Philadelphia I-95 Collapse: Steel vs. Fire

The safety and structural integrity of bridges are crucial aspects of transportation infrastructure. While steel is renowned for its strength and durability, exposure to high temperatures can significantly weaken its structural integrity and cause an event like the June 11, 2023 I-95 collapse in Philadelphia, PA.

A burning tanker truck beneath a steel road deck posed a significant threat to the bridge's structural integrity with severe consequences, as witnessed in the recent collapse. In this short article, we explain the effects of extreme heat on steel and its ability to withstand the elongation and buckling forces that arise under these conditions.

Temperature Threshold of Steel

When exposed to high fire temperatures, steel, although strong and durable, can weaken and compromise the stability of the road deck above. The temperatures generated by a typical gasoline fire can range from 1,200 to 1,500 degrees Fahrenheit, whereas the temperatures at which steel is produced and rolled range from 2,600 to 2,800 degrees Fahrenheit. As the temperature rises, steel undergoes thermal expansion, which can lead to buckling if the excessive elongation is restrained, which is likely the case in most road bridges across the country.

Design Limitations of Structural Steel

While some expansion and contraction are expected due to daily seasonal changes in temperature, a fire of more than 1,000 degrees Fahrenheit would result in the elongation of the 100+ foot steel support beams well in excess of the design limits. In addition, when the steel that comprises the bridge girders is heated beyond 1,000 degrees Fahrenheit, the steel experiences a notable reduction in its structural integrity, causing it to lose its load-carrying capacity.

Envista's experts possess the expertise and capabilities to conduct thorough investigations into bridge collapses and other structural steel and fire-related incidents, like the I95 collapse in Philadelphia. With their specialized knowledge in the field of forensic engineering and fire investigation, Envista experts’ understanding of the complexities of these incidents can determine the factors contributing to the collapse.