Scott Blair/Southwest Contractor Unsecured girders with residual protective material slipped off pier caps.

A 122-page report by CTL Group, a Skokie, Ill.-based investigative consultant, blames “a number of factors adding together in a critical combination” as the reason for a 114-ft-long bridge section under construction to fall. No one was injured.

Nine of 11 precast, pre-stressed girders of a bridge section on the Loop 202 Red Mountain Highway dropped 25 ft from their pier caps. The girders on the westbound lanes of the 87.8-ft-wide bridge section, each 2.5-ft-deep and 105,000-lb, had been placed atop the pier caps three weeks prior. They fell into the Central Arizona Project’s nearby canal, cracking upon impact. The girders are being replaced at the contractor’s expense, estimated at $185,000. Pier caps sustained only minor scraping.

Results from the four-month investigation cite “bearing eccentricity” and unremoved girder protective material as contributing to the incident. Other potential factors include thermal expansion, wind load and a lack of temporary lateral bracing. No work was done on the unsecured girders while awaiting the cast-inplace diaphragms, says Doug Nintzel, Arizona Dept. of Transportation spokesman. Temporary bracing, although a common practice, is not required under ADOT contract specifications.

But that will soon change. ADOT is now updating its specifications to require temporary bracing for all girders after they are placed and before permanent braces are added. It was one of the report’s many recommendations for future construction, including checking for girder centering and clearing surfaces before placement.

“Specifying temporary bracing in all cases is another step we can take to enhance safety,” says ADOT state engineer Sam Elters. “While this was a rare event and there are always risks in construction projects, we are prepared to work with our contractors to prevent any such accidents in the future.”

The 4.8-mile, $195-million project, is not expected to be delayed by the incident. Phoenix-based Pulice Construction Inc., the general constructor, has a 650- working-day schedule. Royden Construction Co. is the Phoenix-based subcontractor responsible for girder manufacturing and erection.