Loading Dock Design

The loading Dock is a key component of any facility, whether it is a warehouse, grocer, retail outlet, plant, or other material handler. Through a variety of equipment loading docks can speed up traffic and capture costs that add up if left unattended. With careful planning many of the risks and expenditures associated with a design lacking proper safety features can be alleviated. Improving dock function, employee safety, and effective transfer of goods from your facility to its intended destination should be a primary concern of all conscious business owners and purchasers.

Common problems on the loading dock are often rooted in initial design elements which do not take into consideration future dock uses or the evolution of manufacturing and production. Often times docks will have poorly planned approaches, small doorways, excessive slopes, gravel approaches, improper bumper projections, and docks that are too low to accommodate any standard over the road trailers.

By planning for the future steps can be taken to safeguard against large remodeling costs later. The initiation of future planning can take many forms, whether that is installing knock out panel walls for future door expansions, or building your dock to standard height and using wheel risers for smaller trucks. These simple inexpensive concepts can save you and your customer’s time and money further down the road.

Due to the diversity and variations that may exist at the loading dock, any specification, drawings or other material pertaining to the loading dock should be developed and approved by an experienced professional architect and reviewed by an experienced loading dock professional. Follow best practices for compliance to traffic engineering conventions in design to meet state and local codes.

It is important to include in the specifications of any project that the selected manufacture must provide; specifications, approval drawings, installation manual(s), owner's manual(s) and employee equipment training, to the owner.

SAFETY MATTERS

Despite the loading docks potential to save money it has exponential safety risks which can cost your company in excess of one million dollars from direct and indirect costs. Financial hardships affect your tenants, customers, employees and bottom line, for this reason aggressive dock safety practices are considered good business sense.

The figures speak for themselves in 2004 the National Safety Council reported that direct costs from accidents was a $85 billion dollar industry; letting insurance companies cash in on costs associated with medical costs, wage indemnity, and claims administration fees. Dwarfing direct costs indirect liabilities resulting from injuries, damaged equipment, goods, lost production, diminished operation quality, process interruptions, yield losses, replacement labor, overtime, litigation, and higher insurance can mean for every dollar paid to direct costs an additional $5-$10 will be paid over time to indirect liabilities.

Note: It is the employer's responsibility to ensure proper training and operating practices of their employee's.

APRON SPACE

The approach leading up to a bay door, known as the Apron Space, is an area necessary for trucks maneuvering into position at the loading dock opening. When planning this extension of your dock recognizing the needs of current and future potential freight is fundamental to the long term viability of the facility. Factors to consider are the direction of traffic flow, total vehicle lengths received, and materials used for the landing and leading up to the dock.

A simple guideline for determining apron space is to take the sum of the longest possible combination of truck and trailer and multiply the total length by two, then adding an additional safety factor of 5'0" to 10'0" on the outcome. (i.e. a truck with an overall length of 70' requires a minimum apron space of 150’).

Keep in mind that a dock receiving box trucks and trailer jockey trucks today may not be using these in later years. Always consider long term construction in order to avoid costs in later years.

If the apron space is to be surfaced with asphalt, a concrete landing strip must be poured. This is necessary due to asphalts tendency to become malleable under heat, resulting in depressions changing your truck differential to the dock. This is a serious problem which can make a leveler or board ineffective as well as making it difficult to properly secure wheel risers due to uneven ground.

A gravel-covered loading dock apron should be avoided because it creates uneven and unsafe dock conditions.

Note: unless the loading dock is designed to handle peak traffic loads, space must be provided for a truck waiting area. This should be stuated so as not to impede the movement of trucks positioning for docking and leaving the facility.

TRUCK BAYS

Truck bays are a complicated portal requiring many pieces of equipment in order to operate safely and efficiently. Factors which ensure the safe function of those pieces of equipment is relative to dock door displace-ments from each other as well as adequate staging space within the facility.

For docks with multiple loading bays door displacement is crucial to effective loading and as a deterrent to bottlenecking from cramped staging areas. Typically the minimum displacement for doors is 12’ on center of the opening. This provides an overall truck width of 10’ including the mirrors. With greater displacements loading is made more economical, safer, and easier.

When determining the number of loading bays needed to support your product flow, consider the number of trucks received per day, delivery schedules, how many pallets can be loaded or unloaded per hour at one opening, and the number of trailers typically staged at your dock.

Bottle necks inside and outside your facility should always be avoided. Bottlenecking within your dock is the result of too little space for staging; this causes blind spots and reduces the mobility of your loaders, increasing safety risks and lowering productivity. Outside your dock on the apron, bottlenecking occurs when trucks are staged for loading without adequate room for safe departure of other trucks leaving the facility. Another form of restriction from bottlenecking occurs when there is not enough room on the sides of the trailer to safely turn out away from other trucks on the apron. By utilizing a 14’ door differential trucks can safely and effectively exit and couple with the loading dock. This also provides additional space between doors for staging.

When considering what adequate space for staging is, consider the largest freight received at your facility; be sure not to design your dock around smaller trucks if there is a possibility of receiving over the road LTL trailers in the future. A 60' long trailer 8'6" wide requires a minimum of 510 square feet of staging area and can be loaded to a height of 10'0". Note: Each client's staging area requirement may very, so we recommend that you consult with your client to find out exactly how much staging area is required for your project.

DOCK APPROACH

Level dock approach
The most effective approach grade for a loading dock is approximately a 1%-2% incline. This puts the top of the trailer further away from the wall, while also channeling water runoff away from the facility and your product. (Note: when raising the nose of the truck to couple with a tractor the grade is changed, the dock bumper projection must be able to accommodate this change in incline)

Declining & Inclining Approaches
Docks with either of these approaches need careful planning before implementation. First, a declining dock has a tendency to move the top of the trailer towards the wall of the building; this causes damage to your facility and equipment. For inclined approaches the problem is similar, with the ICC bar coming closer to the wall under the bumpers. Second, if the incline or decline is too severe employee, equipment, and product safety come under risk of toppling during unloading & loading. Steep grades increase wear on loaders and can make certain types of equipment like motorized pallet jacks inoperable.

NOTE: A decline / incline dock approach grade should never exceed 10%.

Determining Dock Approach Grade
The required dock bumper projection is determined based on the percentage of grade. To calculate the grade, measure the difference in height from dock level to a fixed point 50' directly out from the dock. Divide the height by the length measured, using inches (e.g. 18" difference over 600" distance. 18/600 = 3% grade). for every percent of slope apply an additional 1” to the basic 4.5” dock bumper projection.

DOCK TYPES

Cantilever Loading Dock Design
In a cantilever loading dock design, the foundation wall (dock face) projects past outside building wall. This can prevent damage to the building wall, should a dock bumper fail.




Enclosed Loading Dock Design
This design often used by package handlers utilizing fleets of box trucks, allows for control against pilferage while improving efficiency and comfort; it also doubles as space for overhead cranes loading/unloading flat bed trucks. It is the most expensive loading dock design requiring greater initial investment and maintenance. A main concern for this type of dock is the need for ventilation, adequate air-exchange, due to the exhaust fumes of motors operating within.




Flush Loading Dock Design
The most common type of loading dock used today is the flush loading dock. This dock shares the same foundation as the wall. When the building wall projects past the foundation due to the use of metal or other finishing material, dock bumper projection must be considered more closely; i.e. bumpers should always be a minimum of 4.5” from the wall, if the wall projects 1” past the foundation where bumpers are mounted, then the bumper will need to have at least one more 1” of projection.




Open Loading Dock Design
United States Postal Service uses the open loading dock design for its delivery trucks with an overhead canopy covering the dock. Open loading docks cannot be heated or cooled and it provides little protection for materials, packages and employees. Due to its exposure to the weather floor drainage needs to be considered, also due to the height OSHA may require; edge markings, run-off protection and hand rails.




Saw Tooth Loading Dock Design
Saw tooth loading dock designs are effective where dock apron space needs to be minimized. The staging area between docks is typically non-usable.

DOCK HEIGHT

Optimal dock height plays a critical role in providing smooth product transfer...The following selection criteria must be considered for a proper loading dock height.

1. Service range of the variety of trucks to be service and mid-point.
2. The maximum grade capability of your client’s material handling equipment, consistent with dock leveler and board length.
3. Dock leveler and board length that can accommodate the height difference from dock to truck, and truck/trailer "float" during loading/unloading.

The average loading dock height is between 48” and 52”. Many facilities may have more specific qualifications for their loading docks which can put them above or below this level. When considering your client’s application determine the highest and lowest truck received, in addition find the average truck bed height (note whether the trailers are refrigerated or not). If the differences in dock height are too great to service all traffic consider options such as wheel risers. This allows a dock to receive standard trailers at a 48” dock height and box trucks which would come in below the operating range of many boards and levelers.

Knowing the maximum grade capability of your material handling equipment can help determine the dock height and dock leveler length. The maximum grade capability of a pallet jack is 3%, electric pallet jack 7%, electric lift truck 10% and gasoline fork tucks is 15%. When planning the dock height always try to strive for the least incline/decline approach to load/unload the vehicles that arrive at the dock, this will provide a longer life for the material handling equipment and the dock leveler.

DOOR SIZE

Selecting the proper door width and door height is critical for a smooth transition of products and pallets from the truck to the loading dock. Improper size of the loading dock doors can create extra-labor for loading/unloading trucks, reducing efficiency causing product/package damage and possible employee injury.

Loading Dock Door Widths

When conducting proper planning for your dock door always take into consideration the maximum legal truck width of 8’6” (without permit). This is important due to several factors, first if your door is 8’ wide an 8’6” trailer with side by side pallets will become difficult if not impossible to unload, second if the truck comes in off centered with the opening, additional repositioning will be necessary; these two factors lead to time lost on the dock and more opportunities for accidents to happen. For these reasons the ideal dock door width is 9’ wide, this reduces the possibility of door track damage, and also provides more room for acquiring pallets seated in the rear of the trailer.

Note: Greater door widths should be considered if wide-load permitted trucks are to be serviced, and at least one door should allow for the greater width, if a future need may require it.

Loading Dock Door Height

There are three standard door heights that are typically specified, 8', 9' and 10' high doors. The 8' high door can accommodate many single high pallet applications, but does not provide full height access to the maximum trailer height. The 9' high door provides improved access to the maximum trailer and load height. The 10' high door height typically provides the best access to the maximum trailer height. However if full access to the back of the truck is required consider the following formula; with the determine the fixed dock height you choose, subtract that height from the maximum trailer height, and round up by the foot, (example: 13'6" maximum trailer height minus 4' dock height equals 9'6"; consider a 10' high door) for full access to the back of the truck.

Note: Greater door heights should be considered if special permit trucks are to be serviced, and at least one door should allow for the greater height, if a future need should require it.

DOCK BUMPER ARRANGEMENTS

For the most comprehensive dock protection, a combination of vertical and horizontal bumpers, provides the greatest protection for both facilities and tractor trailers. For example, an 8’ wide bay door receiving trucks at a straight approach are best protected by 24” high bumpers on either side and a standard 10” high bumper in the center. This allows a variety of trailer heights to be accommodated without the risk of trailers coming in below the 10” bumper centered in the opening. For refrigerated docks, extra length dock bumpers work as a vital component of the door seal effectively controlling air flow from the base of the door when used in conjunction with a dock seal. Overlapping angles are available for use on docks where a continuous bumper is undesirable. 

• Use combinations of bumpers for optimal protection 
• All bumpers have customizable widths
• When installed properly all bumpers are maintenance free
• Always verify the types of trucks being received before planning a loading dock

Bumper Heights

Dock bumper heights are relative to the recycled tire pads used for manufacturing, typically these come in 6”, 10”, & 12” Heights. While the industry standard dock bumpers are built to this, greater heights are effectively achieved by stacking pads on top of each other. This allows for the production of 20”, 24”, & 36” high bumpers.

For best results always choose bumper heights which will best accommodate your traffic and facility. 6” dock bumpers are traditionally used on docks where a lip protrudes from the wall and has a face of 10” or less. 10” dock bumpers are the most widely used for docks where trucks come in at approximately equal heights or when only standard size trucks are received. The 12” Dock Bumper, our tallest single pad size, is a heavy duty product constructed with three pins through the center of rubber slats rather than the two pins used for 6” & 10” bumpers.

Always remember the combination of 20", 24", or 36" vertical bumpers, with standard sizes, provides extended depth protection for varying truck heights; (Fig. 1) or the lower steel members of trailer bodies.  Consider these for docks that accommodate panel and pebble trucks as well as over the road trailers.

Vertical units with steel faces are particularly applicable with truck leveling devices that raise the entire truck to dock level.  The Combination of horizontal units with, (Figs. 3 & 4), vertical units prevents a loaded trailer from dislodging shorter bumpers as the truck bed rises during unloading (Fig. 2).

Dock Bumper Thickness

Dock bumper thickness is the second most important component besides placement of the bumpers. The determinant of bumper thickness is either the slope of dock approach or various obstructions protruding from the dock face. The typical projection for a dock bumper is 4.5”, this is intended for a dock with a level approach & no obstructions around the door way. Bumpers should always place the top of a trailer a minimum of 4” between the tallest trailers top and wall. For approaches sloping down towards the dock greater thicknesses are required.

To measure your slope, attach a string to the floor of your dock and pace 50’ away following the approach of the trailer. Using a line level determine the line drop at 50’. Divide this number by 600 and you will have your percentage of slope. For every percent of slope figure 1” of additional projection on a standard 4.5” bumper projection. For example, a 5% slop requires a 10” bumper projection.

BUMPER INSTALLATION

Install bumpers (Fig 10) 1" to 2" below dock level.  Use 3/4" or 5/8" lag bolts or sleeve anchors; minimum length 3" and use corresponding shield if required.  Use 3/4" "J" bolts with a minimum length of 8" with 1 1/4" projection.

For Open Docks
Open docks without predetermined docking positions, are best suited to a combination of several bumper sizes and placements (Fig.3). When using 36” horizontal dock bumpers maximum spacing should be 24” between units with a minimum of 5” on centers (Fig.6).

• If trucks are approaching at an angle a continuous bumper or overlapping angles should be used to limit the chance of a trailer corner coming in contact with the wall.
• Typically when continuous protection is necessary overlapping angles can provided economical benefits by reducing the number of holes drilled and the number of materials used for installation (Fig. 5).
• Overlapping reduces the spacing between each bumper to 4", and is applicable to any laminated bumper model.
• Overlapping angles on adjacent bumpers increases the protected area.   
• Special-length bumpers to fill out dock spaces are also available.
• For open docks or wide bays, extra-length, one-piece dock bumpers can also be used for maximum coverage and appearance (Fig. 7)

For 8', 9' or 10' Bays
For 8', 9', or 10' bays a variety of combinations exist.  Loading Dock Supply recommends a combination of standard and vertical bumper designs (Fig 3 & 4) for dock protection.

For Refrigerated Doors (with or without dock shelters)
Refrigerated doors generally require a, solid one-piece construction, bumper for a complete seal around the truck and dock (Fig. 7). The same applies to doors sealed to maintain temperatures (Similar results can also be achieved with overlapping angles see (Fig .5). With shelters, the rubber surface of the bumper must extend under the vertical members of the Shelter pad to complete the seal.

For Portable Dock Plates
Effectively use your dock plate by centering a 36” bumper below the door opening, this allows for simple plate insertion even when a truck is already docked. Allow space for your plate legs and mount vertical bumpers at the desired distances on either side.

For Adjustable Dock Boards
When using 14” hole centers, height should be a minimum of 12”. Most boards adequately handle 4.5” & 6” bumper projections without impairing lip penetration into truck opening. Fig 8 shows damage from "short spacing". Fig 9 shows "lateral safety zone" impact absorption advantage provided by longer bumpers.

Disclaimer
Every effort has been made to accurately describe our products and to define their general usage. Determination of the suitability of any product and any application contemplated by the Buyer is the sole responsibility of the Buyer or User. In the event of improper product selection by the Buyer, Loading Dock Supply makes no warranty or guarantee of results to be obtained since use and application by the Buyer are beyond our control. Our goal is to quote you 1.) The "right" bumpers for the application at hand. 2.) To provide customer service that will "save" you money. 3.) To have "satisfied" customers need for all their Loading Dock Supplies.