NTSB has published a report into the collapse on 30 March last year of a 28m-long span of the Interstate 85 north overpass in Atlanta, Georgia, which collapsed an hour after construction materials stored beneath it were set on fire. One person was arrested and later charged with criminal damage to property.
Georgia Department of Transportation (GDOT) had been using the area as storage for 76 reels of high-density polyethylene conduit and nine racks of fiberglass conduit. The materials were left over from an earlier project and were secured inside a chain-link fence.
GDOT determined that five bridge spans adjacent to the collapse - two in the northbound direction and three in the southbound direction - required removal due to structural damage from heat exposure. Excessive heat had caused the loss of pretension of the bridge reinforcement bars, and the bridge spans exhibited delamination and cracking throughout the bottom flanges. The US$15m replacement project took just 43 days (link opens in new tab).
The NTSB determined that the probable cause of the fire and subsequent collapse of the span was excessive heat from the ignition of 76 reels of high-density polyethylene conduit and nine racks of fiberglass conduit stored beneath the overpass. “Contributing to the bridge collapse was the decision of the Georgia Department of Transportation to store construction materials beneath the bridge and its failure to assess the increased fire risk due to the presence of these combustible materials,” said the report.