As the Civil Engineer Friend to many, people often talk with me about infrastructure. This is cool. I enjoy being able to inform, debunk, and even foster enthusiasm for a topic a lot of people never think about until a disaster hits the news. I have seen a lot of misconceptions floating around, though, and I want to address a few of them today. The Miami bridge collapse is on everybody’s mind lately, and people wonder if they’re safe on the bridges they use daily, so grab a cup of coffee and let’s talk about bridges.
Misconception 1: The Romans built better bridges than today’s engineers do, and if we funded our state DOT’s better, maybe they could build us things as good as what the Romans had.
While I’m not one to turn down funding, this isn’t what we need it for. In fact, due to advances in Ultra High Performance Concrete (UHPC), we could build bridges that last as long as the Roman ones do, maybe longer. There are materials out there so strong that demolishing them when needed is actually a real challenge. So why don’t we build entire bridges out of that, and just use them for centuries on end?
The answer is pretty simple. When I sit down at my desk to design a bridge, I have a challenge that the engineers of Ancient Rome did not have. The population is growing at a much faster rate than it was back then, and I have to consider traffic projections. Today’s bridges reach functional obsolescence long before structural deficiency. If we spent the money to build an entire bridge out of UHPC, everybody would be demanding for it to come down within 40 years because it would be too small for the demands of those times. Who cares that it would have probably lasted for centuries? If it isn’t serving its purpose, the extra construction costs were a waste.
With the way populations are rising in most major cities today, we need to be focusing more on taking the focus off car commuting, and expanding public transit, including light rail, than on showing each other pictures of Roman bridges and saying, “Why can’t our engineers do this anymore?” We can. You don’t want us to. Trust me.
Misconception 2: Accelerated Bridge Construction means “build a bridge fast”. It’s far better to take our time and do it right.
Everyone is talking about Accelerated Bridge Construction (ABC) ever since last Friday when an ABC bridge dropped a span in an open street in Miami. While I’ll refrain from speculating on the cause of that collapse, I will say, without hesitation, that ABC technology was not to blame for it. ABC is not just building a bridge faster than usual. It is an entirely different set of methods for construction. Things that would normally be cast in place are instead precast, and moved into place in large units (girders with the deck already on, entire abutments, etc), held there by UHPC, like a giant Lego set. It’s actually an amazing process that we should be fascinated with, not fearful of.
There are numerous reasons to use ABC. Some bridges go through the habitat or migration path of protected species, meaning long lasting construction projects are not an option without severe environmental consequences. ABC can allow a bridge to be replaced for the good of the human users without negative effects to the local wildlife. The same can be said of fragile marshes. In some areas where the ground freezes, bridges through protected marsh land have been replaced through ABC during months when the ground is frozen, allowing the construction to be completed with no disturbance to the marsh. ABC is a more environmentally friendly way to replace a bridge.
Economics are another important reason that we should be using more ABC, not less. A major roadway that’s shut down or restricted for months to years on end for a standard bridge replacement, costs millions in commerce and productivity. Plus, in states where construction cannot happen year round, this can be exacerbated further, and the benefits of ABC become even more substantial. ABC is more expensive than standard bridge construction, but when costs to society are factored in, it’s practically a steal in many cases.
ABC is safe. There are countless guides, methods, checks, and balances for how to do this, and how not to do it. More contractors are beginning to understand it, and there are nationwide initiatives to educate engineers and contractors about it (I attended a seminar on it earlier this month, in fact!) We cannot let one bad incident detract from use of a technology with such an otherwise positive history. There are ABC bridges all over the country. You’ve probably driven on one, maybe more. You were fine.
Misconception 3: Someone from the state DOT said there are 60 bridges in my city that need repairs! What are you people even doing?! I can’t possibly drive on a bridge that needs repairs!
Bridge repairs are one of my favorite things ever. Given the choice, I’d rather fix an old bridge than design a snazzy new one any day of the week. (I do both, but I really love old bridges that look like lost causes.) Let me tell you about the most common repairs that I do:
Rail retrofits are far and away the most common repair request we get. What this means is that the rail on a bridge is functionally obsolete. Usually, they’ve put a lot of asphalt overlays on the bridge, causing the rail to be a couple inches shorter in relation to the roadway surface than it was when installed, so it doesn’t meet today’s standard for height. Sometimes the rail is just old, and a style the district engineer does not prefer. Sometimes it’s had a lot of vehicle impacts and looks nasty. We then retrofit a new rail that meets today’s standards, and will hopefully be good to go for decades to come. The old rail probably wasn’t unsafe, but the new rail is better.
The next most common repair that I design is surface repair of concrete. What this means is that over the years, usually when the bridge is around 50 years old, the concrete starts to delaminate in certain places. This doesn’t mean the bridge is bad or that you’re going to fall through it. It just means we need to chip away that delaminated concrete, clean the reinforcing steel in some cases, and replace it with new concrete that is of better quality. This is far more common in some districts than others since concrete composition is highly regional, deicing salts are not used everywhere, and some bridges are in marine environments, but overall, it’s an extremely common repair.
Other repairs that should never ever scare you include heat straightening of steel girders due to vehicle impact, addition of a drainage flume, shot blasting a deck to apply a new overlay, addition of new riprap at slopes, cleaning and resetting of steel shoes and bearings, cleaning and sealing of expansion joints. I’ve designed all these repairs and then some, and every single bridge stayed open to traffic, never had a questionable load rating, and nobody was ever unsafe on them.
We do these repairs so the bridges won’t become unsafe. All of those bridges needed repairs so they wouldn’t pose a hazard to anybody. They didn’t need repairs because they were already a hazard. We do everything we can to keep them from getting to that point, and there are programs that exist that prioritize exactly that (these are my favorite programs to participate in at work).
That’s not to say there aren’t some repairs that are more concerning, and some that result in dangerous situations. There are. You wouldn’t be allowed on those bridges. We risk our licenses on keeping the people safe and we’re extremely picky when it comes to what bridges we allow to stay open for that exact reason. We have boots on the ground on all of our roadways every day, and when something concerning is observed, we don’t hesitate to close a bridge. If you get hurt, we never practice again. It’s really that simple. We have a huge interest in keeping you safe.
Oh, and one last thing on this one. Sometimes there’s something that looks really scary, but actually isn’t, like a big hole in the concrete (Riprap) slope under a bridge, or a cracked wingwall, really ugly stuff that makes it look like the bridge is falling down. The only way that could hurt you is if you fell in it or tripped over it. It’s not a structural problem with the bridge. There are numerous other things that look scary, but really aren’t structurally damning. However, I have been part of a team that closed a bridge permanently over a pattern of cracks that we could not see until we got out of the truck and walked the deck slowly. The really scary stuff, you probably can’t see as you drive by. That’s why bridge inspectors are out there doing their job every day, and bridges are on a schedule of inspections that allows us to catch problems before they become dangerous to users.
I’m glad we’re talking about infrastructure. This is something people need to take more of an interest in, not just when there’s a disaster and it becomes cool to criticize engineers and weigh in on our chosen methods, but every day. It’s like anything else, there are a ton of misconceptions. It isn’t that people tell lies about us, but that most members of the media don’t really understand what goes into designing things that are meant to be used by every person in society. It’s a big job, and I’m glad to do it, even on the days when it seems like everyone has an opinion on how it should be done better. If I can ask one thing, I would want everyone to keep focused on facts, research, and expert accounts, and not to get sidetracked by sensationalism and pithy memes. We can appreciate our Roman heritage without thinking we should go back to their methods. We can acknowledge a tragedy without scrapping everything associated with it. We can, and we should, keep all things in perspective in order to do our best work.