Coils typically were loaded at the car body bolster location for direct load transfer to the freight car trucks then to the rail. The underfame of boxcars, reefer cars, gondola and flat cars structural members consist of a full length center sill and side sills, crossties, crossbearers and end sills. The centersill sides are z shaped or I beams, with top and bottom covers plates welded together in the past riveted this creats a boxed structural member to carry torque,beading and shear loads. The crossbearers and crossties are I shaped structural elements that today are welded to the centersill webs and the webs of the side sill which are C shaped channels. The crossbearers are considered continuous beams because of the vertical plate welded between the inside faces of the center sill web, this plate is in line with the webs of the crossbearers. The crossties are not continuous beams there is not vertical plate welded between the inside faces of the center sill webs. The light weight (Empty Weight) of the car excluding the trucks and live load in this case the coil weights is transferred to the center sill by the crossbearers,crossties, side sill and end sill. Train line dynamic forces from the couplers are transferred to the center sill and side sill either in compression or tension also there are dynamic vertical forces(rock and roll) transferred from the body and truck bolters at the side bearing locations. All loads on the center sil are transferred to the truck bolsters at the center plate locations, using stress analysis the loads carbody, lading and trainline are combined in designing these cars. The sides of reefer cars, gondola cars and box cars are considered as girders in this design analysis. Side posts on gondola cars are panel stiffeners and prevent shear buckling. The picture of the car with the heavy coil loading between the body bolster(truck centers)would have caused the car to collapse, modern coil cars are designed for this this type of coil loading within design limitations. I forgot to mention the old tank cars small gallon capacity than today's stub sill tank cars had the same structural framing as that of the gondola type car framing. Older coal and hopper cars had a full length center sill and angle side sill and end sills, the hoppers were part of the center sill assembly. Their car body sides had vertical side posts and the exterior slope sheets generally had angle welded to then transversely to prevent bulging and possible collapse. All cars are designed using an elastic analysis( stress below yield point of the steel structural shapes and plates benging or allowable shear stress) no plasticity or permanent deformations also inroads are being made on fatigue anaylsis.
The actual stress(bending,shear,buckling,principal using elastic theory) are divided into the allowable yield stress or allowable shear stress(58 percent of yield stress) to determine the factor of safety against AAR recommended standards.
