Capacity is one of the most critical specifications to determine when selecting the dock leveler to use in a loading dock installation. For Pentalift dock levelers, the capacity indicated on the serial number plate, quotation, or order 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 based the specific application(s). Improper and too low capacity selection will lead to many unwanted issues including dishing of the dock leveler deck plate, to 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 manufacturer. Additionally, dock leveler manufacturers will make design recommendations, including the recommended capacity. To provide the recommendations the manufacture will require specific information on the application. The information requested may seem substantive and unimportant however complete information is vital to properly determine and provide appropriate recommendations.
Typically capacity ratings for dock levelers range from 25,000lbs. to 80,000lbs. Over 95% 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. The 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 considers the dock levelers capacity based on the load of the dock leveler being in motion (dynamic). The dynamic capacity considers a range of forces that will be applied to the dock leveler due to movement and impact multipliers. These movement and impact multipliers will dramatically increase the actual loads being applied to the dock leveler structure. Some factors considered in dynamic capacity considerations are: Fork lift load, fork lift speed across the dock leveler, percentage of grade that the dock leveler deck is at as the moving load crosses it, frequency of use, if the fork lift is turning while on the dock leveler, attachments on the fork lift that might multiply the load, number of fork tires, width of the fork lift tires. There can be other dynamic factors to consider beyond those listed here. 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. In many cases it results in dock leveler replacement.
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:
Weight of the heaviest fork truck to be driven across the dock leveler: 8,824 lbs.
Weight of heaviest load to be handled by the fork truck: 2,000 lbs.
Number of wheels: 4
Loads/Trucks per shift: 2
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 onto the dock leveler and transitions to climb the angled deck assembly of the dock leveler. The dynamic total load multiplier should be adjusted higher accordingly. {We should see if we can add some information on inclines targets)
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. This is addressed by applying a dock leveler with a thicker deck plate. 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. Future use and requirements should also be considered. A customer using a light fork lift today could be using a heavier fork lift with a heavier load in the future Increasing the dock leveler capacity is relatively inexpensive in relation to the overall cost of the dock leveler.
Based on the above, it is very evident that loading dock capacity is a serious and significant subject. If you want to know more about calculating dock leveler capacity, please contact your Pentalift Representative.
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