Modern Steel Construction March 2024: Bridge Authority

Rob Connor has helped make Purdue University a leader in steel bridge research.

Connor, the Jack and Kay Hockema professor in the Lyles School of Civil Engineering at Purdue University, won a 2023 AISC Lifetime Achievement Award and the 2018 T.R. Higgins Lectureship Award for his significant contributions to advancing design in steel bridge fatigue, fracture, and other performance issues. He’s also the director of two cutting-edge Purdue engineering facilities: The Center for Aging Infrastructure (CAI) and the Steel Bridge Research Inspection Training and Education Center (S-BRITE).

Connor’s research interests have focused on fatigue and fracture, field testing and remote monitoring of structures, nondestructive testing, large-scale structural testing in real time, and redundancy, among other areas. He has helped grow S-BRITE into a nationally acclaimed training and test center that obtains decommissioned bridges from around the country.

Connor spoke with Modern Steel Construction about his career, research projects, S-BRITE, and more.

I did my undergraduate work at Drexel University in Philadelphia, and I’m from the coal mining region of Northeastern Pennsylvania. I started as an electrical engineer because I naively thought it involved lighting and wiring. I liked working with my hands. But it was mainly ones and zeros, which wasn’t my thing.

Then I took a class called statics, where I first learned about forces. The professor said if you go outside the building after class, there’s a railroad bridge—look at it, and you’ll see the pins and rollers we discussed in class. I went out, saw a train going over it, and thought, “I can see that and relate to that.” That week, I switched to civil engineering and focused on structural engineering. That little thing changed my direction in engineering.

Were you in the design world for a while first, or did you go straight into teaching?

I graduated from Drexel in 1990 and started work with a company called Greiner Engineering, which has since been bought and absorbed into other companies. I took a job there because they had great experience in bigger bridges. I was also taking graduate classes part-time. I worked for about four years doing bridge inspection and design in the Philadelphia area.

That’s a long path. I went to Lehigh University for my grad work in 1994 because I wanted to know more about fatigue and fracture. I did my master’s and PhD there, then stayed as a research engineer. I loved the work there. It was a great learning atmosphere, especially in fatigue and fracture. But I wanted to have a little more involvement with students.

An opportunity arose at Purdue University, which had just built a gigantic structural engineering lab. I joke that it still had “the new lab smell” when I arrived. That was back in 2005. I was fortunate enough to get hired, and I’ve been there since.

Amit Varma, a good friend from my PhD days at Lehigh, had also started at Purdue about a year earlier. He’s also a Higgins Award winner. Mark Bowman and Judy Liu, other researchers I knew, were also there. It had a good base of steel people.

That was when I was still at Lehigh— my first National Cooperative Highway Research Program (NCHRP) project. It was on heat straightening of girders and the effect on their fatigue and fracture performance. That led to many other NCHRP projects that probably put all the gray hair on my head. But that was the first big one.

At Purdue, we’ve been very fortunate to land some great projects. I can’t pick a single project, but I have a theme I’ve worked on for 10 to 15 years: trying to rationalize the topic of the fracture-critical member. That has been a career-long focus through multiple projects examining inspection, inspection reliability, and behavior system analysis for big fracture tests. I’ve enjoyed that theme, and it started at Purdue.

What is the significance of the terminology change from fracture-critical members to non-redundant steel tension members?

It’s a game-changer for the steel bridge industry. Fracture-critical is a terrible term from a public relations perspective. The idea is that a bridge without enough redundancy or perceived redundancy would probably collapse if one component fails. If you think about an airplane, the landing gear is fracture-critical. If it fractures due to a fatigue crack, that’s a bad day. If a pilot said, “Welcome to the fracture-critical aircraft,” you’d probably get off. But we called certain highway bridges that. It’s not an attractive term.

Fracture-critical bridges are subjected to special requirements in fabrication and design. However, the big issue is the long-term in-service inspection. The required in-service arm’s length fatigue inspection every two years is expensive and risky for the inspectors because they must get up close to the bridge. You’re closing lanes, causing traffic backups, and risking traffic incidents.

My 2018 T.R. Higgins lecture tried to rationalize that rather than putting a finger to the wind regarding how to manage steel structures that are deemed to have nonredundant members. Instead, we could take an integrated approach to ensuring reliable long-term performance.

After more than a decade of research, the work resulted in codified approaches that were incorporated into two AASHTO Guide Specifications. These Specifications allow engineers to evaluate a member traditionally classified as a fracture critical member and determine the consequence of member or component failure. Depending on the outcome of the analysis, various in-service inspection strategies that are tailored to the member can then be employed.

AASHTO approved these documents in 2018. However, the federal laws governing bridge inspection needed to catch up to allow full implementation. When the new Code of Federal Regulations came out in June 2022, the industry could fully implement the AASHTO Guide Specifications, and that’s a game-changer for the steel bridge industry. We can now treat these members more rationally. We can use efficient designs, such as twin tub girders or trusses, and explicitly consider redundancy. We don’t have to worry about the consequence of a member failing because we do the analyses to verify various failed member scenarios. The analysis also identifies the truly critical members, should they fail, thereby giving owners an engineering-based reason to focus inspection efforts on the components with the most risk.

HNTB gave a presentation that revealed they’re using the work and incorporating the concepts into their designs. Several state departments of transportation are using it, from what I understand, and the consulting community is also implementing the specifications. It’s neat to see a rational approach to addressing an assumed failure mode come to fruition.

What are some recent and current projects in Purdue’s structural engineering lab?

The lab is bustling. It’s a great facility. The strong floor for testing is about 11,000 sq ft. For scale, we have a 35-ft span railroad bridge with ties and rails in the lab. We’re doing some testing on it. I’m doing small pull plate tests with a student. We also have some big bridge girders with pack out corrosion we are testing. We’re continuing down the path of redundancy or built-up members.

One challenge owners face with older bridges is related to pack-out corrosion, where plates get bent apart. Corrosion gets in between old, riveted members; they bend and look bad. But more research into its actual effect on capacity and fatigue is necessary.

So we acquired some members with real damage from old bridges. We also simulated pack-out damage of our own. We tested these in the lab—long-term fatigue tests, strength tests, cold temperature tests, and followed up with finite element analysis. Then, we did the same thing on the compression portion of the member to see if it would buckle more quickly or lose capacity.

The objective is to determine when this problem needs to be addressed and how we can get guidance into the AASHTO Standard Specification for Highway Bridges. That has been an ongoing one and has been a lot of fun. There is a lot of other large-scale work going on by my colleagues that is great for the students to observe.

S-BRITE is about a 20-acre outdoor facility, and we’ve developed about 10 acres that Purdue provided for the facility. (Editor’s note: Read more about S-BRITE in the October 2019 issue of Modern Steel Construction titled “Wanted: Old Steel Bridges”).

I teach several courses in fatigue, and it’s always a challenge to explain to students and professional engineers or inspectors where exactly to look for cracks, what a crack really looks like in service, and other considerations. We also realized many inspectors have negligible or zero firsthand experience spotting cracks, at least when they are new inspectors. Furthermore, new bridges rarely have any issues with fatigue cracking.

To improve the training, I thought it would be neat to keep a few components with damage, whether that’s due to corrosion, fatigue, or impact damage. I pitched it to the Indiana Department of Transportation, and they supported it. The Federal Highway Administration also thought it was a unique idea. As we discussed the concept with others, we found many other state departments of transportation were excited to use out-of-service bridges to improve training.

The main portion of S-BRITE is a training facility where we have four complete bridges and many other components from bridges. As you can imagine, we want damaged members, because we’re trying to train bridge inspectors and designers to detect damage, identify problem details, and observe retrofits firsthand. It also helps with undergraduate and graduate steel classes where the professor is trying to explain steel details, such as very large-bolted joints. We have the largest collection of components from the Interstate 35W bridge in Minneapolis that collapsed in 2007.

It’s an incredibly unique facility and allows some great collaborative research opportunities. For example, if someone is interested in using drones for inspection, we have bridges with damage, but we don’t have to worry about worker fall protection, traffic control, or risk to the public because it’s in a controlled environment.

Another big part is our outreach of professional training, where we help DOTs with problems and provide training to their staff.

What’s your acquisition process for bridges and members that go to S-BRITE?

The center is well known now, especially in our partner states. DOTs will reach out and mention they have a bridge going out of service in a year or two, ideally.

Recently, the Texas Department of Transportation said they have some components from a bridge. They sent the plans and inspection reports and asked if those would aid training and research at the center. We then review the information and let them know what component we would ideally like to save. That’s generally how the acquisition process happens right now. Any state DOT that knows of us can do that. It doesn’t have to be a partner state.

We tell them we can always say no, but once the components go in the melting pot, they’re gone. If the members are unique or have characteristics of something that would be good to share with people, give us an opportunity. Generally, we pay for shipping and put it on our truck.

Some larger bridges arrive disassembled. We have a 90-ft span through truss, both truss lines, and all the floor beams. That came in four major pieces, and our staff put them back together.

The I-35W pieces draw people’s attention. The other attention-grabbers are plate girders from the old Interstate 90 Dresbach Bridge in Minnesota with webs about 23 to 24 ft deep. Those girders are huge, and you can see them from a mile away. Those pieces are relatively short because they’re so tall, but their scale has made an impression on many visitors. They all want to stand on the flange and have their picture taken.

This article was excerpted from my interview with Rob. To hear more from him, find the March 2024 Field Notes podcast at modernsteel.com/podcasts.

Geoff Weisenberger (weisenberger@aisc.org) is the editor and publisher of Modern Steel Construction.

Field Notes is Modern Steel Construction’s podcast series, where we interview people from all corners of the structural steel industry with interesting stories to tell. Listen in at modernsteel.com/podcasts.