Miami Beach, Champlain Towers South apartment building collapse, Part 02 151

[dik]

thread815-484587


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

-Dik

 

[TheGreenLama]

Roga50, I watched that video interview and from that it sounded fairly clear cut in that the board had absolute authority. But in the Washington Post article I posted earlier it sounded like condo owners had tremendous ability to foot drag and play politics. So I'm still a bit confused.

https://www.washingtonpost.com/inve...592282-d98e-11eb-ae62-2d07d7df83bd_story.html

 

[dik]

Maybe the real cause... deteriorated until it broke...

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

-Dik

 

[MOJOJOHN]

Seismograph readings from buildings under construction in the area might help in understanding the sequence of events.

 

[Roga50]

Roga50, I watched that video interview and from that it sounded fairly clear cut in that the board had absolute authority. But in the Washington Post article I posted earlier it sounded like condo owners had tremendous ability to foot drag and play politics. So I'm still a bit confused.

There's a reason why we call them "condo commandos" down here

 

[Awestruc]

A few thoughts after reading through the threads:

1. It would seem "eyeball" inspections are not enough to determine whether or not a building is in grave structural danger especially since all components are not visible, including the foundation elements. Even if an inspector or engineer felt collapse was immanent, they would still face the reality of condemning a building that is considered prime real estate in the middle of its useful life. That is far different than condemning an abandoned building. The backlash of peers, officials, owners, agents, and politicians could cost you your career. We are always told "buildings don't just fall down in America". So who wants to be the first to say "Well this one is about too!"

A solution, which is already being used on site, could be to monitor buildings using modern day surveying equipment. Every new building could be surveyed upon completion and every 10 years afterward. The deflections and loading conditions could be recorded and cataloged for comparison throughout the structures life. Old buildings could be evaluated the same way only the task would be more difficult with no starting point to compare too, however still useful. This would provide scientific evidence if there were a problem and would protect inspectors and engineers from having to make judgement calls. Given the 3D laser technology today, this is more achievable than ever.

2. A building made of thin two-way flate plate floors on columns using frame action and minimal shear walls to resist shear is not a redundant or robust structure. They are used for cost savings, speed of construction, and floor height. The design is governed by punching shear and when one goes where does it stop. Whether the slab punches first (dropping onto the floor below and doubling the unbraced length of the column) or a column buckles or is damaged (doubling the span of the slab and pulling on all of the adjacent columns), it seems progressive failure is inherent in this type of construction until it runs into a wall or change in framing that provides support.

3. The design load requirements by ASCE should be examined thoroughly after this for condos or commercial space over parking garages. As of now the loads are 40 psf for residential spaces, 100 psf for lobbies, corridors, and egress paths, and 40 psf for parking garages? I understand that parking garages have been value engineered to nothing and that 40 psf is pretty close to actual loading and that no residence is ever likely to see anywhere near 40 psf...even if they have tile over tile over tile floors, but the end result is the basement and first floor levels being pushed to their limits on a routine basis (not including dynamic loading and vibration, which are ignored) while the upper floors hardly ever see 20psf. Then try explaining to someone how the pool deck and lobbies should be the most robust slabs designed for 100psf when they are empty most of the time and yet cars are packed into the garage like sardines in the same picture...

A solution could be to increase the loading requirements for parking garages to 100psf located under residential/commercial spaces, especially towers (with no LL reduction). This would result in thicker slabs, more reinforcement, bigger columnns, and more foundation elements such as pilings. In addition more concrete cover could be specified to protect against damage from vehicles (Murphy's Law?)

4. Structures located in corrosive environments should be designed for corrosive environments.

5. That D-ring detail is scary as hell! Some poor crew is supposed to dangle themselves off the side of this building hanging by horizontally epoxied bolts into a 40 year old column made of questionable concrete? Count me out. Haven't there been studies showing this is done improperly 9 out of 10 times? Aren't horizontal and overhead applications only supposed to be done by a certified technician? Why not clamp a steel bracket around the column? Something that can be inspected for safety.

 

[saikee119]

TheGreenLama (Structural),

Your middle photo, with rescuer and dogs standing outside, brings a chill down my spine.

You called the rebar unzipped. To me the whole span' every reinforcment has debonded from the span. I have been wondering why the roof has so many irregular lines which are now proved to be the grooves in the concrete when the reinforcement was originally forcibly removed from the slab.

The rescuer and the two dogs were standing on the same ground floor slab which has since dropped on a lower floor like a pancake. The dropped and severed section has concrete and rebar which is hidden but in the next span, with ceiling and water, the rebar that was forcibly pulled out from the slab can be seen without any concrete attached above a pond of water. There is a serious construction defect here suggesting the concrete and rebar were not bonded structurally to resist load but separated in a clean cut manner. It is a miracle the span of this two-way slab that didn't drop, still hanging with grooves on its underside, now has all rebar in one direction removed, at least on its bottom side.

Whoever is doing investigation has to cut cores from the remaining concrete to verify its commpressive strength, cement content, chloride contend, density, ultra-sonic speed and water absorption at least. That concrete quality is highly suspicious to me.

 

[jorton]

I'm very impressed by the effort and thought many have put into their comments here.
I was a bit shocked by the clean rebar at first, but I think it may be a red herring. In every floor or wall there will be one direction of bars which are not contained within the reinforced mass. The clean bars only had chairs and cover concrete under them. As the adjacent floor pulls downward on the bars it will tend to "unzip" them from the concrete. In slow motion this would cause a bit of cover to break off, the exposed portion of bar would bend dramatically, and then the next bit of cover would break off. I think the fast but sequential bending of short lengths of rebar may pop all of the adhered concrete off. The clean bars have a pronounced curve - even those not draped over other items. I'm not sure where the top bars are in all this though. Seems they should have prevented the behavior I'm describing.

 

[NOLAscience]

What are the chances the Florida officials will decide to bring down the standing portion of the building with a controlled demolition rather than take a chance that it will come down on its own during the approaching tropical storm?

and bradw1128,
The city can evacuate the area and close Collins Ave if the tropical storm will bring > 30 mph winds. The building should be brought down, and it should be brought down onto the plaza and pool area. The area is mostly open and available and is already damaged (understatement). Don't damage Collins Ave and the infrastructure underneath. But first the city has to end Search and Rescue and begin Recovery.

 

[NOLAscience]

Many of us agree that the "surveillance video" starts after the collapse was initiated.
I hope that the grand jury will subpoena the original video.

The surveillance video from the next door Blue and Green building was probably started on the motion from the first slab falling. There may not be anything more on "the original video".

 

[NOLAscience]

I have found with 30 years of inspection experience that the ACI minimum concrete cover is severely deficient.

I'm interested in your thoughts. What would you propose for rebar concrete cover when poured against forms and when poured against existing earth? Should the "against earth" requirements differ for different types of soil?

 

[DB27]

So is this enough to make this (the blue bit) the most highly stressed bit of pool deck and hence most likely to fail first?
There i one drawing showing a beam which looks to be in that location but no evidence in the collapse photos.

I don't think it is a coincidence that the beam was removed on S5 Rev.1 Dated 1-17-80. **Corrected below, this was not the most current S5.**

It's also interesting that many of the columns remain, but I don't see evidence that K/14.1 is still standing (edit: visible in photos, but I would be interested is a closeup). If the beam at the slab drop (K/12.1 to K/16) failed at mid-span due to the missing beam, it would create a sudden eccentric load to column K/14.1, possibly causing it's collapse.

One sign that the beam at the slab drop was failing is that there was visible ponding at the location of the added slab drain on the pool deck.

 

[NOLAscience]

3. The design load requirements by ASCE should be examined thoroughly after this for condos or commercial space over parking garages.

Good post. First off, "tile over tile over tile floors" should not be allowed by the rules of the building, and, believe me, the occupants know when work is going on and they will tell the board if you are having renovations done without permission of the building's management. Remove tile before installing new tile; simple as that.

With only one layer of flooring, I think 40 psf is quite adequate for residential buildings. I would estimate that my 36 ft x 22 ft living room contains furntiture that produces less than 5 psf of loading. Add 10 psf for tile and grout. Maybe a solution is to further limit the Live Load Reductions allowed (which would have same effect as increasing the 40 psf loading) for buildings over 5 floors.

Codes have been revised since 1981 to provide better slab to column connections. This was mentioned briefly on the original thread.

I'm sure some masters thesis could investigate parking garages in actual use vs design loads; this may have already been done. Maybe someone will do a search.

 

[aggualaqisaaq]

The enhanced TikTok video (from the user above) appears to show the bushes from the 111 planter among the initial debris in the parking garage:

 

[saikee119]

As a professional engineer across the pond it is my experience that the site concrete seldom holds up well against the design standard.

The Morabito Consultant report identified a defective pool deck above the garage due to the waterproofing no longer effective. Its recommendation, quoted "extremely expensive", was to remove the top paving, bedding sand layer, the mortar screed (which the author of the opinion it had been laid flat and didn't drain to cause the waterproofing layer failure) and the waterproofing to expose the reinforced concrete ceiling slab of the underground garage. His method was to redo everything on top of the garage roof celing. While this appears peritent as the existing structure was known to leak water my problem is that the pool deck was the only part of the building structure that didn't collapse! as indicated by the site photo.

When concrete is constructed soundly it is reasonably impervious to water penetration. Anyone who has laid or used standard size, say 3' by 2' or 2' by 2', paving precast slab can testify it is not easy to pass water through its 2" thickness. A precast paving slab is made from cement mortar in a factory with adequate or superior compaction. I am not here to argue if the concrete is bad or good in the collapsed structure but it must be an interest to everyone here if we can cut some cores from the remaining structure or even select undamaged parts from the debris, to find out its density, water sbsorption, ultra sound speed and ultimately it as-cast compressive strength. In my experience a poor concrete will have to be lighter or less dense, with higher water absorption, low ultra sound speed (steel is about 6km/s, good concrete is about 4.5 to 4km/s) and insitu strength significantly lower than the specified strength. ACI 318 even allows a generous margin below strength before an engineer can condemn the concrete structurally inadequate.

In fact in every concrete report I delivered in my career I wouldn't address its structural inegrity unless I could verify its as-cast compressive strength. When rebar has been corroded I always insist on chemical tests on concrete to establish its chloride content. Thus I never put my personal opinion in my reports because everything has to be based on facts and test results which are verifiable by a third party.

The three other submissions to the local government agency for repairs have been mainly for the balcony structures which are not issues in this collpase. Many repairs, like resin injections on cracks and cosmetic repairs have been executed on this building according to Marabito report but many have failed or deteriorated. Thus the root cause of the deterioration has not been identified or the structure has been assume to deteriorate like a normal RC structure that does not warrant an in-depth investigation.

We still lack key evidence to know the root cause of this collapse.

 

[BlakeStr]

Nattel Construction, Inc. filed as a Domestic for Profit Corporation in the State of Florida and is NO LONGER ACTIVE. This corporate entity was filed approximately forty-two years ago on Tuesday, June 19, 1979 , according to public records filed with Florida Department of State.

I don't know if this was a rebith of an experienced bankrupt builder, an inexperienced start up that somehow landed 3 new 12 story buildings, or a mafia shell company.

 

[Sym P. le]

... appears to show the bushes from the 111 planter among the initial debris in the parking garage

I believe you're right! Adding a divide layer using the bluish colour of the white "column 27" reveals the greenery (and also further brightens up the scene).

 

[Keith_1]

[highlight #D3D7CF]ChiefInspectorJ (Specifier/Regulator)1 Jul 21 17:36
[highlight #D3D7CF]I have found with 30 years of inspection experience that the ACI minimum concrete cover is severely deficient. And on top of the space requirement there is a tolerance to that dimension allowed.In field tolerance on any thing are lucky to be 3/4" especially since concrete is not smooth and some aggregates are at the surface not perfectly flat like a crysta[/highlight][/highlight][highlight #D3D7CF][/highlight]

I sure hope that 3/4" was at the corner lapped section of a minor column and not above the lap in the midsection of a 8" shear wall. I'am not being critical just trying to put into context what the allowable tolerances for field construction are. Double and triple mat transfer beams are the worst thing I personally had the displeasure of keeping the concreate in tolerance.

In my experience an Architect calls out the basic structure, and sets his interior layout on those dimensions, which results in the SE guys feeling constrained to make everything fit.

 

[spsalso]

Nattel Construction, Inc. appears to have been formed by the developer of the project (Nathan Reiber) for the purpose of building it.


spsalso

 

[MIStructE_IRE]

It seems to me that the pool level patio deck failed first. From that point on, the deck is no longer restraining the columns which in turn become excessively slender and buckle resulting in the catastrophic and total failure we have seen.

Why the deck collapsed initially - looks like corrosion of rebar as many others above have alluded to already.

In the event of such a deck failure, I don’t think even the current disproportionate collapse requirements are sufficient.

 

[AtomixPro]

New article today from the Miami Herald on Nathan Reiber, the beginnings of this project and all the various entities, people involved. Open in Incognito to get around paywall.

https://www.miamiherald.com/news/local/community/miami-dade/miami-beach/article252467273.html