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Comment by kitcar | Hacker News Reader

This comment on the article is more interesting than the article itself IMHO http://disq.us/p/24slwwt

Unshortened: https://avc.com/2019/10/cross-laminated-timber/#comment-4643...

That commenter is doing a lot of gymnastics to avoid talking about reinforced concrete's hidden failures. It's difficult to determine reinforced concrete failures before it gets bad, and repairing it is very expensive. Concrete can get really complex depending on how you make and apply it, and what it's exposed to.

I agree with the author that water is now a bigger deal than fire for wood construction, and we need way more testing for taller construction, perhaps even designs tailored to the material.

"The issue with CLT as a building system is exactly that -- its behavior as a whole when subjected to differing forces as statistically magnified by the great number of joints. There are a ton of connections in a CLT building. Thousands of them. One connection failure can create a cascade of failure that may destroy the building. Each connection has the fingerprints of a single worker. One bonehead can wreck a connection."

That's a non-negligible practical problem and a perfectly valid point.

And it's difficult to take the residential approach of "just over-spec" when you're building mid-rise+.

But yet elsewhere in the world they can build multi-storey CLT buildings

https://www.theb1m.com/video/top-5-the-world-s-tallest-timbe...

- completed in 2012

- completed in 2015

- completed in 2017

- completed in 2015

- completed in 2017

Mmhmm.

> That commenter is doing a lot of gymnastics to avoid talking about reinforced concrete's hidden failures. It's difficult to determine reinforced concrete failures before it gets bad, and repairing it is very expensive.

Care to elaborate? Concrete has already been extensively studied and has enjoyed widespread use, including under seismic loads. I don't understand how in this day and age where rc structures have been used for over a century there is any mention of "hidden failures".

Concrete in general can fail from simply being mixed poorly, which the slump and strength tests used on each batch are meant to address. But also additives can sometimes be added to concrete, which in some cases react with surfaces/chemicals over time and cause all sorts of problems.

For reinforced concrete failures, see here: https://en.wikipedia.org/wiki/Reinforced_concrete#Common_fai... https://www.usbr.gov/ssle/damsafety/risk/BestPractices/Chapt... By the time there's spalling the reinforcement is already rusted and breaking up the concrete. Of course you can say "Oh but we know all that now, so just design it right and you're good!" Sure. Unless you make a mistake, in which case you won't know it until the structure is crumbling. And remember, "it's a monolith", so good luck with those repairs.

I'm not saying CLT is better - but let's not kid ourselves, reinforced concrete isn't perfect. It's just cheap, strong, and easy to install.

I felt the same way. They said a lot of plausible things, but their motivation seemed more to be “don’t disrupt my life by pursuing alternatives to concrete” than “here is a reasoned and well-structured argument against CLT”. It read like a series of talking points. Glad it’s not just me.

JLM and his comments are a treasure. Check out his blog at https://themusingsofthebigredcar.com/

Now I want to know how it will recover after fires. I read it will burn/collapse well after occupants have escaped. But will a building with some burnt CLT members be a total loss?

JLM's comments some days are better than Fred's. The guy has been a high ranking army officer, built a lot of the newer skyscrapers in Austin and now is retired from CEO of a Fortune 500 company.

Really? It seems like a lot of words to say "unfamiliar material bad." Surely the people advocating CLT have thought of some of these obvious downsides, and have ideas for how they're addressing them. If those are inadequate, then talk about that. Instead we get "In my professional judgment it is driven by a certain "gee whiz, isn't this cool" environmental state of mind." Excuse me if I want facts and not someone's un-sourced, un-backed-up "professional judgment".

The comment repeatedly states that CLT is neither new nor unfamiliar, one main issue is that CLT requires many joints with individual properties (many points of failure with manufacturing errors specific to the people that worked there) whilst concrete behaves / accepts load as a singular structure.

Admittedly, this isn't an argument against CLT but instead against anything that doesn't behave as a single structure under load - but it does point out that CLT isn't a suitable replacement for all building materials everywhere. High rise buildings need the safety of reenforced concrete, with it's load handling and simplified calculations (due to lack of joints), and until something can perform in a similar manner it's not likely to be replaced.

> "unfamiliar material bad."

I think its more "unfamiliar material" has different properties than we're used to, and there will need to be some adjustment.

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