letter to NIST

Originally posted by exponent
NIST could not verify the as-built construction of WTC7 as WTC7 has been destroyed. Walking round and confirming that welds were up to spec, that plates were correctly fitted, that appropriate bolts were used is not possible because the building no longer exists.

Again, we have to ask: why? Because someone decided it was a good idea to ship all WTC 7 steel out for smelting as soon as possible.

The first steel highrise building to succumb to fire and someone thinks it a brilliant idea to just throw it all away? Whoever that is should be held accountable IMO.

BTW, we can't claim that it was just because NIST was too late in getting an investigation. There were a lot of engineers screeming in the beginning about no access to the site and the steel being shipped off without anyone looking at it and congress even had to pass a law.

See my thread here:

www.abovetopsecret.com...

So, what was so important in WTC 7 (where no one died) to clean it up fairly first? While there may have been more survivors in the rest of the complex.

reply to post by Griff

They probably were in a hurry to clean up WTC7 for the same reason they were in such a hurry to remove the core of the towers that they left those dangerous pieces of facade standing.

Originally posted by Griff

I have seen what you state. I still think it's a bad design if true. My opinion of course.

I'd have to agree.

While I don't design buildings, when I was young and in shape I was a house framer. That never would have flied as a brace. I would have brought it up to someone before it was buttoned up.

So what's the verdict?

Would a column buckling prevent connector failure?

Originally posted by Seymour Butz
So what's the verdict?

Would a column buckling prevent connector failure?

Let's ask Cardington.

In their tests, the connections failed due to tension forming from the cooling of the buckled beams. Not from the buckling itself.

Now, the question becomes: Did NIST take tension caused by cooling into account?

Originally posted by Griff


Let's ask Cardington.

In their tests, the connections failed due to tension forming from the cooling of the buckled beams. Not from the buckling itself.

Now, the question becomes: Did NIST take tension caused by cooling into account?

I'm not being clear enough.

I'm asking if there is a reason why, in anything that you've learned, that a column buckling couldn't fail a connector due to some factor that I'm unable to see?

Cuz when I think about it, if a column were to buckle, a necessary consequence of that would be a gross misalignment at the connector. Resulting in either bolt shear or a tear-out at the flange.

Originally posted by Seymour Butz
Cuz when I think about it, if a column were to buckle, a necessary consequence of that would be a gross misalignment at the connector. Resulting in either bolt shear or a tear-out at the flange.

If this where the case, how could one column buckling (column 79) pull the rest of the building down with it? If it's not connected to anything anymore?

It's a catch-22 here.

Originally posted by Griff

Originally posted by Seymour Butz
Cuz when I think about it, if a column were to buckle, a necessary consequence of that would be a gross misalignment at the connector. Resulting in either bolt shear or a tear-out at the flange.

If this where the case, how could one column buckling (column 79) pull the rest of the building down with it? If it's not connected to anything anymore?

It's a catch-22 here.

Ha ha, now I misspoke.

I should have said girder, not column.

So, if the girder were to buckle, laterally as you suggested, is there something that I'm unable to fathom that would prevent the connector failing?

Also, wouldn't col 79 still be connected to the floors above floor 13? And, wouldn't it still be connected to floors on the other 3 sides? It could pull those down, at least until THOSE connectors failed.

Originally posted by Seymour Butz
So, if the girder were to buckle, laterally as you suggested, is there something that I'm unable to fathom that would prevent the connector failing?

Not really. But, then again, you have to take into account the whole floor system is connected and not just pieces and parts.

Also, wouldn't col 79 still be connected to the floors above floor 13? And, wouldn't it still be connected to floors on the other 3 sides? It could pull those down, at least until THOSE connectors failed.

Well, the connections either failed OR they were strong enough to pull the remaining floors. Both can not happen. It has to be either one or the other. Because if they were strong enough to pull the remaining floors with it, then the shear load wouldn't be acting on it anymore as the floors would be insync with the connections and not producing any shearing action anymore.

reply to post by Griff


The girders have headed anchor studs welded on top of the beam that makes it composite with the concrete floor deck. This braces it against lateral torsional buckling. It also adds a fair amount of strength.

Originally posted by Anonymous ATS
The girders have headed anchor studs welded on top of the beam that makes it composite with the concrete floor deck. This braces it against lateral torsional buckling. It also adds a fair amount of strength.

Question now becomes: Enough strength to hinder connection failure? Honest question.

Also, I understand what you are saying. That is why I said to Seymour that it wasn't just pieces and parts but a composite system.

Originally posted by Griff

1-Not really.

2-But, then again, you have to take into account the whole floor system is connected and not just pieces and parts.

3-Well, the connections either failed OR they were strong enough to pull the remaining floors. Both can not happen. It has to be either one or the other. Because if they were strong enough to pull the remaining floors with it, then the shear load wouldn't be acting on it anymore as the floors would be insync with the connections and not producing any shearing action anymore.

1- That's what I envisioned

2- yes, I agree with your and Anon's posts

3- ok, so let's say that the connectors on col 79 failed instantly on the floors above 13 when col 79 buckled. That would leave those floors supported on one end only and they fall. If they don't fail on the col 79 end, then the floors get puled down. If they fail on the ext column end, the floors fall.

I see no scenario whereby the floors above 13 couldn't fall when 79 buckles, leaving the ext columns unbraced and liable to buckling.

Originally posted by Seymour Butz
I see no scenario whereby the floors above 13 couldn't fall when 79 buckles, leaving the ext columns unbraced and liable to buckling.

Are you saying that the exterior would partially collapse then as they lose their support from east to west unlike what we see in video? Or are you saying until all were unbraced and were allowed to then buckle all nice and neat into themselves at once? Myself, I would imagine the first.

[edit on 9/4/2008 by Griff]

[edit on 9/4/2008 by Griff]

reply to post by Griff


I don't follow. Could you explain how a connection would not fail from the member having a thermal expansion of roughly 3 inches?

reply to post by Newtons.Bit


Welcome to ATS Newton!!

Originally posted by Newtons.Bit
I don't follow. Could you explain how a connection would not fail from the member having a thermal expansion of roughly 3 inches?

It depends on what connection you are talking about.

If it is the beam to girder connection, the force is acting directly through the connection so no shearing. The connections would become in tension once the beam starts to cool and retract though as seen in the Cardington tests.

If we are talking about the girder to column connections, we are talking about shear as well due to the beams pushing against the girder perpendicular to the connections which would also cause moments to develope in the connections. Which, I have stated is possible to shear the connection. Depending on strength and bracing of the girders ect.

Disclaimer: This is all opinion so far as I haven't hardly done any calculations.

[edit on 9/4/2008 by Griff]

Originally posted by Griff

Are you saying that the exterior would partially collapse then as they lose their support from east to west unlike what we see in video? Or are you saying until all were unbraced and were allowed to then buckle all nice and neat into themselves at once? Myself, I would imagine the first.

I was responding to this:

Griff - If this where the case, how could one column buckling (column 79) pull the rest of the building down with it? If it's not connected to anything anymore?



So if your theory about thermate in the towers holds water in your eyes, then unbraced ext columns should too.

Besides, I don't know of anyone saying that col 79 "pulled" the building down with it. You're making up that argument.

In other words, you've constructed yet another strawman.

Originally posted by Seymour Butz
Besides, I don't know of anyone saying that col 79 "pulled" the building down with it. You're making up that argument.

What would you describe it as then? If the connections to column 79 failed, then it is no longer able to hold floors on the east side of other columns only. What about the other side (west of these columns) that is being braced with their floors? But, I'll admit, maybe I am seeing it wrong.

Originally posted by Seymour Butz
So if your theory about thermate in the towers holds water in your eyes, then unbraced ext columns should too.

I never said differently. What I did say was that in my opinion, a progressive collapse happening in the interior would do as you say, cause the exterior to become unbraced. The only difference is I believe it would happen in a progressive manner the same as the interior.

Originally posted by Griff

Originally posted by Newtons.Bit
I don't follow. Could you explain how a connection would not fail from the member having a thermal expansion of roughly 3 inches?

It depends on what connection you are talking about.

If it is the beam to girder connection, the force is acting directly through the connection so no shearing. The connections would become in tension once the beam starts to cool and retract though as seen in the Cardington tests.

If we are talking about the girder to column connections, we are talking about shear as well due to the beams pushing against the girder perpendicular to the connections which would also cause moments to develope in the connections. Which, I have stated is possible to shear the connection. Depending on strength and bracing of the girders ect.

Disclaimer: This is all opinion so far as I haven't hardly done any calculations.

[edit on 9/4/2008 by Griff]

The beam to girder connection is a simple shear tab. Restrained expansion will result in shear across the bolts of the shear tab. The picture in the NIST report shows the coped beam flange of the girder right up next to the girder flange, however in practice it probably had a somewhat larger gap. There's nothing more annoying than getting out into the field and seeing the coped flange is just barely too small.

Calculations are in order. It would be much easier to see what you're talking about if you would assign numbers to your assumptions. Typically, composite floor slabs brace beams in both lateral torsional buckling and compression buckling (I don't have a source for that on hand, I think it's in one of the AISC design guides), however with the amount of expansion going on, it is probably safe to assume that the floor slab has cracked and no longer braces the beam against buckling. That doesn't mean that the girder(or a beam) should only be braced at locations where other members frame into it.

A quick and dirty analysis should be conducted to determine the inflection point of the sum of P/A and M*c/I to determine where the compression flange is actually in compression. The unbraced length could then be determined by the length of this area.

It's probably safe to neglect bending at the connection from rigidity of the bolt group. AISC typically allows one to ignore that up to 9 bolts (I can source this if needed). Likewise, I don't think we need to consider the failure of the plate as a limit state. There's no need to do block shear calculations for something this simple: the bolt capacity will likely be close to the overall connection capacity.

reply to post by Newtons.Bit


Welcome to ATS. You obviously know what you are talking about. I can't disagree with anything in your post. We'd also have to take into account the p-delta affect. I look forward to learning from each other.