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Type IV Construction
We are continuing to look at the different types of construction and the characteristics of each. This post will outline considerations of Type IV or Heavy Timber construction.
Heavy timber construction is a type of construction we don’t see popping up in new buildings very often. However, there are still a great many buildings that are or were Type IV construction in our jurisdictions. We need to identify these buildings in both circumstances.
True heavy timber construction does not have void spaces. It is built with masonry or brick exterior walls with large diameter, six inches and more, interior structural components. There have been debates about how these large beams and structural elements hold up to fire and some have found the large diameter wood components to hold up longer than steel. The reason for this is that the steel will elongate and deform at around 1000 degrees and is prone to failure at that point. The large diameter components may burn, but they hold their integrity longer than the time it takes for steel to deform. Obviously, there are variables, but an interesting bit of information.
These fires burn hot and for a long time. These are typically large buildings and have an additionally large fire load, making extinguishment difficult. Many times we find these buildings in more urban areas and in highly dense locals. However, churches and resort lodges are common places for this type of construction. Exposure protection is of the utmost importance and establishing an effective collapse zone is important.
When these building get remodeled and are altered, they can then be considered Type III construction. The reason for the Heavy Timber classification is the benefit of the extended time of burning and the lack of void spaces. We lose some of that as false ceilings and new framed walls and floors are added to create lofts or office space. Just something to consider because you will need to plan accordingly for the interior changes that are being made to these types of buildings.
Train hard, master the basics and have plan before you go to battle. Stay safe.
Lodge picture from Vermont Timber Works, visit them at vermonttimberworks.com
Replies to This Discussion
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Permalink Reply by John Crabbe on
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I will have to do some research, but when talking about building construction in my fire science class we had a picture of a heavy timber beam with a bent and distored steel beam resting on top of the wood beam.
On a side note, there are many large beams used in modern construction however, they tend to be laminated beams. While the dimensions are large and the load they can support can be significant, if it is a glued beam, be cautious....glue and fire don't get along well.
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Permalink Reply by Jason Hoevelmann on
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Good point about the laminated beams. Thanks again.
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Permalink Reply by Jack/dt on
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In heavy timber construction we're typically talking posts (columns) with a minimum 8" dia. in either dimension with beams a minimum 6" in width and 8" depth. Old industrial mills are typical of heavy timber frame construction.
Heavy Timber is stated to be able to withstand fire as a result of the charring that occurs which acts as a form of insulation, which is why heavy timbers can last much longer in direct flame impingement.
"Melted" steel beam over wooden timber beam
What I can find is that laminated beams are claimed to have fire resistance characteristics very similar to heavy timber.
A test report here - http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/tt/tt1131.pdf states:
'The test specimens were completely charred on all sides and showed the characteristic longitudinal and lateral shrinkage cracks in the charcoal layers. The longitudinal joints
(glued joints) between the laminae were clearly visible. In none of the
specimens, apparently, did the bond (adhesion) between the boards disappear;
only in isolated cases did the charred remnants of the top or bottom boards
of the specimen become partially separated.
...it can be concluded with a high degree of probability,
from the results of the temperature measurements, and from the breaking loads
as well as the condition of the glued joints at the conclusion of the tests,
that the change in load-bearing capacity of the specimens from the end of the
fire to the condition l~ to 2 hours after the fire, was small. Neither in
the remaining wood nor in the glued joints did we find any indication of
damage as a result of the fire.
Glu Lam on its website states the following
According to this link - http://www.moelven.co.uk/images/glulam%20in%20fire.pdf
"Glulam supplied by Moelvin LTS is manufactured using adhesives which comply with class 1 of BS EN 301, is not flammable and does not lose its integrity when exposed to prolonged elevated temperatures."
http://www.awc.org/pdf/wcd5.pdf
http://www.westernwoodstructures.com/pdf_files/Fire_Resistive_Desig...
http://www.aitc-glulam.org/shopcart/Pdf/superior%20fire%20resistanc...
http://www.moelven.co.uk/images/glulam%20in%20fire.pdf
http://usglulam.com/products/glulambeams/
http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/tt/tt1131.pdf
Here's a question for the class:
What are Flitch Plates, where would they be found and how does heat affect it and the structural integrity therein?
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Thanks for the additional info there Jack.....also that would be the picture I was talking about.
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A flitch plate, I believe is a piece of steel between two beams made of wood to give it more strength. The heat can warp the steel between the two beams and cause a failure for those components.
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I agree
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Permalink Reply by Wade Seely on
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I used to work in a large retail store that had heavy timber gluelam beams. the thing that worried me is that they were supported by steel columns. The beams themselves might withstand the heat,but what happens when their support structure is gone? (and the london bridge is falling down)
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