Can Skyscrapers Fall Over on Their Side?

[JMartJr]

Has a skyscraper ever fallen over on its side?

 

[Mendel]

Has a skyscraper ever fallen over on its side?

High-rises have.

The topple below was facilitated by a hole in the ground, see slide 3.

Source: https://m.imgur.com/gallery/vzJ3Q

Article:

On June 27, 2009, Block 7, one of eleven 13-story apartment buildings making up the Lotus Riverside compound in Shanghai, toppled over, completely intact. The high-rise was still under construction, and luckily, most of the workers were able to evacuate the building when they felt it start to fall over. [..]

Block 7 met its demise just one day after 272 feet of a nearby riverbank collapsed, proving the area was unstable and that the soil was loose.

Source: https://www.bestonlineengineeringdegree.com/the-10-worst-high-rise-building-collapses-in-history/

If you think of a domino toppling, as soon as it starts leaning, its contact with the floor is a relatively small fulcrum edge. This edge takes the load of the whole building, and gets overloaded. If that domino was a skyscraper, that edge would immediately disintegrate, and thus initiate the straight-down collapse of the structure.

The facade of the WTC towers managed to "fall over" in great swathes because it had detached from the building's floors and now was basically a bunch of steel columns, akin to a trees falling. But unlike a tree (or a steel pipe), a building typically has very little structural resistance against a sideways force, and that makes earthquakes so devastating.

 

[Thomas B]

Has a skyscraper ever fallen over on its side?

If that domino was a skyscraper, that edge would immediately disintegrate, and thus initiate the straight-down collapse of the structure.

As a civil engineering student, one of the first things I learned in structural design classes is that massive steel frame buildings will collapse essentially into a heap regardless of how or where they may be fatally damaged.

I take it there is something about the buildings in this video that makes them not "skyscrapers" or "massive steel frame buildings" in the sense you're talking about. I don't know, they're probably reinforced concrete structures, but isn't the structural concept roughly the same (wind and gravity loads have to be distributed throughout the building). Some of these buildings in any case seem very capable of falling over.

I'd love to see some simple load path diagrams that demonstrate the difference. (Conspiracy theorists clearly believe that the WTC towers and WTC7 were more like these Chinese apartment towers. Maybe showing them the difference in terms of the load paths as the building leans over would help.)

Why doesn't the fulcrum edge immediately disintegrate in the case of these buildings?

 

[Mendel]

Why doesn't the fulcrum edge immediately disintegrate in the case of these buildings?

To me, it looks like it does. The bottom part of these buildings gets crushed as the top part gathers the rotational momentum to tip over.

 

[Thomas B]

To me, it looks like it does. The bottom part of these buildings gets crushed as the top part gathers the rotational momentum to tip over.

The building that starts collapsing at 0:12 seems to come down on the fulcrum edge and stop (there's even a small a jolt) after which it falls over.

And the three buildings at 0:25 seem to be doing exactly what @Marc Powell says isn't possible for "massive steel frame buildings".

The "symmetry" of WTC 7's collapse was not unlikely at all. It was a result of the building's massive inertia and its relatively small ability to resist dynamic forces. WTC 7 was not a monolith and could not possibly topple over like a tree felled by a lumberjack. This is something that most conspiracy theorists and even a few physics teachers and college professors (David Chandler, Leroy Hulsey, et al.) just cannot seem to grasp. As a civil engineering student, one of the first things I learned in structural design classes is that massive steel frame buildings will collapse essentially into a heap regardless of how or where they may be fatally damaged. This is because, upon the initiation of collapse, inertia tries to keep the building where it is while developing dynamic forces work to move it. Loads almost instantly transfer from failed members to others which also successively become overloaded and fail resulting in the building coming straight down.

Here the demolition people seem to have found a way to fell the buildings like trees.

These buildings seem to be behaving like monoliths/dominoes. It would be interesting to hear what makes them different from WTC7 and why WTC7 therefore couldn't possibly have fallen over.

 

[Ann K]

The building that starts collapsing at 0:12 seems to come down on the fulcrum edge and stop (there's even a small a jolt) after which it falls over.

And the three buildings at 0:25 seem to be doing exactly what @Marc Powell says isn't possible for "massive steel frame buildings".

Here the demolition people seem to have found a way to fell the buildings like trees.

These buildings seem to be behaving like monoliths/dominoes. It would be interesting to hear what makes them different from WTC7 and why WTC7 therefore couldn't possibly have fallen over.

Sorry, I've not been following this discussion closely, but from Wikipedia's discussion of WTC7:

"The building's internal fire suppression system lacked water pressure to fight the fires. The collapse began when a critical internal column buckled and triggered cascading failure of nearby columns throughout"

Is the key word here "internal"? It's not a domino being pushed from the side, and it's not a collapse under a fulcrum edge, as in a couple of the examples given above. The location of the stresses is significant, perhaps more so than the specific construction.

 

[Thomas B]

Is the key word here "internal"? It's not a domino being pushed from the side, and it's not a collapse under a fulcrum edge, as in a couple of the examples given above. The location of the stresses is significant, perhaps more so than the specific construction.

Yes, that's sort of the question I was asking. Was it lucky that the column that failed was in the location that it happened to be in? As I understand @Marc Powell, luck had nothing to do with it because "massive steel frame buildings will collapse essentially into a heap regardless of how or where they may be fatally damaged." But since these Chinese buildings do fall over (after being fatally damaged by demolition charges), rather than collapsing into heaps, I'm assuming there must be something in their specific construction that explains how this is possible.

 

[Marc Powell]

The building that accidentally fell over in Shanghai and the apartment buildings that were demolished in China look to be of reinforced concrete construction and much shorter that any of the buildings that collapsed on 9/11. Here is a video of a simulation that demonstrates the effect of inertia on the collapse of a tall steel frame building.

 

[Thomas B]

the apartment buildings that were demolished in China look to be of reinforced concrete construction and much shorter that any of the buildings that collapsed on 9/11. Here is a video of a simulation that demonstrates the effect of inertia on the collapse of a tall steel frame building.

Thanks. That's a convincing demonstration. Seems like it's mainly a question of how tall the building is.

As an aside, it really looks like Kostack could demonstrate all the relevant principles quite effectively.

 

[Marc Powell]

I heard that he is working on a simulation of the WTC tower collapses that will demonstrate the validity of the historic narrative and hopefully quell criticism of the NIST reports.

 

[Mendel]

The building that starts collapsing at 0:12 seems to come down on the fulcrum edge and stop (there's even a small a jolt) after which it falls over.

After the bottom half was already crushed, who knows what shape the pile of rubble is at this point.

And the three buildings at 0:25 seem to be doing exactly what @Marc Powell says isn't possible for "massive steel frame buildings".

They're not steel frame buildings. I also suspect the start of their collapse was edited out.

 

[FatPhil]

The building that accidentally fell over in Shanghai and the apartment buildings that were demolished in China look to be of reinforced concrete construction and much shorter that any of the buildings that collapsed on 9/11. Here is a video of a simulation that demonstrates the effect of inertia on the collapse of a tall steel frame building.

I love how none of the girders bend!

However, the "with taller buildings, the driving force is relentlessly downwards" aspect is a useful single-parameter variation that does bring some insights to a more complex situation. There's no reason to believe that other materials, or simulations that don't treat girders as atomic units, would not have that same trend (and fortunately, the laws of physics support that property being true).

 

[Mendel]

There's no reason to believe that other materials, or simulations that don't treat girders as atomic units, would not have that same trend

generally, connections between girders are weaker than the girders themselves

 

[Jeffrey Orling]

Collapse was initiated locally leading to local column buckling
Collapse was a FLOOR collapse
Floor mass/debris dislodged columns at the base
columns are UNLOADED when floors collapse
They also loose lateral support

 

[Edward Current]

However, the "with taller buildings, the driving force is relentlessly downwards" aspect is a useful single-parameter variation that does bring some insights to a more complex situation. There's no reason to believe that other materials, or simulations that don't treat girders as atomic units, would not have that same trend (and fortunately, the laws of physics support that property being true).

There is also just the scaling of gravity, and the square–cube law, which are counterintuitive for lay people. One can imagine a tennis ball can, or a soda straw or what have you, standing vertically on a flat surface, in a fictional environment where gravity is steadily increasing. There's no reason for the can or straw to tip over; at some point it will just collapse under its own weight, and come straight down.

 

[Jeffrey Orling]

To tip over would require a very rigid structure and a large enough lateral impulse. Of course if one side of the axial structure was removed low down.... it would tip like a cut tree.

WTC collapses were floor collapses, first and foremost and by axial structures (columns) which lost bracing or were undermined.

 

[Mendel]

There is also just the scaling of gravity, and the square–cube law, which are counterintuitive for lay people. One can imagine a tennis ball can, or a soda straw or what have you, standing vertically on a flat surface, in a fictional environment where gravity is steadily increasing. There's no reason for the can or straw to tip over; at some point it will just collapse under its own weight, and come straight down.

When I crushed a soda can, back in the days before can deposit machines, it almost never crushed straight.

 

[Jeffrey Orling]

When I crushed a soda can, back in the days before can deposit machines, it almost never crushed straight.

proves nothing

 

[Mendel]

proves nothing

it shows that using "soda" and "can" in an appeal to intuition may not be the best idea

a tree that gets felled is also "gravity driven" and doesn't require much lateral force if at all.
A steel frame building has properties to distinguish itself from these examples.

 

[Jeffrey Orling]

it shows that using "soda" and "can" in an appeal to intuition may not be the best idea

a tree that gets felled is also "gravity driven" and doesn't require much lateral force if at all.
A steel frame building has properties to distinguish itself from these examples.

A tree loses all support on one side.. we saw the same thing with the top of 2 wtc.

 

[Ann K]

a tree that gets felled is also "gravity driven" and doesn't require much lateral force if at all.
A steel frame building has properties to distinguish itself from these examples.

A tree that breaks off due to lateral stresses (blown down, or perhaps struck by another falling tree) generally acts as a unit, and tends to rotate around its center of gravity. The result is a kick-back, where the top goes one direction but the base goes the other, and can end up many feet away from the broken stump. That's why trees are felled with angular cuts to transfer the force of gravity laterally so it acts to send the tree in the desired direction, ideally with the tree still attached by an uncut portion that keeps the base attached to the stump to prevent that kick back.

 

[Edward Current]

When I crushed a soda can, back in the days before can deposit machines, it almost never crushed straight.

Would that be true if you were applying exactly even force exactly straight down, and to all of the can's mass, rather than the force and your foot being at nonzero angles and applied to the top only?

 

[FatPhil]

Would that be true if you were applying exactly even force exactly straight down, and to all of the can's mass, rather than the force and your foot being at nonzero angles and applied to the top only?

And - was the base of the can fixed or loose. Buckling behaviour is very different depending on the degrees of freedom at the end. C.f. @Ann K's tree example.

 

[Woolery]

When I crushed a soda can, back in the days before can deposit machines, it almost never crushed straight.

Side bar: For those looking to crush cans straight (whether underfoot or against one's forehead), pinch the waist of the can a smidge prior to crushing. It will collapse neatly.

Warning: never attempt to crush a Foster's beer can against your forehead. Foster's beer cans remain undefeated against human foreheads.

 

[Abdullah]

I don't have a definite answer to this question, but I would not be surprised if it was "no".

What is well known is that a key driving force in building toppling us the reaction force from crushing of the structure, wheb not aligned with the center of gravity.

Fir the sake of argument, let us model the crushing resistance of a storey as follows: 0.8g for 1m followed by 0g for 3m. Therefore the acceleration will be 0.2g for 1m followed by 3m freefall

For the first 1m drop
v²=u²+2as=0²+4 so v=2,
½at²+ut-s=0 so t=1

For the next 3m v²=2²+60=64 so v=8
5t²+2t-3=0 so t=⅗

So total t=1.6

Now let's try a different resistance profile. This one will be representative of a building with a 4m length subdivided into an infinite number of storeys each having the profile mentioned above.

But the shape of the intrastorey profile no longer matters at all at thus scale,: we simply get a constant resistance of 0.2g throughout the 4m drop

0.8g/4=0.2g therefore a=2
v²=2as=64 so v=8

So total t=1

Notice how the second value is less than the first one? The infinite storey model falls in just 62.5% of the time of the 1 storey model. Therefore the average resistance for the infinite storey model is just 39.1% that of the 1 storey model. Therefore the infinite storey model experiences less torque during collapse, and therefore rotates less.

 

[Jeffrey Orling]

For a tower to fall over its frame would and connects of members would have to be much more stiffer than needed to self support and carry live loads.
The plane impact can cause massive local damage... but that destruction "consumes" much of the kinetic energy of the plane. You see this in the twin towers. What led to their collapse was the fires which led to structural failures and falling mass which was turned from a static to a dynamic load.

 

[FatPhil]

I don't have a definite answer to this question, but I would not be surprised if it was "no".

What is well known is that a key driving force in building toppling us the reaction force from crushing of the structure, wheb not aligned with the center of gravity.

Fir the sake of argument, let us model the crushing resistance of a storey as follows: 0.8g for 1m followed by 0g for 3m. Therefore the acceleration will be 0.2g for 1m followed by 3m freefall

For the first 1m drop
v²=u²+2as=0²+4 so v=2,
½at²+ut-s=0 so t=1

For the next 3m v²=2²+60=64 so v=8
5t²+2t-3=0 so t=⅗

So total t=1.6

Now let's try a different resistance profile. This one will be representative of a building with an infinite number of storeys each having the profile mentioned above.

0.8g/4=0.2g
v²=2as=32 so v=5.66

So total t=1.41

Notice how the second value is less than the first one? The infinite storey model falls in just 88% of the time of the 1 storey model. Therefore the average resistance for the infinite storey model is just 77% that of the 1 storey model. Therefore the infinite storey model experiences less torque during collapse, and therefore rotates less.

Your equations are as true in 1 dimension as they are in 3. Therefore I don't know how you can conclude from them anything outside that 1 dimensional embedding. You certainly can't even talk about torque, due to the lack of a 2nd dimension.

2 dimensions should be all you need for a simple model, as there will be no spiralling, so you may chose a privileged orientation to align 1 of the axes along. (I.e. you define the direction the building topples in to be the 2d plane you're interested in.) However, 1 dimension does not suffice.

 

[Mendel]

Your maths is incorrect, I believe.

For the first 1m drop
v²=u²+2as=0²+4 so v=2,
½at²+ut-s=0 so t=1

For the next 3m v²=2²+60=64 so v=8
5t²+2t-3=0 so t=⅗

So total t=1.6

Now let's try a different resistance profile. This one will be representative of a building with an infinite number of storeys each having the profile mentioned above.

0.8g/4=0.2g

a=0.8g=8m/s²
s=1+3=4m
v²=2as=64 => v=8m/s, same as above, and necessarily so because the conversion from potential to kinetic energy occurs the same way.

½at²-s=0
4 t² - 4=0
So total t=1s

I'm not sure what "infinite storeys" has to do with that, you've simply compared the model of 1m resistance, 3m free fall with a model of 4m homogenous resistance. We've debunked papers written with the latter assumption because no building works like that.

 

[Abdullah]

@Mendel thank you for pointing out that glaring error. The corrected math above now even more strongly supports my conclusion.

BTW "infinite storeys" means just that, with the caveat that the infinitely large model has been shrunk to just 4m. Sorry for not mentioning that.

 

[Abdullah]

@FatPhil my point is that the driving force for the angular acceleration - reaction force misaligned with CG - is less for buildings with more storeys, even if we make the charitable assumption that the same proportion of each building is asymmetrically failed

 

[FatPhil]

@FatPhil my point is that the driving force for the angular acceleration - reaction force misaligned with CG - is less for buildings with more storeys, even if we make the charitable assumption that the same proportion of each building is asymmetrically failed

In 1 dimension, there is no *angular* anything. Your equations were 1-dimensional, as I explained before.

 

[econ41]

Your maths is incorrect, I believe.

Actually the maths is inappropriate. There is no definition of:
(a) What is the mechanism causing the "crushing resistance". What is being "crushed". Be aware that is the one factor that caused much confusion in debate from 2001-2 through to 2007-8-9-10 and still gets recycled to this day.

(b) What forms the "pivot" for toppling. AFAICS no one in recent discussion has identified that what, how and where the pivot is formed is the key factor defining how the location of the CoM results in toppling.

So it matters not whether the maths is correct. It is inappropriately applied whether right or wrong.

a=0.8g=8m/s²
s=1+3=4m
v²=2as=64 => v=8m/s, same as above, and necessarily so because the conversion from potential to kinetic energy occurs the same way.

½at²-s=0
4 t² - 4=0
So total t=1s

I'm not sure what "infinite storeys" has to do with that,

I'm unclear as to what purpose is served by manipulating fundamental equations when the underlying mechanism is not defined.

you've simply compared the model of 1m resistance, 3m free fall with a model of 4m homogenous resistance. We've debunked papers written with the latter assumption because no building works like that.

The same points I would raise.

 

[econ41]

What is well known ...

Whether well known or not in general it has been the cause of much confusion in the debate about the 9/11 WTC collapses. With most of academia going off the rails from misinterpreting the early work of Bazant. And Bazant himself going down the same false trail with Bazant & Verdure - the "CD/CU" hypothesis is WRONG for WTC collapses. AND the primary cause of the errors - the misapplication of 1D approximations to a scenario that is very much the opposite of 1D.

is that a key driving force in building toppling us the reaction force from crushing of the structure, wheb not aligned with the center of gravity.

So what causes the "not aligned". Surely it is or depends on what forms the pivot - the hinge which is not directly under the CoM thereby creating a toppling moment?

Fir the sake of argument, let us model the crushing resistance of a storey as follows: 0.8g for 1m followed by 0g for 3m. Therefore the acceleration will be 0.2g for 1m followed by 3m freefall

Maybe true in your gross reliance (implicit reliance) on a 1D scenario. What is being "crushed"? How does it result in tilting which is the pre-cursor to "toppling"?

For the first 1m drop
v²=u²+2as=0²+4 so v=2,
½at²+ut-s=0 so t=1

For the next 3m v²=2²+60=64 so v=8
5t²+2t-3=0 so t=⅗

So total t=1.6

Applied to what?

Now let's try a different resistance profile. This one will be representative of a building with a 4m length subdivided into an infinite number of storeys each having the profile mentioned above.

What do you mean by a "resistance profile". You seem to be assuming a lot. Including that the "resistance profile" is 1D - homogeneous across the 2 horizontal dimensions of the Tower's floor plan. Why would such a profile topple?

Therefore the infinite storey model experiences less torque during collapse, and therefore rotates less.

What torque? What causes torque?

 

[Jeffrey Orling]

What isn't being crushed are the axial structures. Some of those structures buckle as a result of load redistribution, loss of bracing, mis alignment of tops and bottoms.

Slabs which lose proper bearing or are overloaded by new super imposed loads (dynamic) will collapse locally and even globally and this can set of a run away scenario (it did).

"One thing leads to another" - failures progress and go unstoppable runaway. Local failures progress to global failures because of / via lateral structures which make the frame composite.

 

[econ41]

What isn't being crushed are the axial structures.

Take care. You are drifting to the specific WTC 9/11scenmario and "what really happened". That is not the topic under discussion which is more generic. AND as framed by @Abdullah it presumes crushing of axial structures AKA "columns".

 

[Abdullah]

@econ41 torque is given by force into sine of it's angle with the moment arm. Therefore torque is proportional to force.

@Jeffrey Orling axial.losd bearing members would be crushed in a crush up collapse

 

[Jeffrey Orling]

@econ41 torque is given by force into sine of it's angle with the moment arm. Therefore torque is proportional to force.

@Jeffrey Orling axial.losd bearing members would be crushed in a crush up collapse

are you referring to a demolition done at the base of a structure such that the building collapses absent couple/support at its base?

 

[Abdullah]

@Jeffrey Orling my scenario is one where s fixed proportion of the building at the base is asymmetrically deprived of vertical support.

This is in contrast to a minimalist scenario where only one storey is deprived of support, where the trend of reduced rotation at large sizes is even more pronounced

 

[Jeffrey Orling]

My sense is that designs are not vulnerable (fatal) to a single column failure.

 

[econ41]

My sense is that designs are not vulnerable (fatal) to a single column failure.

MOST designs are probably not vulnerable. BUT that does not make it a global truism. At least to prima facie standard WTC7 was vulnerable. So the burden of proof is on anyone who claims it was not.