Report: Defective epoxy to blame for 17th St. Bridge fencing collapse

An independent investigation has found defective epoxy, or industrial strength glue, on anchor bolts caused a large canopy fence to collapse from the 17th Street Bridge last summer.

The one-ton steel and aluminum structure broke free from a bridge wall and crashed onto the downtown connector in midtown Atlanta the night of Aug. 13, 2011. No one was injured.

The Georgia DOT hired forensic engineering firm Wiss, Janney, Elstner & Associates to investigate the reason for the collapse.

Friday, the firm released the findings of its study and concluded epoxy that was used to adhere bolts from the fence to the bridge weakened and failed.

"The primary cause of the canopy failure relates to epoxy anchor adhesive, the disproportionate mixing of adhesive compounds, and inclusions or trapping of air voids in anchor holes," forensic engineer Mark Moore said.

Moore also said the epoxy was poorly mixed and applied to anchor holes. He said the same material was used in a large tunnel project in Boston where a concrete ceiling tile fell, killing a motorist.

"The poor performance of the epoxy anchors was similar to that which was observed by the NTSB on the collapse of ceiling panels in the I-90 tunnel in Boston in 2006.

The canopy fence was erected in 2004.