Designing A Truck Dock
There are a number of things about a truck dock that add up to truck docks needing to be more than an afterthought.
I am not thinking of a distribution center when I say that. The docks are the central focus of that kind of building and will get plenty of attention. I am thinking here of the incidental truck dock that may be a convenience or an efficiency measure. In that case safety is a paramount concern, but every truck dock that isn't part of a professional trucking operation should have a safety focus because people will sometimes use the dock who haven't been trained.
The first design step is to contact a local manufacturer's rep for dock levelers. They can look at your situation and give you great advice about the best way to set up the dock.
Here are a few things to consider about the dock, the building and the equipment:
Determine the range of truck sizes that you are most likely to have using the dock. At the small end of the range, pickup trucks, panel vans and box trucks will have a completely different set of requirement than a semi-tractor trailer. Those differences will be in truck-bed height, truck length, turning radius, and overall truck height.
Trucks have beds that range from 24" to 50" above the pavement. There isn't a standard. Even the weight of the truck's load will cause the height to vary slightly as the truck is loaded or unloaded. The ideal is to locate your floor level within a few inches of the most common truck-bed height you expect to have. However other issues can impact this decision, e.g. the slope of the apron, type of dock leveler and the type of material handling equipment that will be used. A manufacturer's rep can be invaluable in helping to get this right.
Although trucks are limited to 8'-0" in width, the dock door should be larger so that misalignment with the truck placement doesn't reduce the opening into the truck. 8'-6" and 9'-0" are fairly standard widths. The type of Dock Seals (see below) you choose should be coordinated with the door width. Door height is less of an issue. 8'-0" is the minimum and 10'-0" is the maximum. 9' usually works fine.
The gap between the building and the truck-bed and the variation in truck-bed heights require a device to make the transition. A dock board is a light weight plate that rests on the dock floor and spans the gap, resting on the truck-bed. Dock boards are a bad idea. There are simply too many ways to get hurt using one. The solution is a dock leveler. Dock levelers come in various sizes, range of movement up-down, weight capacities, and type of operation - manual and hydraulic. A Manufacturer's Rep. is the solution here, too. Otherwise plan to spend a day researching this $15,000 (+/- $5,000) piece of equipment.
Dock bumpers are another necessary piece of equipment. These are compressible 4"-6" thick blocks used to keep the truck from hitting the building. The truck hits the bumper instead. Amazingly there are a number of choices here, too. Personal preference/experience enters into it. Vertical mounting addresses varying truck-bed heights.
The truck restraint is a safety feature. It is powered into place once a truck is docked and hooks onto a bar that large trucks are required to have. This prevents the truck driver from pulling away from the dock prematurely or the gap between truck and building becoming too large. Truck Restraints may soon be mandatory if they aren't already. People have been killed when the truck leaves unexpectedly.
A dock seal closes the gap between the truck and the building like giant weatherstripping. This is a comfort and energy issue. Seals come in a variety of styles - from fabric shelter curtains that lay against the truck, to cushions that compress, to inflatable cushions. They all need repair or replacement from time to time. They aren't necessary, strictly speaking, for the once a week/month type dock usage.
Let's change the focus to exterior considerations. Here are a few things to consider about locating the dock, covering the dock, clearances, approach and apron.
In addition to the location within the building where it makes sense to locate the truck dock, there is also the consideration of where on the site the dock can be accommodated. The change of grade to accommodate the dock height and the apron needed to maneuver the truck to the dock are big determinants in location. The dock can't go just anywhere.
CANOPY / OVERHANG
Truck docks are used rain or shine. When it is raining, water runs down the face of the building and drips into the dock opening unless you have prevented that with an overhang or canopy. The overhang is preferred because it can usually extend farther over the truck. Canopies get complicated if your wall surface is metal siding. Check Vertical Clearance below.
The maximum height of trucks is 15'-1". This is unlikely to change. Interstate bridges are built with this clearance in mind. Make sure that you can move around the site and under any canopy or overhang. Worst case is snow-covered pavement. So plan on 15'-6" of clear space.
Unlike an automobile, a segmented truck needs to back up so that the driver can see his target from his side window. The mirrors on both sides are useless when backing up. This means that the truck should be driving counter-clockwise to the building, pull past the dock area and back into the dock bay. This is the exact opposite of what you plan for a passenger drop-off. A 'spotter' is often needed to guide the truck driver if he is approaching clockwise with limited maneuvering space.
APRON SIZE AND SLOPE
The largest trucks are 73' long and have a 50'+ inside turning radius. The apron can get really big if anything else is in the way, like another truck parked in the next dock bay. Truck bays should be a minimum of 12' wide up to 15'. Consider heavy duty concrete for the apron or at least where tires will sit and where they will be turning. Occasionally you will have a real problem with fitting the dock to the site. That's when you cave in to using the 45-degree-dock-trick. The 45-degree-dock-trick, as its name implies consists of putting a 45 degree bump on the building face to orient the dock in a more favorable direction.
I think the ideal slope for the apron is 1%-2% sloping away from the building. For distribution centers they like drains placed between the rear tires and the front tires so that the truck sits dead level at the dock. Do that if you can. When the truck is sitting on a slope of more than 1%, the chance of accidents increases because the pallet jack, or fork lift can roll on its own. Avoid sloping down toward the dock. The top edge of the truck will hit the building wall first. This is hard to design around, and the trucks are not made to come in contact with the building at the top edge.
The main thing to remember (for the last time) is to call in a manufacturer's rep to guide you and to review your drawings in progress. Do that, and also avoid short-sighted compromises that will forever hamper the dock.
You will be happy with the result.
Check out Truck Dock Details too.
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