In this second part of Designing Truck Docks, the focus will be on exterior considerations.
Part one (found here) focused on the truck, the dock, the building and the equipment.
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.