Drywall carts are used to ferry materials around construction job sites. When these carts are overloaded and traverse wood sub-flooring panels, they can cause damage, especially when these panels are wet from exposure to the elements.
If you consult the APA guidelines which can be found in Table 1 of Voluntary Product Standard PS 2, Performance Standard for Wood-Based Structural-Use Panels, APA Form No. S350 (download a free copy here) you can get an indication of static load capacities. While these findings don’t offer accurate measurements of the performance of wood panels on the job site, they can offer some guidelines as to the maximum loads which should be allowed in loaded drywall carts.
The general guidelines state that most panels can withstand a static load of 400 pounds when dry and about 300 when wet.
The standard drywall cart has 2”x 8” wheels which result in a ½ sq. inch of contact area per wheel. Most drywall carts have the capacity to haul 3,000 lbs or 750 lbs per wheel if the load is evenly distributed. This is in excess of the standard capacities.
Overloaded drywall carts can even exceed the design capacity of the entire floor system (joist species, depth, span, spacing and subflooring) so care must be taken to avoid these kind of problems.
If you must haul large carts over your subfloor, try laying a second layer of panels over the first to augment panel strength and to prevent damage.
Care must also be taken when stacking drywall on the floor system prior to installation. Drywall should be laid on the floor with the long direction perpendicular to the floor joists. This will avoid overloading the design capacity of the floor system.