Officials remain puzzled over an Aug. 9 bridge collapse in Mesa, Ariz. Early signs point to a construction incident rather than structural failure. On Thursday, around 8:30 a.m., a 114–ft–long bridge section that was under construction fell for no apparent reason. No one was injured. Nine of 11 pre-cast, pre-stressed girders of a future bridge on the Loop 202 Red Mountain Highway, just east of Power Road, dropped 25 ft from their pier caps. The girders on the westbound lanes of the 87.8-ft-wide bridge—each 2.5-ft-deep and 105,000-lb—had been placed atop the pier caps three weeks prior.
The bridge had been awaiting final bracing with concrete diaphragms when the girders fell in succession like dominoes. There was no wind or seismic activity. The construction sequence called for girders to overhang pier caps by 2.8-ft to 2.11-ft. until they could be permanently secured. No work had occurred while awaiting the diaphragms which are cast in between girders and ends and tied together with rebar, says Doug Nintzel, Arizona Dept. of Transportation spokesman. Leaving girders resting unsecured for a time is common industry practice, say officials.