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And yet, for all the destruction - and for all the disbelief. Americans felt as they watched the towers collapse - engineers unanimously say that the buildings performed "magnificently" after terrorists crashed a plane into the side of each. Because the towers stayed standing for about an hour each, they gave rescue workers enough time to get tens of thousands of people out. The towers owed their resilience largely to their architect, Minoru Yamasaki and structural engineer Leslie Robertson. The men's original design enabled the buildings to withstand the impact of the planes, only after jet-fuel fires weakened their steel beams. Constructed with cheaper methods, many other buildings would have collapsed immediately. Today's most common skyscraper design places vertical support beams throughout a building. Others have diagonal beams as their means of support. But the World Trade Center was built before those were the standards.