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
Eng-Tips.com Forum Policies

 

[BlakeStr]

This article says a crane was at the building.

https://www.usatoday.com/in-depth/g...g-collapse-investigation-underway/5333761001/

 

[BlakeStr]

The posted plan explained to be top bars shows #4 cantilever bars and based on the quantities shown they appear to be about a 13" spacing.

 

[bones206]

P16 is on top of a column. P15 and P17 are between columns. See the column anchor on the left side of the penthouse (that anchor also could have been the failure point.)

Correction, P15 & P17 are also shown on top of columns, typically these are installed between columns, so this is odd.

You appear to be correct. I misinterpreted the dashed line calling out "EXISTING WALL BELOW" as the support line for the cantilever. Not sure why the parapet section shows a bearing wall as the support if there is no wall. Also, the section calls out 5'-6" cantilever, which doesn't seem to match the 7'-0" cantilever shown in the penthouse plan.

As a side note, the anchorage of the parapet wall is very weak IMO. (4) #5 dowels (hooked? no hooks?) going into a 6" slab at tie columns spaced @ 20'-0". That's very little anchorage for a roof parapet in a hurricane region.

 

[Js5180]

Could the round object in the ramp video be a jet fan for ventilation?

 

[Roga50]

I'm sure he wouldn't move from me million-dollar condominium to a tent because the government told you to.

People in million dollar condos down here have other alternatives that won't affect their bottom line at all.

 

[spsalso]

Around here, a million dollars buys you a closet with a solar panel on top--livin' the good life!


spsalso

 

[Js5180]

Can anyone identify:

1. The cardboard box in this picture, ending in “ECK”
2. The blue wrap
3. The approximately 4” layer of material above the slab at the far right of this picture?

(Credit Miami Herald)

These all appear to be on the roof, just outside the penthouse corridor.

 

[DroppedBits]

Can anyone identify:

1. The cardboard box in this picture, ending in “ECK”
2. The blue wrap
3. The approximately 4” layer of material above the slab at the far right of this picture?

1) Looks like the Greenheck logo. Probably the box for an exhaust fan. From the photo below, the exhaust fans looks relatively shiny/new.
2) Possibly wrap from the factory for the exhaust fans.

 

[Js5180]

Wow. I am impressed. That answers the question.

 

[warrenslo]

What you also see in this picture is the roof anchors were not needed - they can access the building from the ground level with a cherry picker.

We need to reevaluate requiring them on older structures that may not be able to withstand the installation or testing requirements. This is a sort of grey area where OSHA requires the anchors and the building code generally doesn't really provide any guidance.

 

[warrenslo]

Also - if the cantilever collapsed and most of it landed on the 12th floor roof - that’s a drop of 10 feet or so. How likely would the building initially survive that?

Above the bedrooms of x11 only the 12th floor and penthouse had cantilevers, the remaining was the two strips of bedroom windows below. If the cantilever broke off it would have fallen into the pool deck where the column was damaged. In the surveillance footage this area seems to already be missing. I'd imagine there is more to the video they haven't shared yet unless the video was on a motion sensor and triggered when the main collapse started.

 

[warrenslo]

This building was 40 years old which is 14,600 days, but this collapse happened the day after a crane was loading roofing materials on the roof and the day after fall protection anchors were installed. The parapet detail Warrenslo posted has a 5'-6" cantilever, but when analyzed the moment hinge point should be center of support which is about 5'-10". The slab is only 6" thick and the reinf only #4@13" oc. Using structure dead loads plus 10 psf for roofing material and 30 psf for live load, the factored moment is 4.08 k-ft/ft and the factored capacity is only 3.99 k-ft, so assuming perfect conditions, this was a design error. Add rebar corrosion, which is likely under the hot wet roof, possible damage by the installation and testing of the epoxy bolts, and possible live load overload from roof materials or removed debris stockpiles, and it is highly possible that this cantilever slab failed first. The impact of falling concrete is the weight times the fall distance/deceleration distance. If the height is 120 feet = 1440 inches and the deceleration is 2", a 50 lbs piece of concrete imparts 50lbs x 720 = 36,000 lbs. 500 lbs = 360,000 lbs. Negating wind friction, for a 120' fall, the debris would be traveling 60 mph at impact.

Could the pool slab handle this impact?

 

[StrucDesignPE]

Saw this article early this morning:
Link

Allyn Kilsheimer, who was hired by the city to examine the incident, confirmed to The New York Times that there are signs less steel reinforcement was used during construction than called for in the original 1979 design to connect concrete slabs below a parking deck to the building's vertical columns.

 

[Retiredat46]

FWIW, here's a picture of one of the post anchors snipped from

https://www.miamiherald.com/latest-news/jdzgc4/pic...

in post in first part by bradw1128 (Civil/Environmental)24 Jun 21 20:46

In this video of early rescue you can hear what sounds like a car alarm.

https://www.miamiherald.com/news/local/community/m...

It's surprising you don't hear more, but how long the security alarm sounds varies between models.

 

[Retiredat46]

Quote ((article quote))
Allyn Kilsheimer, who was hired by the city to examine the incident, confirmed to The New York Times that there are signs less steel reinforcement was used during construction than called for in the original 1979 design to connect concrete slabs below a parking deck to the building's vertical columns.

Those deficiencies were noticed early in the first part.

 

[JohnRBaker]

Not sure is this item has already been posted or not, but if it has, sorry for the redundant post:

Surfside Condo Wreckage Hints at First Signs of Possible Construction Flaw

https://www.msn.com/en-us/news/us/s...igns-of-possible-construction-flaw/ar-AALJKsd

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[JohnRBaker]

Yep, I should have looked more carefully

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[799931]

The slab steel does look light but it's hard to say definitively.

Is the implication that there aren't enough bars left going through the column? Bottom steel is missing? Something else?

Even if the slab steel is light, I still struggle with why the failure occurred now and not in the first 40 years.

 

[Js5180]

Let’s assume that the surveillance camera was motion triggered. It’s a professional camera mounted on a pole just east of the 8701 building.

In my experience, motion triggers are software based - if enough of the pixels change, it’s triggered. However, the point of the motion trigger is to reduce the amount of unnecessary storage, and the camera is always powered on. There is a look-back period built in, usually 30 seconds or so. The recording system saves the video from 30 seconds before the event.

So even if the surveillance camera was motion triggered, it should most likely still have video for some interval prior to the motion.

 

[Murph 9000]

Even if the slab steel is light, I still struggle with why the failure occurred now and not in the first 40 years.

It could be a latent defect that forms one of the holes in the Swiss cheese. For example, just a hypothetical for discussion, weak connections on a few columns, combined with stress and vibration from the adjacent construction at 87 Park, combined with someone reversing a 14,000 lb F-350 truck up to the planters to unload construction equipment, combined with cumulative structural damage. I invented the heavy pickup truck, just as a straw to break the camel's back.