An initial review did not identify the cause of a recent bridge collapse in Pittsburgh but concluded it began at the structure's west end, the National Transportation Safety Board said in a preliminary report issued Monday.
The report said investigators found no primary fractures in sections of welded steel girders they examined that were considered “fracture critical.” A fracture critical area in a beam is the part most likely to show damage if the bridge has suddenly given way.
The Forbes Avenue bridge gave way early Jan. 28, sending a city bus and four passenger cars down about 100 feet (30 meters) to the bottom of a ravine carved by Fern Hollow Creek.
A fifth vehicle drove off the east bridge abutment and landed on its roof. In all, 10 vehicle occupants were injured, the agency said. Natural gas lines ruptured and required the evacuation of nearby homes.
The collapse occurred just hours before President Joe Biden visited Pittsburgh to tout a new $1 trillion infrastructure law.
The NTSB said it is extracting bridge components for closer study. A final report from the agency could take more than a year.
The 447-foot-long (136-meter) bridge, built in the early 1970s, exhibited deterioration during an inspection in September, but it was not considered bad enough to warrant its closure. The bridge has had a 26-ton (24,000 kilo) posted weight limit since 2014.
There were no fatalities, but several people required hospital treatment. A UPMC spokesperson said that by Monday, all had been released.
The state highway department has said $25.3 million in National Highway Performance Program funds will be used to rebuild it.
