National Steel Bridge Alliance

Reliable by (Redundant) Design

What does a two-winged aircraft have in common with steel bridges?

The answer is reliable and safe service through redundant structural design. Aren't the wings fracture-critical, though? No! Effective and efficient redundancy in design can be achieved through system or member-level mechanisms utilizing engineered damage tolerance that is linked to the structure's inspection intervals.

This applies to new steel bridge designs and legacy bridges, taking advantage of efficient steel designs having:

  • System redundant members (SRM) for damage-tolerant bridges
  • Internally redundant members (IRM) for damage-tolerant bridge members
  • Steels with increased fracture resistance
  • High probability of damage detection through visual inspection of exposed tension-carrying components
  • Mitigated inspection risk factors for improved worker and public safety
  • Improved inspection resource allocation for bridge owners. One DOT is currently removing more than 20 bridges (totaling over 100 spans) from their fracture critical inventory during an initial implementation of the AASHTO SRM guide specification.


Check out these resources to learn more: