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Timber Towers Are On the Rise in France (citylab.com)
A reader shares a report: Spurred by concerns over climate change and the negative impacts of concrete manufacturing, architects and developers in France are increasingly turning to wood for their office towers and apartment complexes. Concrete was praised through much of the 20th century for its flexibility, functionality, and relative affordability. In France, the material ushered in an era of bold modernist architecture including housing by Auguste Perret and Le Corbusier. Today, however, wood is lauded for its smaller environmental footprint and the speed with which buildings can be assembled. "Wood had largely disappeared and was seen as a quaint material," says Steven Ware, a partner at the architecture firm Art & Build, whose latest wooden office building opened in Paris's 13th arrondissement earlier this summer. "[But] the energy it takes to put a concrete building up, to run it, and then dismantle it when it becomes obsolete was too much. Using mass timber in office buildings seemed like something we had to do." The production of cement, one of the main ingredients in concrete, generates an estimated 5 percent of the world's carbon emissions. Trees, in contrast, capture CO2, helping offset emissions produced by a typical building process. And then there's the string of other construction advantages that make wood economically appealing. It's lighter, which means digging smaller foundations in the ground. Crane costs come down, as they're no longer hauling blocks of cement hundreds of feet in the air. Driving a nail into a slab of wood requires a lot less energy than driving one into concrete. Months can be knocked off the construction timeline.
Sounds like a good way to have a towering inferno. The stuff we put inside large buildings burns quite readily. But the fire generally stops in a single room. But if you suddenly make everything out of wood, what's to stop the fire from spreading everywhere?
Lumber supply forests are harvested and replanted these days.
Recently, as in this week, they completed a low-emission earthquake-resistant timber tower in Portland, Oregon.
Fire risks tend to come from inefficient fire suppression systems and lack of coatings. Or inadequate emergency exits. As we've seen from London, England, concrete towers clad in flammable plastic are more of a fire trap than wood timber buildings are. It really depends on the full architectural design.
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Wood can be grown and harvested sustainably on tree farms where generation after generation of trees selected for structural properties and rapid growth are cultivated. Any such "green" inspired building program should/would ensure that all the timber used comes from such sources. And so yes, building permanent structures out of wood does lock up CO2 as long as the structures stand - whereas CO2 released in the production of concrete is in the air for centuries.
The actual material used for framing a structure has nothing to do with the fire safety (or lack of same) in an inhabited structure. Metal and concrete framed structures are no safer on that count than wood. The fire hazard that threatens life is entirely due to the furnishings and utilities inside the structure. By the time a frame of wood frame building starts to burn the interior is already destroyed, and the inhabitants have either escaped or are dead. Note that modern construction techniques using fire proof gypsum board that isolates the structure from the interior (gypsum does not burn and actually absorbs energy as it decomposes).
Wood is a pretty remarkable material. It is in fact an advanced composite material produced by natural nano-factories. It compares favorably with far more expensive synthetic composites, and beats them all in cost. Used properly (taking advantage of the anisotropic properties of wood beams) a good wood beam comes with a factor of 3 in stiffness/weight ratio of the best performance ofunidirectional carbon fiber epoxy composite, and beats structural steel. Sitka spruce is used in the upper stage of Trident II SLBM missile since it had the best properties for the role, over all other candidates.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
Are they really comparing the energy cost of driving a nail?
Wood has a place but IMO if you want a durable structure use reinforced concrete. Maybe this wave of construction is only expected to stand for 30yrs?
My (small) multi-unit in Canada is built with wood timbers and is 218 years old. As long as you keep it dry, wood can be very durable.
Also there is a fair amount of carbon sequestered in the building itself. That's assuming the building doesn't burn, which is why I won't get into a tall wooden structure.
The type of wood buildings they're making nowadays don't burn very easy. (not talking about timber framed houses like the US, but the kind used for taller buildings such as this article). They take wood- cut it in strips, arrange the strips in alternating directions (for added strength) and then glue them together with a fireproof glue.
They're actually more fire-safe than steel buildings. Steel will melt or lose strength with fire (as in 9/11 twin towers)- the modern timber buildings resist fire at higher temperatures than it takes for steel to lose integrity.
"That's the way to do it" - Punch
You're on the right track to some of the "devil in the details".
Soft woods like pine grow quick, but the wood is, you know, soft. Wouldn't want to live in a skyscraper made of that!
Calling pine a soft wood, and implying that it wouldn't serve well in a structural sense, is perpetuating a myth. SPFs (spruce, pine, fir) are highly regarded for their structural properties. Douglas fir, Southern Yellow Pine, Sitka Spruce, Hemlock...all have excellent MOE/MOR ratings, while yes, having low Janka Hardness ratings. Along with time-to-yield and price, these structural properties are why SPFs rule the US stick-built construction supply.
AFAIK, the hardier the wood, the longer it takes for the tree to grow. That means a long-term investment in your re-planting, and a lot can happen to your plot of re-planted little sprouts (bugs, deer, fires, suburban sprawl, drunk kids on ATV's, massive natural gas deposits) while you wait the lifetime or two for your trees to grow to full size.
Harder wood trees, do "generally" take longer to grow. However, today's new-growth trees pale in comparison to the mostly gone old-growth trees from a properties comparison. The hardness may be there, but their MOE, MOR, and density are usually lower, and their stability and durability are much more volatile. But, again, those are generalities. The science behind wood is quite fascinating; much more in depth than I imagined when I got into woodworking.
The Wood Database is a great resource.
You don't rate a fire-resistant structure by its ability to sit baking indefinitely at a certain temperature, but by the number of minutes or hours it provides safety while people evacuate and/or extinguish the fire. And once you have a fire-safe structure that doesn't collapse and compromise its egress paths, you worry about fire safety of the building which includes ventilation, fire suppression, and materials to avoid asphyxiating the occupants in a poison gas chamber.
Thick timber chars on the outside when exposed to extreme heat. This is almost a self-healing, temporary insulation to slow the heat transfer to the rest of the wood on the inside of the timber. That's why a big log in your fireplace burns for many hours and doesn't immediately explode your house from over-pressure. The timber continues to be able to bear most of its rated load while this outer surface is burning.
Meanwhile, steel will quickly conduct heat throughout and soften until it suffers a load failure, long before it has reached its liquid phase. The twin towers didn't collapse because the steel was solid one minute and liquid the next. It collapsed because it became soft enough for large horizontal spans to sag and separate from their supports, fall a whole story, and exceed the load-bearing capability of the level below.
Steel structural members have to have fire insulating layers to mitigate this type of problem and allow people to escape. The violence of the plane impacts in the twin towers destroyed egress routes, trapping people. It also tore away a lot of the fire insulation (asbestos) meant to protect structural steel, so the collapse happened sooner than it might have in a typical fire.