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:
- AASHTO Guide Specifications for Internal Redundancy of Mechanically-fastened Built-up Steel Members
- AASHTO Guide Specifications for Analysis and Identification of Fracture Critical Members and System Redundant Members
- T.R. Higgins Lecture at the 2018 Steel Conference: Towards an Integrated Fracture-Control Plan for Steel Bridges by Robert J. Connor, PhD
- Modern Steel Construction Article: Revisiting Redundancy: Part 1
- Modern Steel Construction Article: Revisiting Redundancy: Part 2
- Robert Connor, AISC Engineering Journal, 4th Quarter 2019, Transformative Approaches for Evaluating the Criticality of Fracture in Steel Members
- Modern Steel Construction Article: Are You Sure That's Fracture Critical?
- AISC's Steel Solutions Center