Trailer Deck Point Load and Dunnage Spread

Whether a concentrated load spread on dunnage stays inside a trailer deck's rating, and how many feet of bearing it takes if it does not. Trailer decks are rated in pounds per LINEAR FOOT, because that is how the crossmembers under them are designed: a 48 ft deck rated for 55,000 lb is carrying roughly 1,150 lb on every foot of its length, and it assumes the load is spread that way. A machine standing on four small feet puts its whole weight into a square foot of deck between two crossmembers, which is not what the deck was designed to do -- four 6 by 6 in feet under a 12,000 lb machine is one square foot of total bearing and 12,000 psf into the deck plate, an order of magnitude past what any deck plate carries, and the feet go through. Dunnage exists to convert that point load back into a linear one: timbers run across the deck, perpendicular to the crossmembers, spread the load along the trailer's length, and it is the LENGTH of that bearing along the trailer -- not its width, and not the timber's cross-section -- that divides the load. The most useful output is the last one. A 12,000 lb machine on a deck rated 1,200 plf planned on two 8 ft timbers puts 1,500 plf into the deck at 125% of the rating; ten feet of bearing lands exactly at the rating and twelve feet gives a comfortable 83%. A screen, never a stamp: the trailer manufacturer's published deck rating and concentrated-load rating, and a qualified person, govern.

bearing_pressure_psf = load_lb / (feet_count x foot_area_sqin / 144); linear_load_plf = load_lb / dunnage_bearing_ft; utilization_pct = linear_load_plf / deck_rating_plf x 100; required_length_ft = load_lb / deck_rating_plf.

Trailer deck capacity rated in pounds per linear foot, with dunnage converting a concentrated load into a linear one over its bearing LENGTH along the trailer, by name; the deck rating is the trailer manufacturer's published figure, entered rather than bundled. A screen, never a stamp; the manufacturer's deck and concentrated-load ratings and a qualified person govern.

The spread arithmetic is public. The deck rating and the load's own bearing geometry are entered by the user.

Estimate. AHJ and licensed professional govern.

Field names used by the API: load_lb, feet_count, foot_area_sqin, dunnage_bearing_ft, deck_rating_plf, bearing_pressure_psf, linear_load_plf, utilization_pct, required_length_ft

• Decks are rated plf pounds per LINEAR foot, reflecting the crossmember design and assuming a spread loadtrailer manufacturer deck ratings
• Length divides the load the bearing LENGTH along the trailer divides the load, not the bearing width or the timber's cross-sectionload-spreading practice
• Bare feet go through a few square feet of bearing puts thousands of psf into a deck plate; the psf line is the reason dunnage existsflatbed practice