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What kind of failure it will be? St
13

What kind of failure it will be? St

RE: What kind of failure it will be? St

STability. There doesn't appear to be any sort of lateral load resisting system. That's why all the columns on the main floor move in unison. A strength failure likely would've been just a single column going down.

RE: What kind of failure it will be? St

Both. Lack of form works is the main reason.

RE: What kind of failure it will be? St

This things give me the shivers.

First guess would appear to be stability. Hard to tell what type of structural system it is. I would guess steel beams/decking and columns but the video clarity isn't the best. You can't can't see what is happening along the right side of the building either.

All of the columns appear to move along the first floor, in the same direction at the same time. I would like to think the members were not undersized as they are not really seeing their full design load at all.

RE: What kind of failure it will be? St

The workers are pouring concrete at the far end, and one operates a leveling/troweling machine all around the slab, do you see any form works at floors below?

RE: What kind of failure it will be? St

Wow.... I'd say that this is primarily stability No significant lateral load resisting system. So, the second you get a little bit of lateral displacement or lateral loading, the lateral displacement increases until 2nd order / stability effects cause strength failures and the whole thing goes down.

RE: What kind of failure it will be? St

I agree with Josh.

Anyone notice the guy on the main level? He was most certainly killed instantly.

RE: What kind of failure it will be? St

Maybe it’s the monitor, but those columns looked out of straight from the get go. P-Delta gone wild?

Obviously some proper bracing would have kept it vertical.


RE: What kind of failure it will be? St

At work.


At failure.

RE: What kind of failure it will be? St

The camera has a lot of distortion, which is why the third level shows a significant bow, compared to the second level.

Seems to me to be a very ad hoc "design" since there is nothing resisting lateral forces, so even if it had successfully completed construction, any wind likely would have toppled the building, with possibly a lot more people in it.

TTFN (ta ta for now)
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RE: What kind of failure it will be? St

Usually the floor should be fully supported during concreting, and the full shoring shall at least stays through the end of curing period, then reduce the shoring only when the concrete has achieved specified strength. In this case, the contractor are in a hurry to complete the project by removing the form works too soon, while the concrete is very young with very little strength. The concreting activity near the edge produces an eccentric loading effect, causing sway mechanism that pushed the structure to fail.

RE: What kind of failure it will be? St

It's not clear whether there ever would have been shear walls to be built, though. Seems to me that if there were shear walls in the design, the engineer should have either designed them to be present during the floor pours, or had required shoring, but it seems dubious to me that sufficient shoring could have been installed that wouldn't have interfered with the pour, vs. building the shear walls in the first place.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: What kind of failure it will be? St

Yeah, I can't imagine a situation where you would pour the columns but not the shear walls. Generally speaking for cast-in-place type construction you do a vertical pour (columns and walls) then a horizontal pour (slabs and/or beams). So I don't see why the shear walls would have been left out.

If, however, it was supposed to be braced with steel bracing, then sure I can see why that would interfere with construction. But that means then you have to provide an alternate temporary bracing until all lateral load resisting elements are installed.

RE: What kind of failure it will be? St

I see an engineering disconnect is happening. We shall walk out our office and look how things been constructed, at least occasionally.

RE: What kind of failure it will be? St

I don't believe there was any formwork on either level at any time. Looks like the floor system was intended to carry a concrete topping, so no formwork was necessary. Looks like a stability failure; the columns behaved as though they were hinged at the second level.

BA

RE: What kind of failure it will be? St

Definitely looks like columns stop and start and beams are continuous on the near face. So a big stack of pinned members which performed as expected.

RE: What kind of failure it will be? St

Looks like weak axis failure resulting from lack of bracing to me.

RE: What kind of failure it will be? St

Quote:

Looks like the floor system was intended to carry a concrete topping, so no formwork was necessary.

It is a possibility, but depending on the age of the concrete, I've difficulty to accept "no formwork" is necessary. See how many workers gathered in a small area of the slab, a highly unbalanced live load pattern.

RE: What kind of failure it will be? St

retired13,

When the collapse occurred, the concrete on the upper level was being finished, so its age was zero, yet there is no falsework visible below it.

BA

RE: What kind of failure it will be? St

The floor system is the 'formwork' here. Cannot tell what type of floor it is though. But it isn't uncommon in precast (double tees, flat slabs) and composite steel deck floors to not require any falsework or propping.

RE: What kind of failure it will be? St

Don't looks like hollow core or double tee either, but not steel framing though.

RE: What kind of failure it will be? St

Quote (Agent666)

So a big stack of pinned members which performed as expected.
Best explanation here. The structured performed as you would expect. There really isn't much else to it. Beyond speculating on what ISN'T there.

Quote (Agent666)

The floor system is the 'formwork' here. Cannot tell what type of floor it is though. But it isn't uncommon in precast (double tees, flat slabs) and composite steel deck floors to not require any falsework or propping.
Excactly.

The half dozen posts claiming formwork have just left me scratching my head in confusion.

RE: What kind of failure it will be? St

Stability. Pin ended columns fell over.

RE: What kind of failure it will be? St

If this is an conventional RC structure, too early to impose localized live load will lead to failure like this. For precast concrete structure, for all pinned condition, what is there to provide stability? My hair almost gone.

RE: What kind of failure it will be? St

Image below captures the failing structure just second before collapse. Note the dish shaped floor slabs.

RE: What kind of failure it will be? St

I'd say that's a few seconds into the collapse initiating and we'll beyond the point of no return... Static equilibrium. It did not collapse because of anything to do with the floors in my opinion.

The stopping and starting of the columns probably with pin like end connections, combined with a possible lack of rotational restraint to the beams in this configuration causing the beams to role over appears to be the nail in the coffin, causing the whole thing to rapidly lose stability.

I thought it was fairly obvious it's a steel structure. You can even see the columns are an I-Section shape if you look at the floor. The cross sectional dimensions are non-sensical if it was in fact a concrete structure.

RE: What kind of failure it will be? St

Maybe limited by the angle, couldn't see beam though.

RE: What kind of failure it will be? St


What power shovel is doing there?
Is there any soil settlement-like situation occurred before starting a collapse; in front left side column area? so the lateral loads introduced into the frame and bow in floor can be seen there.

and obviously as (Agent666) mentioned , "So a big stack of pinned members which performed as expected" is true.

Cheers! -VH

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