CBD Tornado's

I reall hope someone can give me some insight on what happened to downtowns when a tornado struck the premises. For instance, Oklahoma city...if i recall, a twister struck the CBD a few years back but i never saw any damaged photos. I cant remember any other large cities getting hit except milwaukee near the airport and minneapolis in the suburbs. How do the buildings stand up against the tornado when it enters within proximity. N.O. downtown had countless windows blow out in their towers after the hurricane struck. I love to make the connection with weather and how architects design buildings to withstand such impact. SF is an example of a big city constructing buildings that prevent collapses from earthquakes. What ever happened to OKC that day of the tornado! Some one fill me in and discuss>