The influence of buckling

[chippy]

How many of you were aware of the fact that buckling was actually a major factor in the collapse of the World Trade Center? From a layman's point of view, you'll likely say "well duh, of course it buckled, that's how it fell on itself, silly!"

And this is why it's very dangerous to be a layman and try to hypothesize about what happened on 9/11.

Here. Educate yourselves.

(edit: there's some dumb rule that you can't post links until you've posted 15 times. So here is the Euler formula for buckling: P_cr = (pi^2 * E * I) / L^2, where P_cr is the amount of inward force a beam can endure before buckling, E is the modulus of elasticity (which varies for different materials), I is the moment of inertia which defines the geometry of the beam, and L is the length of the beam)

On the top you will find the Euler formula for buckling, which is a good approximation of the amount of force a beam can endure before it buckles. Notice the L^2 term on the bottom?

Now, consider the fact that when the airplanes hit the WTC, many floors of support were knocked out. These supports kept the lengths of the beams as small as possible to reduce the influence of buckling. But when these supports get knocked out, the beams increase in effective length. If a beam was 10 feet long for one floor and lost a few floors of support, its effective length may increase to 40 feet, meaning that there's 40 feet of beam between its upper and lower support. Remember L^2? If a beam's length increases by a factor of 4, then the amount of force a beam can support before it buckles reduces by a factor of 16.

SIXTEEN.

What if another floor was knocked out? That would decrease the amount of force a beam could support by a factor of 25! Once one beam fails, the building will topple in its direction, bringing extra momentum with it and initiating the pancake collapse of the towers.

Throw in a little heat from the fire that most definitely weakens the steel, and you shouldn't be surprised that the building would fall at all.

And please, stop arguing that the fire wasn't hot. If it wasn't hot, people wouldn't have chosen to jump down to the ground 100 stories, which is one of the most terrifying ways you can die.

[JamesB]

And please, stop arguing that the fire wasn't hot. If it wasn't hot, people wouldn't have chosen to jump down to the ground 100 stories, which is one of the most terrifying ways you can die.

Good post. It is hard to argue this point with the truthers though. I have even seen posts speculating that they were pushed by special forces operatives dropped by helicopters. When you have completely lost touch with reality, anything seems logical.

[jaydeehess]

Now what happens when a column buckles? It either bends over or snaps. In either case it, or debris from it, then impacts other columns with a horizontal velocity so even if an adjacent column was not buckling yet it now gets slapped on the side which just adds to buckling forces.

No matter though since many are the CT's that will state that the core of the WTC towers should have been able to stand on their own. Many will also state that the core columns took all of the gravity load and were in fact built to take 5 or more times the actual gravity load of the building.

Do I have to point out the problems with these statements?

[Unfit4Command]

Good post, I haven't heard of this formula till now.

I still can't believe that some members of the "Truth Movement" still think that buckling never even occured. This is one of those theories where the CTs are ignoring mountains of pictures proving them otherwise.

These are a few of my favorites:
http://img.photobucket.com/albums/v721/rhearhy/WTC/saggingfloors4.jpg

http://img.photobucket.com/albums/v721/rhearhy/WTC/saggingfloors7.jpg

http://img.photobucket.com/albums/v721/rhearhy/WTC/bow2-1.jpg

http://img.photobucket.com/albums/v721/rhearhy/WTC/saggingfloors8.jpg

[chippy]

Now what happens when a column buckles? It either bends over or snaps. In either case it, or debris from it, then impacts other columns with a horizontal velocity so even if an adjacent column was not buckling yet it now gets slapped on the side which just adds to buckling forces.

Right. Or they could fly straight outward, which explains why you can see beam components in...aw crap I can't post links yet! This rule is stupid. But you've seen the pictures. There are beams flying out horizontally, and the geniuses in the conspiracy department can't figure out why they could move horizontally if the building is falling vertically. When the beams buckle, they do snap out horizontally. I mean, if it's that hard to picture, find a stick in your backyard, press it down until it breaks, and see if it falls straight down or if it shoots out to the side first!

[R.Mackey]

Good post, and welcome, Chippy.

I've argued the beam equation before, but the bottom line is the Troothers are utterly immune to any kind of legitimate education. Which is why (like you, I suspect) I stopped talking to them entirely and focused on others who really want to learn.

Another point I often make, referencing the picture of the structure buckling, is that structural steel fails at about 3% strain. In other words, if you can see it bending, it's bad... really bad. The WTC collapses should surprise absolutely no one with any formal training whatsoever, unless one literally runs from the evidence.

Sadly, many people do.

[JamesB]

Good post, and welcome, Chippy.

Another point I often make, referencing the picture of the structure buckling, is that structural steel fails at about 3% strain. In other words, if you can see it bending, it's bad... really bad. The WTC collapses should surprise absolutely no one with any formal training whatsoever, unless one literally runs from the evidence.

Sadly, many people do.


LOL When I did my radio interview last week the host asked me about WTC7. I brought up the damage and fires and such and summarized it with, "Firefighters placed a transit on it, and discovered it was leaning. For a 47 story building, that's bad."

Great minds think alike I guess. ;)

[Minadin]

Well, that really depends on what you mean by strain.

Most steel structures are over-designed by about 1.5x. Meaning that the actual live+dead load is 2/3 of what the members can take. So, if it's taking 103% of what it should, it would not be a big deal.

At 3% deflection you can visibly see it bend and that is indeed very bad. We normally design buildings first for the structural strength and then doublecheck it for deflection. A deflection of more an 1/4 inch or so for a floor is VERY noticeable and will cause people to feel unsafe even if it isn't structurally true. So oftentimes a structure will be even more oversized for just that reason.

Any time steel visibly bends in a building it is not good. In the WTC, there were so many different ways that the steel could bend, for so many reasons, that it is almost suprising that it did not fail earlier. In truth, the collapse was caused in part by the steel failing in a couple of different ways. One added to the other.

[uk_dave]

It's also worth remembering that whilst steel does have some flexibility, the materials used to make it look pretty such as plaster or marble are very rigid and prone to cracking at the slightest movement.

So when the woowoos get all incredulaous that marble panels had been destroyed in the foyer after the plane impact they are failing to take into account that these panels are just thin slabs of material held in place with either a mechanical fixing or adhesive and they don't take kindly to the type of movement the tower would experience by having a plane slammed into it.

But then, there are many things that the woowoos fail to take into account in their fantasies

[Magic 8 Ball]

If it wasn't hot, people wouldn't have chosen to jump down to the ground 100 stories.

Chosen to jump?
I perfer "the heat forced them out."
I don't want to be anal, but your statement does seem to imply suicide (even though I know that's not intended). I heard people say "they jumped" a number of times and I believe it is only because the reporters covering the event, were saying it. I watched 9/11 live on TV and never once thought anyone was jumping. I couln't tell if someone was making a conscious effort to jump or there was another force at hand. I always figured that the pressure coming from the heat pushed them out of the building. I am no expert in fire, but I have seen and felt heat that can push things away involintarily.

[uk_dave]

I seem to recall seeing video of one guy trying to climb down, presumeably to the storey below..... it doesn't bear thinking about. :(

[JanH]

Good post, chippy.

UK Dave: When some stupid social anthropologist imported 9-11 woo to Norway I was compelled to make myself more familiar with the evidence. I spent weeks studying documents, videos, pictures and virtually relived the whole monstrosity again (I was actually on a plane in the vicinity of Afghani airspace when this happened in 2001!). It was emotionally draining, to put it mildly, and this greatly increased my disdain for all the sloppy and dishonest woo tactics. It's a dirty job, but somebody has to do it...

[Bell]

I seem to recall seeing video of one guy trying to climb down, presumeably to the storey below..... it doesn't bear thinking about. :(

That was shown in NG's Inside 9/11. Very sad to see that man fall :(

About the buckling, I posted a link to this video (http://video.google.com/videoplay?docid=-5405555553528290546) a few times before. It clearly shows the buckling ocuring at the south tower.

[Bell]

Chosen to jump?
I perfer "the heat forced them out."
I don't want to be anal, but your statement does seem to imply suicide (even though I know that's not intended). I heard people say "they jumped" a number of times and I believe it is only because the reporters covering the event, were saying it. I watched 9/11 live on TV and never once thought anyone was jumping. I couln't tell if someone was making a conscious effort to jump or there was another force at hand. I always figured that the pressure coming from the heat pushed them out of the building. I am no expert in fire, but I have seen and felt heat that can push things away involintarily.

I prefer to use the term 'fall' since that doesn't imply the people made the choice consiously.

A very simple experiment to experience what heat can do, is to turn on an oven, say 200 degrees celcius, and then stick your hand in it. You will automaticaly withdraw your hand. I'm not sure if that's what you meant by 'heat pushing things away' or if you mean physically pushing away?

[Bell]

Right. Or they could fly straight outward, which explains why you can see beam components in...aw crap I can't post links yet! This rule is stupid. But you've seen the pictures. There are beams flying out horizontally, and the geniuses in the conspiracy department can't figure out why they could move horizontally if the building is falling vertically. When the beams buckle, they do snap out horizontally. I mean, if it's that hard to picture, find a stick in your backyard, press it down until it breaks, and see if it falls straight down or if it shoots out to the side first!

Those 'beams' would be the aluminum panels that covered the outside of the towers.

http://media.washingtonpost.com/wp-srv/photo/attack/images/newyork/10pm/ny_4.jpg

[jaydeehess]

People indeed "chose" to exit the building but there were not many "choices" one could make.

Obviously if there were any other way out they would have chosen to make use of it.

Instead, the people who jumped were either exposed to unbearable heat and the only way to stop that pain was to exit the building through a window, or they were subject to choking, acrid, smoke that made the eyes, throat and lungs feel like they were burning, makes one cough uncontrollably, makes you dizzy and is generally a living hell from which the only respite is , again, exiting the building via the window. They would indeed know that this is suicide but in such cases when the pain is so great people will choose relief in the form of death. These are instances in which the person requires escape or rescue not in 30 minutes, not in 5 minutes not in 30 seconds but simply cannot bear up any longer. It is torturous, literraly!

If the heat were physically pushing them out in the form of causing the atmosphere in the room to flow outward fast enough to compel them out then the heat would incinerate them before they exited the building.

[jaydeehess]

Those 'beams' would be the aluminum panels that covered the outside of the towers.

http://media.washingtonpost.com/wp-srv/photo/attack/images/newyork/10pm/ny_4.jpg

In the bottom left of the photo though we do see a perimeter column 'tree'.

Besides the buckling forces there is another horizontal force. All the material that is coming down within the footprint of the towers does what? It hits the remaining tower. It then must pile up but can only do so before it slides off the side. Before it does so though, if the perimeter column tree is still fastened to the remaining tower it is now being hit at the fastening level, by the debris that is pileing up. Take an empty milk carton and start filling it with sand. You will notice the sides bowing outward due to the pressure of the sand piling up inside. You can fill the carton all the way to the top and it will survive with little problem. Now do this again except pour the sand in from a height of 5 feet above the carton and mix in rocks about half the size of your thumb. The carton will explode long before you fill it. Why? The pressure is building much faster than the carton can distribute it and besides simply flowing to the sides the sand/pebble mix is retaining some of the velocity it had gained in falling so it hits the sides harder than in the first slow fill, the pebbles also concentrate momentum more than the first sand only fill so forces are very assymetric on the carton.

Such forces acted on the perimeter columns in the WTC and imparted sometimes large horizontal velocities on them. Near the top of the collapse this would mean that those perimeter column sections had more time to travel horizontally while they fell. Further down the mass of debris would tend to knock out the perimter column sections sooner and thus they would have less horizontal velocity(the mass is piling up faster and thus the momentum transfer takes place over a shorter time period but less momentum is transfered)

[JamesB]

In the bottom left of the photo though we do see a perimeter column 'tree'.

Besides the buckling forces there is another horizontal force. All the material that is coming down within the footprint of the towers does what? It hits the remaining tower. It then must pile up but can only do so before it slides off the side. Before it does so though, if the perimeter column tree is still fastened to the remaining tower it is now being hit at the fastening level, by the debris that is pileing up. Take an empty milk carton and start filling it with sand. You will notice the sides bowing outward due to the pressure of the sand piling up inside. You can fill the carton all the way to the top and it will survive with little problem. Now do this again except pour the sand in from a height of 5 feet above the carton and mix in rocks about half the size of your thumb. The carton will explode long before you fill it. Why? The pressure is building much faster than the carton can distribute it and besides simply flowing to the sides the sand/pebble mix is retaining some of the velocity it had gained in falling so it hits the sides harder than in the first slow fill, the pebbles also concentrate momentum more than the first sand only fill so forces are very assymetric on the carton.

Such forces acted on the perimeter columns in the WTC and imparted sometimes large horizontal velocities on them. Near the top of the collapse this would mean that those perimeter column sections had more time to travel horizontally while they fell. Further down the mass of debris would tend to knock out the perimter column sections sooner and thus they would have less horizontal velocity(the mass is piling up faster and thus the momentum transfer takes place over a shorter time period but less momentum is transfered)


Bah! A milk carton would only behave like that if it were hit with a Star Wars death ray! :cool:

[T.A.M.]

Chosen to jump?
I perfer "the heat forced them out."
I don't want to be anal, but your statement does seem to imply suicide (even though I know that's not intended). I heard people say "they jumped" a number of times and I believe it is only because the reporters covering the event, were saying it. I watched 9/11 live on TV and never once thought anyone was jumping. I couln't tell if someone was making a conscious effort to jump or there was another force at hand. I always figured that the pressure coming from the heat pushed them out of the building. I am no expert in fire, but I have seen and felt heat that can push things away involintarily.

I disagree...to an extent. I think that the heat, and the thought of burning to death, perhaps a more horrible and time involving death, was the more horrendous of the options. It is absolutely horrible to think, but I believe many of them were left with death by burning, and death by plummetting to the earth below, and most took what they felt would be the quickest, painless death. Most would have lost their breath, passed out, and been unconcious before they even reached the ground, so death would have been instant, and virtually painless. the other option would have been much longer, and painful...IMO.

TAM

[The Almond]

Nice analysis Chippy, it's always great to have a math/science type around to kick a few equations around. When I was back at Clemson, I was on a radio show where a caller made the, "The fires weren't hot enough" argument and I used the thermal expansion and hooke's law to prove that a temperature change of 500 degrees centigrade would result in a 174 psi stress over the entire beam.

The caller challenged me saying that steel failed at 36,000psi and that little stress couldn't hurt anything. I then proceeded to demonstrate that a distributed load of 174psi over 210 feet on an 8 inch beam was the equivalent of 3,000,000 pounds of load at one point on the beam. The caller hung up.

The point is that you can't always use mathematics to prove your point. For people to accept math, they have to demand that their argument be mathematically and scientifically valid. That's something conspiracy theorists simply don't do.

[Minadin]

When I was back at Clemson, I was on a radio show where a caller made the, "The fires weren't hot enough" argument and I used the thermal expansion and hooke's law to prove that a temperature change of 500 degrees centigrade would result in a 174 psi stress over the entire beam.

The caller challenged me saying that steel failed at 36,000psi and that little stress couldn't hurt anything. I then proceeded to demonstrate that a distributed load of 174psi over 210 feet on an 8 inch beam was the equivalent of 3,000,000 pounds of load at one point on the beam. The caller hung up.


Not to mention, that same 36ksi steel, when heated to about 1000 degrees Fahrenheit (that's close to your 500 Centigrade), becomes roughly 18ksi steel, which doesn't help at all. You have these steel structural members that are loaded at 24ksi failing because of the heat, just due to their design loads, not even considering the stresses and other forces caused by expansion. When they fail, the load they carried has to transfer to other areas where the steel is still intact, but these are now subjected to those new loads in addition to their design loads, and the new loads are being applied in ways and directions that those members weren't designed to handle.

[JamesB]

:D Nice analysis Chippy, it's always great to have a math/science type around to kick a few equations around. When I was back at Clemson, I was on a radio show where a caller made the, "The fires weren't hot enough" argument and I used the thermal expansion and hooke's law to prove that a temperature change of 500 degrees centigrade would result in a 174 psi stress over the entire beam.

The caller challenged me saying that steel failed at 36,000psi and that little stress couldn't hurt anything. I then proceeded to demonstrate that a distributed load of 174psi over 210 feet on an 8 inch beam was the equivalent of 3,000,000 pounds of load at one point on the beam. The caller hung up.

The point is that you can't always use mathematics to prove your point. For people to accept math, they have to demand that their argument be mathematically and scientifically valid. That's something conspiracy theorists simply don't do.


You went to Clemson! Did you study under the great Judy Wood?

[The Almond]

:D


You went to Clemson! Did you study under the great Judy Wood?

No, thank God. For people who don't know much about Clemson, the real heavyweight was Robert F. Nowack. I was a civil engineering student, and I had no need to take classes from Wood (and I was strongly advised not to take classes from that loon). Nowack, a professor for nearly 45 years at Clemson, was my professor for the Statics and Dynamics classes I would have had to take from Wood.

Students of Wood, for the most part, hated her. She used to take lecture time to try to convince students that the WTC was part of a controlled demolition. Needless to say, none of the students ever bought into that crap.

[JamesB]

Hmm, I can't understand at all why she didn't get picked up for tenure...

[RenaissanceBiker]

Just so we all are using the same terminology, beams are horizontal and columns are vertical. The main load in a column is parallel to the column. The main load in a beam is perpendicular to the beam. Euler's formula is for loads parallel to the stress member.

[rwguinn]

Just so we all are using the same terminology, beams are horizontal and columns are vertical. The main load in a column is parallel to the column. The main load in a beam is perpendicular to the beam. Euler's formula is for loads parallel to the stress member.

That convention keeps it simple for the non-engineers--I'll buy it...and will comply...or at least try to...

[R.Mackey]

Well, that really depends on what you mean by strain.

Most steel structures are over-designed by about 1.5x. Meaning that the actual live+dead load is 2/3 of what the members can take. So, if it's taking 103% of what it should, it would not be a big deal.

At 3% deflection you can visibly see it bend and that is indeed very bad. We normally design buildings first for the structural strength and then doublecheck it for deflection. A deflection of more an 1/4 inch or so for a floor is VERY noticeable and will cause people to feel unsafe even if it isn't structurally true. So oftentimes a structure will be even more oversized for just that reason.
Just to clarify, when I was trained in solid mechanics, strain (http://en.wikipedia.org/wiki/Strain_%28materials_science%29) had a very specific meaning. In the simplest case of homogeneous strain, strain and deflection basically mean the same thing...

Design vs. yield strength is different, of course. The WTC core columns were apparently overdesigned by a factor of 1.67 (from F.R. Greening's letter "To Whom it May Concern", page 11, in the {ahem} Journal of 9/11 Studies (http://www.st911.org/), Sept. 2006), slightly higher than the typical 50% safety factor but still pretty average.

Otherwise, we're in good agreement. :D

[Free Thinkr]

I seem to recall seeing video of one guy trying to climb down, presumeably to the storey below..... it doesn't bear thinking about. :(
I think I speak for just about everyone when I say that those videos are some of the most horrendously disturbing/depressing videos of all time. Even when I see the stills the bile resurfaces, and I instantly become enraged. The worst part is that a sizable portion of our own population is willing to exonerate those responsible so that they can pursue their own deranged theories for entertainment.

[PerryLogan]

One does get repulsed. But keep in mind the conspiracy folks are mentally ill. They can't be held to normal standards of moral discernment. Facts bounce off of them; logic escapes them. This thread alone has debunked their claims a hundred times--but of course they will never know.

The Truthers live in a bad comic book in which the government is always out to get you and everyone is an agent or a shill. They are completely alienated from their society and have no real connection with other human beings. The horrors of 9/11 are just a movie to them.

[William Rea]

How many of you were aware of the fact that buckling was actually a major factor in the collapse of the World Trade Center? From a layman's point of view, you'll likely say "well duh, of course it buckled, that's how it fell on itself, silly!".....And please, stop arguing that the fire wasn't hot. If it wasn't hot, people wouldn't have chosen to jump down to the ground 100 stories, which is one of the most terrifying ways you can die.

And what you fail to point out is that Euler applies to slender columns where the length is a minimum of 30 times the width and no bending moments are applied at the joints. Where moments are applied at the pin joints (the columns are restrained at each end) the critical load rises by a factor of 4. For shorter columns P crit becomes so insignificant that they are more likely to fail in compression.

The factors in your favour are a) the eccentric loading from the non-uniform damage across the floors (which should have resulted in the floors above the damage toppling off) and b) the Young's Modulus E element of the equation which will be affected by the heat during the elastic strain portion of the deformation, once plastic strain is achieved then most equations break down. Most people are happy to talk about the drop in strength from the heat but nobody talks about the ductility and toughness imparted into the structure by the heat.

I'll leave the calculations up to you!

[William Rea]

Just to clarify, when I was trained in solid mechanics, strain (http://en.wikipedia.org/wiki/Strain_%28materials_science%29) had a very specific meaning. In the simplest case of homogeneous strain, strain and deflection basically mean the same thing...

Just to clarify further in this context, Strain in a single axis can also be a % reduction in length under compression and not just an increase as seen under tension. In volumetric terms it becomes more complex than is required in the context of this thread.

Deflection necessitates both tensile and compressive strain in the member under load and the distance of the material from the primary or neutral axis of bending is why the Moment of Inertia (I) is important. It can be roughly approximated to be the thickness of the beam.

The material in the cross section that is furthest away from the neutral axis will need to strain the most to allow deflection.

[gumboot]

The factors in your favour are a) the eccentric loading from the non-uniform damage across the floors (which should have resulted in the floors above the damage toppling off)


Please tell me you're joking...

-Gumboot

[William Rea]

Please tell me you're joking...

-Gumboot

I wouldn't joke about something as serious as this.

[Gravy]

Most people are happy to talk about the drop in strength from the heat but nobody talks about the ductility and toughness imparted into the structure by the heat.

I'll leave the calculations up to you!William, are you suggesting that the WTC buildings may have been strengthened by the fires in them? If so, that's certainly a novel argument and I'd appreciate it if you could expand on it for a layman like me. And if you could explain how the top floors of the towers could have "toppled," that would be great.

[rwguinn]

And what you fail to point out is that Euler applies to slender columns where the length is a minimum of 30 times the width and no bending moments are applied at the joints. Where moments are applied at the pin joints (the columns are restrained at each end) the critical load rises by a factor of 4. For shorter columns P crit becomes so insignificant that they are more likely to fail in compression.

The factors in your favour are a) the eccentric loading from the non-uniform damage across the floors (which should have resulted in the floors above the damage toppling off) and b) the Young's Modulus E element of the equation which will be affected by the heat during the elastic strain portion of the deformation, once plastic strain is achieved then most equations break down. Most people are happy to talk about the drop in strength from the heat but nobody talks about the ductility and toughness imparted into the structure by the heat.

I'll leave the calculations up to you!

Pardon me, but your ignorance is showing...
Any engineers out there (besides me) wonder how you impose a moment at a pinned joint?:confused:

the joints were not "pinnned", they were fully restrained (more than 1 fastener), which allows a moment input, which decreases the necessary vertical load required to initiate buckling.
It was a "self-eating watermelon" situation--the worse it got, the worse it became.
Also, Young's Modulus decreases with temperature, which reduces stiffness, which increases deflection under load, which increases relative strain, which enhances the onset of buckling.

[RenaissanceBiker]

I'm a civil engineer specializing in water resources. I took a lot of classes in structures in college (B.S. and M.Eng. from U. of Louisville). I still have my books in my office in Charlotte. I'm working in Atlanta right now so I can't look anything up. However, I believe rwguinn is correct. I don't know of any common construction material that gets stronger under intense heat.

[chippy]

There is actually an equation I can use to determine whether the Euler buckling formula or another buckling formula is to be used. I'll see if I can dig it up.

[The Almond]

Most people are happy to talk about the drop in strength from the heat but nobody talks about the ductility and toughness imparted into the structure by the heat.


If we're going to take the modulus of toughness as the area under the entirety of the stress-strain curve for steel, then toughness will not increase as the modulus of elasticity decreases.

And what you fail to point out is that Euler applies to slender columns where the length is a minimum of 30 times the width and no bending moments are applied at the joints.

I pounded out the math on this one. No only is this "30 times the width" not in any of my literature, it just doesn't make sense. My Mechanics of Materials book does mention that Euler's formula fails for short, thick beams, but also adds, "if a short or intermediate-length stocky column is considered, then the applied load, as it is increased, may eventually cause the material to yield, and the column will begin to behave in an inelastic manner." It seems to me that the objection to using Euler's formula for thick columns is that they behave inelastically, not elastically. My analysis shows that the number is far closer to 20*W for thick columns and 10*W for thin columns. An I beam with a y-y moment of inertia of 259 in^4 exceeds Euler's buckling formula at 119' tall, but the ridiculous 30*W rule would apply at a mere 60'. It seems to arbitrarily define a column as being unusually thick at 60' in length.

[R.Mackey]

And what you fail to point out is that Euler applies to slender columns where the length is a minimum of 30 times the width and no bending moments are applied at the joints. Where moments are applied at the pin joints (the columns are restrained at each end) the critical load rises by a factor of 4. For shorter columns P crit becomes so insignificant that they are more likely to fail in compression.

Well... you're not entirely wrong. In treating beams, the slenderness ratio is significant in that above about 30 you can simplify (http://en.wikipedia.org/wiki/Euler_Bernoulli_beam_equation) the expression (length >> width being one of the assumptions, and 30 being a good rule-of-thumb threshold). And it is also true that a column pinned at both ends has four times the yield strength (http://en.wikipedia.org/wiki/Buckling) of a column that is not constrained at the ends -- the factor of four being the energy difference between first-order bending and triple-curvature.

However, none of these observations apply to the WTC cases. As the NIST report demonstrates, sagging floors -- those members that would have kept the columns pinned -- led to deflection as though the column ends were free. And the slenderness ratio is greater than 30 in that case.


The factors in your favour are a) the eccentric loading from the non-uniform damage across the floors (which should have resulted in the floors above the damage toppling off)
No. Just... no. We can get into this if you want, but please put some thought into it before making this assertion again!


and b) the Young's Modulus E element of the equation which will be affected by the heat during the elastic strain portion of the deformation, once plastic strain is achieved then most equations break down. Most people are happy to talk about the drop in strength from the heat but nobody talks about the ductility and toughness imparted into the structure by the heat.
If you're talking about strain hardening and annealing (http://en.wikipedia.org/wiki/Annealing_%28metallurgy%29), it doesn't help you in this case. You wind up with materials that are more rigid, but more prone to fracture, and with decreased ultimate strength.

Also missing is that the heating itself creates significant displacement, and non-uniform as well. As the floors heat and cool, it stresses the connections between floors and columns immensely, further induces deflection in the columns, and contributes to the failure. Again, read the NIST report.

[William Rea]

Pardon me, but your ignorance is showing...
Any engineers out there (besides me) wonder how you impose a moment at a pinned joint?:confused:

the joints were not "pinnned", they were fully restrained (more than 1 fastener), which allows a moment input, which decreases the necessary vertical load required to initiate buckling.
It was a "self-eating watermelon" situation--the worse it got, the worse it became.
Also, Young's Modulus decreases with temperature, which reduces stiffness, which increases deflection under load, which increases relative strain, which enhances the onset of buckling.

All I can suggest is that you read what I wrote over again.

I cannot take responsibility for your errant response but I will accept your apology for calling me ignorant when you have fully read my post.

[rwguinn]

All I can suggest is that you read what I wrote over again.

I cannot take responsibility for your errant response but I will accept your apology for calling me ignorant when you have fully read my post.

I have read your post. As for an apology,now, There's something that ain't gonna happen.

[William Rea]

I have read your post. As for an apology,now, There's something that ain't gonna happen.

Yeah, I kind of figured you wouldn't have the class required to do an apology.

[rwguinn]

Yeah, I kind of figured you wouldn't have the class required to do an apology.
Wrong again.
You jst need to repeal all the rules of material science, substitute your own.
Being right would be helpful.

[William Rea]

Wrong again.
You jst need to repeal all the rules of material science, substitute your own.
Being right would be helpful.

Tell me which ones I have got wrong? I'm sure that when you really thoroughly read it through a light will come on somewhere.

Hint - You might want to read back through to the post I was answering.

[The Almond]

Tell me which ones I have got wrong? I'm sure that when you really thoroughly read it through a light will come on somewhere.

Hint - You might want to read back through to the post I was answering.

It's pretty clear to me what rwguinn was saying. Your first post implied that a moment was being applied at a pin connection. Now, if that's not what you intended to say, that's fine, correct it. Clearly, however, pin connections do not transmit moments, only x and y forces.

[William Rea]

William, are you suggesting that the WTC buildings may have been strengthened by the fires in them? If so, that's certainly a novel argument and I'd appreciate it if you could expand on it for a layman like me. And if you could explain how the top floors of the towers could have "toppled," that would be great.

No, I suggest you look up the terms strength and toughness in the engineering sense along with ductility if you want to understand what I said.

I have explained how the toppling is feasible in previous threads.

[William Rea]

It's pretty clear to me what rwguinn was saying. Your first post implied that a moment was being applied at a pin connection. Now, if that's not what you intended to say, that's fine, correct it. Clearly, however, pin connections do not transmit moments, only x and y forces.

Read it again. I'll quote you back what I said with some highlights to show you...

"And what you fail to point out is that Euler applies to slender columns where the length is a minimum of 30 times the width and no bending moments are applied at the joints. Where moments are applied at the pin joints (the columns are restrained at each end) the critical load rises by a factor of 4. For shorter columns P crit becomes so insignificant that they are more likely to fail in compression."

I think it speaks for itself when you read it with an open mind.

Enough distractions now?

[The Almond]

No, I suggest you look up the terms strength and toughness in the engineering sense along with ductility if you want to understand what I said.


Umm, pardon me for implying this, but this is a rather dishonest troll tactic. If you're not willing to define terms or provide more expanded explanations of your ideas, then how do you expect to engage anyone enough to do this research? If Gravy's analysis of your claim is wrong, explain why and provide a clear definition of terms. The contradictory "you just didn't understand me" is a rather childish form of debate.

[William Rea]

Umm, pardon me for implying this, but this is a rather dishonest troll tactic. If you're not willing to define terms or provide more expanded explanations of your ideas, then how do you expect to engage anyone enough to do this research? If Gravy's analysis of your claim is wrong, explain why and provide a clear definition of terms. The contradictory "you just didn't understand me" is a rather childish form of debate.

Ok so now it's dishonest and trolling to expect people to understand fairly basic engineering terms when discussing engineering structures but on the other hand it's acceptable for every idiot to come in and attack basic engineering principles that I put forward and then expect me to educate them! I love that.

I suggest you readjust your focus and withdraw the trolling accusation however cleverly cloaked you made it.

[The Almond]

Read it again. I'll quote you back what I said with some highlights to show you...

"And what you fail to point out is that Euler applies to slender columns where the length is a minimum of 30 times the width and no bending moments are applied at the joints. Where moments are applied at the pin joints (the columns are restrained at each end) the critical load rises by a factor of 4. For shorter columns P crit becomes so insignificant that they are more likely to fail in compression."

Your bolded part is exactly where the objection comes from. Moments can't be applied at pin joints. If the columns are restrained at each end, the moments are there. If you mean that the moments are applied infinitesimally close to the pin joint, then the positive moment will be applied to one side of the restraint and the negative moment will be applied to the other. This method of sectioning is commonly employed to solve indeterminate structures.

If, on the other hand, you mean that the column is restrained at both ends and a moment is applied at the center of the column, then that would certainly break no mechanical terminologies. It's simply a matter of expanding your explanation. Commonly, a joint implies that two pieces of, in this instance, steel are joined together. For simply supported beams, the end members are commonly called a pin connectors, not joints. It's also helpful to note that one of the end members is actually a wheel connector, not a pin.

I think it speaks for itself when you read it with an open mind.

Implying that close-mindedness is at issue is fallacious. Semantics, terminologies and the inherent weaknesses to text based debate are at issue.

Enough distractions now?
Distraction is not an issue when defining terms and analyses. If you wish to conduct a meaningful debate, this exchange is a necessary part of that.

[rwguinn]

No, I suggest you look up the terms strength and toughness in the engineering sense along with ductility if you want to understand what I said.

I have explained how the toppling is feasible in previous threads.
and I submit to you that toughness is a non-sequiter in the case of the towers collapse.
Certainly, you can bend steel a heckofa long way by local heating--any amateur blacksmith can tell you that. They will also tell you that it is easier to bend heatedmetal--a reduction in Young's Modulus. It also follows that if F remains constant, a reduction in Young's Modulus means it bends faster, and when a longitudinal load is also applied (like collumns holding up a building), the element (collumn) becomes well-nigh useless--and the load transfers to somewhere else, via a load path which was not designed to take that particular load, in that particular direction.

Yep, the top floors "toppled". More correctly, they rotated. The CG of those floors moved laterally between 6 and 12 feet before the bending moment in the hinge side of the building failed those collumns , and since the top floor's rotation had very little time to build up angular velocity, and since the failure would also cause an opposite rotation--about the laterally-displaced CG --the building came pretty much straight down

Any more "questions"?

[The Almond]

Ok so now it's dishonest and trolling to expect people to understand fairly basic engineering terms when discussing engineering structures

If you wish to discuss the basics of structural analysis, I suggest doing it at a professional convention or in an academic setting. This forum, like most others, is primarily staffed by the laity. It is not unreasonable, therefore, for someone in the laity to request a full and honest disclosure of terms and principles from an educated engineer. I would refer you to the ASCE's code of ethics for the factual and honest dissemination of knowledge from the engineering community to the laity.

but on the other hand it's acceptable for every idiot

Appeal to intelligence

to come in and attack basic engineering principles that I put forward and then expect me to educate them! I love that.

Perhaps you are unfamiliar with the nature of the James Randi Educational Foundation. It is absolutely acceptable for each member of this forum to expect you to educate them on basic engineering principles. If you find this part of the organization's mission unacceptable, you are free to leave.

I suggest you readjust your focus and withdraw the trolling accusation however cleverly cloaked you made it.
Suggestion noted and declined. I have noticed trolling behavior and made a full and honest accusation against its institution, not against you. Please refer to the forum rules regarding name calling and civil debate for further discussion.

[Darth Rotor]

a) the eccentric loading from the non-uniform damage across the floors (which should have resulted in the floors above the damage toppling off) and
You don't support this statement.

I fear that you are modeling the entire tower as a single column with a heavy load attached at the top (mushroom), when the model and method used to construct WTC 1 and WTC 2 was a three dimensional lattice. NIST describes the benefits of this design as allowing for more rentable area (fewer required vertical members) as it distributed about a fifth of the load bearing into the floor supports.

Except in the set of floors (from the pictures, it appeared to my eye that between three and six floors were directly influenced by the impact) where impact occurred, load distribution could be expected to perform as designed. In the damaged floors, loads were still distributed horizontally somewhat, though in a degraded lattice, which led to floor sag, failures, and some photographs indicate the internal buckling of vertical members associated with the forces from the floor.

For the top to fall off or topple, a significant number of vertical members would have to fail under tension, not in torsion. It doesn't appear that the loads (based on the tilt angles I have seen in various photographs) in the upward direction were sufficient to cause this mass failure (partly due to load distribution via the lattice) before the sag and buckling combination induced the failure in torsion and compression, leading to the "buckling" failure referred to in the OP.

For simplicity, it might be more productive to argue material science in one point, and separately describe why the toppling "should" have occurred.

DR

[William Rea]

Your bolded part is exactly where the objection comes from. Moments can't be applied at pin joints. If the columns are restrained at each end, the moments are there. If you mean that the moments are applied infinitesimally close to the pin joint, then the positive moment will be applied to one side of the restraint and the negative moment will be applied to the other. This method of sectioning is commonly employed to solve indeterminate structures.

If, on the other hand, you mean that the column is restrained at both ends and a moment is applied at the center of the column, then that would certainly break no mechanical terminologies. It's simply a matter of expanding your explanation. Commonly, a joint implies that two pieces of, in this instance, steel are joined together. For simply supported beams, the end members are commonly called a pin connectors, not joints. It's also helpful to note that one of the end members is actually a wheel connector, not a pin.

Implying that close-mindedness is at issue is fallacious. Semantics, terminologies and the inherent weaknesses to text based debate are at issue.

Distraction is not an issue when defining terms and analyses. If you wish to conduct a meaningful debate, this exchange is a necessary part of that.

I couldn't be sure but I was pretty certain that this thread would probably end up somewhere abouts in this zone when I first posted in it. It kind of proves to me what I have come to realise which is that this forum is more about politics than it is about truth.

I'll cite that not a single one of you asked Chippy to qualify any of his opening post because it agreed with your worldview. When someone doesn't agree with your worldview the pack of baboons races in and destroys the thread with inane interjections on topics they simply will never have the intelligence or education to grasp.

It explains to me why Christophera has been under constant hammering by you clowns.

Thanks for the entertainment.

[mcMike]

Design vs. yield strength is different, of course. The WTC core columns were apparently overdesigned by a factor of 1.67 (from F.R. Greening's letter "To Whom it May Concern", page 11, in the {ahem} Journal of 9/11 Studies (http://www.st911.org/), Sept. 2006), slightly higher than the typical 50% safety factor but still pretty average.

I would like to emphasise this point since in so many places the safety factor is mentioned all the way up to 6. Here's direct reference:

[ Federal Building and Fire Safety Investigation of the World Trade Center Disaster ]
Part III – Baseline Performance, April 5, 2005

"The allowable stress design method has an inherent factor of safety for structural components. For example, the safety factor for yielding and buckling is:

• 1.67 and 1.92 for core columns in the original design and SOP cases, and for all columns in refined NIST estimate case.
• 1.26 and 1.44 for perimeter columns in the original design and SOP case (discounting the 1/3 increase in allowable stress under wind loads).

Source: http://wtc.nist.gov/pubs/WTCPart III - Baseline Final.pdf (p. 35)

And the very same code in Canada:

[ Safety Factors in the National Building Code of Canada 1970 ]
Type of construction Basic Safety Factor Steel and Aluminum
Yield or plastic resistance 1.67
Elastic Buckling 1.92
Source: http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd147_e.html (http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd147_e.html)

Our "own" (in)famous Prof. Heikki Kurttila uses factor of 6 in his calculations to prove that the progressive collapse was impossible. :(

[The Almond]

I couldn't be sure but I was pretty certain that this thread would probably end up somewhere abouts in this zone when I first posted in it.

What zone is this?

It kind of proves to me what I have come to realise which is that this forum is more about politics than it is about truth.

Oh? How does one go about producing the truth? Does one ask for clarifications, explanations and definitions, or does one make pronouncements based entirely on strength of expertise and expect everyone to agree?

I'll cite that not a single one of you asked Chippy to qualify any of his opening post because it agreed with your worldview.

What does Euler's equation have to do with world view? He made an argument based on his understanding of Euler's equation. If you're going to challenge it, great, do so. Chippy is an ME student, and I'm certain he'd be more than happy to discuss the issue with you.

When someone doesn't agree with your worldview the pack of baboons races in and destroys the thread with inane interjections on topics they simply will never have the intelligence or education to grasp.

Wow, a lot of appeal to intelligence and name calling going on there. I wonder why you've resorted to this.

It explains to me why Christophera has been under constant hammering by you clowns.

Christophera has demonstrated over 200 pages in that debate that he is unwilling to yield to any form of counter-evidence, rather preferring to redirect questions and defer proofs to "common sense." Have you read that thread recently?

Thanks for the entertainment.
If you're interested in being entertained, we have an entertainment and humor subforum.

[William Rea]

If you're interested in being entertained, we have an entertainment and humor subforum.

Lol, this forum looks like an intellectual desert when compared to the entertainment and humour subforum, perhaps you're right.

[William Rea]

You don't support this statement.

I fear that you are modeling the entire tower as a single column with a heavy load attached at the top (mushroom), when the model and method used to construct WTC 1 and WTC 2 was a three dimensional lattice. NIST describes the benefits of this design as allowing for more rentable area (fewer required vertical members) as it distributed about a fifth of the load bearing into the floor supports.

Except in the set of floors (from the pictures, it appeared to my eye that between three and six floors were directly influenced by the impact) where impact occurred, load distribution could be expected to perform as designed. In the damaged floors, loads were still distributed horizontally somewhat, though in a degraded lattice, which led to floor sag, failures, and some photographs indicate the internal buckling of vertical members associated with the forces from the floor.

For the top to fall off or topple, a significant number of vertical members would have to fail under tension, not in torsion. It doesn't appear that the loads (based on the tilt angles I have seen in various photographs) in the upward direction were sufficient to cause this mass failure (partly due to load distribution via the lattice) before the sag and buckling combination induced the failure in torsion and compression, leading to the "buckling" failure referred to in the OP.

For simplicity, it might be more productive to argue material science in one point, and separately describe why the toppling "should" have occurred.

DR

Thanks for the well considered comments DR, I see where you are coming from and would love to discuss the merits of each paradigm that has been applied to the collapse but this won't ever be the place to do that as long as I have a hole in my ar*e.

[rwguinn]

Lol, this forum looks like an intellectual desert when compared to the entertainment and humour subforum, perhaps you're right.
Anyone else notice that when presented with a scenario argued from logic, design, and engineering, he quits answering and runs away?

[R.Mackey]

I couldn't be sure but I was pretty certain that this thread would probably end up somewhere abouts in this zone when I first posted in it. It kind of proves to me what I have come to realise which is that this forum is more about politics than it is about truth.
Look William Rea, this will certainly come true if you lead the conversation in that direction with these kinds of inflammatory and immature comments.

If you really want to discuss this, then all you have to do is ignore comments that are rude or unconstructive. And respond to comments that are reasoned and educational. Like mine (http://forums.randi.org/showthread.php?postid=2134512#post2134512), for instance.

Yet you choose to do the opposite. Well, it's your choice.

[chipmunk stew]

I couldn't be sure but I was pretty certain that this thread would probably end up somewhere abouts in this zone when I first posted in it. It kind of proves to me what I have come to realise which is that this forum is more about politics than it is about truth.

I'll cite that not a single one of you asked Chippy to qualify any of his opening post because it agreed with your worldview. When someone doesn't agree with your worldview the pack of baboons races in and destroys the thread with inane interjections on topics they simply will never have the intelligence or education to grasp.

It explains to me why Christophera has been under constant hammering by you clowns.

Thanks for the entertainment.

I'd just like to point out that there's a handy "Ignore" function you can utilize to screen out the pack of baboons with their inane interjections. That way you can concentrate on the substantive objections to your assertions without all these pesky distractions.


:monooh: oo oo oo EEEE EEEE EEEE!

[The Almond]

Lol, this forum looks like an intellectual desert when compared to the entertainment and humour subforum, perhaps you're right.

This is a childish response.

[jaydeehess]

While it is entirely true that ductility will be greater in a heated column that certainly will not aid in the column's 'job' in supporting a load. All it will do is reduce the column's ability to fracture under load. There are indeed pictures(no I don't know where to find them now) that show columns that have been bent almost 180 degrees. That would be very difficult to accomplish without heating that portion of the column. What it also illustrates is that the load that caused this bending was not moving laterally a great deal which suggests that the collapse was not sliding away from the vertical axis at the time the column was bent.

Other columns show fracturing instead which would be consistent with a suddenly increased load on a column that is still relatively cool which would occur if enough heated columns started failing in quick succession.

The columns that fail need not all be on the same level and it is obvious to anyone who has read the NIST reports that the fires on each floor were worse at different loactions. The main cause of this being that the planes did not hit the buildings wings level. This put aviation fuel into one side of the building from the right wing at upper fire floors while putting aviation fuel into the other side of the building at lower fire floors. Fires progressed around the floors heating columns. Some of those would have foreshortened during the heating under load but cooled as the fire burned down in that area and progressed to other areas where it would heat other columns. These newly heated columns now have already been handed an extra load due to the foreshortening of the now cooled columns. Those now cooled columns will have regained their strength as they cooled BUT due to any deformation that occured during heating they no longer have the load applied through their vertical axis.

Now you increasingly have columns which are more prone to buckling due to their loads not being in line with their vertical axis and others that while still dimensionally intact are losing their strength. This is happening on various columns around the building even though it may be occuring at several different levels.

In the South tower this occurs along with the assymetric damage done to the columns by the plane's impact which immediatly caused a lean of the upper section. In the North tower the damage was much more symmetric as the aircraft hit more centrally and on the side which was parallel to the long horizontal axis of the core(South tower was hit on the short axis).IIRC

In the South tower the above heating damage is done which introduces a more pronounced lean but the angular momentum is actually small since the angular velocity is so small. A point is reached at which loads cannot be redistributed to stop further leaning and the building starts to rotate but simply cannot go very far before the columns at the hinge point fracture and the whole mass drops vertically about its CG (isn't it more proper to say center of mass?). It may still be rotating but is now doing so about its CG rather than at the hinge point and that CG is falling straight down. Since the CG did not move a signioficant percentage of the horizontal distance between it and the outer edge of the building , MOST of the mass is falling upon the lower section of the building.

In the north tower more columns had to undergo the heat stresses above since there was much less stress due to the upper section leaning(not to mention that the upper section is much smaller than in the south tower). On the other hand more fuel was dumped into this building than in the south tower since it hit more centrally and thus the fires were more widespread and since it was more central the fires were also more symmetrically dispersed about the vertical axis(though, again , on several levels).
Still, a point is reached at which redistribution of loads cannot occur fast enough to halt settling and columns fail in quick succession, cold columns perhaps fracturing , while hot columns bend while still attached to the floor above.

Now the falling debris crushes the flooring of further levels removing lateral supports of many columns which then buckle. while they buckle and are buffeted by falling debris they transmit shock along their length below the collapse point. This means that the sounds of collapse are heard by persons on the ground two ways. By the sound transmitted along the columns AND by sound that travels through the air to the ground. The former would reach the ground first since sound travels so much faster in steel than throiugh air and would appear to come from lower floors.

[rwguinn]

While it is entirely true that ductility will be greater in a heated column that certainly will not aid in the column's 'job' in supporting a load. All it will do is reduce the column's ability to fracture under load. There are indeed pictures(no I don't know where to find them now) that show columns that have been bent almost 180 degrees. That would be very difficult to accomplish without heating that portion of the column. What it also illustrates is that the load that caused this bending was not moving laterally a great deal which suggests that the collapse was not sliding away from the vertical axis at the time the column was bent.

Other columns show fracturing instead which would be consistent with a suddenly increased load on a column that is still relatively cool which would occur if enough heated columns started failing in quick succession.

The columns that fail need not all be on the same level and it is obvious to anyone who has read the NIST reports that the fires on each floor were worse at different loactions. The main cause of this being that the planes did not hit the buildings wings level. This put aviation fuel into one side of the building from the right wing at upper fire floors while putting aviation fuel into the other side of the building at lower fire floors. Fires progressed around the floors heating columns. Some of those would have foreshortened during the heating under load but cooled as the fire burned down in that area and progressed to other areas where it would heat other columns. These newly heated columns now have already been handed an extra load due to the foreshortening of the now cooled columns. Those now cooled columns will have regained their strength as they cooled BUT due to any deformation that occured during heating they no longer have the load applied through their vertical axis.

Now you increasingly have columns which are more prone to buckling due to their loads not being in line with their vertical axis and others that while still dimensionally intact are losing their strength. This is happening on various columns around the building even though it may be occuring at several different levels.

In the South tower this occurs along with the assymetric damage done to the columns by the plane's impact which immediatly caused a lean of the upper section. In the North tower the damage was much more symmetric as the aircraft hit more centrally and on the side which was parallel to the long horizontal axis of the core(South tower was hit on the short axis).IIRC

In the South tower the above heating damage is done which introduces a more pronounced lean but the angular momentum is actually small since the angular velocity is so small. A point is reached at which loads cannot be redistributed to stop further leaning and the building starts to rotate but simply cannot go very far before the columns at the hinge point fracture and the whole mass drops vertically about its CG (isn't it more proper to say center of mass?). It may still be rotating but is now doing so about its CG rather than at the hinge point and that CG is falling straight down. Since the CG did not move a signioficant percentage of the horizontal distance between it and the outer edge of the building , MOST of the mass is falling upon the lower section of the building.

In the north tower more columns had to undergo the heat stresses above since there was much less stress due to the upper section leaning(not to mention that the upper section is much smaller than in the south tower). On the other hand more fuel was dumped into this building than in the south tower since it hit more centrally and thus the fires were more widespread and since it was more central the fires were also more symmetrically dispersed about the vertical axis(though, again , on several levels).
Still, a point is reached at which redistribution of loads cannot occur fast enough to halt settling and columns fail in quick succession, cold columns perhaps fracturing , while hot columns bend while still attached to the floor above.
This is using more words, and incuding examples, of what I said above. Wordiness is unfair!:D
so far, the score is
logic & science 2
Billy Rhea 0

[RenaissanceBiker]

I'll cite that not a single one of you asked Chippy to qualify any of his opening post because it agreed with your worldview. When someone doesn't agree with your worldview the pack of baboons races in and destroys the thread with inane interjections on topics they simply will never have the intelligence or education to grasp.


I did attempt to clarify the OP by defining "column" and "beam". I also stated that without access to my reference library I could not provide exact definitions of terms and applicability of formulas.

You are the one who made an unsupported statement about "the ductility and toughness imparted into the structure by the heat" and left the calculations up to us. You expect us to prove your statement to ourselves? I am willing to listen to your explanation, but I fear that one is not forthcoming.

As I said before, I have a B.S. and an M.Eng. in civil engineering from an ABET accredited university. I am also a licensed professional civil engineer in four states. I have the intelligence and qualifications to grasp what you are saying. So far, it seems to be wrong.

[The Almond]

As I said before, I have a B.S. and an M.Eng. in civil engineering from an ABET accredited university. I am also a licensed professional civil engineer in four states. I have the intelligence and qualifications to grasp what you are saying. So far, it seems to be wrong.

Seconded. Licensed civil engineer in 2 states, BSCE and MSCE from an ABET university as well. I specialized in construction materials and reinforced concrete design.

[rwguinn]

I did attempt to clarify the OP by defining "column" and "beam". I also stated that without access to my reference library I could not provide exact definitions of terms and applicability of formulas.

You are the one who made an unsupported statement about "the ductility and toughness imparted into the structure by the heat" and left the calculations up to us. You expect us to prove your statement to ourselves? I am willing to listen to your explanation, but I fear that one is not forthcoming.

As I said before, I have a B.S. and an M.Eng. in civil engineering from an ABET accredited university. I am also a licensed professional civil engineer in four states. I have the intelligence and qualifications to grasp what you are saying. So far, it seems to be wrong.

Rich Braggart!
at $250/year fior Texas, 50 for Colorado, 125 for New mexico--I settle for 1 license.
ETA:
Graduate of ABET accedited university (NMSU-not football team worth mentioning (yet), but in the top 10 research and graduate placement, anyway) and many years of Mechanical analysis (stress, acoustic, vibration, and loads)

[RenaissanceBiker]

I'm a consultant in the wastewater industry. My firm pays my licensing fees. I specialize in open channel hydraulics, but have always enjoyed structures.

Mr. Rea, would you please provide us with your qualifications? Otherwise, it just seems like you are dismissing those who don't "agree with your worldview."

[rwguinn]

I'm a consultant in the wastewater industry. My firm pays my licensing fees. I specialize in open channel hydraulics, but have always enjoyed structures.

Mr. Rea, would you please provide us with your qualifications? Otherwise, it just seems like you are dismissing those who don't "agree with your worldview."

My firm does too-that's me-But I don't do any outside consulting at the present, so the license is unnecessary--but is a "pre-prepared" position I have had to use in the past. I love the engineering, but play poorly at the political aspects (you'd never guess that from my attitude on this forum, now, would you?) and absolutely detest the insurance premiums.

ETA:
Open channel hydraulics--isn't that the part where you are supposed to say "S(t-enhanced water flows down hill?"
and the comma is still missing from your descriptor line up by the avatar...

[Gravy]

No, I suggest you look up the terms strength and toughness in the engineering sense along with ductility if you want to understand what I said.I know what those engineering terms mean, and I looked them up to be sure I wasn't misunderstanding. You said

Most people are happy to talk about the drop in strength from the heat but nobody talks about the ductility and toughness imparted into the structure by the heat.

I'll leave the calculations up to you!I still don't have the foggiest idea what you mean, and I'd still appreciate an explanation. That's not asking a lot, is it? You can't expect an "idiot," "babboon," and "clown" like me to suss out your meaning, can you?

[RenaissanceBiker]

Open channel hydraulics--isn't that the part where you are supposed to say "S(t-enhanced water flows down hill?"
and the comma is still missing from your descriptor line up by the avatar...

It does indeed flow downhill, sometimes faster than we want or expect.

As for the comma, sometimes it's missing and sometimes it's not.

[rwguinn]

It does indeed flow downhill, sometimes faster than we want or expect.

As for the comma, sometimes it's missing and sometimes it's not.

OME! Faster than

free-fall?

sorry!:D

[RenaissanceBiker]

Look up "hydraulic jump."

[rwguinn]

Look up "hydraulic jump."

Cool! So wave propigation velocity on the free surface can be less than the free-flow velocity of the body. I did not know that!
That looks like Excedrin headache number 43187!

[gumboot]

Speak english!

:confused: :boggled: :faint:

I'm not an engineer of any sort.

-Gumboot

[rwguinn]

Speak english!

:confused: :boggled: :faint:

I'm not an engineer of any sort.
-Gumboot
Fill in the blanks

IF you can't bewilder 'em with brains, baffle 'em with ________

you have 10 minutes to complete this portion of the "make me an engineer" test...

[The Almond]

Speak english!

:confused: :boggled: :faint:

I'm not an engineer of any sort.

-Gumboot

Hydraulic jump is a pretty neat phenomenon. You have an open channel with water flowing in it. At the base of the channel, you suddenly insert a wall of a certain height. When that wall comes up, a wave forms approximately over the wall, then it travels backwards (against the flow of the water) some distance and settles on a spot. This shows that the wave has a lower velocity than the body of water. I saw this demonstrated back at school, and I still remember it like it was yesterday.

[rwguinn]

Hydraulic jump is a pretty neat phenomenon. You have an open channel with water flowing in it. At the base of the channel, you suddenly insert a wall of a certain height. When that wall comes up, a wave forms approximately over the wall, then it travels backwards (against the flow of the water) some distance and settles on a spot. This shows that the wave has a lower velocity than the body of water. I saw this demonstrated back at school, and I still remember it like it was yesterday.

yeah--what he said--if you google it, there's a neat animation at wikipedia...
What it really amounts to is that you get a standing wave downstream of an obstacle--not a reall problem always--i surmise--but it can become one when the flow volume decreases, and the wave then travels against the flow and slaps snot out of whatever the obstacle is...
Is that close? I had a really, really, hard time in my fluids classes...

[gumboot]

Hydraulic jump is a pretty neat phenomenon. You have an open channel with water flowing in it. At the base of the channel, you suddenly insert a wall of a certain height. When that wall comes up, a wave forms approximately over the wall, then it travels backwards (against the flow of the water) some distance and settles on a spot. This shows that the wave has a lower velocity than the body of water. I saw this demonstrated back at school, and I still remember it like it was yesterday.


That's cool.

I hated science, generally speaking. But the one thing I loved was all the weird demonstrations that you got given. I still remember when our teacher put some Potassium into the school pool.

-Gumboot

[Gravy]

Look up "hydraulic jump."

Is that what William Rea did when the pressure built from above?

[rwguinn]

Is that what William Rea did when the pressure built from above?

Somewhat looks that way. Guess he failed my test...

[jaydeehess]

Cool! So wave propigation velocity on the free surface can be less than the free-flow velocity of the body. I did not know that!
That looks like Excedrin headache number 43187!

Now look up "Laval nozzle" and see that it is possible to move a liquid faster than the speed of sound in that liquid.
(Scientific American --- sometime last year, June July or August maybe an article about a sound equivalent to the event horizon of a black hole) That blew my mind..............

[jaydeehess]

This is using more words, and incuding examples, of what I said above. Wordiness is unfair!:D
so far, the score is
logic & science 2
Billy Rhea 0

My unstated point of course was that the collapses were the result of many things occuring. Some columns failed due to being hit by dense high speed aircraft parts, some by being hit by a great deal of mass of high speed lower density aircraft parts, some by being heated under a load, some by having their loads shifted significantly off vertical after they were heated then foreshortened then cooled, some by quick fracture when a much greater load was suddenly applied, some by buckling after lateral support was removed,,,,,,
------------------------------------
CT theorists are quite fond of stating that no steel building has totaly collapsed due to fire,,, and the towers were built to withstand the impact of an aircraft andthen conclude that they should not have failed. They simply cannot fathom that it was the combination of factors that caused the failures.

The two engineering disciplines are very different, structural engineering and fire engineering. Sure the structural engineers said that the building could withstand an aircraft impact. Yes, the fire engineers stated that they designed in fire protection that would allow the building to withstand a fire in any one place for several hours.
What was not anticipated by the structural engineers was that subsequent fires would weaken the steel since they trusted the fire engineers to have the protection in place that would prevent it. What the fire engineers missed was that the impact of a plane would strip off a significant portion of that protection and then the steel would heat up.
Why was this missed? All one need do is check on the number of large aircraft that had impacted high rise steel buildings prior to 9/11/01. It simply was not something that had happened very often before and in some of the few instances where it did the building was typical post and beam and/or a long horizontal axis structure (like the apartment building in Germany that was hit by a 747)

Then the CT brings up the Windsor building in Madrid. This is a good point to bring up but not for the reason the CT believes. ALL steel columns above (IIRC) the 12th floor collapsed in this building. The only thing that saved it from total collapse were the central core concrete columns , none of which failed. Futhermore the steel failed despite the intact fire protection and the fact that the building's structural integrity was never compromised at any time by having a large mass thrown against it.

"Ohhh, but WTC 7 did not have a plane hit it and is a post and beam building ",one hears them cry.
Except it DID get hit by large pieces of the north tower. These pieces had less velocity than did the aircraft that hit the towers but consisted of much denser material (on the whole) than the aircraft. Pictures of WTC 7 before the collapse and the statements of the firefighters on the scene let us know that there was a great deal of structural damage on the south side of the building. The CT sites seem to show almost exclusively, photos of the north and east sides of this building which were co-incidentally ( I am sure) the least damaged. Added to this is the fact that WTC 7 is only a typical post and beam construction above the level of the pre-existing Con-ed building and that long cantilever structures distributed the vertical loads and that this also allowed some portions of the south side to have multi-story high ceilings in the same area where a large amount of damage is reported by firefighters.


Yep , wordy again. Somehow it seems incongruous to talk about such a complex subject in two or three sentence bites.

Is it now about 5 to 0 ????

[RenaissanceBiker]

Yep , wordy again. Somehow it seems incongruous to talk about such a complex subject in two or three sentence bites.

Is it now about 5 to 0 ????

Excellent post, but you have to list your credentials. It's the only way to be ignored rather than dismissed.

Edit: I don't mean to imply you must have credentials for your post to be relevant. Your summary is right on the money, regardless of how many letters you can add to the back of your name. I was commenting on how credentials seem to be perceived by Mr. Rea.

[Spins]

Excellent thread, this is also something I always ask CT'ers who believe in a CD, I've never had a reply yet.

The exterior columns were gradually bowing and buckling prior to the collapse, this is clearly visible on the photographs. Doesn't this indicate that the collapse of both towers was a gradual process and not a sudden CD, IMO yes! As the fire took hold and the weight of the structure above the weakened area exceeded the strain energy capacity of the deforming structural members the global collapse started.

Here is the NIST collapse sequence for both towers…


In WTC 1, the aircraft impact caused damage to the north and south walls, floors, some core columns, and insulation. The subsequent fires caused sagging of the floors on the south side of the office area, where insulation was damaged, and inward bowing of the south wall. The damage to the core columns resulted in local load redistribution to the remaining core columns. The subsequent fire-induced high temperatures caused the core to displace downward from plasticity and high creep strains in high stress and high temperatures. The downward displacement of the core resulted in load redistribution from the core to the exterior walls. With continuously increased bowing, the entire width of the south wall buckled inward. The section of the building above the impact zone tilted to the south as instability progressed horizontally to the adjacent east and west walls. Global collapse occurred as potential energy of the falling upper structure exceeded the strain energy capacity in the deforming structural members.

In WTC 2, the aircraft impact caused damage to the south and north exterior walls, floors, and columns in the southeast corner of the core. The floor damage and the subsequent fires caused sagging of the floors and local floor/wall disconnections, and resulted in bowing and buckling of the east wall. The damage to the core columns and fire-induced high temperatures resulted in local redistribution to the remaining core columns in the southeast corner, which redistributed the core column loads to the east and the south wall columns, as the core leaned toward the south and east. With continuously increased bowing, the entire width of the east wall buckled inward. The section of the building above the impact zone tilted to the east and south as instability progressed horizontally to the adjacent north and south walls. Global collapse occurred when the potential energy of the falling upper structure exceeded the strain energy capacity in the deforming structural members.

The results of the global analysis of both WTC 1 and WTC 2 showed that global collapse of both towers was initiated by the instability of the exterior walls pursuant to their excessive inward bowing which progressed horizontally to adjacent walls.

http://wtc.nist.gov/NISTNCSTAR1-6D.pdf

[jaydeehess]

Excellent post, but you have to list your credentials. It's the only way to be ignored rather than dismissed.

Edit: I don't mean to imply you must have credentials for your post to be relevant. Your summary is right on the money, regardless of how many letters you can add to the back of your name. I was commenting on how credentials seem to be perceived by Mr. Rea.

I am afraid my credentials are not impressive.

I have one year of university physics after which I switched to an electronic technology course(an electronic diploma got me a job. A B.Sc. in physics gets one,,, qualified for teacher's college or admittance for a master's degree program).

I have 25 years experience in electronics feild including almost a decade as an el-tech for NavCanada.

My prefered reading material is "Discover" and "Scientific American" magazines.
My understanding of physics can be illustrated by my stating that I just finished the book "God's Equation-Einstein,Relativity and the expanding universe" by A.D.Aczel. Some passages in this book represent the limit of my understanding of physics since it contains some mathematics topics that are hard to get one's head around. If you pick it up at a library you'll get what that means.

I have read much of the NIST reports, I read and understood the Bazant-Zhou paper, AND I have read many of the CT web pages. Guess which papers I find the most convincing in their research.....

[rwguinn]

I am afraid my credentials are not impressive.

I have one year of university physics after which I switched to an electronic technology course(an electronic diploma got me a job. A B.Sc. in physics gets one,,, qualified for teacher's college or admittance for a master's degree program).

I have 25 years experience in electronics feild including almost a decade as an el-tech for NavCanada.

My prefered reading material is "Discover" and "Scientific American" magazines.
My understanding of physics can be illustrated by my stating that I just finished the book "God's Equation-Einstein,Relativity and the expanding universe" by A.D.Aczel. Some passages in this book represent the limit of my understanding of physics since it contains some mathematics topics that are hard to get one's head around. If you pick it up at a library you'll get what that means.

I have read much of the NIST reports, I read and understood the Bazant-Zhou paper, AND I have read many of the CT web pages. Guess which papers I find the most convincing in their research.....

Oh, goodie--You have sufficient credentials to be ignored, too!
You used the words "I" "read" "Scientific" in the same sentence. The first two, espicially, make you insufficiently qualified to be a CT'er. They "View" and "lookit the pichers!" It's the only way to acquire "raw Data"!:D

[William Rea]

Although it hardly seems worth it now that I have concluded that this is a political forum, which is moderated as such, and not as the JREF heading suggests "a place to discuss skepticism, critical thinking, the paranormal and science in a friendly and lively way". I have listed my qualification below which is quoted from a previous thread...

"By the way I am a BSc (Hons) in Mechanical Engineering, and for the US people I guess I ought to add that I majored in structural properties of materials. I am a practical rather than academic Engineer hence I did not continue with any formal post graduate studies or research). I am currently working with high temperature non-ferrous superalloys as I have gained an extensive practical knowledge of metallurgy in my 20 years work experience (which I have become expert in despite my original degree being mechanical)."

[William Rea]

Excellent post, but you have to list your credentials. It's the only way to be ignored rather than dismissed.

Edit: I don't mean to imply you must have credentials for your post to be relevant. Your summary is right on the money, regardless of how many letters you can add to the back of your name. I was commenting on how credentials seem to be perceived by Mr. Rea.

In which way is it that I perceive credentials, give some examples of this?

[Arkan_Wolfshade]

Although it hardly seems worth it now that I have concluded that this is a political forum, which is moderated as such, and not as the JREF heading suggests "a place to discuss skepticism, critical thinking, the paranormal and science in a friendly and lively way". I have listed my qualification below which is quoted from a previous thread...


It is moderated per the user agreement outlined here http://forums.randi.org/showthread.php?t=25744

[RenaissanceBiker]

How about when I listed my credentials and asked you to explain how a structure becomes tougher when heated? Explain that and I'll apologize for saying you ignored my request for it.

[jaydeehess]

How about when I listed my credentials and asked you to explain how a structure becomes tougher when heated? Explain that and I'll apologize for saying you ignored my request for it.

That statement made me do a double take as well. I would also be very interested in knowing how it is that heated steel is actually tougher than room temp steel.

As I said before, it would make it more ductile and therefore less prone to fracture. It is also true that using heat to 'temper' steel makes it harder but that only occurs after it is cooled and by that time a structural member under stress while being heated has had it dimensions altered by creep and is no longer as effective as it originally was.

That statement made me do a double take as well. I would also be very interested in knowing how it is that heated steel (in the context of the WTC tower fires) is actually tougher than room temp steel.

[rwguinn]

That statement made me do a double take as well. I would also be very interested in knowing how it is that heated steel is actually tougher than room temp steel.

As I said before, it would make it more ductile and therefore less prone to fracture. It is also true that using heat to 'temper' steel makes it harder but that only occurs after it is cooled and by that time a structural member under stress while being heated has had it dimensions altered by creep and is no longer as effective as it originally was.

That statement made me do a double take as well. I would also be very interested in knowing how it is that heated steel (in the context of the WTC tower fires) is actually tougher than room temp steel.

Well, gosh--
We learned in Materials 101 that "toughness" is a measure of how far you can deform a material without it breaking...
In advanced courses, we learned that the key there, of course, is "a measure of", not "THE measure of"
The area under the stress-strain curve has a lot to do with it, but I am not a materials guy, so I don't know all the details--but as he claims to be a materials expert, he should know. Obviously, he doesn't.

[jaydeehess]

That's the point exactly. If a material's ability to resist breaking is to be the measure of 'toughness' then an elastic band is incredibly 'tough'. I don't reccomend such material as the choice for construction of skyscrapers though.

[rwguinn]

That's the point exactly. If a material's ability to resist breaking is to be the measure of 'toughness' then an elastic band is incredibly 'tough'. I don't reccomend such material as the choice for construction of skyscrapers though.
The other thing he fails to consider:
Once the shape of the structural element changes plasticly, the element has...
......
drumroll....
.......
.......
failed!