Loading requirements, column spacing, flexibility of design, deflection, seismic considerations at the project location and supporting sub-structure must be considered regardless of the type of mezzanine.
A uniform load is one that is spread out evenly over the deck surface. A uniform load can be determined by dividing the total load [live applied] load plus dead weight. (decking, framing, sprinkering, lighting etc…) by the area of the deck surface.
Example: A load of 12,500 pounds is going to be spread equally over a 10′ x 10′ area. The uniform live load would be 125 lbs. per square foot: (12,500 lbs. / 100 sq. ft. = 125 PSF)
In this example the mezzanine would be designed for the 125 PSF load. Code considerations and future plans also need to be considered in live load calculations.
Special loading conditions should also be taken into consideration during design. Pallet landing areas, heavy machinery, shelving, pallet rack or other items need to be identified during planning. These conditions may result in very heavy point (concentrated) loads under shelving, rack posts, or legs supporting machinery. Pallet loads tend to be uniform over a relatively small area and can result in a higher design load requirement in areas where they may be located. Any of these conditions may result in the requirement for heavier or supplementary framing under the load location.
Another type of load is dynamic loading which can be induced by rolling platform trucks, pallet jacks or carts.
The distance between mezzanine column supports will affect the cost of the project, the amount of deflection, the depth of framing steel, the column load on he supporting floor and the degree of traffic movement under the mezzanine.
Deflection, whether horizontal or vertical, should be controlled within acceptable limits determined by the intended use of the structure. Too much horizontal deflection can be give the sensation of the structure swaying. Excessive vertical deflection may result in a bouncy or springing sensation on the deck.
Horizontal deflection is usually controlled through the use of properly designed connections, knee braces, or increasing column and base plate sizes on small structures. Mass and weight will play a role in controlling horizontal deflection of larger projects.
Vertical deflection is determined by considering the actual load being applied together with the span, spacing and strength of the supports.
Design flexibility encompasses all aspects of the intended use of the structure. Will it be used for storage, offices, manufacturing, conveyor equipment support or a combination of uses? Is the loading requirement uniform or concentrated? Are there obstructions or fixed building characteristics which must be considered in the design? Will the system size be increased late on?
Most mezzanines can be built using standard designs with little or no alterations. Some situations will require custom applications.