Condo Wreckage Hints at First Signs of Possible Construction Flaw

[Throck]

https://www.nytimes.com/2021/07/03/us/florida-condo-collapse-steel-rebar.html

In addition to the contractor some projects have a site rep/inspector hired by the owner through the engineer/architect. Things are getting thick.

[BigmanPigman]

1. I read that article yesterday and then went to this video...

It makes sense that one factor is the lack of rebar in the columns. Once the "punch thru" failure happened in the columns it was a domino effect over several minutes.

[Maraya1969]

4. Did the Twin Towers have rebar in them? I have never believed that they fell

just because they were hit but this collapse seems familiar. Unless the Twin Towers had rebar which should have stopped it I would think.

Edit: Here is from Google but it doesn't explain if the concrete was reinforced.


"In all, the towers were assembled from more than 200,000 pieces of steel manufactured around the country, 3,000 miles of electrical wiring, 425,000 cubic yards of concrete, 40,000 doors, 43,600 windows and six acres of marble."

[localroger]

10. The towers had pure steel, not concrete, columns

...and yes the floors were reinforced. The weak point was the hooks which "hung" the floors from the peripheral and central steel columns. This was an unusual design meant to give lots of unobstructed interior space, but once the first floor fell from its heat-weakened hooks, the others could not resist the forces of collapse and came down too.

[Chainfire]

11. Sure the twin towers concrete had steel reinforcement. You can't construct a concrete bird bath

without reinforcement. Concrete alone is very weak. Where the engineer doesn't require rebar, they will use a strong steel wire mesh that resembles fencing to reinforce concrete. There are some other ways to strengthen concrete but they are not as common as wire mesh and reinforcing steel bars.

The Twin Towers used a different construction technique than the Florida structure where the floors of the towers were supported by bar joists. Think of bar joists as lightweight steel beams. The reason that the towers fell has been well documented. Sheared columns, disabled fire protection systems, and intense heat from the airplane fuel fire softened the bar joists allowing them to sag and pull away from the vertical columns, leaving no support for the floors. Once one or two floors pancake, the lower floors can't take the extra shock and load so they begin a vertical domino effect.

The Twin Towers were not engineered to withstand the assault by the huge, fast moving, flying fire bombs that the the airplanes became. They may well have survived the impact of the planes if there was no fire, but they couldn't take the shock, the shear and the intense fire.

Well engineered and properly constructed tall buildings are safe, the engineering and construction is well understood. The 16 story Manhattan building in Chicago was built in 1891 and still stands today. When the results of the Florida disaster are fully investigated, there will be a lot of blame to go around. A lot of systems failed to bring that building down. It is a damn shame.

[BigmanPigman]

14. I recall reading that Bin Laden

wasn't sure the fuel would add to the damage so he was pleasantly surprised with that added bonus.

[msongs]

2. account required to read article. nt

[AllBlue]

5. See the article here w/o paywall

https://archive.ph/a26My

[Scrivener7]

3. The story of Gabriel Nir, a resident, and his mother escaping their first floor apartment.

[NJCher]

15. Incredible luck

Eom

[Demovictory9]

6. uh oh for the "better maintained" sister building... probably it has the same flaw

[Crazyleftie]

7. Misleading statement

Typically the architect IS ALWAYS hired by the owner for site representation. The representation can be daily, weekly, or even monthly. Lack of $$$ (typically by greedy owners) for adequate representation/inspection especially on large projects can create problems. Lenders require the architect (in some cases an independent rep) to review/approve monthly billing so the minimum visits are monthly. As an architect I have come across quite a few miserly/greedy owners/developers who skimp on these services (as well as the quality of the design/construction). I believe this builder/owner probably was one of these.

[Throck]

8. Typically I've seen structural engineers used for inspection.

The inspector was on site every day 8 to 10 hours. They kept logs, made sketches and took pictures. They took concrete samples and sent them to labs. They checked materials coming on site to make sure they're as specified by the structural engineer. The site rep will also schedule additional specialty inspectors as needed.

[Crazyleftie]

9. What you are referring to

are testing agencies, who take the concrete samples for testing. They are typically not engineers. And as I said the scope and type of inspections and by whom is determined by the owner/developer and some times they are very minimal. These testing agencies may or may not inspect the rebar or structure.

[Throck]

12. Site management and quality control are multi person/company involvement.

The site manager/engineer is usually there full time and is the conductor of the orchestra/ ringmaster of the circus. Daily on site reports for record keeping. A recent project I worked on had 4 full time licensed engineers on site every day. That team coordinates the concrete testing agency, weld x-ray people, electrical inspections. The boxes of records could fill a trailer until it gets digitized.

[burrowowl]

13. K&R