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  1. #1
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    Question Building Construction Question(s)

    Hey guys,
    I've got an up coming training that I'm doing on building construction and I wanted to offer the guys a few specifics on certain building materials. So if anyone can answer these questions for me, I'd appreciate it:

    What's the average temperature or length of time exposed to fire that metal materials (i.e., joist hangers, gusset plates, 16 penny nails, etc.), wood materials (engineered wood vs. milled lumber), and concrete (either poured walls or block), commonly found in residential construction begin to fail?

    O.k., I suppose that's not mutiple questions, just a multi-part one. But if anyone can offer some insight into this, or anything else you've come up with throughout the years, I'd greatly appreiciate if you'd share. Thank you in advance!

    -Mike Eckhardt
    Safety/Training Officer
    Morgan Twp. Fire Dept.
    Valparaiso, In


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    MembersZone Subscriber firepimp's Avatar
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    Dont quote me Im saying this from my head , Metal gusets found in trusses I believe fail 7 - 15 minutes.

    Wood Im not sure.

    Concrete normally holds up very well under fire condition untill cooled then it spalls and cracks. Reinforced concrete doesnt hold up as well.

    Like I said dont quote me but I think thats what i remember. Theres some info if any help.
    " We are not extraordinary people , we are people caught in extraordinary situations. " Chapter 1 IFSTA Manual

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    I can't seem to find any specific time in Branigans Building construction....I'm sure I'm overlooking it.

    I do know our dept procedures state in our Taxpayer Buletin that it is around 5 to 10 minutes... but as far as that being the scientific answer I can't find one just this minute.

    FTM-PTB

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    Billy Goldfeder's website www.firefighterclosecalls.com has a slide show presentation about enginnered wood I beams that is quite an eye opener!
    ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
    Lt. Ray McCormack, FDNY

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    Yeah, I definitely thought that Branigan would have something too, but apparantly I as well am overlooking it, FFFRED. Gonzo, Pimp, definitely appreciate the imput and I will put it to good use. Hope to gather some more info from this thread to help keep from any appearances on firefighterclosecalls.com! Keep it comin' guys!

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    You got good info there. There are other good sources in NFPA and SFPE references I will look at when I get a minute.

    Please don't forget about the single most important factor in dealing with buildings with trusses, engineered construction, etc.

    RECOGNITION! This will involve pre-planning and knowledge of construction types. Make sure this is either part of your program or a follow-up ot it.

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    I don't know if you will ever come up with a "time". The failure will begin when the temperature reaches the materials point of breakdown. That is why the term "Heat release rate" is so important. In a very very broad range let me give you an example. A four hour rated door will last much longer than four hours when exposed to a cigarette lighter and not nearly four hours when exposed to a rocket engine. The lighter and rocket engine have a very different heat release rate. As one of our brothers indicated recognition and the rapid application on water are your best bet.

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    MembersZone Subscriber E229Lt's Avatar
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    Dont quote me Im saying this from my head , Metal gusets found in trusses I believe fail 7 - 15 minutes.
    Sorry, I quoted you

    Gusset plates come in different styles. You are referring to a gang nail plate which has teeth stamped out the back approx 1/2-3/4 inch. These will fail rapidly.

    A stronger and also common gusset plate is a steel plate with nail holes (Sometimes referred to as Teco nails/plates) These are very strong and resist early failure when properly installed.

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    TTT

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    http://www.woodtruss.com/index.php

    Try this site. There is also contact emails and numbers for questions.
    IACOJ

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    Mike,
    jmichael hit on an important point - failure depends on a number of factors and often is more comlicated than stating just a time or temp to failure. The severity of the fire is key and that will be important in creating a certain time-temperature exposure to any particular building structural element or any other bldg material for that matter.

    A waste basket burning in an empty large warehouse isn't going to put much of a thermal stress on any part of the bldg.
    Beyond the fire severity, the other key issues are whether the bldg component in question is load-bearing or not. Much greater impact obviously for load-bearing components. A non-load bearing component may fail, but it will not typically result in any localized or bldg collapse.

    For load-bearing components, critical is how much of the design load is being applied at the time of the fire and how much of a safety factor was used in design. Less design load at the time of fire and larger safety factors mean longer times to failure.

    For some real rough ranges - steel starts to lose strength and stiffness at about 500F and is typically considered to have completely failed at 1000F (that's the actual steel temps, not the fire temp - larger the steel component, longer to heat up); for wood, charring starts at about 550 F and charring proceeds at a certain rate through the wood member. Charred wood is considered to have no structural strength, so the wood member is becoming physically smaller with regard to that portion of the member that contain carry a load; concrete - you've typically got straight concrete in compression and then steel reinforcement in tension; concrete can be considered similar to steel, 500 F starts to lose strength, 1000 F is assumed to have failed; for the steel in tension, same temp effects as a steel member except you have some concrete providing a thermal barrier; concrete can spall though, reducing the thermal barrier effects.

    In addition to covering temp effects on the different material types I would stress to other key concepts:
    1. if you get into a flashover/post-flashover fire with unprotected (no additonal fire resistance) steel and wood structural members in particular, these members will fail very rapidly regardless of getting into detailed analysis of time to failure
    2. the bldg codes allow unprotected construction (except for single/two family dwellings in the U.S.) typically only in bldgs where the life safety hazard is low and that anyone in the bldg is expected to have evacuated before the bldg fails structurally due to fire - which means basically that these buildings are "disposable" since little, if any fire resistance is needed to protect the bldg occupants. A very important factor to consider when evaluating risk to fire fighters associated with these bldgs.

    Good luck

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    Originally posted by Mulldog
    http://www.woodtruss.com/index.php

    Try this site. There is also contact emails and numbers for questions.
    A word of caution on sites that are sponsored by the building materials people...be very careful to review any info. The builders would advocate building structures out of balsa wood if they could get away with it. I was putting together a class one time and found a site that offered info on a particular type of engineered wood structural member. The article dealing with fire resistance basically blamed poor fire suppression tactics for the failure of their component.

    That site was NOT the one listed in this post. I will continue trying to find that site. Just look at these with a critical eye.

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    then again gusset plates are installed on ever truss from every angle through out the house , teco plates if you would like to call them also known as hurricane straps or other naes are installed in entrys and only on whetre the trusses meet conrete so not that safe and gussets will give out way faster and cause way more damage just my expieience being a framer.
    " We are not extraordinary people , we are people caught in extraordinary situations. " Chapter 1 IFSTA Manual

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    MembersZone Subscriber EFD840's Avatar
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    ^^ Was that last post in English?

    Gusset plates come in different styles. You are referring to a gang nail plate which has teeth stamped out the back approx 1/2-3/4 inch. These will fail rapidly.
    Lt, I used to work in a truss shop and although it has been a while, but I'm sure we regularly used plates with 1/4" teeth.

    Maybe codes have changed, or maybe my memory is bad. Either way, these are obviously prone to rapid failure.

    There's also the village idiot factor when it comes to these prefab trusses. Most of my co-workers weren't the most detail-oriented. It wasn't uncommon to have plates installed where 75% or more of the plate covered a beam and only a small portion covered the joint. Lots were caught and redone but there's no doubt many more are holding up roofs today.

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    Originally posted by firepimp

    Concrete normally holds up very well under fire condition untill cooled then it spalls and cracks. Reinforced concrete doesnt hold up as well.
    That doesn't seem right...besides, where in building construction are they using unreinforced concrete?


    As for the rest of this subject matter...outside of illustrative purposes in the classroom, knowing the temperature at which certain building materials fail or trying to clock it in an effort to anticipate collapse are not overly helpful on the fireground.
    Too many variables that we can't answer until the roof is laying on the floor.

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    teco plates if you would like to call them also known as hurricane straps or other naes are installed in entrys and only on whetre the trusses meet conrete
    TECO plates are in a lot more places than this. Basically, where ever a beam is travelling horizontally and joins another horizontal beam. The beam will be "toenailed" in, but will have a TECO also. All floors have to have that in my area. However, you can skip the TECO plates if you put a "ledger" board (2x2") in their place.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    quote:
    --------------------------------------------------------------------------------
    Originally posted by Mulldog
    http://www.woodtruss.com/index.php

    Try this site. There is also contact emails and numbers for questions.
    --------------------------------------------------------------------------------


    "A word of caution" that was offered by George

    George,
    Did you go to this site and see that they are working with the Houston FD on testing or did you just hop up on your pedistal to be heard??? I am not saying this site it a gold mine BUT I do find it to have adequate credentials. Any company that is testing to improve fire safety with a fire department (not some engineering firm) is showing something. They also encourage questions to be sent to them so that they can educate people with their findings.
    I would not and have not posted anything that has not been thoroughly looked at. As always if I am wrong let me know.
    IACOJ

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    Actually, regular and reinforced concrete should behave pretty much the same when exposed to fire, all things being equal. Steel and concrete have just about the same coefficient of thermal expansion, which is why the two materials are used together so much. Concrete and steel members can be used together for buildings and bridges because both materials expand and contract at the same rate. The spalling that occurs when concrete is exposed to fire most often is the result of the water molecules trapped in the concrete converting to steam as they are heated (we all know how much more volume a given amount of H2O occupies when it is converted from water to steam). This expansion will crack the concrete. I'm guessing that it looks like the condition is worsened when the member is cooled because the force of the hose stream breaks off the already cracked concrete.

    I saw this first hand when we had a gasoline tanker burn up under an highway overpass. The exterior concrete spalled off down to the rebar and walking around under the bridge was like walking on a gravel driveway. The bridge suffered a lot of cosmetic damage, but was still able to carry full highway loading.

    Anyway, to the original question. There are so many variables involved that I doubt you will find any hard and fast times published. You have to know your buildings and how they are constructed. Are the critical joint areas fire protected? What has been burning and for how long? Once a room and contents fire has breached the wall sheathing and has directly attacked the framing of the building, you need to be very careful and prepare for the worst.
    Chris Minick, P.E., Firefighter II
    Structures Specialist, MD-TF 1

    These statements are mine and mine alone
    I.A.C.O.J. Building crust and proud of it

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    MembersZone Subscriber firepimp's Avatar
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    The whole concrete thing I said comes out of the ifsta manuel , and I was just quoting on frameing Ive done in florida I didnt say everywhere every code and house is the same. Reinforced concrete is concrete with rebar in it ,and yes lots of house's in florida do not have reinforced concrete that supports trusses and what not. Thst just what Ive seen and read never said quote me on the stuff.
    " We are not extraordinary people , we are people caught in extraordinary situations. " Chapter 1 IFSTA Manual

  20. #20
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    Originally posted by Mulldog
    quote:
    --------------------------------------------------------------------------------
    Originally posted by Mulldog
    http://www.woodtruss.com/index.php

    Try this site. There is also contact emails and numbers for questions.
    --------------------------------------------------------------------------------


    "A word of caution" that was offered by George

    George,
    Did you go to this site and see that they are working with the Houston FD on testing or did you just hop up on your pedistal to be heard??? I am not saying this site it a gold mine BUT I do find it to have adequate credentials. Any company that is testing to improve fire safety with a fire department (not some engineering firm) is showing something. They also encourage questions to be sent to them so that they can educate people with their findings.
    I would not and have not posted anything that has not been thoroughly looked at. As always if I am wrong let me know.
    It would benefit you to read my posts. I DID NOT condemn this particular site. I never said it and I would never say it. What I did was share information that I have gained in my experience investigating fires where lightweight construction has been an issue and some general things that I have found.

    It seems like there is a general sentiment these days to challenge everything I type. Bring it on. I said it before and I will say it again. I don't post it if I am not right.

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