Unless I'm mistaken, the purpose of the bracket is to stiffen the body through tensioning forces (i.e., stretching forces parallel to the sides of the V), not shear or compression forces on the bracket, which as you poit out, it is not strong enough for -- i.e. it will bend. However, it is plenty strong to resist tension forces -- it's steel, and beefy enough not to stretch easily.
If you consider the geometry of the bracket, the underbody, and the attachment points, you can get an idea of what I'm talking about. It resists twisting of the entire body because the dimension traversed by the sides of the V will lengthen if the body twists along it's long axis in either rotational sense. Seems to me it would help quite a bit in resisting this twisting action, stiffening the frame from that particular sort of deformation.
The bracket would also help stiffen the chassis against "saddle" drooping. Remember that all the upward suppport forces bear on the suspension mounts, while there is an equal and opposite downward force due to gravity that is centered roughly midpoint on the car. In a coupe or sedan, the pillars and roof form a very rigid truss structure that resists any sagging due to metal fatigue over time. The convertible is more susceptible due to the lack of the roof structure. The V bracket will help resist this sagging as well.
As you note, however, it is not a strong construct when it comes to compression or lateral (i.e. normal) forces. As such, any opposing bending action (like scraping the bottom) where the force vectors are reversed from typical will result in easy failure of this component.
Dave
obLu said:
Oh I know that's what they're supposed to be there for. But take them off sometime and see how easy they flex. I was commenting on what a waste of space that bracing is since it's so flimsy.