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

 

[tab101]

I suggest posters suggesting that all damage to the pool deck/parking area is solely a result of the main building collapse should review the collapse footage again

https://www.youtube.com/watch?v=KR29pLccutY

There are mere seconds between the 2 sections of the building collapses.

Obviously eyewitness testimonies aren't completely reliable, but here we have many testimonies (and video) testifying some sort of obvious collapse in the pool / parking area, a significant time before the main building collapse. Enough time to make a phone call and describe what has been happening before being caught in the main collapse. Enough time to go to security, escape the building, etc.

Watch the video of the collapse, look at the first portion of the building collapsing, then imagining trying to make a phone call, go recover your family, etc etc in the mere seconds before the second portion collapsing.... there is simply not enough time.

 

[structuralex]

@tab101:
The eyewitness testimony refers to the pool deck collapsing, which is a couple minutes before the start of the security footage.

 

[tab101]

@structuralex yes agreed. There are suggestions here that the damage was caused during the building collapse, not prior. And that (for example) the woman who spoke on the phone to her husband and told him about the pool area collapsing before being (presumably) killed in the building collapse had made that phone call and had that conversation in the mere seconds between the first part of the building collapsing and the remaining part as seen in the security footage. I am pointing out that the theory that there was no obvious damage to the pool deck / parking area at least minutes before the building collapse is inconsistent with the multiple eyewitness testimonies, the security camera footage and other evidence available.

 

[MOJOJOHN]

Engineers inspecting for damage to South Florida condominiums in the wake of the Surfside Towers South collapse should be aware that the only engineers allowed to inspect threshold buildings (Threshold building means any building which is greater than three stories or 50 feet in height, or which has an assembly occupancy classification as defined in the Florida Building Code which exceeds 5,000 square feet in area and an occupant content of greater than 500 persons) or to do 40 year certifications for them must be licensed as Special Inspectors (S.I.), by the Florida Board of Professional Engineers.

Older buildings built before the Threshold Building definitions came into effect are included if they meet the current definition above.

While local Building departments are apparently not aware of this requirement, as demonstrated by their Special Inspection Forms and 40 year Recertification Forms which do not require an S.I., anyone not licensed as an S.I. who does the work may be subject to disciplinary action by the Florida Board of Professional Engineers.

Any engineer who does this kind of work should become aware of the requirements of the Florida Statutes, including F.S. 471, F.S. 455, F.S. 553.71 and the 61G-35 Florida Administrative required by the Florida Board.

 

[structuralex]

It seems these 2 events are somehow connected even though they happened on opposite ends of the building:
- The pool deck collapsed a few minutes before the main building collapse, as per many eyewitness accounts.
- Apparent rubble and burst water pipe a few minutes before main building collapse, as per video by neighbour.

 

[LittleInch]

DB27 might have something here.

The original 87th terrace was a car park / access to the beach

Then they cleared the previous building in about 2015 and then it looks to me like they sheet piled the perimeter, much closer to the existing wall / boundary.
Did this affect the possibly weak join between the slab and the wall?

So if the slab to wall joint failed then you have a slab with several metres of cantilever with point loads on those columns.

Can someone better than me find the details of the slab to wall joint?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[w-streng]

Post of 29 Jun 21 14:21

Not that this caused the failure, but fully agree about the lateral stability in the East-West, it seems hopelessly insufficient. Laterally, the building is obviously relying on frame action and some bracing from internal walls and possibly a bit of ‘outrigger’ help from the slabs built into the core.

I also did a calc and find that columns on I8, K8, L8, M8 are far from meeting ULS requirements. If you strip all the load and material factors out (to understand why the building stood for so long), the concrete was loaded to about 50% of its specified strength. Possibly cube results showed higher strengths to assist. So, on paper, almost no redundancy. PS, Trenno, I used 13 suspended slabs and then 14 from K to P where the penthouse was built on the roof. So my check was for the basement columns and have similar concerns.

I find that columns on grid 10 are closer to satisfying ULS. But having said that, the 460mm fold in the slab (step beam) along grid 10, together with the planter beams all coming into a column which already had 5.5% area of steel, mixed with pour/construction joints and probably a mixture of concrete strengths (slab vs column) and possible concrete compaction challenges makes this a very vulnerable area. I wonder too if the external podium slab wasn’t cast off the critical path resulting in cold joints, compromised continuity etc.

So may things to consider that a visual inspection won’t always pick up. All the evidence from witnesses supports an initial collapse at the upper visitors parking, or at least in that vicinity. If I were on the team I’d prop the podium of the sister tower and carry out some column head inspections to rule out punching shear shortfalls, whether a result of corroded rebar or poor rebar placement or whatever. I wonder if that gazebo structure on the podium was approved. I’d also carefully inspect the underside of gridline 10 for any distress and take a serious look at the column design on grids I.

 

[structuralex]

Here's a section detail of the perimeter basement retaining wall. The ground floor plan calls up #5@12.

 

[waross]

An interesting exercise. Step through the first ten seconds of the last posting of the video. Click on the video to stop it and then use the comma to step backwards and the period to step forwards.
There may be four or five steps per frame, but it is not consistent. At times a frame will jump to the next frame in only one step.
At the start of the video, the building collapse appears to have started. There are 5 or 6 lights showing.
A few steps later all but two of the lights are out.
Then a light goes out in the surviving building as well as the two lower lights.
One frame before the one second mark, a light comes on lower down in the collapsing section of the building. It is there for about 4 steps.
It is interesting that some lights stayed on even as the building was falling.
Ten steps into the first second, the second section of the building (behind the first section and a part to the right) starts to collapse.
Nine or ten steps before the ten second mark, the third and final section of the building starts to collapse.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[structuralex]

I just went through some of the documentation, and one thing that immediately stood out was the highly technical details relative to what a construction worker would be expected to understand.

Refer to the 2 details below as an example. I was taught to notate the drawings clearly enough that a layperson would understand.

However these would be something you'd typically find in Concrete Standards. It's the engineers job to 'translate' it without risk of misunderstandings.

I'd say it's plausible that this was a contributing factor to the collapse.

 

[StrucDesignPE]

I just went through some of the documentation, and one thing that immediately stood out was the highly technical details relative to what a construction worker would be expected to understand.

Refer to the 2 details below as an example. I was taught to notate the drawings clearly enough that a layperson would understand.

However these would be something you'd typically find in Concrete Standards. It's the engineers job to 'translate' it without risk of misunderstandings.

I'd say it's plausible that this was a contributing factor to the collapse.

In my experience, the details you show are pretty common and are intended more for the detailer who is producing the rebar shop drawings.

 

[waross]

I once saw a unique reaction to a similar lack of detail.
It was for a fire water supply line, The routing had a number of corners that were not square and would require specially fabricated fittings.
On the bidders walk around tour, the estimaters pointed out to each other all of the problem spots so that know one would have a low bid as a result of overlooking an expensive detail.
One bidder, Stan, ignored the problem areas in his bid. He got the job.
For each problem area he designed and had fabricated the needed parts.
Then, under the heading of "Not Detailed on Bid drawings" he sent the invoice including engineering and drafting time to the engineer as an extra charge.
The engineer allowed the invoices as extras.

Same job:
There was a hard, nonnegotiable deadline set by the fire marshal. If fire water was not available by the deadline the fire marshal would close a vital terminal in a new public transit link.
The bidders were all contemplating work around the clock and massive overtime expenses.
Stan made a proposal to the Fire marshal.
I will supply a temporary fire water service within a few days., if you will accept that as meeting your deadline, and allow time for the permanent work to proceed in an economical fashion.
The Fire Marshal was most concerned with protection of the public as soon as possible and agreed to the plan.
Career wise, he was able to send the signal that he had negotiated an arrangement whereby the public safety was assured sooner and at much less cost than originally expected.
Stan made a lot of money on that job.
It was fun working for Stan. I miss him. (RIP)

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[spinspecdrt]

These seem typical to me. Typically shop or placing drawings would break it down further for installation.

 

[Teguci]

The yellow column in the Tik Tok video is on grid 10 (the south side of the building). The refuse in the background looks like the failed plaza slab. The failed water line is probably the line that fed the pool.

 

[dik]

More likely that the reinforcing had corroded and the expansion products had compromised the concrete. There could also be insufficient cover.

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

-Dik

 

[JG2828]

Here is a download of the TikTok video for posterity sake. Stuff gets deleted from that site all the time.

https://files.engineering.com/getfi...e6b2-4a2a-9575-f13660d8a168&file=download.mp4

 

[dik]

See my comment above... I would suggest it was a defect; normally placed reinforcing does not 'unzip', it stays in place to support concrete.

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

-Dik

 

[Archie264]

The drawings seem to show the swimming pool ending at either Column Lines M or N, depending on which version of drawing you look at. It's unclear how the pool steps and the jacuzzi are accounted for. Could either of those have affected the continuity or development of the two-way reinforcing in that area enough to make a difference? I know that in non-typical areas of a two-way slab steel placement can require quite a bit of judgement. And the slab failure does seem to hit right at the corner of the jacuzzi.

 

[Santos81]

The yellow column in the Tik Tok video is on grid 10 (the south side of the building). The refuse in the background looks like the failed plaza slab. The failed water line is probably the line that fed the pool.

It’s M8. The debris visible in that video is where M9.1 should be. The pipe is a sanitary line.

 

[Murph 9000]

It’s M8. The debris visible in that video is where M9.1 should be. The pipe is a sanitary line.

No, it's M9.1 (or M10 on sheets that don't have a 9.1 row labelled). M8 is the lower end of the ramp, where the half wall ends. The full height wall on the left is the eastern stairwell shear wall (which would be M2–M4, approximately).