Bottom Side Rails
Two basic designs of bottom rails are available on FRP trailers and van bodies.
Fig 1 shows one design of single shear construction. The bolts are in single shear because the rail is in two pieces with a rub rail separate from the trailer frame. The bolt-to-frame load is carried through the joint between the frame and panel only. Single shear rails offer adequate strength and allow easy access to the panel for repair. All single shear bottom side rails should have continuous fastener bearing strips on both the inner and outer sides to prevent fasteners from pulling through the panel and to provide adequate clamping force.
Fig 2 shows a double shear bottom side rail design. The double shear design offers significantly greater strength than the single shear design, but it does not allow easy access to the panel for repair.