, which put down more pressure per square metre than the vehicle does. And it carries impact, because components are not always set down gently.
The design answer is a slab designed for the worst of those, with joints placed away from the working positions and a surface that can be repaired locally. A slab that has to be broken out to repair one corner is a slab that closes the workshop.
The other interface is the pit. A service pit under a haul truck is a hole in the floor that has to be drained, ventilated and safe to walk in, and its edges are where the slab detail matters most. Precast or cast-in-place, the pit has to be designed with the slab rather than added to it.
4. Doors, and the vehicle that arrives with something on its back
Door sizing is usually taken from the truck. It should be taken from the truck in its worst arriving condition.
A machine that arrives with a raised body, a loaded bucket, a mounted ladder or an attached implement needs a door that clears all of it. On a maintenance workshop this is common rather than exceptional, because the machines come in as they are, not as the catalogue shows them.
Door height in the order of 9 to 10 m (30 to 33 ft) is not unusual for this reason, and it changes the gable end from a wall into a frame. That frame has to be designed as a portal, not as a braced wall with a hole cut in it — a large opening removes the panel that was providing the stability, and the structure then relies on whatever is left.
5. Services: air, oil, power and the things that hang from the roof
A heavy vehicle workshop has a dense set of services above the working area, and they all want to hang from the same roof.
Air lines, lubrication lines, welding sockets, task lighting, exhaust extraction and the crane all occupy the space between the hook height and the roof. If the roof is designed only for the crane, the rest gets added later by drilling whatever is convenient, which is how a purlin ends up carrying a load it was never designed for.
The useful approach is to put a service corridor in the design: a defined zone above the crane envelope where the services run, supported by members that were sized for them. That also keeps the services out of the crane's path, which is a safety question before it is a structural one.
6. What I want before drawings
- The largest component removed, its weight, and where it must be set down.
- The crane type and its working envelope, including the hook approach at both ends.
- The vehicle's worst arriving configuration, for the door.
- Wheel loads, outrigger loads and the weight of the stands.
- Whether a pit is required, and how it drains.
- The wind speed to be used, taken from the applicable code at the project site rather than a round number, plus the large door and ridge detail — a workshop with a 9 m opening at one end is loaded internally, and the fixings around that opening are where a storm finds the building.
A haul truck workshop is built around the component, not the truck. Get the component and the crane envelope right, and the truck will fit inside whatever you build.