Miami Beach, Champlain Towers South apartment building collapse, Part 03 148

[SFCharlie]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.

Miami Beach, Champlain Towers South apartment building collapse

Miami Beach, Champlain Towers South apartment building collapse, Part 02

Thank you

SF Charlie
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[Spartan5]

If the roof cantilever did fail first, it would have dominoed all the balconies on each floor below, which would have been plenty of weight dropping to destroy the plaza slab.

And with nary a single 911 call from anyone about any of this.

Given all that was observed by the people who escaped while the progressive failure occurred from the bottom up over the course of several minutes, it would be a major anomaly for there to be no reports from the units above during the progressive failures of the balconies that would have preceded all of it.

Pancaking of the balconies starting at 1:10 or so when the first noises were heard on the ground just seems like a real stretch to me. More people would have gotten out or made calls if that was the case.

 

[bones206]

Typically the load test is performed by testing, by tying two anchors together, then jacking them with a load meter until yes, 25 percent of the load is met. The 5000 lbs is an ultimate load, they are test loaded until 1250 lbs.

What is the point of load testing to 25% of the load you are rating it for? What does that prove? In my opinion all that test proves is that the anchorage is rated for exactly 1250 lbs with a safety factor of 1.0000. You can't just waive your hand and say that since it didn't fail at 1250 lbs, it must be good for 5000 lbs. What am I missing?

 

[Sym P. le]

I find it intriguing if not improbable that a random TikTok video would reveal such dastardly evidence from the shadows, however buildings don't just fall down by themselves and a vehicle collision with a column has always been considered as a potential precipitating event. This vehicle would now be under considerable rubble given that the tower fell slightly to the south. It's not likely that an Einstein determined which column would take down the building but accidents do happen and disgruntled folk do exist. The story of the couple that moved into a motel and left their vehicle behind has me scratching my head.

Thanks for your responses.

 

[bradw1128]

As far as litigation goes or 'take away lessons', would a car hitting a column or a weakened roof/balcony element falling change anything? Neither should cause a building to collapse.

As far as litigation, who knows? My experience in much, much simpler cases is that everyone who possibly had anything to do with the loss gets sued. Then that gets narrowed down during litigation until they find the few parties most at fault with the biggest pockets.

As for 'take away lessons' I think it's our job as engineers to think of the unthinkable. If that thing has some reasonable chance of happening and making our designs fail, then we need to keep working. I agree that this building seemingly had huge latent problems of its own. A vehicle collision in a parking garage or improper drilling in a roof slab shouldn't collapse a building, but that fact that we're talking about it implies that it's plausible.

I don't think it's inevitable that huge problems have to turn into huge, catastrophic failures. Simple fixes might add a little bit of cheese to the swiss cheese and keep this from happening again: a little more impact protection to the garage, a little more care in placing roof anchors, a little more slope to the pool deck, a little more this, a little more that...

I think non-engineer decision-makers have a lot to learn too. Maybe it's time to rethink building high rises 50 feet from the beach. Maybe city zoning ordinances need to relax minimum parking requirements so we don't sacrifice shear walls for a few extra parking spaces. Maybe this was just a fluke and nothing needs to change. It's going to take a while to understand the implications of all this.

We don't know all the causes of this, but I think most of us agree it was a combination of many factors, some of which might actually be pretty cheap and easy to fix the next time around.


Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

 

[bones206]

Pancaking of the balconies starting at 1:10 or so when the first noises were heard on the ground just seems like a real stretch to me. More people would have gotten out or made calls if that was the case.

Maybe my logic is flawed. The upper cantilevers are longer than the lower balconies, so it's possible a portion could have collapsed that wasn't directly over the column of balconies. Not likely, but possible. It's hard to ignore the timing of the anchor installation if it was in fact installed and tested within 24 hours of the collapse. Just trying to keep an open mind.

 

[RickyTickyTavi]

What is the point of load testing to 25% of the load you are rating it for? What does that prove? In my opinion all that test proves is that the anchorage is rated for exactly 1250 lbs with a safety factor of 1.0000. You can't just waive your hand and say that since it didn't fail at 1250 lbs, it must be good for 5000 lbs. What am I missing?

This a distinction between ultimate load and service load in the concrete and steel codes. I didnt make the rules, but the thought process for fall arrest systems are that they are only used once: When someone has an uncontrolled fall off of the building and their harness system catches them. The 'real' falling load is about 1250 lbs, but to account for different falling conditions, faulty construction, heavier set workers, possible factors unforeseen a 4x factor is applied and that is the design basis of the engineer. In sum, They are designed for 5000 lbs ultimate load and a 1250 lb service load. Basically the load factor is designed. Its similar nomenclature to how people have been talking about how the live load rating of the structure is 40 psf, or 100 psf (depending on the location) but those are service loads. When you apply the load factor, depending on the load combination, the actual design load can be 64 psf or 160 psf, respectively. Ultimate, vs service.

 

[bradw1128]

It's not likely that an Einstein determined which column would take down the building but accidents do happen and disgruntled folk do exist.

I would assume an accident. People drive drunk. Elderly drivers get confused and hit the wrong pedal. People get their foot stuck. In the middle of the night in the dark especially, none of those things alone would be surprising. Someone took out the stone planter and fountain at the entrance of my neighborhood this spring when they understeered the turn from the intersection. So yeah, accidents do happen.

The story of the couple that moved into a motel and left their vehicle behind has me scratching my head.

That sounded odd to me too, but I figured the hotel was close by and maybe only had paid or valet parking that they didn't want to pay for.

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

 

[TheGreenLama]

With respect to a collision in the garage bringing down the building. With each passing day in which we do not have a public statement addressing this issue the likelihood goes down. Right now, 8 days after the event, I'd say it's near zero. The first thing police are going to do is interview everyone in the area and pull all CCTV footage, much of which we've never seen, to determine if a crime was committed. And if there was any hint of individual(s) intentionally or unintentionally bringing down this building they would immediately hold a press conference to announce this news.

 

[warrenslo]

A few additional things I have noticed:

1. The "anchor" (fastener) detail for the "roof anchors" (fall protection) is mislabeled, it specifies carbon steel with a Hilti model number for stainless steel. Stainless steel is to be used in corrosive environments.

2. Roof structural drawings note 8" floor & roof slabs but cantilever detail at parapet show cantilever as only 6" slab (most likely to reduce weight.) Therefore, if the roof anchors were installed on the cantilever the slab would be 2" thinner.

3. The inspection documents uploaded by the city this morning end in 2019 (the end of the document is in the 1990s.) An HVAC unit appears to have been replaced in December 2019 and is the last record in the document provided.

 

[IEGeezer]

RE: The "Swiss Cheese" model or, more accurately, slices of Swiss Cheese.

I don't think there will be any single factor that led to this collapse. I think it will ultimately be a series of factors all coming together at the worst moment.

In my view:

1. The first hole in a slice of Swiss Cheese is the Penthouse. Perhaps a contributing factor as it ate into safety margins but likely didn't, by itself, cause the collapse.

2. Second hole in a second slice: Corrosion/Lack of Maintenance/Improper Structural Repair. Again, unlikely to be the sole cause, but likely a contributing factor.

3. Third hole in a third slice: Overloading of upper parking area near the lobby. Not confirmed. Years ago I had experience with a parking structure on the beachfront in the Miami area that was showing signs of failure. The condo association contracted with an engineer that added steel supports at the top of the columns on the lower level to reinforce the slab against punching shear. Eventually someone recommended removing layers that had been added over the years when resurfacing the upper (exposed) parking deck. I figured that the structure had thousands of metric tons of extra weight on it. When resurfacing the upper parking deck, the condo association hadn't scraped the old layer off before simply adding new layers on top. Again, not likely to be the sole cause, but, if confirmed, may be a contributing factor.

 

[Teguci]

Current hypothesis -
Top steel deterioration creates a hinge along Grid 11.1 near grids L to M (south edge of the planters).

- To the north, the plaza moment and some load redistributes to the building columns on grid 9.1. Because of the stepped slab to the building (the 30" tall beam would fail in shear at other locations), this moment into the building columns can be as high as 230 ft-k. The 8-#11 bars in the 16"x16" columns (excluding any consideration for concrete and compression) are good for 250 ft-k. I think it's reasonable to think that this extra moment could be what caused the structural cracking and popping noises experienced by witnesses. I figure the column would form a sine wave in the N-S direction.

- On the south side of grid 11.1 (the aforementioned hinge), load is redistributing onto columns at grid 13.1 with the slab close to yielding (I get 90 in-k/ft for allowable slab moment).

With top reinforcement deteriorated (I'd suspect the bars near the column to not be as deteriorated - high point but who knows), the 2 way shear capacity at grid 13.1 is reduced and punching shear occurs at these plaza columns which progresses suddenly to the majority of the pool plaza area failing those columns in punching shear and putting a shock load as well as significant slab moment (now unsupported due to failures at columns)on the column at grids K/9.1 (which has a small beam framing into it). This moment eventually fails that building column. And then the building.

 

[dik]

I would suggest the first hole, in the Swiss cheese, was the general deterioration of the concrete and reinforcing due to corrosion and criminal neglect.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ingenuity]

From a historical perspective, if we look at the L'Ambiance Plaza collapse in Brideport, Connecticut in 1987 (failure during construction using Lift Slab, with 28 deaths) there were no less than 6 (published) separate theories on cause of the collapse. The National Bureau of Standards (now NIST) was also involved with authoring a report on this collapse.

 

[Retiredat46]

I think the correct interpretation of the specification is that 25% (that is 1 out of every 4) of the Hilti adhesive anchor bolts will be load tested to 5000 pounds. It talks about measuring the elongation in the anchor bolt during the test, which is something I don't think you could do if you were pulling on the post.

The anchor post itself isn't tested, but it's designed to withstand a 5000 pound pull in any direction assuming the individual bolts are installed correctly. The working load is only 1250 pounds, though.

 

[SFCharlie]

To paraphrase LittleInch, More good evidence = better answers.
How can we get more surveillance views?

Has anyone heard how they are going to get the pets out (of the un-collapsed part), before demolition?

Thanks

SF Charlie
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[DB27]

It looks like column I/12.1 was not built to be 24"x60" below 1st floor to carry the offset beam.

S4

S5

 

[Ingenuity]

This is the typical adhesive anchor field tension test setup for individual anchors:

 

[Retiredat46]

Thanks for that, Ingenuity (Structural)

 

[lucky555]

October 2020 9-page Morabito report obtained by the Miami Herald, concrete testing “yielded some curious results”. But no mention of what it was or numbers etc. “exploratory demolition” in five locations. "Experts said they were struck by what wasn’t said."
source: Miami Herald

 

[Roga50]

Well, as we suspected, there's my barricade I mentioned in the previous page of the thread...