Kinzua Bridge, Mount Jewett, McKean County, Pennsylvania

The failures were caused by the badly rusted base bolts holding the bases of the towers to concrete anchor blocks embedded into the ground. An investigation determined that the tornado had a wind speed of at least 94 miles per hour (151 km/h), which applied an estimated 90 short tons-force (800 kN) of lateral force against the bridge. The investigation also hypothesized that the whole structure oscillated laterally four to five times before fatigue started to cause the base bolts to fail. The towers fell intact in sections and suffered damage upon impact with the ground. The tornado took less than 30 seconds to destroy a bridge that had stood for over a century.
Aftermath
The state decided not to rebuild the Kinzua Bridge, which would have cost an estimated $45 million. Instead, the ruins are intended to become a visitor attraction used to show the forces of nature at work. Kinzua Bridge State Park had attracted 215,000 visitors annually before the bridge collapsed, and was one of twenty state parks chosen by the Pennsylvania Bureau of Parks for its list of "Twenty Must-See Pennsylvania State Parks". The viaduct and its collapse were featured in the History Channel's Life After People as an example of how corrosion and high winds would eventually lead to the collapse of any steel structure. The bridge was removed from the National Register of Historic Places on July 21, 2004.