Have you heard the joke about engineers?
Mechanical engineers build weapons. Civil engineers build targets.
I know what you are talking about with dynamic loading, I'm a trained stage and arena rigger for the entertainment industry. The shelving wasn't loaded that badly above the bottom shelf (which had two boxes of solid BOOKS on it) but each shelf was supposedly rated to like 80lbs IIRC. I was using the Home Depot mid-size cardboards that had about 12 lbs or so in each one. The stuff was more bulky than heavy. The shock loading should have been within the stress level of the shelving, but the steel on these things wasn't much more than about 22/24 gauge. Really thin. It's strength (such as it was) came from being designed to be loaded on-edge by the MDF shelf surface. Any twisting of the structure would have (and probably did) compromise the vertical L-shaped legs of the structure. Twisting shear forces are a bugger. The interior walls of my trailer are removed so that I can strap directly to the vertical wall supports, but obviously in this case the straps didn't help matters.
I will be replacing these shelves in the future with some nice rolling mesh racks or similar... Rated to 2k lbs. I already know those will be just fine, as I drove 3 of them to a storage facility while shrink-wrapped and fully loaded... And they were perfect. The downside: They are $80 each at Costco.