The certification requirements dictate what loads the landing gear must take, they do not dictate what happens when they are exceeded. This is where real design takes place; to make sure that when it fails it does so in the most benign fashion possible. In this case it would be that the landing gear shear off, but with the MD-11 it appears that it tends to break the wing spar. Note the BA 777 at Heathrow; had it been built like the MD-11 and the wing spar had broken instead of the landing gear going through the wing that one might well have ended up on its back as well, and in that case it is highly likely that there would have been fatalities. If the gear would have detached in the same manner perhaps none of the three MD-11's that flipped on landing would have done so.