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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[GPR_Tech]

Does anyone know what columns were slated to be reinforced with new Drop Panels?
(Note #10 on Drwg S2C-1.0) calls for new Drop Panels.
(picture of pool deck columns just added for info)

https://www.townofsurfsidefl.gov/do...0-year-re-certification.pdf?sfvrsn=9e2a1194_3

 

[miningman]

98% of the posters todate seem to be structural engineers and perhaps that is how it should be but I think most people here would agree that there has not yet been a "smoking gun" identified. I cant help but feel that an earlier post might be closer to identifying the smoking gun.

am not a structural engineer. I can only say that in South Florida there is a lot of limestone embedded in the soil. Regular flow of water in and out of the area around limestone will cause said limestone to dissolve. There have been also reports that the ground around the build had been sinking slightly each year. The water from the pool deck would also contribute to these processes. What I am think is a sudden subsistence of the ground under the building starting in the pool area. This would cause the building structure to fall a short distance with a sudden stop or impact. This impact cause a chain reaction cause the floors to collapse from the bottom up.

Has a local geotechnical engineer been invited to investigate this possibility?? Are there other buildings in the locality that demonstrate similiar effects??

 

[Santos81]

1. If debris from the roof were hitting the ground outside of 111 it wouldn’t sound like it were coming from the unit above. And after falling 12 stories it would have to sound a lot louder than annoying construction noises. It would have sounded like it was coming from outside. And they would have rushed to their windows to see what it was.

I think the more likely culprit of the sounds described by the Nir’s as coming from above/in the wall are the remains of the fractured cast-iron sanitary risers that pass through their unit rebounding around. The daughter was in the shower at the time and her statement about expecting to see the wood floor all around when she came out of the bathroom adds some additional support to that. She would have been standing directly over one.

 

[spinspecdrt]

In the NW portion of the building. In areas that didn't collapse.

 

[dold]

Structural drawings state 25% are to be load tested after installation (5000 lbs)

We do not know if they were load tested for inspection.

5000 lbs on one of those cantilevers, especially the penthouse patio with long spans could have damaged the concrete causing it to fail later.

Load testing adhesive/epoxy anchors in this sense does not mean pulling on the post/davit. Anchor load tests are performed with a special rig (hydraulic jack with center holes) that fits around the individual anchor bolts and the bolts are stressed until they reach their proof load. Elongation is also measured and limited to the amount specified in the detail. I have a hard time seeing how this would cause an entire 8" section of roof-balcony to collapse. At worst, there would be a concrete breakout failure in the area (probably 8"x8") immediately around the anchor bolt.

 

[RickyTickyTavi]

Structural drawings state 25% are to be load tested after installation (5000 lbs)

We do not know if they were load tested for inspection.

5000 lbs on one of those cantilevers, especially the penthouse patio with long spans could have damaged the concrete causing it to fail later.

Someone at a press conference needs to ask the city if the roof anchors were load tested at inspection and if so specifically which locations.

As someone who has designed and observed post installed fall arrest systems on buildings as old as 120 years old and a observed the load test. No. 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. 1250 lbs is not going to bring down a building. This Dik indicated earlier, the anchors a red-herring and not relevant to the overall collapse. Ive attached what the load test of a new fall arrest system into a 1940's era building looks like for reference. If a 1/2" cable can bring down a building: You have bigger problems.

Edit: Just going to add, that the wind pressures from uplift and down forces on those cantilevered sections are probably more than 1250 lbs for wind speeds well below code level events. The fall arrest system is highly unlikely to be a contributing factor.

 

[bradw1128]

Another thought on the possibility of a vehicle collision with a parking garage column instigating the initial failure:

Many (most?) newer car models have a black box (Event Data Recorder) that records - among other things - the speed directly before a crash event. That would be a way once they get to the bottom of the debris pile to see if any of the vehicles in the garage might have hit something and how hard.

I also wonder if any of the onboard assistance services (OnStar, etc) got a notification of an accident in the vicinity in the time before the collapse. These services are cell network and GPS dependent, so they may not work reliably in an underground garage, but it might be worth checking out.

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

 

[AtomixPro]

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.

 

[warrenslo]

Relevant article discussing this, please read before dismissing this hypothesis. Link

In the preamble of the new general industry standard OSHA refers many times to the 1910.66 permanent power platform standard recognizing that the regulated equipment is the same or similar . This standard tells us that all related equipment including roof anchors require functional testing not load testing.

In accordance with (1910.66(g)(1) osha required that all completed building maintenance equipment installations shall be inspected and tested in the field before being placed into initial service to determine that all parts of the installation conform are functioning as required. Federal osha further explains in section 1910.66(g)(2)(ii) that; All parts of the equipment shall be inspected, and where necessary, tested to determine that they are in safe operating condition. Mandatory testing of any part subject to wear is specified in section 1910.66 (g)(4)(1) which also includes governors and safety brakes .

IWCA -I14 industry standards effecting window cleaning equipment is more specific . They require all roof anchors to be lab tested to 2500 lbs half of its ultimate load . This test is a design tool or as a comparison model. Where by, the factory load testing of 2500lbs or half the ultimate load of 5000lbs is necessary in order to prove the anchor design against its theoretical calculations.

On site testing is not given extensive or specific treatment in the codes and regulations, so interpretation and sound engineering judgement are necessary to determine appropriate loads and testing method.

Load testing programs can have the following benefits :

Load testing may be necessary in determining structural capability of installations with out prior certification.
Load testing of adhesive roof anchor installations is universally required by all manufacturers.
Load testing is almost always required in determining failure if an anchor is used In the event of a fall or any type of equipment failure .
Load testing of anchors may be required to yield the necessary documentation in order to producing engineered drawing.
Load testing may be the only feasible option in determining if the existing installation is structurally sound.
The following information can be used to develop an effective test program to yield meaningful results. A proper program requires a test prescription to be developed by a professional engineer. Once this is done a carefully selected test load will need to be prescribed to address the specific components. The engineer must have first hand experience in the design and testing of this type of equipment because roof anchors and rigging equipment are designed with various components and sub-system that have variable working load and safety factors.

To ensure the structure is not damaged the engineer must review the building drawings to identify if the building structures can handle the concentrated loads necessary to test certain components.

Any load test program even if it is similar to past projects, will need to be somewhat customized in order to test within the allowable stress of material and not to damage the base structure.

Despite the engineers best effort, risks remain during load test operations. These risks include a possibility of building collateral damage including damage to the structure , roofing or anchor . In most cases the benefits of testing outweighs the risks, but those risks must always be kept in mind when pursuing a load testing program.

1. Roof anchor testing can cause catastrophic failure of an already damaged building - we have had them fail before on wood structures.
2. The anchors being installed at the time of the collapse were on the bootleg penthouse which has large unbraced spans across the large decks.
3. The structural drawings for roof anchors listed two concrete slab depths 6" vs. 8" - which was used for the calculations.

So the question remains, were the roof anchors field-tested less than 24 hours before collapse, and if so, which anchors were tested?

 

[Spartan5]

Concurrent with the removal of debris, they towed at least two damaged vehicles away from the site. FWIW. Can’t say for certain they came from inside the garage.

And

https://twitter.com/trentkellywplg/status/1410174182604804097?s=21

 

[dik]

That he is using 3/4" cover makes me a little suspicious of what his credentials are. I'd also have removed 1-1/2" of conc from around the columns to provide some direct bearing. Missed it...

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

-Dik

 

[Santos81]

Another thought on the possibility of a vehicle collision with a parking garage column instigating the initial failure:

Many (most?) newer car models have a black box (Event Data Recorder) that records - among other things - the speed directly before a crash event. That would be a way once they get to the bottom of the debris pile to see if any of the vehicles in the garage might have hit something and how hard.

I also wonder if any of the onboard assistance services (OnStar, etc) got a notification of an accident in the vicinity in the time before the collapse. These services are cell network and GPS dependent, so they may not work reliably in an underground garage, but it might be worth checking out

It’s unlikely a collision significant enough to trigger the EDR Data Save occurred. Same goes for eCall Telematic response. You either have to trigger airbag deployment or experience a very significant rapid vertical load reversal rate. What may be of assistance are the time stamps for Alarm Event Data. There’s no shortage of vehicles visible at the site that have this as standard.

 

[dik]

From the condition of the building, he could have hit the column with his car door when he opened it...

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

-Dik

 

[Spartan5]

1. Roof anchor testing can cause catastrophic failure of an already damaged building - we have had them fail before on wood structures.
2. The anchors being installed at the time of the collapse were on the bootleg penthouse which has large unbraced spans across the large decks.
3. The structural drawings for roof anchors listed two concrete slab depths 6" vs. 8" - which was used for the calculations.

So the question remains, were the roof anchors field-tested less than 24 hours before collapse, and if so, which anchors were tested?

1. The anchors, if tested, did not cause a catastrophic failure of the building collapse while being tested. The catastrophic failure would have happened hours, days, weeks after the test.
2. The anchors were installed well before the collapse. Not at the time it happened.
3. Not that it matters, but how do we know what was used for the calculations? Is there a comprehensive design report that went along with the plans? By what mechanism would this miscalculation cause the failure?

Maybe they were installing the anchors and conducting the test in secret at night under the cover of darkness because they knew they were not in compliance with the plans and that the slab was too thin. When they loaded up one of the anchors a large piece of roof fell off. Fortunately they were all on the side that remained. So they hightailed it down and were able to escape before the whole building came down. Just a theory.

 

[OHIOMatt]

Relevant article discussing this, please read before dismissing this hypothesis

I have read it, and subsequently reaffirmed my dismissal of your hypothesis, as have numerous others with long histories of relevant and insightful comments and input on hundreds of threads. You have a right to your opinion, as we have the right to dismiss it.

 

[RickyTickyTavi]

1. Roof anchor testing can cause catastrophic failure of an already damaged building - we have had them fail before on wood structures.
2. The anchors being installed at the time of the collapse were on the bootleg penthouse which has large unbraced spans across the large decks.
3. The structural drawings for roof anchors listed two concrete slab depths 6" vs. 8" - which was used for the calculations.

Emphasis mine. This is point were trying to make. 1250 lb load test from an anchor is not a lot of load/weight.

To add to this, the 1250 load test loads are typically performed in a manner that cancels out or creates the reactions locally. Insufficient to create catastrophic failures unless something more serious was occuring. They dont load test these things by dropping weights off the side of the building all at the same time. Thats not how the load test works. They also dont bring 1250 lbs and sit on the anchor. Also not how it works. Even with a 6" vs 8" slab, or the large unbraced spans, the 1250 lb point load is so inconsequently low, relative to the building loads that it would not surprise me if the same portion of the structure incurred a wind load from an afternoon thunderstorm several magnitudes larger than the forces were talking abou there.

 

[warrenslo]

From another article:

In recent years, the American Concrete Institute and the Concrete Reinforcing Steel Institute (ACI and CRSI) developed an Adhesive Anchor Installer (AAI) certification program for horizontal and overhead installation of
adhesive anchors that are subjected to sustained loads. This program was developed to address many deficiencies related to installation of adhesive anchors into concrete substrates that could drastically reduce their load-carrying capacity. Although the adhesive anchors for the described condition are typically installed vertically downward, the authors recommend they be installed by a certified ACI/CRSI AAI to ensure quality workmanship.

Link

 

[bones206]

@RickyTickyTavi - even though the anchor testing you indicate is what YOU are experienced with, does not mean that was the testing performed on these roof anchors at this building. The drawings clearly call for load testing to 5000 lbs on individual anchors. Who knows what was actually done? Perhaps they misunderstood or ignored the drawings and tensioned a cable to 5000 lbs between anchor points in a setup similar to your photo. What if they did that same test all along the cantilevered portion of the roof? I can see that cracking the slab along it's length by inadvertantly pulling the tip of the cantilever up with the tension cable. Maybe they also ignored the GPR instructions and drilled/cored through a bunch of the cantilever rebar? 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.

Although I think warrenslo is incorrect on some of the details, I don't think their theory should be dismissed out of hand.

It's scary how many plausible explanations there are for this collapse. The "swiss cheese" risk model is already down to 10% cheese, and we've only just skimmed the surface of the investigation.

 

[warrenslo]

Concurrent with the removal of debris, they towed at least two damaged vehicles away from the site. FWIW. Can’t say for certain they came from inside the garage.

I understand they are towing the damaged vehicles on the street to the north of the site in preparation for demolishing the remaining structure.