Question concerning structural steel design and thermal expansion...

Gamolon

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Gamolon
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Any input would be appreciated.

I am in a debate with someone who believes that structural engineers incorporate some type of physical mechanism or "allowance" into an internal steel support structure that will compensate for thermal expansion due to office fires.

I worked in an engineering firm years ago and never did I see a structural engineer design into their structural system, a means to compensate for thermal expansion due to office fires.

It is my understanding that this is NOT designed for and that is what fire-proofing and sprinkler systems are used for. To PREVENT this type of thing from happening in addition to preventing the weakening of steel.

Can someone please shed some light on this subject?

Thanks in advance.
 
Gam,

You're absolutely correct as to my knowledge. I just spoke to my dad (who, BTW, is a structural engineer) and he has never heard of anyone incorperating any tolerance for thermal expansion. BUT, he did say that some highrise structures being designed post-911, may incorperate that into their design.

But, pre-911, he hadn't heard of anyone doing that.

Maybe one of the engineers of the forum could elaborate?
 
Architect would know about this. I think I saw some writeup or news article that discussed measures against such expansion being necessary in the light of code changes implemented after the NIST report published, but I don't recall with any clarity.

While this may be tedious, since it would involve a ton of posts to leaf through, you should look up Architect's posting history. He's discussed design many times in this subforum, and the posts have been illuminating.
 
NIST is the federal body from which recommendations for building codes emanate in the USA. Building codes are implemented on state and city levels, so the NIST recommendations are not the building codes per se that engineers conform to, but most states and communes certainly adhere to these standards.

The central finding of NIST's study on WTC7 was that the thermal expansion of a long floor span caused progressive collapse. To their knowledge, this phenomenon had never before been identified as the reason for a building collapse. More importantly, this possibility was not accounted for in NIST's recommendations for building codes. Consequently, NIST amended its recommendations accordingly, and many states and communes followed that recommendation.


It is possible that some building codes here or there already took care of this phenomenon, but most certainly didn't. In particular, the building codes in effect for NYC at the time all WTC highrises were built contain no such provisions.


Structural engineers typically have their keenest eye on making sure that building codes are adhered to when designing a structure. Most probably exceed the minimum requirements, and may or may not think of additional potential weaknesses not governed in the codes. Still, adhering to codes is a top priority, as it relieves them of responsibility in case of a catastrophe.


Ergo: Since thermal expansion of long floor spans during fires was not identified by building codes as an issue to be dealt with by structural engineers, then it wasn't dealt with by most engineers.




(There are of course structures where very long spans are the norm and where engineers have always implemented solutions to deal with thermal expansion: Bridges are an obvious example, and I am sure that large domes are another, and supertankers likewise need to be stable and oil-tight both in rough tropical and arctic seas. Aircraft designers routinely deal with expansion and contraction due to varying outside pressure. Etc. Such long spans are more of an exception in office buildings)
 
ElMondoHummus said:
Architect would know about this. I think I saw some writeup or news article that discussed measures against such expansion being necessary in the light of code changes implemented after the NIST report published, but I don't recall with any clarity.

While this may be tedious, since it would involve a ton of posts to leaf through, you should look up Architect's posting history. He's discussed design many times in this subforum, and the posts have been illuminating.
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There is nothing in Chapter 6 (Structural Design) or 22 (Steel) of the IBC regarding thermal expansion from fire.
 
Animal said:
There is nothing in Chapter 6 (Structural Design) or 22 (Steel) of the IBC regarding thermal expansion from fire.
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How about in proposed code changes? Last I looked - admittedly, last year or even ealier than that - many of the NIST recommendations were still being studied/discussed by the ICC.

Again, I'm outside this field, so I have no problem with being told I'm wrong. It's just that, something about that topic and code changes is tickling the back of my mind somehow, and I haven't had time to run it down in the forum's search function.
 
ElMondoHummus said:
How about in proposed code changes? Last I looked - admittedly, last year or even ealier than that - many of the NIST recommendations were still being studied/discussed by the ICC.

Again, I'm outside this field, so I have no problem with being told I'm wrong. It's just that, something about that topic and code changes is tickling the back of my mind somehow, and I haven't had time to run it down in the forum's search function.
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My understanding is that most changes were made to protect the fire systems (along with occupant escape). Stand-pipes moved inside more robust core areas, that sort of thing. If you can maintain the fire systems thermal expansion/contraction is not a major concern (that hasn't be dealt with before)..
 
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ElMondoHummus said:
How about in proposed code changes? Last I looked - admittedly, last year or even ealier than that - many of the NIST recommendations were still being studied/discussed by the ICC.

Again, I'm outside this field, so I have no problem with being told I'm wrong. It's just that, something about that topic and code changes is tickling the back of my mind somehow, and I haven't had time to run it down in the forum's search function.
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I haven't seen the 2009 code yet.......it hasn't been adopted here, so I have shell out the hundred it cost for the full set yet, so I do not know if anything is in there.
 
Buildings and other structures will account for thermal expansion in various components caused by daily and seasonal temperature variations. For example a brick face can undergo significant expansion and contraction in the course of a hot day and needs to have the supporting elements adjust to that. A long enough building might have an expansion joint somewhere along the length of it, running through all the components. Buildings which are strung together, such as one often finds in hospital complexes for example, will have joints between the disparate parts. Also, connections of beams to columns are often designed with some room for movement to account for the building's expansion, contraction, and general motion due to use.

Fire protection is generally handled with spray-on fireproofing and sprinkler systems. Not sure about code changes since 9/11.
 
sylvan8798 said:
Buildings and other structures will account for thermal expansion in various components caused by daily and seasonal temperature variations. For example a brick face can undergo significant expansion and contraction in the course of a hot day and needs to have the supporting elements adjust to that. A long enough building might have an expansion joint somewhere along the length of it, running through all the components. Buildings which are strung together, such as one often finds in hospital complexes for example, will have joints between the disparate parts. Also, connections of beams to columns are often designed with some room for movement to account for the building's expansion, contraction, and general motion due to use.

Fire protection is generally handled with spray-on fireproofing and sprinkler systems. Not sure about code changes since 9/11.
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Correct correct... Most structures HAVE to have a tolerance for it in daily use. I've noted in the past that a bridge suffered collapse from it due to an engineering error during construction, so it follows that if improper design can lead to this problem, any condition that grossly exceeds the measures taken for everyday occupation of the structure can as well. As far as I've seen from my university studies designs tend not to over engineer to an outrageous level. We build to code but for example we don't really design for seismic activity in places where earthquakes don't really happen; you can, but there'd be little point in it other than using more of the budget. We can use One Meridian Plaza as a reference case even though the building didn't collapse. Firefighters saw large cracks in the concrete, and the steel members were warped because they expanded while restrained.
 
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Animal said:
There is nothing in Chapter 6 (Structural Design) or 22 (Steel) of the IBC regarding thermal expansion from fire.
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Sorry to bump a post two-plus weeks after the fact, but: In looking for something else I just rediscovered that I had actually researched this before and did find passed as well as proposed changes.

As an aside: I need a new brain. I found this info, yet I didn't even remember I had once looked it up. :boggled:

Anyway:
Accepted changes as of 2008:
  • Greater reliability of sprinklers with a minimum of two water supply risers for each sprinkler zone in buildings more than 420 feet high. Each riser is required to supply sprinklers on alternate floors and will be placed in remotely located stair enclosures.
  • A one-hour increase in the fire-resistance rating of structural components and assemblies in buildings more than 420 feet high.
  • Explicit adoption of the "structural frame" approach to fire resistance ratings that requires all members of the primary structural frame to have the higher fire resistance rating commonly required for columns. The primary structural frame includes the columns; other structural members including the girders, beams, trusses and spandrels having direct connections to the columns; and bracing members designed to carry gravity loads.
  • Broadening the definition of the primary structural frame to include bracing members essential to vertical stability (such as floor systems or cross bracing) whether or not they carry gravity loads.
  • Increasing bond strength for fireproofing to nearly three times greater than currently required for buildings 75-420 feet high and seven times greater for buildings more than 420 feet high.
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Propositions for future code upgrades:
  • Requiring buildings more than 420 feet high to be designed to survive a building contents fire to burnout without more than local failure of the structural frame.
  • Requiring structures not to suffer a collapse disproportionate to a local initiating failure caused by an accident or incident.
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I need to leave it to others here to say which of the currently passed items reflects acceptance of which aspect of NIST's findings. On top of that, what regulatory bodies changed regulations? I don't know, I'm afraid, but in 2008, the ICC did indeed ratify changes to code.

So anyway, Grizzly Bear, Animal, anyone else with knowledge about this: Feel free to riff on this from here. If there's something I need to be told about this that I as a layman may not know yet, feel free. I'm here to learn.
 
ElMondoHummus said:
I need to leave it to others here to say which of the currently passed items reflects acceptance of which aspect of NIST's findings. On top of that, what regulatory bodies changed regulations? I don't know, I'm afraid, but in 2008, the ICC did indeed ratify changes to code.

So anyway, Grizzly Bear, Animal, anyone else with knowledge about this: Feel free to riff on this from here. If there's something I need to be told about this that I as a layman may not know yet, feel free. I'm here to learn.
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When I get around to dropping the few hundred $$$$ for the 2009 codes, I will chime in. :D
 
There's nothing in IBC or ASCE7 that requires engineers to design a typical office building for fire loading. However IBC requires a fire protection system with a "fire rating" protecting the structure, stairwells, elevators and egress ways. This fire rating is typically measured in the hours (up to four). The system is generally composed of the structure, sometimes load bearing, sometimes not and whatever material is used to protect it such as spray on fireproofing, asbestos, gyp board, shaft wall, etc. The rating is determined entirely through experimental results and the code allows little deviation from the specific tested system.

The restraint of the structural system will modify the total rating of the system. However systems with restrained structural members, such as beams that cannot physically expand without pushing against the rest of the structure, generally have better fire ratings.

Random factoid: a two-story sprinkled structure requires no fireproofing (unless the building is made out of flammable materials).

Don't spend money on the IBC if you're not a professional. I'm an engineer. I'm supposed to buy the code to support the research. If you're not, don't bother. It's adopted law. You can legally download the text of it.

Finally: EMH brought up the proposed additions to the code to require a design for an entire burn-out scenario. That has been soundly rejected by both the engineering community and the building owners. It simply isn't worth the cost. The likelyhood of a skyscraper burning uncontrolled for 8 hours is unlikely. 9/11 was a rather special event: the collapse of WTC1 and WTC2 knocked out most of the water supply in lower Manhattan and the firefighters just didn't have the will to send more men into an extremely dangerous situation. That isn't, and shouldn't be, a design scenario.
 
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Animal said:
When I get around to dropping the few hundred $$$$ for the 2009 codes, I will chime in. :D
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Yeah, I was told once that those blasted books are frikkin' expensive. I sympathize. :(

Oh, upon looking further things up: I discovered other approved changes since then. Those, however, are mundane in regards to 9/11 conspiracy fantasy; these deal with evacuation and emergency workers communications, not structural support issues like the first bunch of approvals. So they're irrelevant as far as conspiracy peddlers are concerned. Although I'd imagine that they're equally important to building designers, since they're also concerned with designing buildings you can get out of in emergencies. Heck, there's a whole NIST subreport I've only cracked once because it deals with egress/escape issues. Yet, that's arguably one of the most important reports out of them all, once you surface from the conspiracy abyss.

ETA: Oh, Newton's Bit posted. Cool. He's a professional in the field; he'll know way more than I do about this.
 
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Newtons Bit said:
There's nothing in IBC or ASCE7 that requires engineers to design a typical office building for fire loading. However IBC requires a fire protection system with a "fire rating" protecting the structure, stairwells, elevators and egress ways. This fire rating is typically measured in the hours (up to four). The system is generally composed of the structure, sometimes load bearing, sometimes not and whatever material is used to protect it such as spray on fireproofing, asbestos, gyp board, shaft wall, etc. The rating is determined entirely through experimental results and the code allows little deviation from the specific tested system.

The restraint of the structural system will modify the total rating of the system. However systems with restrained structural members, such as beams that cannot physically expand without pushing against the rest of the structure, generally have better fire ratings.

Random factoid: a two-story sprinkled structure requires no fireproofing (unless the building is made out of flammable materials).
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It is more complicated than that, it would depend on the area of the building, the use group and the construction type.




Don't spend money on the IBC if you're not a professional. I'm an engineer. I'm supposed to buy the code to support the research. If you're not, don't bother. It's adopted law. You can legally download the text of it.
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Almost all states amend the IBC. So you nned the code for each particular state you work in.
 
Newtons Bit said:
Finally: EMH brought up the proposed additions to the code to require a design for an entire burn-out scenario. That has been soundly rejected by both the engineering community and the building owners. It simply isn't worth the cost. The likelyhood of a skyscraper burning uncontrolled for 8 hours is unlikely. 9/11 was a rather special event: the collapse of WTC1 and WTC2 knocked out most of the water supply in lower Manhattan and the firefighters just didn't have the will to send more men into an extremely dangerous situation. That isn't, and shouldn't be, a design scenario.
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Say, I actually spoke to the defeat of that proposal in this post: http://www.internationalskeptics.com/forums/showthread.php?postid=7108505#post7108505

Have I gotten what I said in that post right? I think so, but you're the professional, not me.
 
AZCat said:
You can read the ICC codes online for free, even the 2009 versions. Check out this link from the ICC:
http://www.iccsafe.org/Store/Pages/FreeCodes.aspx

It's kind of a pain because of the way they've organized the browser, but free is free...
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Thanks for the link......I looked at the Michigan codes.....they have 2003 online, Michigan just went to the 2009 on Mar 11, so I will have to shell out the $$$ shortly. :mad:
 
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