The closure of the westbound side of the Washington Bridge is raising questions about the safety of Rhode Island bridges, many of which are over half-a-century old.
Morning Host Luis Hernandez discussed bridge safety, and modern tools engineers can use to ensure bridges are safe, with Vikas Srivastava, an assistant professor of Engineering at Brown University.
This interview has been edited for length and clarity.
Luis Hernandez: What was your reaction when you first heard the news about the Washington Bridge, that they had to shut it down?
Vikas Srivastava: Surprise, number one, right? Normally when you go through all the bridges, you don’t expect them to have these kind of sudden problems that can be actually catastrophic enough, potentially, that you have to shut down the bridge. And of course, then you start to worry about all the inconvenience and the traffic problems that we’re going to have.
Hernandez: Rhode Island has 800 bridges and at last check, 15% of them are considered “structurally deficient.” Just three other states have a higher percentage. Help me understand though, when I see that term “structurally deficient,” what does that mean exactly?
Srivastava: The bridges are supposed to carry loads. Your carry load is the traffic that’s on an ongoing basis, but they are also designed to carry unwanted events, your Mother Nature events, collision being an example, right? And in order to take those loads of the forces, the bridges are engineered to be structurally sound, the steels and the concrete and how they are connected to the ground. When a design is either at a flaw or there’s some material problem that over time, the material that is supposed to take that load has kind of had the damage in the material capacity or the disintegration of some of the material characteristics that it’s not able to take the load, that is your structural deficiency. So at some point, it is not as strong to take the load as it was supposed to be. Now, if it’s not as strong as it’s supposed to be, sometimes a minor deficiency, you can fix it and it is still under the safety limit. If the structural capacity or the deficiency is not able to take the load, it can have catastrophic consequences. And when these things are catastrophic, it’s a chain of events that the failure of the bridge can happen very rapidly. That is a real scenario we all worry about.
Hernandez: The bridge, very quickly they shut it down and it didn’t take that long before we found out we have to destroy it and start over. The governor at one point said we avoided a catastrophe. How close do you think we were to a catastrophe?
Srivastava: So nobody will know how close we were to catastrophe. But I think the understanding was this was serious and the observation they found, I think, from the December 2023 inspection — they had one of the pair out of 12, these tieback steel rods, the two of them basically were broken and if all 12 of them are broken, we know that the bridge will not be able to take the load and that section will collapse. The fact that two of them are broken, the other ones can break in the next few months. It could have taken the next few years. Who knows? Things can rapidly deteriorate and the failure can be catastrophic. So I think it was a wise decision by the governor to close the bridge.
Hernandez: I’m thinking about now the east side of the bridge, and they are now going to tighten the lane so they could fit more cars. Can that bridge withstand this extra heavy load for another couple years?
Srivastava: I hope so. As a person who drives on those roads, I hope so. I feel confident. I really think the Rhode Island Department of Transportation folks are really knowledgeable. They are looking at all the possible scenarios. So if they feel comfortable with the east-side integrity, I’m pretty confident in that.
Hernandez: This is something I’m learning in researching this conversation, how we inspect bridges today and how we use technology. I understand now we could use virtual reality and AI in checking the integrity of the bridges. Is that how we’re doing it now, basically? How does that work?
Srivastava: This is how we should be doing it in the future, I guess. I’m not sure if we’re doing it that way right now. One example is digital twin. Digital twin is when you have a real bridge going through the traffic and taking the loads and you have a computer replica of that same structure and the loads and you are actually continuously analyzing your computer structure to monitor what’s happening in the real bridge because sometimes it’s harder to really see what’s happening in the structures in the real bridge. Because you have only certain periodic inspections and those inspections as of now are a little bit more qualitative so they can compute, simulate on a computer and really we can get the warning much before the actual bridge has problems.
Hernandez: If they put you in charge, what type of bridge would you replace the westbound bridge with?
Srivastava: We should seriously think about putting sensors, a set of sensors, an array of sensors on the bridge to be able to monitor what’s happening at the bridge on a continuous basis. Right now, what we do is we have the bridge and you expect certain kinds of loads in the traffic if you’re looking for problems. But if you have sensors, you can actually not only monitor the health of the bridge, you also are monitoring what kind of load is going over for a period of time, and that will give a real assessment of how the bridge is going to perform for a long time. You’ll get a warning and quantitative measures of the problems with the bridge or the kind of things that it has seen much before you go and do the inspection. Inspection combined with this kind of sensor monitoring will be very, very helpful.
Hernandez: Talking about bridges, we have the tragedy with the Francis Scott Key Bridge in Baltimore. Engineers have raised questions about that construction, noting that the piers didn’t have protective barriers. The Washington Bridge is a very different kind of bridge, but we do have several bridges spanning waterways with cargo traffic, like the Newport Pell Bridge further south. Is that something we should be concerned about here in Rhode Island, the same kind of thing that they saw in Baltimore?
Srivastava: That bridge failed very catastrophically, very rapidly, the moment the ship hit one of the columns of the pier. The whole bridge collapsed within seconds. I think the challenge there is that at the time, the understanding of what cargo ships would look like may [have been] different. Our current modern day cargo ships are huge. With that size ship hitting the structure, I think a lot of bridges will probably not be able to take that load. So there’s a reality of what modern day society looks like versus the old bridge design. I mean, there’s a mismatch.
Hernandez: Okay. So thinking about that going forward into the future, we don’t know what kind of cars will be driving. We don’t know what kind of ships we’ll have. So many things that we have to consider as we’re rebuilding this bridge. How should we put all that into consideration?
Srivastava: That’s a very good question. Number one, we should really do a good analysis of what happened to the old bridge, right? What are the special circumstances [involved with] the failure so we don’t repeat the mistake again, right? But one of the important things that you pointed out, and I want to bring it up, is anticipating the loads or the forces that the bridge is going to have going forward. The design should be good for 100 years. So now we’re looking for society or Mother Nature for the next 100 years. It is a difficult and challenging task. But this has to take priority in terms of designing the bridge. What kind of cars will you drive? How many cars will be going on the bridge on a daily basis? Right now, I think the Washington Bridge has almost 100,000 cars passing a day. And the climate, how the climate may change down the line. You have hurricanes, tropical storms, you have the wind load. You can have. also. flooding events. And, of course, unwanted situations like this collision, right? I mean, this we saw. So what can be the worst case scenarios or how frequent that will be, right? All these things have to be really predicted and accounted for in the bridge design if you really want to design it for a hundred years to last.