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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[05dtaylor]

I would add to MOJOJOHN's list that inspection reports should be required to more fully describe failure scenarios that could occur based on the building design, and then postulate a sequence of events where the observed deficiencies eventually lead to failure.

For our Dam Safety Inspection & Hazard Analysis Reports we include a Potential Failure Mode Analysis(PFMA), a.k.a. Failure Mode & Effects Analysis (FMEA). Part of developing the PFMA usually includes a round table discussion involving a representative from the various applicable involved parties such as different federal & state regulators, owner, operator, emergency management, first responders, the consulting engineer, etc.

 

[DavPc]

Triggers aside, the most troubling aspect is how little warning there was that the building was in imminent danger of collapsing.

What was it? Perhaps at most 10 minutes between the calamity in the garage level and the rest of the collapse? Even the FIU bridge was waving its figurative arms shouting, "DON'T INSTALL ME!" as soon as the concrete forms were removed - days before it fell. Is it not possible for a 40-year old concrete structure to give clear warning signs at least 24 hours in advance that everyone needs to gather their belongings and evacuate?

 

[la belle vie]

The owners at Champlain North should consider retrofits that make it impossible for the pool deck slab to pull down the building.

 

[IRstuff]

Unless someone instrumented the building, it's not clear that there would have necessarily been any human observable "signs."

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[1503-44]

It would seem to require monitoring strain gages placed at all critical points. Once destructive motions initiate, its obviously too late for warnings.

 

[SFCharlie]

I'm an outsider asking a question 'cause I do not know. (I'm not being rhetorical).
Bridges are supposed to be "redundant" (Yes, I know the FIU bridge claimed redundancy).
How can a condo building be redundant and economic? Should the cross beams be strong enough to withstand a column failure? Like I said, I don't have an answer.
By the way, I don't see crossbeams in the wreckage. What takes their place (carrying the tension and compression of the truss that is the building)?

SF Charlie
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[Vance Wiley]

Looking ahead - a link to a ceiling in garage of a Biscayne condo -
I would suggest a yardstick be used to monitor this cracking. The condo assoc manager is aware of the video - - - - watch for the display of urgency - -

https://www.youtube.com/watch?v=y33JbmcUnUI

If he is taking action where is the shoring?

 

[Murph 9000]

I believe that huge "crack" has been identified as an expansion gap between the garage and tower.

 

[Retiredat46]

How can a condo building be redundant and economic? Should the cross beams be strong enough to withstand a column failure? Like I said, I don't have an answer.
By the way, I don't see crossbeams in the wreckage. What takes their place (carrying the tension and compression of the truss that is the building)?

The function of cross beams (resisting sideways movement) is performed by shear walls. They will be found around the elevators and stairwells (where they also provide fire protection) and some other places throughout the building. Just Google shear walls to find out more. There was some discussion in the first thread on this topic about the shear walls in this building being barely adequate for the oceanfront location and environment, primarily wind loads.

I'm sure someone else who is more familiar with the construction of buildings like this will be able to answer your first question.

 

[hpaircraft]

By the way, I don't see crossbeams in the wreckage. What takes their place (carrying the tension and compression of the truss that is the building)?

This building, and most like it, are not trusses; they're more like simple orthogonal frames. What little shear is developed by wind loads and the occasional seismic jolt is reacted by some few shear walls usually located near the core. It is common for elevator shafts to be reinforced to react the shear. It gives me the heebie-jeebies, but it seems to work where it works.

Here in the SF Bay Area this building would probably not have lasted through the 1980s. Our codes demand massive shear braces on relatively close spacing. In many buildings from the 1970s you can see retrofitted X and V steel shear braces just inside the windows installed after the Loma Prieta quake.

 

[moon161]

How can a condo building be redundant and economic? Should the cross beams be strong enough to withstand a column failure? Like I said, I don't have an answer.

Codes, I think. If they all have to be redundant, then redundance is sufficient instead of inefficient. Code enforcement should keep insufficient from being an option.

 

[Vance Wiley]

Hi, Charlie. You are right on target. Redundancy costs money. Redundancy reduces risk. Redundancy can extend the life of a structure which may experience slow degradation from the elements or from wear. How do we decide the tradeoff?
Mostly thru the building codes which are intended to provide "overhead" in the form of extra capacity if needed, account for small design flaws, and allow for construction tolerances. In this case, the use of higher strength concrete would have increased capacity and provided better protection of the reinforcing (reducing the rusting), more concrete cover to protect the reinforcing, and thickened sections of the floor slabs at the top of columns, to name a few. All of which cost money.
You asked "Should the cross beams be strong enough to withstand a column failure?"
I think you are referring to the flat slab of constant thickness each floor - that is a weak spot in this design. The cross beams I am aware of were in the parking ceiling where building columns did not align with parking area columns. And there is the real likelihood that had there been beams formed in the slab and connecting the columns in a grid, effectively forming a frame, this structure would have been much stronger. On the other hand, it served safely for 40 years, and would have served longer if not for the deterioration of many elements.
Engineering learns as we go, and this was an acceptable method of construction 40 years ago. Hopefully it is not used a lot today.
Good designs and good construction can create a better investment in the long term, but that can all be lost if not maintained along the way. Kinda like changing the oil in your car.

 

[Vance Wiley]

Murph - we have learned here that such a joint would be a good thing, I think. But that is a really random and unintended looking joint as I see it. Is the slab holding level across the 'joint'?

 

[Teguci]

Some items that have changed in our building codes that may mitigate against this kind of failure:
- Concrete durability specifications, especially for coastal and snow areas, have become more significant. W/C ratios and concrete strength requirements to prevent chloride intrusion have been adapted.
- Lateral loading for building designs have been significantly increased. Seismic design requirements have been added and wind loading has been adjusted up.
- Flexural driven punching shear for thicker slabs has been addressed in the 2019 update.
- Ties and stirrups are now required to be closed with 135 deg bends in many circumstances due to seismic concerns and torsion.

This is premature since we still don't know what went wrong. However, for those of you in the "We must do something" crowd, rest assured that if a building containing an engineering office fails, it might be because our design manuals and building codes now weigh 3 to 4 times as much as when this building was designed.

 

[SFCharlie]

it might be because our design manuals and building codes now weigh 3 to 4 times as much as when this building was designed.

Yes! When the regs become unusable, they become useless.
Also, Having the regs on line in a searchable data base, not only saves weight, but the engineers time looking stuff up.
Also, if we are making drawings on computer, Some smartypants computer systems team can make software to read and analyze, and even add rebar etc. as per the code. (we do this to design computer chip of multi-millions of elements now, and have been building this software since the late '60s)

SF Charlie
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[la belle vie]

There is middle ground between a fully redundant structure and a structure having details prone to completely unzipping if one thing goes wrong. Even if the investigation concludes that the problem did not come from progressive punching shear of the pool deck, it seems like a bad practice to design something that will progressively fail in a brittle manner. At least detail for ductile failure as is done in seismic zones.

 

[Mark R]

Looking ahead - a link to a ceiling in garage of a Biscayne condo -
I would suggest a yardstick be used to monitor this cracking. The condo assoc manager is aware of the video - - - - watch for the display of urgency - -

https://www.youtube.com/watch?v=y33JbmcUnUI

I posted a long video of that same damage earlier today at 02:52 it had some follow-up about the damage also. Instead of a TicTac video it was a new story that ran about 3 minutes.

 

[hokie66]

The vision of that Key Biscayne building does look like a joint, either a construction joint or a movement joint. In either case, it is ugly, and needs to be investigated and repaired.

 

[1503-44]

SFCharlie, Unfortunately while they are convenient, searchable codes are a two-edged sword. I find many engineers avoid reading the full code and hence miss understanding the interactions of the various sections when it is so convenient to simply search up some detail they need at any given moment, copy/paste and move on.

Redundancy in my experience is not practical in run of the line commercial structures or even offshore platforms. It is not something that is designed into a structure, but something that results indirectly from the normal design process, such as designing a building to separately resist both N-S and E-W wind, but knowing that winds never blow from the both the north AND east at the same time. Or the low probability of having all floors with full live load applied. I've personally never designed any structure to be capable of standing if, for example a floor beam let go and fell onto the lower one, or for some armored car leaving the street at 60mph, crashing into and taking out a first floor column. If an offshore platform loses one of 4 or even 6 legs, its probably going to go totally under, but might survive because the current only flows one direction at a time. While waves could theoretically strike from multiple directions, that was never a design condition. I have designed various control buildings in refineries for blast shock requirements, but that has been the limit of my designed-in redundancy, which isn't really considered to be redundancy if it is a realistic design scenario.

 

[cliff234]

Quote (Teguci (Structural)6 Jul 21 19:54)"...it might be because our design manuals and building codes now weigh 3 to 4 times as much as when this building was designed.''''

One thing I've noticed over the years is a trend towards "digitizing" engineering judgement. And that is one reason codes and design standards are growing in size.

Example: We compute live load reductions based on influence area. In the past engineers had to know what the influence area is, and how to compute it manually. About 20 years ago ASCE 7 provided a new variable, KLL ("Live Load Element Factor"), and a table listing the values for KLL. This factor allows computer programmers the ability to digitize the computation of reduced live loads, and it allows engineers to not have a clue as to how to compute reduced live loads manually.