Yep, classic punching shear failure:



Thanks for posting this failure.

There doesn't appear to be any beams over the entire area that collapsed?

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From the photo, it looks more like "direct shear failure" than punching shear failure, as all the column seem sheared in mid length.

I think the thickness of the top layer soil is throwing off the perspective. If the columns sheared there additional bumps in the picture, and there would be exposed rebar from the columns. The slab looks thin, since it seems to conform to the cars it collapsed onto.

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IRstuff - you are correct, no beams. That's typical flat-slab construction. The slab is designed as a large plate with point supports at the column. The critical failure mode is just what is shown - punching shear, where the slab fails in shear and the column "punches" through the slab as it falls. It's really catastrophic in multistory construction, since the slab below can't handle the weight of the slab above as it impacts it, causing another punching failure, and so on until the building "pancakes" to the ground.

The think slab in the dirt pile looks like the walkway pavement. Look the adjacent garage (un-collapsed), the thickness of slab is quite impressive.

If the slab were that thick, I doubt you could get nearly 40 simultaneous punch shear failures; if a column punch sheared the slab, the cantilever would likely cause column buckles in the adjacent columns. I think what we see on the edges are beams. Moreover, I think a thick slab wouldn't conform to the cars it collapsed on; it would pancake the cars completely, just from the sheer weight and impact.

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Believe or not, in the 90's, I experienced a similar failure in Michigan - a huge under ground water holding tank that collapsed due to extreme hydrostatic pressure caused by an intense rain storm. The plant was undergoing maintenance, so the tank was empty, unfortunately the emergency generator and the sump system both failed, and the subdrain clogged, the built up pressure pushed columns upward and sheared, with floor slab crumbled to pieces, and the flat plate roof slab collapsed by gravity.

I am not saying it is occurring here, but the remnants of the columns in the photo remind me of that - column broken in the shaft due to compression. For punching shear failure, I'll expect to see columns with some slab remnants hanging, as the weak shear plane of slab is located at the column perimeter with a distance d/2 from column face.

Looks like we need a Spanish translator to settle the score then :)

Some photos from below here:

https://twitter.com/BombSantander/status/1217107966878539777

https://twitter.com/BombSantander/status/1216745725272391680

The pictures from the first link are a bit disturbing; if the slab is as thick as it appears in several photos, one would think there would be more rubble around the rebar, and there would be large chunks still intact, but everything under the rebar is in tiny chunks, and the stuff above the rebar doesn't look that thick at all.

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Photos below are extracted from pic provided by azcats.





Pay attention to deflected roof slab above. Could be photographic effect and lighting, the floor looks bulged too.

Here's a video surveying the damage from a drone:

https://twitter.com/Ruptly/status/1216845696575213568