In every structural design class, students are presented with case studies of historical structural failures to learn from. And the case of the condominium collapsed in Surfside, Florida, will certainly be one of them in the future.
Today, Mark Oakeson jumps back on to walk you through some of the aspects he thinks may have led the building to collapse. To do this, he combines his own career and work dealing with structural design on a daily basis with assessment reports evaluating the condo’s conditions.
What You’ll Learn:
- Well-Known Structural Failures of the Past
- Difference Between The ASD and LRFD Design Methods
- Did the Condo’s Design Meet the Requirements of the Code of the Time?
- The Mistake That Possibly Started the Structural Damage to the Building
- What Spalling Concrete Is — And Why It Was a Warning Sign
- Could We Have Avoided The Collapse?
- How Can We Avoid Other Tragedies Like This?
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Resources Mentioned (some links are affiliate links):
Surfside Condo Collapse – https://en.wikipedia.org/wiki/Surfside_condominium_collapse
Tacoma Narrows Bridge Collapse – https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
Hyatt Regency Walkway Collapse – https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse
Pemberton Mill Collapse – https://en.wikipedia.org/wiki/Pemberton_Mill
The Ultimate Civil PE Review Course – https://civilpereviewcourse.com
The Ultimate Civil FE Review Course – https://civilfereviewcourse.com
CEA Youtube Channel – https://www.youtube.com/channel/UCPeFLBZ2gk0uO5M9uE2zj0Q
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CEA Website – https://civilengineeringacademy.com
Reach out to Isaac – [email protected]
Transcript of Show
You can download our show notes summary here or get our transcript of the show below!
Isaac Oakeson: All right! What's going on, everybody? Welcome to another edition of the Civil Engineering Academy Podcast. Mark, I bring you back on. What's going on?
Mark Oakeson: Hey, bro. It's going great. Glad to be here again. Yeah. It's good to be here again.
Isaac Oakeson: Well, we're happy you're here. And I wanted to bring you on to talk about Surfside Florida condos. It's been all over the news for some time now. But as a structural engineer that actually works on similar projects, things of this nature, I wanted to bring you on and maybe talk about, in your opinion, the things that happened at this condo tower collapse. Because I think it's helpful to understand the properties that maybe concrete exhibits and steel exhibits to give us warning signs before stuff like this happens. Because this is a horrible thing.
Mark Oakeson: Yeah. And so, being a structural engineer, and I primarily deal with structural concrete in my career, you hate to see these kinds of things happen. Of course, first priority is, you know, consideration for the individuals that lost their lives in this horrible event that happened. I mean, this thing happened like, you know, it was 1:25 AM, this 12-story building just collapse, and it was, what, June 24th that it happened of this year. As of July 7th, they stopped the rescue operations and then they changed it to recovery operation. And then, you know, searches for victims actually stopped back on July 23rd, and they sifted through the rubble as much as they could to find remains and try to establish identity of any individuals that were lost in the tragedy.
Mark Oakeson: But yeah. Just a horrible deal. Isaac, it's recognized as, like, the third deadliest structural collapse. So if you recall, it's, you know, a lot of case history. You know, when you're taking your structural design classes, sometimes they bring up the old classics, you know, structural failures. There's the Tacoma Narrows Bridge. That's always a fun one that everybody calls up. There was the Hyatt Regency Walkway collapse in Kansas City back in 1981.
Isaac Oakeson: I remember studying that one. Talking about shearing.
Mark Oakeson: And there was a really old one back in 1860. That was a Pemberton Mill, we're 145 people died. So you know, if you look at the history of structural performance -- I mean, if you statistically compare that, it's not so bad. But any incident like this is a tragedy, and obviously we try to avoid it, right?
Isaac Oakeson: Yeah. I think it's a horrible situation. Obviously, it's not good. I am always curious about what they do when they investigate these kind of things. But before we maybe even talk about that, maybe we can walk through maybe how this was designed. I know they're calling these the Champlain Towers, and they were actually built in 1981 by a group of developers, and we've noted that, as part of a three-building complex, with each building constructed 12 stories tall. And these drawings were produced in 1979 under the UBC, or the Uniform Building Code. So how does that relate to maybe the way things might be designed today in terms of that?
Mark Oakeson: Well, back in those days, remember that ASD was the primary method of design. So Allowable Stress Design. Yeah. And so, what you would do is figure what kind of stress a member, for example a beam, was capable of resisting, and then you'd back it off a little bit by using a factor of safety. And it's still actually allowed today. Engineers can still use ASD to design their buildings. They have to stay within, I'd say, some more parameters than they used to. But you know, nowadays, everything is per-strength design, primarily.LRFD.
Isaac Oakeson: All right. Load Resistance Factor Design.
Mark Oakeson: Yes! Which uses more of a, I'll call it as to-cast-it kind of an approach. More probability of failure kind of an approach where -- And you know what I'm talking about, Isaac. Where they use these limit states, right? To figure out what the nominal strength is of a member, and then they back it down by a fee factor, right? Depending on what the chances are of failure.
Isaac Oakeson: And I believe the whole idea that those that were designing a more economical design with LRFD.
Mark Oakeson: Yes. And so you could argue that, because this was UBC, probably there were some components that may have been designed more conservatively than maybe we'd have today.
Isaac Oakeson: So, just talking about the codes. Our understanding is that this was built according to the code that it was needed to be designed to.
Mark Oakeson: Yes. Yes. And I haven't heard anything that -- You know, that gets questioned. The design gets questioned when something like this happens, of course. And it should. But everything that I've heard is that, you know, there isn't a smoking gun that says that this building, even though it was designed per the UBC of 1979, was not actually constructed per that code. I don't think there was any shoddy construction. At least there wasn't anything that was pointing to that. But I mean, they had lots of investigations. The concrete was actually exhibiting warning signs, just like it was supposed to. So there is some, you know, investigations, structural investigations, that were done, and they determined that the waterproofing layer at the pool wasn't sloped sufficiently.
Mark Oakeson: And so the water from the pool was constantly standing on that pool deck and just allow it to sit there. And concrete is porous. It's a porous material. And so it'll soak up water. We deal with that kind of issue on parking structures all the time in corrosive environments. You get the deicing salts and those kinds of things dripping off of cars as they park into the parking structure, and then the concrete's porous and it kind of soaks it up. And then when it gets down to the reinforcing steel, salt on steel is just -- I mean, it's like a corrosion accelerator. It just really, really starts rolling, you know? So this water -- I'm not a hundred percent sure if it was a saltwater pool. It could've been, which would've even worsened the situation.
Isaac Oakeson: Yeah. That wouldn't be good.
Mark Oakeson: Yeah.
Isaac Oakeson: I don't know either what kind of pool it was. But obviously water, and whatever chemicals you've got in the water, plus concrete, if it wasn't designed to try to resist that stuff, at least the best that it can, not that it totally stops it, but if you're not preventing it, it just accelerates it.
Mark Oakeson: Exactly. And so it's those chlorides that really, like, just kill it. And so, over the years, the water just kind of percolated through the concrete, it got to the rebar, it started corroding the rebar, and then everybody started noticing spalling concrete, right? So spalling concrete is where it just kind of pops off in chunks. And when rebar rusts, it expands. And so not only does expanding rebar pop off concrete, which compromises the structural section, right? The cross-section of whatever structural member is being damaged with the water. It compromises that, but it also takes away the bond, right? Between the steel and the concrete. If you've noticed a piece of rebar, it's got little deformations on it, right?
Isaac Oakeson: Yeah. And I've seen this all the time in, like, short, little retaining walls, and like parking places. Or bridges. Pedestrian bridges too. You can see concrete. It's like falling off where you've got salt and water over time, just wanting to corrode that thing. So, yeah. It sounds like similar situation here.
Mark Oakeson: Yes. And then not only does it, like, compromise that bond between the rebar and the concrete, but it also starts compromising the actual cross-section of the steel, the rebar, right? And if you can remember back your concrete design class, Isaac, you know, the area of the rebar is a big structural property, right?
Isaac Oakeson: Yes. It is.
Mark Oakeson: Yeah. Your structural design. And so, if that cross section of steel is compromised, then the amount of tension that that steel can absorb, is lessened, right? And so, years and years of corrosion compromising the structural section there, and then the same dead and live loads that are continuously being imposed on that pool deck. I mean, it just eventually starts sagging, right? They see the spalled concrete, structural members start sagging, and giving you the warning signs, which that's what they're supposed to do. And if nobody reacts in time and makes those structural repairs before something bad happens, we kind of get what we had at Surfside, Florida, going on.
Isaac Oakeson: So, we mentioned the warning signs that happen, and those are kind of built into the design process. But with this particular one, there were investigations made. It sounds like there were some reports made a few times with suggestions on what to repair, and what to do, and the cost of that. So what did you discover on those reports that were developed for that? When did they come out with those?
Mark Oakeson: From what I've read, it seems to me that there was enough investigations going on, at least structural investigations. I would say competent structural that were going on because of the alarming nature of the impending collapse that was there. But what I would think what happened here is that it was kind of resistance from the ownership, right? Of the condominium. They were looking at -- The repair was assessed at about $15 million, which is a big nickel on a condominium of this size. And it was also going to impose a huge -- I don't know. It was going to be a big imposition on the residents of this condominium. They were going to probably get displaced for a little bit.
Mark Oakeson: I mean, to make repairs like that, you have to displace, first of all, everybody from the parking garage, that deck that was supporting the pool. Get everybody -- You know, nobody could park down there. There was probably good structural integrity in the tower itself. So they would've had to have displaced everybody down below, and I'm not sure what other spaces were below [inaudible] down there. But it was just a big inconvenience, right? So you've got this structural failure that's about to happen. The concrete is exhibiting warning signs, telling everybody "It's going to happen. We've got to make the repairs". You've got a reluctant owner that's kind of like, "Man, this is going to cost a lot of money. It's going to displace all my tenants is going to be a pain. I don't want to deal with this". And so there's just kind of a reluctant, you know, process. It's slow to get started and they just didn't get after it quick enough. But they should have gotten everybody out of the parking structure below, they should have got that whole deck shored up with some big, heavy steel shoring, and they should have started the structural repair before all this happened, you know? But hindsight is 20/20.
Isaac Oakeson: Right. So I'm just curious, with hindsight being 2020, though, I mean, what could be done to avoid this in the future when someone else does an investigation of a property. Maybe it's one that's already right there in Florida, maybe it's next to this one. Who knows where the next one is going to be. But I mean, would you recommend not only doing an assessment, like they did, but -- It sounds like really what needs to happen is just that action needs to take place a little sooner than what was discovered.
Mark Oakeson: Yeah. So when a structural engineer makes an assessment, you know, a competent structural engineer makes his assessment and gives you the warning, I mean, as a property owner, you ought to take it seriously. It's what this means.
Isaac Oakeson: In terms of timeline, though, Mark. I mean, the information you're sharing, I think it was from a 2021 report. But they had a report back in 2018 that kind of identified the problem back then.
Mark Oakeson: Yeah! But they still hadn't put a price on what the repair would be, right? So I've got to believe they got the report, and then the owner was a little bit reluctant in reacting, right? To the report. And he thought, you know, "Man, I guess we better get some estimates done from some construction and some repair type contractors that can help us with this problem". And he just didn't know -- I mean, and kind of in his defense, he just didn't know what the magnitude of the repair was going to be, which I'm sure is why he was a little reluctant. Because assessing a repair like this, I mean, it takes a while just to make the assessment, right? You can go underneath and see that the pool deck is sagging. But it's a whole 'nother thing to have an official report done, where a structural engineer makes a full investigation.
Mark Oakeson: I mean, he has to take measurements. Some of those measurements take time to make, right? If he's starting to measure deflections over a certain time period, maybe he's putting strain gauges on different things and trying to make all his measurements. I mean, that takes some time too. And so, I think it just took time. The wheels were slow in turning all of this. And then an owner's not going to want to make a decision until he has a price in front of him. But he can't get a price generated from a competent contractor until the structural assessment is done and the scope of the repair has been defined, right?
Isaac Oakeson: Yeah.
Mark Oakeson: So, it just takes some time to get all that put together. So unfortunately, what should've happened is, they should have gotten everybody out from under there, like I said, before any structural repair had to happen. And they should have gotten that pool deck shored up so that it could have resisted some additional load and not failed like it did. They could've shored that up before it all came down and bought them some more time to, you know, maybe put some numbers on the repair cost, and kept everybody safe. In hindsight, that's what should've happened.
Isaac Oakeson: Well, it's all unfortunate. These cases are obviously going to be in some textbook in the future. It's something to learn from. But it's always interesting to hear what's going on, like current events of today, how these things are investigated. I'm not sure -- I mean, Mark, how they investigate these things to really find out what happened? I know you have these reports and I think they're probably --
Mark Oakeson: Yeah. So before the building falls down, it's relatively easy, right? To do a structural assessment. The building is up, right? You can make your measurements, you can take your surveying shots, you can, you know, paste your strain gauges in key locations, you know? All those things can happen. But post collapse... Man, it's tough. Because you're dealing with just a pile of rubble and twisted rebar. And I mean, you can go back and you can, like, see maybe if rebar, like, the number of bars were, you know, on a structural member. A column or maybe a sheer wall. Maybe the number of bars was there. But man, after everything's come down, it's just a pile of powder.
Mark Oakeson: I mean, think about the 9/11 collapses. That was a structural steel building and the floors were concrete. I think there were composite decks on that one. So you can see just the pile of rubble. So it just kind of rubblizes the concrete. It almost turns it to powder when it's enough of a force that it just compresses that concrete so much it grinds it to a powder. And so in that mess, in that pile of rubble, it's just tough. It's tough to make a structural assessment. So the most valuable thing they've got is like the footage. They've got some security camera footage of how the collapse started in the center of the building. And then there was a section behind the center of the collapse, which was like a sheer wall. Once that pulled away, then there was nothing linking that east tower to the west tower. And then it just came down as well, because it just toppled over. But the short answer is, it's tough after a building's come down to make an assessment. It really is.
Isaac Oakeson: Got it. Well, this has been very insightful for me. Obviously there's news reports about it, but it's always fun to hear when, you know, somebody is in the trenches and doing and designing this stuff, how you hear about it and what your assessment is of the whole thing. So that's what's fun for me to talk about. Very unfortunate event. Like I said, I'm sure it will be studied for a long time and thrown in a textbook somewhere in the future.
Mark Oakeson: Yeah. That's just my assessment. You know, I haven't been involved with every single detail. But as I look at it, that's what I think happened.
Isaac Oakeson: Sounds good. Well, Mark. Thanks for jumping on, sharing your stories, sharing your opinions about things. Appreciate it. It's always fun to bring you back on and talk about stuff.
Mark Oakeson: Yeah, you bet. Thanks, Isaac.
Isaac Oakeson: All right. Thank you. We'll see you in the next one.
Mark Oakeson: See you.
Isaac Oakeson: Bye.
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