Floor loading enigmas

MHMS membership offers you the chance to read up on topics such as building codes and materials handling system loading.

By -- Modern Materials Handling, 6/1/2000

Whether one is selecting equipment, choosing shelves or racks, or, in general, designing a warehouse, the materials handling professional must continue to educate himself and remain current with technology.

Materials handling is a technical profession, requiring its practitioners to be very knowledgeable. One of the benefits of membership in the Materials Handling & Management Society (MHMS) is the access provided to technical articles such as the one excerpted below.

If you would like to read the entire article and also have access to other articles that are available on the members' only site, visit www.mhia.org/mhms .

Loading enigmas. The article excerpted here sheds some light on a few confusing issues pertaining to loads and load requirements. These issues come up on a daily basis in our industry.

In general, all products should be designed to carry the loads intended to be deposited upon them. However, in floor loading, some building codes dictate specific loading requirements that far exceed the actual intended use of such floors.

In the case of mezzanines, the codes now state that the design load should be either 250 lbs./sq. ft. for heavy storage or 125 lbs./sq. ft. for light storage.

A code requirement of 250 lbs./sq. ft. is equivalent to depositing 2 pallet loads, weighing 2000 lbs. each, in a stack throughout the floor of the mezzanine. A 125 lbs./sq. ft. requirement is equivalent to loading the structure throughout with 40 ft. long semi-trailers, each fully loaded to 40,000 lbs.

A more appropriate division of code requirements for mezzanines would set up these load design limits: 250 lbs./sq. ft. for heavy storage, 125 lbs./sq. ft. for medium storage, 75 lbs./sq. ft. for light storage (assembly operations, conveyor-support areas, and the like), and 60 lbs./sq. ft. for office and maintenance platforms.

Pallet racks. Other criteria that enter into play for storage racks are:

• Maximum unit load, the load of one fully loaded pallet;

• Average load, the load of a normal filled pallet;

• Percent utilization, the percentage of the storage system that is full at any one point, and,

• Vacancy factor; which is the opposite of utilization.

In any storage application there is always a maximum unit load, a minimum unit load, an average unit load, and a percentage utilization that affects these loading requirements.

For example, average utilization in a grocery warehouse is 80%. In records storage it is 95%. And in freezer applications it could be near 100%.

The difference between designing (a) a rack system with the maximum pallet load deposited on every pallet position versus designing (b) a system assuming average loading and percentage utilization may be that the rack design for (a) is capable of holding loads twice as heavy as necessary for (b).

It is imperative that all loading criteria and the specific application be taken into account when designing such systems.

The Materials Handling & Management Society (MHMS) exists to enhance the proficiency of the materials handling professional; to promote the efficiency and the dissemination of knowledge concerning the field of materials handling; and to provide innovative, quality educational programs and forums for its members.