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      10-04-2011, 02:04 PM   #45
M3Bahn
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Originally Posted by BrokenVert View Post
You arent following. The opinions of architects dont matter because architects dont do any structural designs.

Engineering is a broad terms and covers such disciplines as chemical engineers, petroleum, mechanical, civil, and biological.

There are hundreds more and each one of the listed options can further be broken down into sub disciplines.

Structural and mechanical engineers opinions are the only ones that matter because those are the only engineers that design the structure of buildings. But at that only certain mechanicals matter because only some of the sub disciplines and foci of mechanical actually deal with building structures.

Would you buy a car designed by a pharmaceutical engineer? No. So why would you care about what they say when its on a building?

Haha, nice try, you know I meant the structural and mechanical engineers that signed the petition that you obviously refuse to look at.
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      10-04-2011, 02:10 PM   #46
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Haha, nice try, you know I meant the structural and mechanical engineers that signed the petition that you obviously refuse to look at.
nice one what? I acknowledged that they had an opinion and I said that I disagreed with it and provided proper evidence to support my claim and refute theirs.

I also that that a few of their opinions were invalid because they arent of the proper discipline to have real detailed knowledge about the subject at hand. Which is structures.

Thats science in a nutshell
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      10-04-2011, 02:41 PM   #47
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I'm curious to hear what you think of the video I posted.
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      10-04-2011, 02:52 PM   #48
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I'm curious to hear what you think of the video I posted.
I think the video makes some good points but I'm not a structural engineer.
Thanks for posting it.
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      10-04-2011, 03:01 PM   #49
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But you can see that it collapsed slowly from the inside out, right? You can also see that it doesn't take that much fire to weaken steel. Also, when the steel expands while constrained at both ends, as it would in the middle of a building, it has nowhere to go and enormous stresses build up. This causes buckling, shearing of rivets, and the twisting of columns. You'll notice bridges have expansion joints to allow for the ~150-200 degree range of temperatures they might experience between a freezing night and scorching day. Without these, longer bridges risk failing from the mere heat load of the sun, without basically zero weakening. Girders and columns in buildings can't have expansion joints and even if they could we're talking about a ~1000* temperature increase here.
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      10-04-2011, 03:36 PM   #50
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Here's some engineering for you...

thermal strain = coefficient of thermal expansion * temperature change

Strain = stress/(modulus of elasticity)

For steel, modulus of elasticity is about 30e6 psi. Coefficient of thermal expansion is about 9.6e-6/*F

So, for a bar constrained on both ends and heated 1000 degrees...
Tstrain = 9.6e-6*1000=.0096

.0096= stress/30e6

Stress =288,000psi.

That is MANY TIMES the stress structural steel can handle, which would typically be under 60,000psi. What'll typically happen though is it'll start twisting columns and bending beams to allow some strain and relieve the stress. The building must be designed to accommodate a little bit of this, just as it can accommodate motions due to wind, earthquakes, etc. This is a LOT of force though. This motion will reduce the enormous stress, but allows more strain, so it maligns everything and warps the building, meaning all the stresses are pointed the wrong directions.

Also, don't forget...at 1000*F steel will typically have about half the strength it had at room temp.



It actually has more strength for a bit, but then drops off quickly.

So, lets just wag this. The building is under, potential, 5x the stress, and the strength is cut in half. That's 10x what it's able to take. Even with a VERY conservative 5x safety factor this was just way, WAY too much. It probably failed before a lot of it even had time to get up to 1000*F

Even if the steel is insulated, insulation just slows down the flow of heat- it doesn't prevent it. It just buys you time, and this building was on fire for a long time.

As an engineer, there's just nothing all that amazing about a damaged building that was burning all day collapsing. It had already happened twice earlier that day (although much quicker as the fire was more intense and the structure badly damaged).

Last edited by carve; 10-04-2011 at 06:32 PM.
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      10-04-2011, 06:07 PM   #51
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Perhaps if no other rational argument will carry the day, try this one.

People just aren't good enough to successfully carry off a big old conspiracy. Sorry, not only can't they keep a secret but, they aren't smart enough to think it up, plan it out and execute.
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      10-04-2011, 06:17 PM   #52
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I am a civil/structural PE registered in 6 states by exam.

I don't feel like writing a sermon to display the idiocy of these conspiracy theorists. If you have specific questions ask away and I will explain.
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      10-04-2011, 06:50 PM   #53
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(raises hand). Uhhh...yeah...was my mechanical engineers quick-and-dirty description of what the building was undergoing close enough to get the idea?
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      10-04-2011, 06:53 PM   #54
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Quote:
Originally Posted by carve View Post
(raises hand). Uhhh...yeah...was my mechanical engineers quick-and-dirty description of what the building was undergoing close enough to get the idea?
I can ask the same question. haha
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      10-04-2011, 08:05 PM   #55
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(raises hand). Uhhh...yeah...was my mechanical engineers quick-and-dirty description of what the building was undergoing close enough to get the idea?
You put together that video? Or, are you talking about the thermite?

The video is accurate IMO. Also, a member does not have to outright fail....it just has to deform. Loads are redistributed in ways that the structure is not designed for, then failure occurs due to overstress. The weight of many floors above deformed beams due to heat causes stresses the building is not designed for. So, you could either have outright failure or failure due to undesigned load distribution causing overstress. One could argue they are one in the same, but one could make a distinction. Who knows what exactly happened inside of those buildings to a 100% certainty structurally, but it wasn't some bomb/conspiracy lol. Heat causes stuff to happen to structures they aren't designed for. Period.

Also, fireproofing only works so long. It is typically only rated for 2 hours in my industry.

Here's a story for you; when the second plane hit I was at work and a buddy called me and asked me if they would fall. I said no, since they survived the impact...I could not get on the internet or get to a TV to see the fires. I left work and I was pulling into my driveway when the guy on the radio said the tower was falling. After I saw the pictures I realized the heat was causing the falling, not the impact. I've led several projects where we have rebuilt industrial facilities due to explosions and fires, so this is something I am pretty familiar with along with my stuctural background. Just goes to show a picture is worth a thousand words.

I have had "discussions" about this on other forums. People will believe what they want to believe, and IMO alot of that is politically motivated. I wonder how many of the truthers are democrats, I bet most. FYI I didn't vote for Bush and would never vote republican.
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      10-05-2011, 12:41 AM   #56
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Question for the engineers. OK, so lets say I buy the rational explanation of Tower 7. There have been very similar towers with much larger fires burning for longer that have not collapsed, or have seen a smaller cascade collapse on part of the structure.

If it only takes an office fire to cause a 47 storey building to collapse why has it vere happened before?

And none of you have explained the molten for days pools of steel yet. I know it doesn't fit your rational explanations but it was there. What (a) heated the steel up to melting temperature and (b) kept it so hot for so long?
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      10-05-2011, 04:19 AM   #57
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Quote:
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Question for the engineers. OK, so lets say I buy the rational explanation of Tower 7. There have been very similar towers with much larger fires burning for longer that have not collapsed, or have seen a smaller cascade collapse on part of the structure.

If it only takes an office fire to cause a 47 storey building to collapse why has it vere happened before?

And none of you have explained the molten for days pools of steel yet. I know it doesn't fit your rational explanations but it was there. What (a) heated the steel up to melting temperature and (b) kept it so hot for so long?


WTC 7 didnt have a functioning sprinkler system, also firefighters essentially ignored 7 because of the immediate search for survivors in the wake of towers 1 and 2 falling. Not that they could do much, because there was no water pressure due to broken lines.


Most of the time firefighters are doing their best to beat back a blaze. This reduces the heat involved in a fire and it also reduces the severity of a fire, so the building doesnt undergo the same set of events that led to the collapse of 7.


I can believe that some steel melted during the collapse. Friction can heat steel just as much as fire. So some steel wouldve melted due to very high point frictions due to the forces of a 110 story building coming down. Especially on the members directly exposed to the fire, as they were already heated to about 2/3 of their melting point.


Concrete is also a good insulator. I dont see it as happening but in theory you could have a few puddles melted by friction and then kept warm inside a shell of concrete. (but like I said I dont really see that happening)
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      10-05-2011, 11:05 AM   #58
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Quote:
Originally Posted by JCE View Post
I wonder how many of the truthers are democrats, I bet most. FYI I didn't vote for Bush and would never vote republican.
Well on this forum, none of the conspirators are democrats, and I think that goes for the general population. The anti-govt crowd has moved over to the tea party.

And while I appreciate the PE's and civil eng's checking-in here, I'm more confounded by the logic of these truthers than anything. What do these people actually believe? Do they agree that terrorists flew the planes? If so, then what do they think happened? The US govt coincidentally detonated the trade center & pentagon at the same time they were hit by planes?

Maybe the planes were flown by agents of the US govt? And the planes were used as a ruse to cover-up the planned detonation? I mean, this is seriously crazy sh!t.

Anyone can say "I don't think agency X is telling the whole truth", but it's another thing to take the conspiracy to it's batshit nutso conclusion. Really, what's this been all about for the last 10 years?
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      10-05-2011, 11:22 AM   #59
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JCE: I was referring to what I said in post 50. It's similar to what you said in #55, but with some notional numbers thrown in.

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There have been very similar towers with much larger fires burning for longer that have not collapsed
Where? Show me a fire in a similar fully furnished building that has burned completely uncontrolled for 7 hours. No firefighters. No sprinklers. Just an evacuated building.

I'm not familiar with the molten steel so I can only speculate. A lot of energy is released in the fire and collapse. Even if there was thermite used to cut girders, it would be a tiny increase to the total energy of the system. What seems to be happening is a bunch of fire smoldering with what little oxygen it can get from air and steam, with the heat having nowhere to go, and then getting a big whiff of air as the rubble is cleared. Ever hear of a "backdraft" in firefighting? Something like that.

Where's the thermite connection? Are you saying they set off charges 6 weeks later?
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      10-05-2011, 02:16 PM   #60
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Can you guys explain what they are talking about, I understand the steel weakening but why would it melt?





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      10-05-2011, 02:22 PM   #61
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JCE: I was referring to what I said in post 50. It's similar to what you said in #55, but with some notional numbers thrown in.



Where? Show me a fire in a similar fully furnished building that has burned completely uncontrolled for 7 hours. No firefighters. No sprinklers. Just an evacuated building.

I'm not familiar with the molten steel so I can only speculate. A lot of energy is released in the fire and collapse. Even if there was thermite used to cut girders, it would be a tiny increase to the total energy of the system. What seems to be happening is a bunch of fire smoldering with what little oxygen it can get from air and steam, with the heat having nowhere to go, and then getting a big whiff of air as the rubble is cleared. Ever hear of a "backdraft" in firefighting? Something like that.

Where's the thermite connection? Are you saying they set off charges 6 weeks later?
THe 911 conspiracy "films" all basically put that under the rug and acted like there was a small fire and then boom it all came down perfectly at free fall. Rather than facing the fact it was an extreme impact of a jet liner plus hours of fires. Part of one of the towers crashed into the backside of Tower 7 and cut a huge slice into it. Of course the 911 conspiracy movies don't show that side.

This is the first time a jet liner crashed into a building so to say simply that fires never lead to a collapse is irrelevant.
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      10-05-2011, 03:24 PM   #62
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Bahn, you crack me up...you are alot smarter than I am thats for sure...

If I am ever in ATL area we need to go get a beer together...on me.



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Can you guys explain what they are talking about, I understand the steel weakening but why would it melt?





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      10-05-2011, 03:29 PM   #63
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Bahn, you crack me up...you are alot smarter than I am thats for sure...

If I am ever in ATL area we need to go get a beer together...on me.
Beer summit!!!!!!!!!!!
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      10-05-2011, 03:52 PM   #64
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Quote:
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Can you guys explain what they are talking about, I understand the steel weakening but why would it melt?
This vv
Quote:
Originally Posted by BrokenVert View Post
I can believe that some steel melted during the collapse. Friction can heat steel just as much as fire. So some steel wouldve melted due to very high point frictions due to the forces of a 110 story building coming down. Especially on the members directly exposed to the fire, as they were already heated to about 2/3 of their melting point.

Concrete is also a good insulator. I dont see it as happening but in theory you could have a few puddles melted by friction and then kept warm inside a shell of concrete. (but like I said I dont really see that happening)
Basically, the collapse of a mass as great as the WTC, with all it's momentum, is like a mini version of how a star like our sun was formed; by the collapse of a tremendous mass, emitting vast amounts of energy. That's what caused the extreme temps, and the weeks of smoldering. It's the combination of great mass, pressure, and entombment by the concrete.
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      10-05-2011, 05:43 PM   #65
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Bahn, you crack me up...you are alot smarter than I am thats for sure...

If I am ever in ATL area we need to go get a beer together...on me.


I have the place picked out already.

http://www.derbiergarten.com/

Never been but the beer looks appropriate for german car enthusiasts.
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      10-05-2011, 06:21 PM   #66
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Can you guys explain what they are talking about, I understand the steel weakening but why would it melt?
Did you even read my post?


When I was a kid, there was an abandoned house across the street. A neighbor, my good friend's dad, got tired of looking at it, bought the property and got the fire department to burn the house down. They let it burn almost to nothing before putting it out.

I checked the house out the day before and noticed a coffee can of nails sitting just inside the door. A couple of days later, my friend and I noticed a solidified puddle of steel in the same spot. Clearly this indicates a government conspiracy and the use of thermite to destroy the building, and the fire dept setting it on fire was just a cover story.

(This was in your neck of the woods, mact333- near Lucia Falls)

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