Technical Background Available: "Fracture-Critical"

April 2, 2024


CHICAGO - Various news stories about the Francis Scott Key Bridge collapse have discussed the design and noted it included fracture critical steel members, which are more correctly known today as Nonredundant Steel Tension Members (NSTMs).

Broadly speaking, the public misunderstands what this technical language means, and it is commonly incorrectly covered in the press as being a deficiency. Expert engineers at the National Steel Bridge Alliance and the American Institute of Steel Construction are available to the press to provide background.

"Some people hear the term and think it means a bridge is less safe because specific steel members are critical to the structural integrity of the bridge," said Charles J. Carter, SE, PE, PhD, executive director of the National Steel Bridge Alliance and president of the American Institute of Steel Construction. "In reality, this is a classification that results in special design, fabrication, and inspection provisions that create a higher level of safety for those parts of the bridge."

Carter has already served as an expert source for multiple news outlets covering the incident, including the BBC, the Wall Street Journal, the Washington Post, and local media in a variety of markets.


For more information contact:

Dani Friedland
Director of Marketing Communications

American Institute of Steel Construction

The American Institute of Steel Construction, headquartered in Chicago, is a non-partisan, not-for-profit technical institute and trade association established in 1921 to serve the structural steel design community and construction industry. AISC's mission is to make structural steel the material of choice by being the leader in structural steel-related technical and market-building activities, including specification and code development, research, education, technical assistance, quality certification, standardization, market development, and advocacy. AISC has a long tradition of service to the steel construction industry of providing timely and reliable information. 

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