Analysis of Structural Materials Exposed to a Severe Fire Environment

The Interstate (I) 580 overpass collapse occurred on Sunday morning, April 29, 2007. The fire that eventually led to the overpass collapse started at about 3:38 a.m. when a gasoline tanker truck carrying 32,500 L [8,600 gal] of gasoline crashed and caught fire. The tanker truck was heading south along I-880 at the time of the accident. While nearing the I-580 overpass, the vehicle crashed on the 50-foot-high ramp connecting westbound I-80 to southbound I-880. The driver escaped from the burning vehicle and was treated for burns to his face, head, and neck. The accident occurred in an area known as the MacArthur Maze, which is a network of connector ramps that merges highways I-80, I-580, and I-880 in Oakland, California. An aerial map of the area is shown in Figures 1-1 and 1-2. Shortly after arriving, the firefighters from the Oakland Fire Department reportedly saw that the I-580 ramp was sagging. Heat from the fire had heated the steel girders to temperatures where the steel strength was reduced and insufficient to support the weight of the elevated roadway. The I-580 overpass collapsed at about 3:55 a.m. The main portion of the fire spread along a section of the I-880 roadway and burned for more than 2 hours. Some of the gasoline went through the scupper drain near Bent1 35 on I-880 and burned on the ground around the support column of the bent.

Photographs of the scene after the fire was extinguished are shown in Figures 1-3 to 1-6. The photos, obtained from the California Department of Transportation (Caltrans) website, show the damage that resulted from the fire. Figure 1-3 identifies the roads and the relevant features of I-580. Two span sections of I-580 fell and landed on parts of I-880. The box girder beam at Bent 19, which was welded steel construction supporting the two adjacent spans, was pulled off of the support columns and partially landed on the tanker truck. The I-580 section between Bent 19 and Bent 20 was draped over I-880 and contacted the ground below (Figure 1-4). A portion of the I-580 span between Bent 19 and Bent 20 landed on I-880. Heat from the fire and stress from the weight of the span construction caused a section of the span to bend over the edge of the I-880 roadway.

After the accident, the tanker truck was located on the I-880 roadway near Bent 19. The main cab of the truck was located between Bent 19 and Bent 20 with the frame rails and the partially melted aluminum tank located under the Box Beam Cap of Bent 19. Figure 1-7, taken during the demolition process, shows the final position and location of the tanker truck with respect to the collapsed I-880 overpass. The tanker truck remains were removed from the I-880 roadway and temporarily located near the accident scene. As shown in Figure 1-8, the major remnants consisted of the truck frame, engine, transmission, axles, and portions of the tank that did not
melt during the fire. Subsequently, the tanker truck was relocated and placed into storage while the California Highway Patrol (CHP) conducted an accident investigation.

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