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Schroder
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PostMon Sep 23, 2019 7:48 am 
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So says the Nature Conservancy and others:
Tall buildings out of timber? In the face of climate change, Seattle encourages it

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In the coming years, Ballard will be home to Seattleís first tall building built almost entirely from wood. Rising eight stories from the current Ballard Blossom florist on Market Street will be a hotel built principally from cross-laminated timber, or CLT ó durable panels made from binding layers of wooden planks with adhesive.

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The huge environmental benefits of cross-laminated timber are its biggest draw: Construction on a cross-laminated timber high-rise emits roughly 25% less carbon dioxide than if the high-rise were concrete, according to a University of Washington study.
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thunderhead
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PostMon Sep 23, 2019 11:11 am 
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Timber buildings are also flammable.  Give me a steel core, and only a steel core.

If you want to use that stuff for nonstructural, go for it.
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IanB
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PostMon Sep 23, 2019 11:18 am 
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mb
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PostMon Sep 23, 2019 11:23 am 
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Steel is also flammable! Worse, it becomes plastic.

Timber has a good property in fires, often will not burn through as much as steel. Steel also melts and deforms before it burns, while timber char actually protects the core. Of course once burnt through, none of them are useful.

https://www.firehouse.com/operations-training/article/21008544/what-the-fire-service-needs-to-know-about-tall-wood-buildings

(Skip to the "Conclusion" at the end if you'd like.)
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thunderhead
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PostMon Sep 23, 2019 2:30 pm 
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Sure you can make a wood beam fat enough so that it has some extra mass to delay its failure in a fire but what about the joints?  A little burning there will open things up in a way they never would in a proper steel component.

Not to mention, steel doesnt add to fuel loading.

Seems to me if you want to sequester carbon, doing so in the structural components of inhabited high rises is a pretty poor place to put it.  Dumping that load of logs in a high cold desert and building your structure out of steel, the way it should be, seems much cheaper in both lives and money.
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Bernardo
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PostMon Sep 23, 2019 3:03 pm 
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25% advantage seems probably close enough to be within the margin of error.
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Stefan
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PostMon Sep 23, 2019 3:50 pm 
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the building probably is built out of wood because it will cost less.  probably has nothing to do with desire for carbon footprint.

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RandyHiker
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PostMon Sep 23, 2019 4:14 pm 
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Timber/gluelam construction is less CO2 emitting simply because manufacturing steel and concrete emit a lot of CO2.

I wonder to what extent this affects the life cycle CO2 emissions of a building.  After including all the CO2 emissions from heating, lighting and cooling the building of say a century of occupancy.
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Grannyhiker
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PostMon Sep 23, 2019 4:56 pm 
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By cutting down trees (more needed for more wood buildings) we reduce the ability of the forest to sequester carbon for the next 50 or so years it takes for the forest to grow back.  Be sure to throw that into the calculations!

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Pyrites
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PostTue Sep 24, 2019 12:31 am 
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Donít worry about steel burning or melting. Depending on the steel about half itís strength is gone at 1000-1100f. Depending on use (beam, bolt, long tie rod) change in dimension might matter too. If you see some above the ceiling and it looks as steel has white stuff sprayed on, it does. Insulation to protect in fire.

Mass timber, often narrowed down to CLT, or cross-laminated timber. Currently itís not likely cheaper that steel and concrete for a given building. It is much faster. The parallel to a steel fab shop for mass timber is CNC. Wood will change dimension slightly with humidity. The CNC cutting of the wood is to nearly aircraft industry tolerances. Instead of a door opening being a little out of square, and maybe planned to be 5/8Ē oversized, opening cut by CNC is for practical purposes is perfectly square, with perfect tolerances. Same with all the cuts for the whole building.

Fasteners, back to steel. So you bury some in the wood, others you use some of that fancy intumescent stuff from Hilti or similar. One way or another they are insulated too.

Wall floor or other joints. Adhesives meeting a spec is required, so it it shouldnít leak air, or smoke.

Currently you can build apartments, hotels, to 18 stories in WA or OR.

Really tall buildings people are putting out on their webpage. I guess itís just to advertise their firm - fantasy only.

There is some concern among fire community about supertall. All current fire testing has been in a null wind condition. Aloft winds are more common and stronger. Ask your local structural or wind farm P.E.

Not just theoretical. Fire fighters have been killed in high rise fires when a window on the windward side blows out aloft.

Induced draft. The key to all metallurgy since the copper age. Humans should have the concept that it affects fire intensity down pat.

Assumed by everyone to be the catís meow in seismic event.

Best.
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NacMacFeegle
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PostTue Sep 24, 2019 8:42 am 
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Grannyhiker wrote:
By cutting down trees (more needed for more wood buildings) we reduce the ability of the forest to sequester carbon for the next 50 or so years it takes for the forest to grow back.  Be sure to throw that into the calculations!

up.gif  ditto.gif My thoughts exactly! We need to be preserving forests for carbon sequestration. The longer we let forests grow the greater the rate of carbon sequestration they will be able to achieve - that exponential benefit is lost if we keep cutting forests down! Far better to increase use of recycled materials.

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Schroder
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PostTue Sep 24, 2019 12:05 pm 
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drm
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PostTue Sep 24, 2019 1:18 pm 
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Grannyhiker wrote:
By cutting down trees (more needed for more wood buildings) we reduce the ability of the forest to sequester carbon for the next 50 or so years it takes for the forest to grow back.  Be sure to throw that into the calculations!

Hmm - if the wood from the trees is in a building, the carbon is still sequestered. Only if it is burned or degraded is the carbon released. Compared to concrete, that is a big carbon benefit. If the trees were still growing, they could sequester more, but I think that is small benefit compared to avoiding concrete mfr.
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Jake Neiffer
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PostTue Sep 24, 2019 1:34 pm 
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A forests capacity to sequester carbon is optimized if the trees are healthy and at an appropriate stand density.  This may require cutting trees to accomplish.
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Bernardo
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PostTue Sep 24, 2019 4:06 pm 
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Nice point GrannyHiker.  These calculations are super complex.

Where in the concrete process does the CO2 get expelled?  Could it be captured?
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