Tokyo to build 350m tower made of wood | Hacker News Reader

Tokyo to build 350m tower made of wood

theguardian.com

146 pointsmarkgavalda96 comments

Fire safety in wooden structures is interesting. A friend who does research in the area explained that, in some ways, wooden beams are simpler to engineer than steel beams when dealing with fire.

The goal, engineering wise, is to put a number on a given structure - how many hours can it burn before it falls?

A steel beam will maintain most of its strength up to the point it suddenly becomes soft and loses all of it. The exact point in time this occurs is hard to predict, because it varies substantially with several variables.

A wood beam will maintain the full strength of the beam, minus the average thickness of wood that is burned off per hour, which is a reasonably well known quantity.

This makes it simple (though not easy, of course!), relative to steel structures, to put a number on a wooden structure - "this building can burn for 2 hours before it is no longer safe for firemen to try to put it out from inside".

The question is: how does the number for a steel structure compare to that of a steel one?

This doesn't answer the question, but on topic: I was working with a building engineer who described a situation where a car engine caught on fire underneath a buildings (large, extended) eve that was built with steel beams, and they did melt, obviously necessitating a lot of fix-up work. He reckoned though that if the beam was built of wood, in that situation you'd just have to clean of some blackened material and carry on business-as-usual.

He also said that of steel, perfect glass, and wood, glass was (strength to weight) the strongest material (I don't remember if this was in compression, or tension, or ...), but it's so affected by its environment (chemically, physically (a scratch)), there's really no such thing as perfect glass, so it's moot.

Currently under construction is this 73m tall residential wooden tower in Amsterdam:

https://hautamsterdam.nl/en/

The name HAUT appears to be a play on the Dutch word for wood (HOUT) and the french word for tall (HAUTE).

I wish France and other would follow on building wood based punscrapers

Note that “haute” is the feminine form, and the masculine version of tall is just “haut.”

Thanks for pointing that out. Now I learned that "cuisine" is feminine.

No, adjective like "haut" change according to the noun it describes and most of the time by appending a "e". A "tour" (the feminine word for tower) will be "haute". An "arbre" (the masculine word for tree) will be "haut". "Cuisine" is a general noun so it does not change, even if it ends with a "e". There are not a masculine or feminine cuisine, it's just a cuisine :).

"Cuisine" is a feminine noun (e.g. "la belle cuisine").

> "Cuisine" is a general noun so it does not change, even if it ends with a "e". There are not a masculine or feminine cuisine, it's just a cuisine :).

"cuisine" is definitely a feminine noun. There is no such thing as a "general" noun. Also, it is the adjective that changes to match the noun, not the other way around.

Those condo prices are eye watering (€1 million+).

Amsterdam has crossed 10K euros / sq meter.

How do regular people afford to buy?

Not. Even not so regular people can't afford to buy. So there is a fairly large contingent of people that rent at exorbitant prices with both parents working and the remainder moved out to more affordable places.

Here's a site with more information on wooden skyscrapers. It has a design for a wooden empire state building.

https://www.metsawood.com/global/Campaigns/planb/cases/woode...

Very interesting! But there is quite literally zero cross-bracing in that structure, which leads me to believe this was designed by an architect and not a structural engineer.

Do architects nowadays not have to be competent structural engineers? If so, it would amuse me greatly: how can you be entrusted in drawing new building shapes if you have no clue on their feasibility?

In other words, have the word 'architect' devolved into a 'building (exterior & interior) designer'?

Architects these days often seem to be large scale sculptors who inflict strange shapes on people who then have to live in or around them, without regard for engineering or human psychology.

Reminds me of the complaints and lawsuits[1] regarding the Stata building at MIT. Apparently in the beginning it had leaks and other lacks of fit and polish.

[1]https://thetech.com/2007/11/09/lawsuit-v127-n53

Not really "these days". Unliveable spaces has a good longstanding tradition. Just check Le Corbusier and Niemayer works.

This is extremely common, check out the book "How Buildings Learn", which has a few chapters on this phenomenon. The type of buildings you are describing are "Magazine" (buildings that get on the cover of architecture magazines)

Architects have to know material physics, structural physics and structural engineering, but they don't need to have specialist level knowledge. There are architects who specialize in innovative structural designs and their work combines both.

From what I've heard, for high-profile 'designer' construction, the architect will draw the outside of the building and hands the design to engineers, who will have to add all the structures so that the building is usable and buildable.

elevator cores are cross bracing

> Internationally recognised leader in timber engineering, Equilibrium Consulting, provided expertise on structural matters.

Well I'll be damned.

Doesn't that solid wood sheathing in the core of the building act as cross bracing?

They plan on finishing it in 2041, more than two decades away. I think this sounds far more like a marketing ploy than an actual building project.

People working in forestry are used to planning long-term, what you sow or plant now will be reaped by the next generation. They just planted the building and are now waiting for it to grow to harvestable size.

http://blog.longnow.org/02014/12/31/humans-and-trees-in-long...

I would love for humans to plant Red Woods and Iron Woods that would someday be harvested. They take so long to grow that they are not replaced, an ultimate testament to selfishness.

You would enjoy reading about this forest:

https://www.atlasobscura.com/places/visingso-oak-forest

Ultra long term planning is hard.

I had the same thought, but actually the super long timeline could also be evidence that they're taking it seriously. Roppongi Hills, another Tokyo development, took about 18 years from the start of planning to the end of construction.

The reason why Roppongi Hills took 18 years was because much of that time was spent acquiring lots from 400 smaller property owners. The construction of Mori tower itself took ~3 years.

This proposal does seem more marketing like marketing than a serious attempt to construct a building in that neither the website nor press release mentioning the location that the tower will be built (Marunouchi).(http://sfc.jp/information/news/2018/2018-02-08.html) (http://sfc.jp/english/news/pdf/20180214_e_01.pdf)

On the other hand, if they are serious about it and haven't decided on the location yet, it means that they probably haven't started acquiring the land, or that they are attempting to acquire it at several locations.

Given the Roppongi Hills example, provisioning 15 years just to acquire the smaller properties seems reasonable (and completely crazy at the same time, depending on the point of view).

Japan is unrivaled in building long-lasting wooden structures using only joinery (no nails, screws). This allows the wood to expand and contract harmoniously without cracking. Multi-story buildings (temples are a great example) have “floating” stories than may shift several feet during an earthquake, all kept together with a freestanding “spine” mounted only to the ground.

Is it harder to build this thing resistant to earthquakes than if it was made out of steel and concrete?

So Tokyo is finally going to build a Skytree made of actual wood this time?

Having just paid for a termite inspection, are infestations not a risk?

Not if the lumber is pressure treated.

structural wood is almost always treated with boron to prevent insect infestation

I first read that as thermite and I asked myself how does it work with wood buildings. (even if, as per this thread, wood is better regarding heat)

Is there a good article on fire safety in these buildings?

Curious as well. Seems like it would be a death trap and help spread the fire more.

Actually wood buildings are safer in case of fire if done right. New techniques (can't find the link) are able to control the way fire spreads and how fast it burns far better, also iirc because the heat that develops is lower.

Safer? Than steel or brick?

Yes.

Yes. The reason is slow and predictable burn that doesn’t affect the structural integrity until it has burned for a very long time. Even without special fire proofing, glulam burns at less than 1mm/minute.

The idea behind a fire safe high rise isn’t that it can’t burn but that when it burns it doesn’t collapse until people have left. That’s why the integrity is measured after 30min burn, 60min burn etc. As a wood beam burns the charring limits the oxygen supply of the fire, slowing the burn.

Steel beams require fire proofing and high temperatures or compromised fire proofing makes them structurally unsound which can cause unpredictable catastrophic failure (this happened in both of the WTC towers).

Is really collapse the the main danger to consider when a fire happens? I would think that when a building collapses from fire, many people in the building would already be dead from smoke and heat. If a wooden building would stand longer but be smoke filled earlier, I am not sure it can be said to be safer.

In a highrise it can be, a collapse can block esacapes for people in unaffected floors above, or crush unaffected floors below.

Everything else around your structural elements are going to be putting out smoke that will kill occupants regardless of whether the structure is steel or wood in situations like this. You worry about collapse for cases when the fire on a lower level traps occupants above, and the more time you can buy to control the fire or evacuate the better.

It's probably safer than steel frame buildings

https://www.economist.com/news/science-and-technology/216369...

Adhering to fire codes must be big part of the costs. How do you fireproof some crazy dude just decides to throw a Molotov cocktail at it?

I don't remember the details, but on a previous article on wooden skyscapers, it was explained how the engineering of the wood, which is also required for the necessary structural strength, made it very dense and practically incombustible. Fire proofing is an inherent quality, not something that's applied and thus could be done poorly.

IIRC.

Wood also just burns, slowly. Steel might not burn but as it gets hot it loses structural integrity very quickly.

The wood is all treated and sealed, so flammability is largely mitigated.

Even with steel, the actual frame of the building is surrounded by firewalls, fire resistant insulation and various suppression systems.

"The W350 tower will be mostly wood, and 10% steel."

Wood and steel.

You might as well call it a steel tower at this point.

Steel is heavy but it's also very strong. You don't need a lot of it to build something. A pure steel building actually ends up being lighter than a concrete building because of this.

Steel with wood fireproofing.

Steel has a great tensile strength but an average compressive strength at best. It's prone to buckling. Concrete is the exact opposite. In a skyscraper you need great tensile and compressive strength in different structural elements. This is why reinforced concrete is such a big deal. The properties of steel and concrete naturally complement each other.

I have a certain dislike for wooden houses because a) they seem to have high maintenance requirements, since wood as an organic material is often attacked by fungi, mould, or insects b) the ones I've lived in were old buildings lacking insulation and draughty, thus freezing in winter. That could be fixed with insulation of course.

Bricks (everywhere, internal walls and all) and concrete (for the floors) are the best - no stupid squeaking, nothing to rot, nothing to break, great soundproofing, good thermal insulation if done right, will last a long time provided no natural disasters. Not even expensive depending on the region.

That said, I don't get the point of a wooden skyscraper. I'd guess it's earthquake resistant, and it's not actual natural wood but a mix of synthetic materials and wood.

Bricks and concrete are absolutely not the best. They have terrible insulation properties, poor sound absorption, and cost more than wood structures.

Wood is an overall superior construction material if you can use it, and I think you're misunderstanding the pressure treatment process. It's normal wood placed in a vacuum chamber so preservatives can seep into the lumber.

Really? I've seen and lived in a lot of houses. Full concrete + brick were much more enjoyable than the creaky (I really hate those noises heh) wood and plasterboard houses. Colder, definitely, but better soundproofed imo.

Don't forget, brick and mortar also holds moisture and is porous. This can lead to spalling in cold weather and rotting whatever's behind it in warm weather.

https://www.youtube.com/watch?v=k1m5VShzxYs

Wood is a great construction material if it's treated against life feeding off it, rot and fire, especially when used in combination with other materials, such as building framing for hempcrete, half timbered buildings (fachwerk).

Creaky wood is a problem long since solved, but development contractors prefer to cut costs and build-to-sell before the underlying causes become apparent.

Use screws, not nails. Nail guns are convenient but they are for framing (playing to the strengths of nails’ awesome sheer strength) not layering (screws have far better tensile strength, poorer sheer strength). Add a zigzag of construction adhesive (insanely cheap stuff) to the joists before installing the subfloor. Leave 1/8th to 1/4th of an inch gap between each plywood sheet to leave room for swelling (in the Midwest that’s in the humid summers, on the coast it might be the other way around). Done.

Screws and nails are fundamentally different and should never be considered interchangeable. The cost difference is minimal given the trade offs involved, but contractors are apt to choose nails any time they can get away with it.

In Norway in Bergen few buildings made from bricks during last 20 years got problems with fungus. Once it gets inside the wall, it is very difficult to get rid of it. Yet wooden houses built over 100 years ago are ok despite a lot of rain (up to 9 feet per year).

It's actually less about insulation and more about air sealing. A hermetically sealed home with no insulation is generally warmer than a leaky home with walls stuffed with insulation.

Also regarding wood, this isn't the kind of wood you're thinking of. It's called pressure treated lumber, and it's an order of magnitude stronger than normal wood. The lumber has preservatives injected specifically to prevent rot, insect damage, and fire resistance.

What about slashing or bludgeoning damage?

I think the wood found in homes is pressure treated lumber which I don't believe is structurally any stronger than non-pt wood, but helps wood withstand the elements and wards off termites, microorganisms and fungal decay. The most common types of Pressure Treatments (at least that I am aware of in Canada) are Alkaline Copper Quaternary (ACQ) and Copper Azole (CA).

However, the wood material usually used to build these mid-rise buildings is cross laminated timber, which does add significant strength to the wood materials. Really cool material actually!

https://en.wikipedia.org/wiki/Cross-laminated_timber

Does Canada really build homes out of pressure treated lumber? I have never once seen this in the US.

Aside from outside uses (decks, patios, landscaping etc.), pressure treated lumber of one sort or another might be used for a few select applications for home construction, such as sill plates or a bathroom subfloor. Nearly all of the wood used for regular homes is non-pressure treated, at least everywhere I have seen in the US.

No, they don't use PT lumber for framing whole houses in Canada, that guy is just making assumptions. They use it exactly like we do, for wood that comes into contact with concrete.

PT wood is roughly 4x the cost and substantially heavier, framing a whole house in it would be nuts.

It will also destroy any fasteners that aren't galvanized or stainless steel, so you definitely wouldn't build a whole house out of it. Depending on the straps that are installed in the foundation, you'll see people use Teco nails or galvanized 10- or 16-penny nails. But regular vinyl sinkers will rust out really quickly.

You're right, I definitely over simplified. PT is a little bit stronger than non-PT, and I'm used to calling anything that isn't normal wood "PT" in the field.

Pressure-treated wood has a very specific pattern and color. It's usually substantially greener or browner depending on the treatment. And there will be small cuts on the surface of the wood in a regular checker pattern. The pressure treatment just injects the preservative deeper into the wood.

It's different from glue-lams or engineered joists, which are just regular old wood that's been glued together.

> A hermetically sealed home with no insulation is generally warmer than a leaky home with walls stuffed with insulation.

Warmer, maybe, but bad for people and good for fungi. Many contemporary buildings are built too airtight, lacking natural ventilation, which causes huge problems with interior air quality and traps moisture inside structures, creating places for mold to thrive.

Airtight buildings are perfectly fine with a proper Heat recovery ventilation system (HRV) that they should be using. HRV's are mandatory when building the PassiveHaus spec.

True. Unfortunately, at least around here a lot of buildings have been built in the past five or so decades that are fine insulation-wise but sorely lacking in ventilation, natural or otherwise, leading to widespread health issues. Many prefab concrete buildings from the 60s and 70s, even 80s, are practically ready for demolition.

Regarding a), it very much depends on how they are built. Little Moreton Hall has been standing since 1504, subsequent restorations required no changes to the timber structure. Isn't it beautiful? Although I suspect it is definitely subject to point b)!

https://en.wikipedia.org/wiki/Little_Moreton_Hall#/media/Fil...

Make no mistake here: the wood used in this will be chemically sealed and pretty much inert. It's actually hazardous waste.

It's just a proposal/advertisement of one company.

Reply on news.ycombinator.com