Maybe this will help:
Dimensions of Flatbed Semi Trailers: Composite Platform
The composite platform trailer measures 48’ x 102” and weighs 10,600 lbs. The flat bulkhead is 48” high. The side structure consists of 5/16” aluminum side stake pockets on the 24 centers. The depth is 1 5/8” x 3 ½” x 4”.
The king pin is situated 36” from the front. The main beam is fabricated steel (grade 130KSI). The flanges are 3/8” x 5” with high tensile 25” web that comes with a 2 ½” arch. The floor is 1 1/8” aluminum with four apitong wood nailing strips. It is rated at 53,000 lbs within a 10’ area.
From this
site.