Total Building Collapse from a Single Column Failure

[jaydeehess]

Oops unintended and erroneous double negative in my previous post

 

[Newtons Bit]

Having a bit of trouble reading that graph. Same graph twice, right?

Yah, no idea why I double-clicked...

Shows loss of 50% at 600C and approx 30% at ~450C.

Correct

My stainless steel wood stove Chimney is rated to withstand 2000F (1093 C)for one hour. Of course neither my woodstove or my chimney needs to carry almost no load. Point is that a wood fire can be expected to generate byproducts that, if ignited, can cause the chimney to reach over 1000 C. I have no trouble believeing that in a fire, the structural steel can reach at least the point at which the steel has lost 25-30% of its normal strength.

If that is a girder, and the girder seat at the column, and this girder has been moved such that it now has only a fraction of its normal contact area between girder and girder seat, its quite concievable that the girder flange and/or the girder seat fails.

Bingo. There's actually a number of different failure modes that can occur from very small bearing areas.

 

[JSanderO]

Yah, no idea why I double-clicked...

Bingo. There's actually a number of different failure modes that can occur from very small bearing areas.

And tell the readers what happens when the "girder fails"... presumably shears at the seat because of insufficient area for bearing.

If the girder and the beams connected to it are composite with the slab... what happens?

a) the slab fractures over the girder and drops down with girder... perhaps with the beams connected to the next girder over???

b) How much floor would you expect to collapse from the failure of one connection of the girder at column 79?

c) How does the girder shearing lead to the collapse of column 79? Isn't load removed from the column when the girder drops off... albeit on the north side?

Please explain.

 

[Newtons Bit]

Wut?

 

[JSanderO]

And they are?

And how does a girder failure lead to column 79 failure?

Let's play Bingo!

 

[Newtons Bit]

And they are?

The most obvious one is an actual bearing failure, see AISC Design Guide 1 for information on that, however different modes such as Web Local Buckling, Flange Shear, Flange Bending, Web Shear, may control depending on the configuration, see AISC 360 for more information.

And how does a girder failure lead to column 79 failure?

See the NIST report on WTC7. tl;dr: unbraced length is inversely proportional to compression capacity.

Let's play Bingo!

Is that the game you're trying to play here?

 

[JSanderO]

The most obvious one is an actual bearing failure, see AISC Design Guide 1 for information on that, however different modes such as Web Local Buckling, Flange Shear, Flange Bending, Web Shear, may control depending on the configuration, see AISC 360 for more information.

See the NIST report on WTC7. tl;dr: unbraced length is inversely proportional to compression capacity.

Is that the game you're trying to play here?

No problem with failure of the beam or girder from in adequate bearing area.

I understand that when the unbraced length increases the bearing capacity is reduced. But if I am not correct, column 79 had several beams framed into it bracing it. Would the failure of one of multiple braces cause buckling of a column so quickly? That sounds odd. Perhaps it lost some capacity... But surely the column had a FOS of perhaps 1.5 to 2.

Perhaps you could explain how this works in lay terms to a dumb architect?

 

[Newtons Bit]

No problem with failure of the beam or girder from in adequate bearing area.

I understand that when the unbraced length increases the bearing capacity is reduced. But if I am not correct, column 79 had several beams framed into it bracing it. Would the failure of one of multiple braces cause buckling of a column so quickly? That sounds odd. Perhaps it lost some capacity... But surely the column had a FOS of perhaps 1.5 to 2.

Perhaps you could explain how this works in lay terms to a dumb architect?

Column 79 had three beams framing into it. See here. Loss of any one could result in one of the two principal axes of the column becoming unbraced. In total, a height of over eight floors lost bracing.

 

[jaydeehess]

Locally its to be expected that if the beams and girder were elevated to the temp range for which steel loses strength/ increases plasticity , then so too was the proximate length of col 79

 

[ozeco41]

Locally its to be expected that if the beams and girder were elevated to the temp range for which steel loses strength/ increases plasticity , then so too was the proximate length of col 79

Naughty. You are thinking. I remember saying the same thing to Mr Szamboti and several others who were calculating the expansion of the 79-44 girder to fractions of an inch whilst blindly assuming that the two columns were not heat affected..... Silly me for thinking

Most people ignored the point -- they were having too much fun ignoring reality in pursuit of multiple decimal place presumed precision of mathematics.....

 

[Robrob]

Most people ignored the point -- they were having too much fun ignoring reality in pursuit of multiple decimal place presumed precision of mathematics.....

That's what I've never understood, the continued debate over "iron rich microspheres," "girder creep" or any other micro-scale bit of trivia when on the macro-scale (e.g. the real world) the evidence is irrefutable.

Do they think by arguing long enough over grains of sand people will forget about the giant log?

 

[ozeco41]

That's what I've never understood, the continued debate over "iron rich microspheres," "girder creep" or any other micro-scale bit of trivia when on the macro-scale (e.g. the real world) the evidence is irrefutable.

Do they think by arguing long enough over grains of sand people will forget about the giant log?

Exactly. AKA "forests v trees" OR "Alligators v swamp draining" ..and one of my pet irritations.

Take as examples two issues which are the same thing but usually treated as somehow different.

One is the debates over whether or not "tilt" will cause (or prevent) axial misalignment of columns. (The other is "Missing Jolt" - brief comment later.)

The thing that causes tilt is failure of columns which, by definition, for each column involved, for the tilt to have occurred i.e. (to make it bleedingly obvious) the space that column "xyz" used to occupy is now LESS because the top section has lowered - which fact of now past history is what caused the tilt.

SO the column ends are no longer in axial contact bearing load. (There are a few easily disposed of "yes buts" but let's keep it simple. )

All the silly claims - mostly by T Sz - that there was no force to cause sideways displacement AND all the fancy maths - by Tony's opponents - to prove "will miss" are based on false premises. It is too late. By the time there is tilt the "will impact/wont impact" stage is past history.

And "Missing Jolt" shares the same fatal error of "anachronism" - by the time T Sz goes looking for his phantom jolt it is already past history.

AND those are only two similar examples of missing the bleeding obvious by focusing too deep into details. Forests and trees syndrome.

Read the OP of this thread - and my earlier answers - then recent posts.

 

[JSanderO]

Column 79 had three beams framing into it. See here. Loss of any one could result in one of the two principal axes of the column becoming unbraced. In total, a height of over eight floors lost bracing.

Color me dumb. If the columns were 2 story in height... the column on floor 13 was framed into as you mention 3 beams (one being a girder) on two floor levels... And the splices of the columns were 3 or 4 feet above floor level (assumption)... loss of one beam would leave this column with 5 other beams bracing it. So it lost a brace a 9 feet above above the lower end... or 3 feet from the upper end.

You are asserting 1 brace failing in one of those two location caused 4 - 24' tall columns (8 floors) stacked to buckle?

I've always understood that grid designed steel or concrete framed buildings can stand with loss of a single column... one one floor. No?

 

[dafydd]

Pardon a layman for intruding, but is all this leading to a claim of controlled demolition? We all know that the buildings collapsed.

 

[Newtons Bit]

Color me dumb. If the columns were 2 story in height... the column on floor 13 was framed into as you mention 3 beams (one being a girder) on two floor levels... And the splices of the columns were 3 or 4 feet above floor level (assumption)... loss of one beam would leave this column with 5 other beams bracing it. So it lost a brace a 9 feet above above the lower end... or 3 feet from the upper end.

You are asserting 1 brace failing in one of those two location caused 4 - 24' tall columns (8 floors) stacked to buckle?

The flooring around column 79 failed over 8 floors. The columns are not magically braced at their splice.

I've always understood that grid designed steel or concrete framed buildings can stand with loss of a single column... one one floor. No?

There's no guarantee. Modern code adds some progressive collapse resistance to concrete construction, but not to steel.

 

[jaydeehess]

Pardon a layman for intruding, but is all this leading to a claim of controlled demolition? We all know that the buildings collapsed.

No, JSO simply takes exception to the NIST scenario. He wants to push his own hypothysis.

 

[ozeco41]

No, JSO simply takes exception to the NIST scenario. He wants to push his own hypothysis.

That is the central point. JSO suggests that transfer truss failure was a more probable initiator than girder walk off. He makes a reasoned argument that, IMO, is a plausible but ultimately unprovable alternate hypothesis.

That central item is then wrapped in a lot of vaguely defined claims in the form of false generalisations about single column failures and the meaning of "cause" - single column failure would always cause OR single column failure would never cause collapse when the true situation is that single column failure could or may form part of a collapse mechanism. It will always be situation specific - not a generic rule. (IMO )

If anyone can explain how you could have a single column failure occur without any other contributory mechanism - I would be interested to hear - but it doesn't change my previous comments.

 

[JSanderO]

The flooring around column 79 failed over 8 floors. The columns are not magically braced at their splice.

There's no guarantee. Modern code adds some progressive collapse resistance to concrete construction, but not to steel.

That's a BS answer if I ever saw one... one girder walks and 8 floors above it collapse?

How dat happen? Bingo because you said so?

The columns were NOT braced at the splices if I am not mistaken.

Ozzie... and JayDee...

Whether or not a girder walked off its bearing seat on floor 13 level or not... I don't see how THAT failure could lead to the column failing... which I assume is buckling. It might begin a cascading collapse of some floor area supported by walked off girder DOWNward. That I can see. Does that cause the column 79 below 13 the buckle?

I ask for some more specificity much as I would ask the CD guys to explain how CD would produce the observed movements.

The OP was about how a single column failure could collapse an entire building. I don't see much support for that concept. And it's even "worse" that that... it's a 2 story column with 2 sets of 3 beams framed into the column at 4' above the bottom and them at about 13 foot above the bottom... with one girder walking off... allegedly leading to the failure of col 79 and the 4-2 story columns above per Newton's Bit.

You can say that's what happened. But that's about on the same level as the truthers and CD.

Show and Tell... SHOW being the operative part here.

Whether TTF is a viable explanation or not... I attempted to explain how the failure progresses from one member to the next and the consequences... ie the cascading progression of failures which would match the observables.

Perhaps you have another example of a single steel column losing one brace and it leading to a building collapse?

 

[Newtons Bit]

That's a BS answer if I ever saw one... one girder walks and 8 floors above it collapse?

That floor and seven floors below collapse. The girder and the floor drop to the floor below. That floor, already weakened by fire also collapses. Then the floor below it, and below it, etc, over 8 floors. Gravity pulls things down, not up.

How dat happen? Bingo because you said so?

Fire.

The columns were NOT braced at the splices if I am not mistaken.

No they are not. Now why do you keep claiming there were "4-2 story columns"? Do you think the unbraced length of each of those four pieces of steel is only two stories?

Ozzie... and JayDee...

Whether or not a girder walked off its bearing seat on floor 13 level or not... I don't see how THAT failure could lead to the column failing... which I assume is buckling. It might begin a cascading collapse of some floor area supported by walked off girder DOWNward. That I can see. Does that cause the column 79 below 13 the buckle?

I ask for some more specificity much as I would ask the CD guys to explain how CD would produce the observed movements.

The OP was about how a single column failure could collapse an entire building. I don't see much support for that concept. And it's even "worse" that that... it's a 2 story column with 2 sets of 3 beams framed into the column at 4' above the bottom and them at about 13 foot above the bottom... with one girder walking off... allegedly leading to the failure of col 79 and the 4-2 story columns above per Newton's Bit.

You can say that's what happened. But that's about on the same level as the truthers and CD.

Show and Tell... SHOW being the operative part here.

Whether TTF is a viable explanation or not... I attempted to explain how the failure progresses from one member to the next and the consequences... ie the cascading progression of failures which would match the observables.

Perhaps you have another example of a single steel column losing one brace and it leading to a building collapse?

I like how these posts of yours go from describing yourself as a "dumb architect" (your exact words), to this. Tell me, were you lying when said you were just "a dumb architect" or are you actually a "dumb architect" and are now making things up? Which version of your claims should I view as true?

 

[jaydeehess]

That is the central point. JSO suggests that transfer truss failure was a more probable initiator than girder walk off. He makes a reasoned argument that, IMO, is a plausible but ultimately unprovable alternate hypothesis.

That central item is then wrapped in a lot of vaguely defined claims in the form of false generalisations about single column failures and the meaning of "cause" - single column failure would always cause OR single column failure would never cause collapse when the true situation is that single column failure could or may form part of a collapse mechanism. It will always be situation specific - not a generic rule. (IMO )

If anyone can explain how you could have a single column failure occur without any other contributory mechanism - I would be interested to hear - but it doesn't change my previous comments.

Well if the structure was a center pole tent…...