I have minimal engineering knowledge. Air speed resistance is linear with surface area as is static pressure from a standing body. A box girder under pressure is not simple. The bone in a skull is a beam of 2 layers of cortex about 2mm thick with trabeculae connectors about 4mm. Surgical chisels are 2mm thick or less to avoid side deflected shock, cracking and so jamming the chisel in surgery. A razor blade striking bone cause erratic cracking from the tip. An analogy may be a naval destroyer with sharp bow hitting a wood wharf with timber piles and cross-timbers. A broad merchant ship may have twice the width in the bow but the effect of high speed wharf collision may not be just half the penetration. The box girder wharf may spread the force out wider causing a shallow complex distortion. The collected broken timbers may further broaden the front force . Could the final effect be a damaged area that is 3, 4, 5 times the width of the merchant ship? A skull has been excavated with excised bone and an Australian Aboriginal wooden sword-blade is assumed to be the cause. These are about 5mm thick at 10mm back from edge but the smooth excision fracture looks like a metal sword cut ( say 3mm thick). Any comments on the stability geometry of box girders will be appreciated .