[rualca]

I'd say the Oklahoma City bombing had a far greater impact in civil engineering and architecture than 9/11. The Oklahoma City bombing jump-started an awful lot of research into new topics such as progressive collapse, quantification and classification of dynamic loads from explosives, structural modeling techniques, and even design of passive defenses to mitigate the impact of these structural actions. Not so much 9/11 in general and the twin towers attack in particular. I invite anyone to run a few queries on Google scholar on the topic to get an idea of how the Oklahoma City bombing pops up in quite a few papers evem up to this day.