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Dock Leveler Design, Capacity and Install:
Our factory trained customer service reps, installation managers and technicians all work together to create the ideal loading dock design, installation or repair for any industrial or commercial applications.
A dock leveler forms a ramp to bridge the distance between the dock and truck. It must be able to compensate for the up and down movement of the trailer during loading and unloading. A dock leveler must support extremely heavy loads, service a wide range of truck heights, and compensate for tilted trucks. A dock leveler includes a ramp and a lip. The ramp is hinged at along its rear edge, and the lip is hinged at the front of the ramp. To use a dock leveler, raise the ramp. The lip will swing out. With the lip extended, lower the ramp until the lip rests on the truck.
The three common types of dock levelers are Recessed dock leveler, Edge of dock [ E.O.D] and Vertical storing dock leveler. A recessed dock leveler is installed in a pit formed in the loading platform and is generally a minimum of 6 ft long . An edge of dock dock leveler is normally installed on the face curb of the loading platform. Vertical storing dock Levelers Available in both hydraulic and mechanical models. Units rise above concrete floor extending to the loading dock. Flat plate option is welded to embedded channel.When it’s time to replace loading dock equipment in any size facility, a performance review is a major planning step. Consider the following questions on dock doors:
[ A] Importance of proper installations for loading dock equipment
A very high percentage of field issues with loading dock equipment can be directly attributed to improper or incomplete installation as well as a lack of proper maintenance. The equipment design is a result of significant engineering and development efforts. The designs have been proven in real world loading dock environments to be extremely reliable. Deficient installations and / or poor maintenance will result in compromised function and operation of the equipment. In some cases it can result in damage or worse, create a safety hazard.
Some errors or oversights experience on a consistent basis are:
- Not following the supplied installation instructions. It is important to follow and complete every step of the documented process.
- Assuming the installation of equipment is the same as the installation of a different manufacturer. This issue is more prevalent with experienced installers, accustom to installing another manufacturer’s product. While similarities exist between all manufacturers of dock equipment, no two are identical. Assuming equipment follows the same installation procedures as a different manufacturer is an unnecessary and potentially costly mistake.
- Missing the vertical weld on dock leveler back frame angle. The vertical weld is important to the installation. It is important that it be made.
- Missing the requirement to remove the shipping bracket tab on the front frame of the dock leveler.
- Missing the requirement to remove the angle on the dock leveler frame used for fork truck handling during shipping.
- Missing the installation of shims to support the dock leveler. Shims are required to be installed in all the required locations indicated in the installation instructions. When shim points are missed, the heavy weight of the fork lift load is transferred to equipment locations not engineered to support the weight. This will result in equipment malfunction or damage. When it comes to loading dock leveler design , capacity, and safety, well thought out loading dock equipment let companies avoid delays, minimize accidents, prevent product damage, meet schedule and ultimately , safety of the customers. It is important that you choose loading dock system is the right size for your dock, offers sufficient load capacity to enable it to operate, and it is safe. You will also need to ensure that the Loading dock system you choose is regularly maintained .
To ensure proper capacity selection, consider these factors:
1 What is the maximum lifting capacity of the fork lift in the facility ?
2 What is the maximum forklift weight[ with battery] in the facility ?
3 Does the fork lift have any attachments ? If so add the weight of the attachment to the weight of the forklift.
4 Fork lift type three wheel / four wheel ?
5 What speed are the vehicle travelling ? 4 mph or less , over 4 mph ? .
6 Fork lift direction onto the dock leveler ; straight or angle approach ?
7 What is the height difference between the vehicles and the dock ?
8 Trailer traffic volume : Light [ 1- 3] Moderate [ 4- 8] Heavy 8 or more ?
9 Number of shifts per day : one , Two, or three.
Calculating Loading dock capacity
Add the gross weight of the load lifting vehicle and the gross weight of the load
For minimal or light usage multiply that by 2 [ not more than four trucks per door per day , 5 rollover cycles per vehicle example
Forklift gross weight is 8,000lbs = gross load is 4,000 = 12, 000 X 2 = 24,000lbs
For normal to heavy usage , a multiplier of 3 to 4 should be applied . [ not more than 8 truck per door per day that is 20 rollover cycles per vehicles .
For applications of higher frequency , greater grade, and higher speeds, a multiplier of 4 to 5 times the total gross load should be used.
We encourage you take the required actions within your organization to ensure all installation procedures are completed as specified in the owner’s manuals and installation instructions. You should also emphasize the importance of routine maintenance with your customers and set up periodic maintenance programs.
[B ] Dock Area Design
Dock area design requires the consideration of the following variables
- Truck / Trailer bed height
- Air ride suspension
- Ocean shipment containers
- Dock approach
- Apron space
- Dock positioning
- Dock height
- Door size
Truck / Trailer bed height
Truck / trailers are built with a range of different truck bed heights . A good loading dock design will accommodate the different truck bed heights that come to dock.
A typical loading dock may at some point , services every type of vehicles on the road . It is essential to take into account the dimensions of the trailers that will be visiting the loading dock. with height frequency. This determines the most appropriate elevation for the dock itself. .Secondary consideration must be given to the dimensions of vehicles that visit the dock less frequently . In e case of a captive fleet [ one style of trailer] being serviced at the facility , then the choice of design is simple. However due to the range of vehicles on the road and the ever increasing use of ‘ Air ride “ trailers . It is vital to consider all of the possible variations that can occur.
Several trends are leading to lower bed heights, Increasing the need for longer levelers
Today’s trend towards wider , lower , higher capacity trailers has lead to the need for longer levelers . Years ago 6’ leveler lengths were standard. Now 8’ and 10 ‘ length are common . These levelers can more safely and efficiently serve the newer trailers.
Low Profile Tires
Truck using low profile tires are becoming increasingly common today. The old standard 24” wheel has been replaced by 22.5 “ wheel, and tomorrows standard could be 19.5 “ wheel. This trend means lower trailer bed heights as much as 5” to 8 “ lower. High capacity or high cube trailers are designed to carry more cargo and have 6’ – 18 ‘ lower bed heights than standard trailers .
Air Ride suspension Vehicles
Vehicles equipped with Air ride suspension system are becoming the most common suspension configuration. These types of suspension system can cause problems at the loading dock. Although the recommended practice for air ride equipment is o purge or dump the air from the suspension before he vehicle is positioned at the dock, all too frequently this is not done. As a result the bed of the vehicle can lower 6” to 8 “ When a load come on to the truck / trailer . This movement can tear up the dock seals / shelters and the dock bumpers and with certain styles of dock levelers , the lip plate may loos its penetration and contact with the vehicle. In certain cases the lip on the mechanical dock leveler could drop into a pendant position creating a barrier which could prevent the lift truck from exiting the vehicle. The 6 ‘ to 8” downward movement by a short deck dock leveler can create a severe decline which may cause difficulties for the materials handling equipment being used to un load the truck / trailer.
Additionally the range of movement of air ride equipped vehicle , when at the dock can subject the operating components more specifically the hold – down of mechanically operated dock leveler to increased stresses which result in great wear and tear and higher ongoing maintenance costs. Further mechanical levelers equipped with mechanical safety legs can complicate loading / un loading operations since they can prematurely engage and stop the downward movement of the dock leveler deck until the legs are manually disengaged. This is referred as ‘ Stump out “ . A Vehicle Restraint should be considered for loading dock servicing air ride trucks / trailers due to the fact when the air is “ dumped “ the truck / trailer can creep forward there by reducing the lip penetration of the dock leveler.
Important design considerations for loading docks servicing Air – Ride trucks / trailers
- Specify a hydraulic dock leveler to minimize ‘ Wear and Tear “ on leveler component.
- Specify a longer deck length dock leveler to minimize the incline / decline
- Specify steel faced laminated dock bumpers for durability and long service
- For dock seals or shelters, specify inflatable models
- Avoid edge of dock type levelers or dock plates which cannot accommodate the “ float “ typical with air ride vehicles
- Specify Vehicle Restraint to prevent trailer creep and maintain lip penetration
Ocean shipping Container
Facilities that must accommodate ocean container freight need to be particularly flexible in terms of the truck bed heights that will need to be accommodated.. Ocean containers and refrigerated containers can have trailer bed heights of up to 62 “ . At the same time these facilities may service frequent deliveries / pick ups by tailgate trucks and low bed trucks. The height difference can be extreme as 30 “ at the low end and 62 “ at the high end . Consideration must be given to multi – height dock designs or to the installation of a hydraulic dock leveler or an elevating dock.
Benefits of Projected / Cantilevered Pits For Dock Levelers Installations
Protect buildings, vehicles and dock equipment from impact by projecting the dock leveler pit. Projecting the pit is often referred to as cantilevering the pit as well. Declining driveway approaches are very common at the loading dock area, incoming vehicles are backed into position at an angle determined by the percentage of walls the decline. The most effective method to address this situation is to project the dock leveler pit forward; the amount of projection is determined by the percentage of the driveway decline. Projecting the dock leveler pit at the onset eliminates damage caused by vehicle impact to the building and the resultant need for aftermarket bumper extensions, longer hinged lip assemblies etc. to address this condition. At loading docks equipped with dock seals, the dock seals can be tapered (more projection on the bottom than the top) to suit the percentage of decline, this assures an efficient and even top to bottom seal without putting undue stress on the building
The dock approach is the area used when backing vehicle into position. The area can be level approach, declined approach [ slight angled toward the building ] or an inclined approach [ slightly angled away from the building ] An ideal design is slightly inclined approach that does not inhibit the positioning of trailer, but allows water run off away from building. This also helps to prevent the potential of damage to the building from trailers that that are severely angled when positioned by jockey trucks. In most cases severely inclined or declined approaches are undesirable.
Declined approach areas are constructed when the floor of the building is even with the exterior grade level. To achieve a proper dock height for truck loading/ unloading operations. the approach to the dock need to be built incorporating a decline to the building. There are some issues or concern with declined approach to the dock . These include: difficult snow removal, water drainage problem, builds up debris and high impact forces to the dock. There are also the potential serious damages to the building wall from impact by the top of the trailer.
Due to the slope of the approach into the dock truck backing into the dock can generate severe impact forces from only a short distance . Increased bumper projection or a projected dock must be provided to avoid building damage. Special consideration must be made when incorporating other dock equipment, when there is an inclined approach to the dock . Dock seals need to be tapered. Effective sealing will not be accomplished and damage to the dock seals is likely may happen. Vehicle restraints must also installed with sufficient projection to ensure there proper operation and effectiveness.
For vehicle restraints that mount to the face of the loading dock , consideration must also be given to the truck bumper height in relation to the fully lowered height of the vehicle restraint. It is important to confirm that the Rear impact guard [ RIG] will not impact the vehicle restraint as the truck back into the loading dock. Depend on the elevation of a specific approaches can increase the probability of concerns in this area.. When reconstructing an existing building , it may not be possible to protect the dock . In such situation it is best to protect the bumpers by the use of build out blocks . The build out blocks should be manufactured and supplied by manufacturer of the dock leveler.
Determining the grade
The required projection is determined based on the percentage of grade . To calculate the grade measure the difference in height from the dock to fixed point approximately 50’ directly out from the dock. Divide the height difference by the length measured using inches [ eg 18” difference over 600” distance 18 / 800 = 0.3X 100= 3 % grade ]
Use the following chart to select the proper dock or bumper projection
Change in height in 50 foot distance from dock face
6” 12 “ 18 “ 24 ‘ 30 ‘ 36 ‘ 42 ‘ 48 ‘
Dock or bumper must project Minimum
5” 6 “ 7 “ 8 “ 9 “ 11 “ 12 “
- For intermediate dimensions use this chart but round up to the higher value .
- Understanding Loading Dock Capacity
- Make sure that the leveler you select has the structural strength to handle the gross weight, speed and frequency of use of your materiel handling equipment. Choosing the right capacity will help you get more productive trouble free years from your dock leveler investment. Evaluate these factors to help determine proper leveler capacity Frequency of use , determine how many trucks will be serviced at that dock opening per day, and how many loads per truck. This can greatly affect the life expectancy of your leveler.
- Gross Load weight
- Combine the weight of your heaviest capacity lift truck, including attachments, plus the weight of heaviest load to determine gross weight
Fork lift capacity [ LBS ] Fork lift weight Empty
Gas / LP Electric with battery
|3,000 – 3,500||5,500 – 7,400||6,500 – 9,700|
|4,000 – 4,500||7,400 – 8,,500||9,000 – 10,500|
|5,000||8,500 – 9,500||10,000 – 12,000|
|6,000||10,000 – 11,500||11,000 – 14,000|
|7,000||12,500 – 13,500||12,500 – 14,500|
|8,000||13,000 – 14,000||14,000 – 15,500|
|9,000||14,000 – 16,000||N/ A|
|10,000||15,000 – 17,000||16,500 – 18,500|
|12,000||16,000 – 19,500||18,000 – 21,000|
|15,000||18,500 – 22,000||N/ A|
- Angle of leveler ramp, consider the typical ramp angle for most of your operations. The greater the angle , the more impact force the leveler must absorb. Fork lift speed how fast your fork lift travel ? The faster they travel more stress impact your leveler face
Capacity is one of the most critical specifications to determine when selecting the dock leveler to use in a loading dock installation. The capacity indicated on the serial number plate refers to the amount of weight that can be evenly distributed across the deck of a dock leveler in the stored position.
It is extremely important to consider and properly calculate the appropriate capacity of a dock leveler needed for a specific application(s). Improper capacity selection can lead to many unwanted issues ranging from the dishing of the dock leveler deck plate, to serious structural failure, which can lead to personal injury or death. The important difference between static and dynamic capacity is frequently misunderstood. When determining the appropriate dock leveler capacity, it is extremely important to become knowledgeable in capacity calculations or utilize the design templates and guidelines provided by the dock leveler.
The configuration of the are required to maneuver and position trailers into places is called the apron space Planning apron space requires recognizing trailer movement and the amount of room it take to achieve that movement. Traffic flow and vehicle length are key factors for consideration. [ ie a truck with an overall length of 70’ requires a minimum apron space of 150’ ] If the apron area is to be surfaced with asphalt , a concrete landing strip must be poured . In warm temperatures, the landing strip will prevent the trailers landing gear from sinking into the asphalt when spotted. At the minimum , size the landing strip for the longest trailer that will visit he deck less 7 feet . A gravel covered apron space should be avoided because it create uneven and unsafe conditions.
A simple guideline for determining apron space is to take the sum of the longest possible combination of truck and trailer lengths and multiply this dimension by two . It is also recommended to add a safety factor of 5 ‘ to 10 ‘ depending on the available room. Remember to always use the longest combination of truck and trailer length dimension. Keep in mind that trailer jockey trucks should not be used to determine apron space , unless used exclusively , because they require substantially less room to maneuver than standard over the road trucks .
Dock positioning involve the physical layout of the dock doors and levelers. The most common dock arrangement is a flush wall with doors spaced on at least 12 ‘. If special trailer frequent the facility, door spacing may need to be increased. Twelve-foot centers allow for an overall truck width of 10’ including side mirror. Narrower spacing is possible when room is limited. When incorporating narrower centers, give consideration to common member dock seals and shelters. Enclosed docks are generally used when Climate Control, Product protection, Security and or overhead lift capabilities are required. They are not common choice due to high construction costs and vehicle exhaust pollution considerations. Where space is limited for vehicle positioning a saw tooth dock arrangement may offer a solution. The building wall is generally set back leaving the dock open and unsheltered from the outside environment. For this reason a canopy should be utilized to offer employs and products protection. One disadvantage of saw tooth docks is the amount of internal floor space taken up.
The dock leveler is intended to accommodate the differences between the loading dock height and the truck / Trailer bed height.. Longer dock levelers will accommodate greater height differences. The longer dock reduces the angle of incline / decline that results when the dock leveler is positioned. The height differential between the loading dock and the trailer bed and the potential for “ float “ of the truck / trailer bed during loading / unloading are time is consider importance in dock area design. Optimal dock height plays an important role in guaranteeing smooth product transfer from vehicle to building and viiee versa . Vehicle beds may range from 30”, to 62 ‘ in height . The question is ‘” what vehicles will be serviced at the facility with greatest frequency and how much will these vehicles “ float “ during loading / unloading operations? . When these questions answered all or majority of the dock should made to accommodate this bed height . A dock area should be flexible enough to accommodate any vehicle. The most common height in the range 48 “ – 52 “.
Improper applications and use of dock levelers , where there is severe grade difference can result in product damage and cause significant safety issues. The stress created by significant incline / decline for the dock equipment can contribute to the premature failure of both the dock levelers and materiel handling equipment in use. Customized dock levelers can be made to suite unique applications and offset the height difference. many manufactures do not offer levelers over 12 ‘ long. We can provide dock levelers up to 20 “ long or customize to meet your needs and application.
Tailgate trucks are the most difficult to accommodate at standard loading dock. Before loading / unloading can be done , the tail gate must be lowered . Once lowered it may be impossible to back the trailer close enough to the dock before impacting the dock wall .[ Note : some powered tailgate retract below the serviced at normal dock areas ] The solution to this situation is to use a self supporting pit design. The dock leveler pit is poured three sided , open to great level. A step is made at the rear of the pit to support the back frame assembly of the leveler . Steel support brackets called chairs are poured into the concrete or welded to the front curb angle to support the frond channel of the leveler. The open pit design also facilitates the easy removal of debris build up from under the leveler , there by improving sanitary conditions
Selecting the proper door size is essential when planning the loading dock. Improperly sized doors can create logistical headaches, reduce efficiency and result in product damage. Consideration must be given to both the variety of trailers that will visit the dock and loading method. Planning now for possible future development / change can save time, money and frustration.
Most older trucks / trailers on the road are at least 96 “ [ 8’ ] door width can service these trucks. But maneuvering room is limited . Another concern with96 “ [ 8 ‘] door width is off center truck positioning. This can lead to further reductions in efficiency and even result in the required to re position the vehicle. Ideally 108” [9’] wide doors should be used to service 102 “ [ 8’ 6” ] wide trailers. Side by side palatalizing is simplified and the potential for product and door damage is significantly reduced. A 108” [9’] door width can also accommodate the unplanned servicing of many oversized loads. For special applications with oversized loads a 120” [ 10’ ] wide door can be incorporated. Wide door s requires more building space which can create a problem when room is restricted.
Doors should be spaced with 12’ centers. This distance will accommodate the majority of vehicles, allow for installation of dock seals / shelters, and the mounting of two way communication light systems.
Trailers can range in heights from flatbed units [approximately 48” ] to closed vans [ 162 “ ] from ground level. . The highest internal height for product loading is approximately 114 “ height , Depending on the application , there are three basic heights that are typically specified keep in mind that the common dock height is 48” – 52 “ normally. Doors 96 ‘ [ 8’] in height can accommodate many loading / unloading operational size. But they do not facilitate full floor to ceiling loading of the trailer with products. The need to optimize the available height [ floor to ceiling ] in a trailer in an effort to minimize freight costs, this need makes the 96 “ [ 8’ ] high door a less desirable choice.
A 108” [ 9 ‘ ] high door permits improved floor to ceiling loading of product, because a higher load can easily pass under the door opening. Fuller and tighter loading is possible with a reduced risk of product damage due to product impact with the door header. The 108 “ [ 9’ ] door . This gap can be sealed with an appropriately sized dock seal or dock shelter. A third typical door height is 120 “ [ 10’ ] . Wider or higher door do provide for even greater loading / unloading flexibility. However they also enlarge the open area between inside and outside there by increasing the potential air exchange and heat/cold loss . The most versatile door size is the 120” [ 10’ ] height will service the full range of loading unloading operations. Of all heights including high cube trailers and ocean shipping containers.
Special considerations should be given when choosing a dock seals or shelter for 120 “ [ 10 ‘] high door . A properly sized dock shelter or an inflatable dock seal for a 120 “ [10 ‘ ] high door provides the greatest degree of unobstructed access to the rear of the truck / trailer. Door size can be specified to any configuration required . Keep in mind of possible future expansions and changes.
Typically capacity ratings for dock levelers range from 25,000lbs. to 80,000lbs. Over 90% of all dock leveler installations fall within this capacity range. It is important to understand that these ratings are static ratings. Static Capacity is an engineered calculation of the dock leveler’s structural capacity. This calculation determines the dock leveler’s capacity to support an evenly distributed “still” load placed on the platform in the stored position.
Static capacity rating for a dock leveler is an indication of the maximum weight that can be evenly distributed on the dock leveler.
Dynamic capacity is a range of motion (dynamic) which involves a range of forces due to movement that can dramatically increase the effective weight of a static load. It relates to the speed, frequency of use, and percentage of grade, and other dynamic factors while the fork lift is traveling across the leveler during use. Dynamic factors result in a reduction of the capacity rating relative to the static capacity rating of a given dock leveler. The dynamic total load multiplier is a number that the total maximum load to be driven across the dock leveler is multiplied by to accommodate the dynamic loads that will be applied to the dock leveler.
When trying to determine the dynamic total load multiplier factor of a dock leveler the following information needs to be considered:
- The weight of the heaviest fork truck or Material Handling Equipment being used including attachments that maybe placed on the fork truck;
- Heaviest load weight that the Material Handling Equipment will be moving;
- Whether a fork truck has three or four wheels as well as the size of the tires;
- How many loads per shift or per day.
The common dynamic total load multiplier is 2.5 when calculating capacity for standard dock leveler applications. However, dynamic total load multiplier can range from 2.0 to 5.0 depending on the severity of the application and the manufacturer. Since there is no recognized industry standard, manufacturers rate their capacities differently. Some may use lower multipliers to be more competitively priced or leave the impression that their particular dock leveler is stronger than other manufacturers. Variables like fork trucks, fork truck weights, type and speed could create the need to increase the dynamic total load multiplier.
Numbers of shifts, weight of loads, percentage of incline and decline for the leveler can also influence the dynamic total load multiplier. When in doubt it is always better to increase the dynamic total load multiplier. There is no such thing as too much capacity and the cost of increasing dock leveler capacity is low relative to the overall cost of the dock leveler. The cost of correcting an under capacity dock leveler installation is substantive.
Below is an example of how to calculate the capacity rating of a dock leveler:
The weight of the heaviest fork truck to be driven across the dock leveler is a total of 8,824lbs with the weight of the heaviest load included being 2000 lbs. To determine the static capacity rating of the dock leveler add the two weights together: Total maximum weight to be driven across the dock leveler =8,824 lbs. + 2,000 lbs. = 10,824 lbs.
We have now determined the total maximum live load the dock leveler may experience. This figure can now be used to determine the dynamic capacity for the leveler using the following simple calculation:
Dynamic total load multiplier = 2.5 (In this case because the application has a normal set of installation parameters)
10,824 lbs x 2.5 = 27,060 lbs therefore the static capacity rating of the dock leveler required is 27,060 lbs. At a minimum, round up to next available capacity. In this case a 30,000 lbs capacity dock leveler suits the application.
This information can be used for making a design recommendation and to prepare a quotation for the proper capacity leveler. There are other additional factors which also need to be considered in the determination of a safe and reliable loading dock.
Degree of Incline
The typical degree of incline and decline of the leveler deck has an effect on the dock leveler. The greater the incline or decline of the dock leveler in use the greater the impact forces when the fork lift drives over the dock leveler. The dynamic total load multiplier should be adjusted higher accordingly.
Abnormal features of the forklift trucks can require you to increase the capacity of a dock leveler.
Abnormal features of the forklift trucks can require you to increase the capacity of a dock leveler. Three wheel fork trucks or trucks with very narrow tires put more of the weight on a smaller surface area which can cause dishing of the deck and / or broken deck beam welds on a dock leveler. Fork truck speed on the dock leveler plays an important role in capacity. The higher the speed of the fork lift the greater the impact forces generated by the forklift. The standard dynamic total load multiplier is based on a fork truck moving across a dock leveler at 5 MPH. If the speed is higher than 5 MPH the dynamic total load multiplier will have to increase.
It is clear that excess capacity is far preferred to insufficient capacity. A dock leveler that is properly applied and serviced should last structurally and mechanically for many years. Once an under capacity dock leveler has been installed there is little that can be done to increase the capacity. The cost of replacement is significant. A customer using a pallet jack today could be using a fork truck tomorrow. Increasing the dock leveler capacity is relatively inexpensive in relation to the overall cost of the dock leveler.
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