“Their manufacture is very accurate, there’s very little work that needs to be done on site,” said Green. “Because of this, construction will be very quick. Someday I’d like to make a building where all you need is a giant allen key to put it together.”
Baobab’s structure consists of a series of these solid timber walls that travel the full height of the tower, along with timber columns and a central timber “core” housing elevators and stairs.
— theguardian.com
21 Comments
All well and good so far but nobody has addressed the issue of flammability.
"...When mass timber is exposed to fire, the outer layer starts to burn and form charcoal. The charcoal layer forms a protective barrier, soaking up heat and insulating the interior timber. As exposure to fire increases, this layer grows, creating even more insulation, and further slowing the burning rate..."
And slated to go up...
In Paris !
And it's not just ONE tower - it's SIX ! Ha ha ha ha.
Certainly a worthy addition to the city. Or it's not. Okay. This is not good enough. Back to the drawing screen.
Ugh. I need a nap.
"...When mass timber is exposed to fire, the outer layer starts to burn and form charcoal. The charcoal layer forms a protective barrier, soaking up heat and insulating the interior timber. As exposure to fire increases, this layer grows, creating even more insulation, and further slowing the burning rate..."
WTF! is this a joke?
Oh, the humanity!
Why does everyone think the quote explaining heavy timber framing and its inherent fireproofing characteristics is so funny?
It's true. Heavy timber performs better than steel in such a scenario. Steel is more elastic and open to deformation at extremely high temperatures.
One main issue with adopting this new high-rise building method on a global scale is the availability of sustainably-sourced, affordable structural wood products that perform at the level of old growth wood (not sustainable, obviously). Another issue I'd anticipate is the increased amount of lateral bracing needed and the additional material at the base to handle gravitational load.
Regardless of the charcoal argument, the 2015 IBC already addresses it specifically for CLT. Read up on Section 602.
http://www.bdcnetwork.com/5-myths-about-cross-laminated-timber
How much fire, heat and smoke will be generated to get to the point of that protective char?
Why does everyone think the quote explaining heavy timber framing and its inherent fireproofing characteristics is so funny?
Because its wrong...The charred timber may indeed be fireproofed post fire, but I find it impossibly hard to believe that the timber would just extinguish itself completely before its structural integrity is compromised because forces are not in the center of beams but at the outer portions (basic tension and compression)...it only take a small notch before the beam looses its integrity. Also, The wood may no longer be on fire with flames, but it will still burn through like hot coal in a camp fire...I have personally burned 2' diameter logs in camp fires with no lighter fluid and they burn pretty much through ...Its common sense...Lastly, there will be other things like furniture burning that will keep the wood hot...
I'm not against the idea of wood buildings...just found that quote ridiculous...
Geez didn't you guys play with fire when you were kids
Bunch of dim bulbs here.
Flammability is the ability of a substance to burn or ignite, causing fire or combustion. Steel and concrete are not flammable.
That wood is highly combustible would tend to negate the positive effects of high temperature structural performance in a high rise building. In other words it doesn't make any difference to occupants if the structure is still standing if it is totally engulfed in flames and toxic gases.
"...When mass timber is exposed to fire, the outer layer starts to burn and form charcoal. The charcoal layer forms a protective barrier, soaking up heat and insulating the interior timber. As exposure to fire increases, this layer grows, creating even more insulation, and further slowing the burning rate..."
I'll see it when I believe it.
The prevalence of forest fires in old-growth forests (which are burning green wood), or fires in timber-frame warehouses suggests that this effect is easily overcome in the presence of kindling. Like furniture, finishes, and everything else buildings hold.
I suppose it could be fire-protected as is done with steel. But then you run into the problems of moisture retention and mold. Wood buildings are far less tolerant of leakage and moisture infiltration in general, which would probably be a bigger problem than fire most of the time.
In regard to performance versus steel: in structures that use gang-nail trusses, the metal truss plates go plastic at temperatures where the wood members are still structurally intact, causing catastrophic failure.
Solid wood potentially buys occupants some exit time in a fire, as the bigger the timber the longer it takes to burn through. In the context of any fire and especially high rises - where exit is exponentially more difficult - there are many other factors to consider such as wood structure feeding the fire and accelerating spread. As noted by mid, encapsulating wood raises other issues as recently demonstrated in the Berkeley balcony collapse.
At the moment this idea is half-baked at best.
plywood fireproofed vs plywood not fireproofed, part of a research project undertaken by my colleague Hiroto Kobayashi. The wood is painted with a silicon transparent paint, non-toxic, but not yet commercially available or certified for construction in Japan. But its going through the system. This + charring thing mentioned above + intelligent joinery that dosnt leave the metal exposed means its all solvable. Im sure there is a tonne of this kind of work going on all over the world. The Tamedia office in Zurich by Ban certainly makes it look like old hat.
There are things to be critical of with tall wooden buildings. Warnings about technical impossibilities are not the interesting ones. I find it more annoying that the architects get a pass on the design cuz its all wood, as if that's the whole story. Ban's project in Zurich is really good, but everyone else seems to be channelling the instructions on the back of a meccano set.
So what about the joints which get saturated with water when the sprinklers go off? Will they swell? Will the mechanical attachments loosen/weaken? Say the building makes it through a fire and and sprinkler-ing and the fire hoses - does the drying out wood, warp and induce unexpected stress & strain in unexpected, incalculable ways in the structural system?
In a 3 or 4 storey place, this might not lead to anything dramatic, but 20 floors? More?
I too think that the design needs to be worthwhile, and not just given a pass because of the fashion fetish of it being "all wood".
So much fear, not a lot of scientific inquiry. There is a lot of scientific information out there on the fire performance of heavy timber and CLT construction, if you care to look for it. It is appropriate for a high-rise? ... maybe, maybe not. That depends a lot more on the client, the jurisdiction, and the risk people are willing to accept. No one is disputing that wood is combustible. They are pointing to heavy timber and CLT as able to perform in fire. Fire performance tests are not combustibility tests.
Also based in science is the concept that wood buildings have a larger hygric buffer capacity than steel construction. This allows them to actually be more tolerant to leaks and moisture intrusion than steel construction (article), depsite what midlander says. Given the same amount of water intrusion into wood construction vs steel, you will have a greater chance of mold growth with less moisture in a typical steel building than wood (even better than wood is mass wall construction). This is not wood decay (evidenced in the Berkeley balcony collapse), but mold growth. Obviously steel would not exhibit decay. However, if you can design and detail your building to first keep moisture out, and second to deal with the moisture that inevitably will get in, you won't have issues with wood decay either. Larger hygric buffers help with the second point, not the first ... that one is on the architects and designers.
Menona asks some good questions. Ones I have not seen addressed by proponents of CLT construction. My guess is that it will cause some issues, none of which couldn't be addressed. I would assume that given a fire event and large amounts of water introduced into the building through sprinklers, etc. you would most likely be looking at replacing damaged CLT panels with new ones. This is only speculation on my part. Actual CLT experts might differ in their responses.
Way too many ifs, work arounds and possible screw ups considering the potential loss of life IMO.
I am sure the engineers of the Hindenburg thought they had figured everything out as well.
They used aluminum oxide paint and had dissimilar metals on the control surfaces but the main problem was that they filled it with hydrogen.
So someone thinks building a skyscraper out of plywood is a good idea? One does not have to be as presient as Nostradamus to realize the essential insanity here.
So much fear, not a lot of scientific inquiry.
...
This is only speculation on my part.
No shit.
its not plywood. Its CLT, or similar. A lot of the assumptions and habits we have about traditional wood structure dont apply. It shares some properties with concrete, some with regular wood. Quite fascinating as a material if you are into that sort of thing.
By chance some of our students just built a CLT house as part of a test to get national approval for it as a structural material and to learn some things about its properties in preparation for taller buildings.
There are some issues with water and fire, even at the small scale we were working at, but I think it is all technical and solvable, if not already mostly resolved. This project by Green is pushing boundaries no doubt, yet its not that far from the real world. No more so than Bilbao was, or falling water, or the philharmonic by H+DeM. Some challenges, maybe some unexpected costs, etc.
When it comes down to it I still find the design to be a bit too much like a generic tower complex. As a proof of concept its amazing, but it would be nice if it was more than that at the same time.
Miles, somehow I knew you would gloss over the main points of my comment.
speculation - a hypothesis that has been formed by speculating or conjecturing (usually with little hard evidence); (source)
My speculation was limited (to Menona's questions), it was acknowledged as such (as you've pointed out), and I offer ways to find hard evidence (actual CLT experts).
If you would like to address my points with any evidence, or provide evidence of your own points, feel free to do so. I will gladly accept it with a fair degree of skepticism as is always necessary in scientific inquiry.
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