TSEC 32: Structural Redundancy in Steel Bridges: What You Need to Know

In this episode, we talk with Jason B. Lloyd, Ph.D., P.E., a Bridge Steel Specialist at NSBA. We found Jason through an article he wrote in the AISC magazine on redundancy in steel and, in this episode, we talk to him about redundancy in steel bridges, steel, and failure critical members.

Engineering Quotes:

Redundancy in Steel Bridges

TSEC 32 Quote 2

TSEC 32 Quote 3

Here Are Some of the Questions We Ask Jason B. Lloyd, Ph.D., P.E. in This Episode:

  • Tell us about your time spent at the Navy Civil Engineering Corps.
  • Talk a bit about what full-scale testing looks like.
  • Do you have anything to do with sourcing funding?
  • From the time you were doing research, can you give an example of a finding that you found to be interesting?
  • Talk to us about your opinion on historical consideration of redundancy in steel bridges, and why you think engineers should think of other modes of redundancy in steel bridges.
  • In your second article, Load Carrying Potential, there is a guide that you mentioned on how engineers can use finite information analysis to classify a redundant structure. Can you talk a bit about this?
  • Can you go over some of the lessons learned or some of the best advice you can give to new or active engineers?

Here Are Some of the Key Points Discussed About Redundancy in Steel Bridges:

  • The NSBA travels the country visiting departments of transportation and interfacing with their clients that have produced designs. They provide them with technical resources and education outreach. They also develop evaluation and design tools that help designers save time and help them with their design process.
  • There is a margin of vagueness when talking about the differences between full-scale, large-scale, and experimental research. Full scale represents the testing of a structure as it would exist in the real world. In many types of research, you can scale the effects of force load displacement down to make the test more affordable. This scaling cannot be done in some cases and the testing needs to be done on large- or full-scale structures.
  • There are certain aspects of engineering that cannot be scaled. One of them is fatigue and fracture. Some conditions affect the behavior of a fatigue or fracture specimen that cannot be scaled down. Fatigue resistance has a random distribution of flaws that are introduced through material processes. By scaling this down, we are reducing the probability that there is a flaw somewhere that would reduce the fatigue resistance of the specimen. Scaling this down would then create an artificial fatigue resistance.
  • This type of research is funded by many different sources, such as federal funding, NCHRP, state funding, pooled fund projects, propriety-funded projects, and many more.
  • A big take-away for Jason in terms of research, after many years of performing field tests on bridges, is that there are incredible reserve capacities that tend to exist in the structures.
  • Bridges are to be inspected every two years, no matter what the age of the bridge is. However, this does not make sense as older bridges are not made with the same quality of materials as newer bridges are, and they might need more frequent inspections.
  • The NCHRP Research Report 883 developed into an AASHTO Guide Specification for the Identification of Fracture Critical Members and System Redundant Members. This standardizes the way that refined analysis can be used to evaluate for redundancy.
  • The adage, “Big doors swing on small hinges,” could define Jason’s career. There have been times when Jason made decisions that seemed to be insignificant, but led to big opportunities. These small decisions led him to the people or organizations that could provide these opportunities. He says that every step in his career has contributed to his growth, and he has a lot of growth left.
  • His advice is to surround yourself with capable and caring mentors, people who have established themselves and care about your career. All his success can be linked to the giants of the industry whose shoulders he stood on. They trusted him, gave him responsibility, and showed him how to get things done.

Jason’s article, Revisiting Redundancy, was motivated by the need to challenge the status quo, and he intended to get engineers to think differently. Decades ago, the only mode of redundancy that could be relied on was multiple load paths. This started the development of bridges with four or more girders, ensuring that if one of the girders failed, the rest of the girders would stay intact and the bridge would not collapse. 

Since then, the quality of steel has gotten a lot better. The toughness of the steel has improved, and it resists fracture in the presence of a notch. The welding processes and the quality of inspection processes have improved tremendously. All of these produce bridges of a higher level of reliability than before. There has not been any fracture critical member that has failed since the fracture control was implemented. 

We now need to look at systems that are considered fracture critical because they lack load path redundancy and quantitatively dilate them for redundancy, whether it is at the system level or the member level. With the research that has been conducted over the past 10 years, engineers now have various ways of approaching redundancy in addition to the load path method.

More Details in This Episode…

About Jason B. Lloyd, Ph.D., P.E.

Redundancy in Steel BridgesDr. Jason Lloyd is the Bridge Steel Specialist, Western Market, for the National Steel Bridge Alliance, a division of the American Institute of Steel Construction. He represents the steel bridge industry on matters of steel bridge fabrication and construction. Jason’s role with NSBA is to provide technical assistance, tools, and resources for steel bridges to bridge owners, designers, fabricators, university programs, and technical committees. Before joining the NSBA, Jason spent seven years as a research engineer at Purdue University’s Bowen Lab and S-BRITE Center, where he specialized in full-scale fatigue and fracture research, field testing of steel structures, and repair and retrofit of steel bridges. He earned his M.S. and Ph.D. from Purdue University. He is currently a licensed professional engineer in the state of Indiana and a former U.S. Navy Seabee. 

Books Mentioned in This Episode:

NCHRP Research Report 883
NCHRP Research Report 883


Purdue’s S-BRITE Center
Modern Steel Construction Magazine
Article: Revisiting Redundancy – Part 1
Article: Revisiting Redundancy – Part 2
Article: Revisiting Redundancy – Part 3
AASHTO Guide Specifications for Analysis and Identification of Fracture Critical Members and System Redundant Members
AASHTO Guide Specifications for Internal Redundancy of Mechanically-Fastened Built-Up Steel Members
Jason’s Contact Details
Connect with Jason B. Lloyd, Ph.D., P.E. on LinkedIn
The Geotechnical Engineering Podcast

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To your success,

Mathew Picardal, P.E. & Alexis Clark, P.E., M.ASCE
Hosts of The Structural Engineering Podcast

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Originally posted 2020-08-20 13:15:49.

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