11 ms·
Cross-Laminated Timber
- VectorLock 7y agoThe first thing that jumps to mind is wondering how they compare fire-safety wise vs. "traditional" concrete and steel framed buildings?
- narag 7y agoNot bad if we believe this video: https://www.youtube.com/watch?v=YuAya0hRjwU https://www.youtube.com/watch?v=YuAya0hRjwU
- gnopgnip 7y agoSteel performs more poorly than you would expect in a fire
- velcrovan 7y agoEven jet fuel can melt it
- bob1029 7y agoI actually wonder if CLT/wood would perform better than steel during an all-out fire in terms of the structural integrity, at least for an initial period of time. The steel structure would more likely survive in-tact, but the wood structure could guarantee a certain minimum bound in terms of evacuation time available to occupants (which might be superior to steel). From my very novice perspective, I feel like wood does not attenuate in structural integrity as its temperature rises (at least not in the same way as steel), and it seems it would also absorb and conduct heat much more slowly than steel. On the other hand, I feel that once a wood-based structure gets hit with a big enough fire, the entire building is guaranteed to be lost due to how hard it could be to fully extinguish the fire (e.g. if the steel in a skyscraper could burn openly, what would that be like?). I did find this related paper which may be of interest to HN: https://www.fpl.fs.fed.us/documnts/pdf2012/fpl_2012_kukay001.pdf https://www.fpl.fs.fed.us/documnts/pdf2012/fpl_2012_kukay001...
- josephpmay 7y agoIt burns slowly enough that it doesn't conflagrate like unprotected hardwood or plywood might, so there's much more time to evacuate. If the fire isn't put out quick enough, however, the building may lose its structural integrity
- deleted 7y ago[deleted]
- willyt 7y agoDifferent failure modes. Mild steel becomes ductile at relatively low temperatures, way before it actually melts, hence why you sometimes see steel beams deform and drape over timber beams in a fire. The ductile transformation happens relatively quickly once you get to the critical temperature on the iron carbon phase diagram for typical construction grade steels. Hence why Steel is usually protected with fire rated drywall like boards, intumescent paint or weird spray on insulation that looks like porridge. Whereas with timber the rate at which it will burn is reliably predicted, so exposed timber structures are designed to be oversized so that the reduced beam sizes will still be effective. This is done using a charring calculation to give the required amount of structural integrity duration which varies depending on how tall the building is and what it is used for. All types of structure will fail eventually in a fire, the assumption is that the fire brigade will tackle it before it goes too far. In the UK, the main fire related problem with CLT is that the exposed surface doesn't meet the requirements for the speed of surface spread of flames so it has to be treated with a fire retardant or you need sprinklers if you want to expose the material. Both of which are expensive.
- Tcepsa 7y agoToday I learned why the bottoms of the staircases in the building where I work look like they've been sprayed with porridge. Thank you!!! (I had assumed it was insulation of some kind but could not figure out why they'd put it there)
- chipsa 7y agoHave you ever tried to set fire to a single log?
- lquist 7y agoAnybody know how these stand up to earthquakes?
- josephpmay 7y agoThe answer is basically that they don't know at this point. (Reference: I did extensive research on CLT as part of a project in LA a few years ago and talked to CLT experts from the Wood Products Council) CLT is stiffer than plywood, and the construction techniques are closer to steel/concrete, so it'll likely need reinforcement or dampering. Traditional wood buildings these days are designed to flex in earthquakes. But it hasn't been extensively tested for seismic properties yet
- Merrill 7y agoIs the main difference between CLT and plywood that CLT is a crossed grain stack of sawn lumber instead of peeled veneers?
- josephpmay 7y agoI don't know a huge amount about the manufacturing of the materials, so I'm not sure. The binding material may also be different for CLT.
- coryrc 7y agoYes..ish. Because plain-sawn veneers also exists so plywood can be made the same way.
- edaemon 7y agoPretty much, CLT is basically plywood with very thick laminations.
- jcampbell1 7y agoTrue, but worth noting plywood is spiral shaved veneers which are unrolled glued with the curves counteracting This is quite different from sawn dimensional lumber. Plywood is entirely cut tangent to the grain / tree rings. Plywood is much weaker essentially because trees evolved to withstand wind and the veneers are cut perpendicular to wind loads.
- tantalor 7y agoSee also https://en.wikipedia.org/wiki/Engineered_wood https://en.wikipedia.org/wiki/Engineered_wood
- kitcar 7y agoThis comment on the article is more interesting than the article itself IMHO http://disq.us/p/24slwwt http://disq.us/p/24slwwt
- floatingatoll 7y agoUnshortened: https://avc.com/2019/10/cross-laminated-timber/#comment-4643481053 https://avc.com/2019/10/cross-laminated-timber/#comment-4643...
- mooreds 7y agoJLM and his comments are a treasure. Check out his blog at https://themusingsofthebigredcar.com/ https://themusingsofthebigredcar.com/
- peterwwillis 7y agoThat 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.
- ethbro 7y ago"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+.
- deleted 7y ago[deleted]
- knodi123 7y agoI can't believe nothing in this article, nor in the articles linked from this article, actually says what CLT is. https://en.wikipedia.org/wiki/Cross-laminated_timber https://en.wikipedia.org/wiki/Cross-laminated_timber
- SamBam 7y agoMy understanding is that it's identical to plywood, just with thicker layers.
- olivierlacan 7y agoNo, it's much closer to Glue Laminated Timber whereas plywood tends to be made of wide sheets of thin timber of varying quality (depending on the quality of the wood and number of sheets glued together). CLT and GLT/glulam aren't made in sheets like plywood, they're usually constructed for a specific purpose (beams, etc.) - https://vicash.com.au/cross-laminated-timber-vs-glue-laminated-timber/ https://vicash.com.au/cross-laminated-timber-vs-glue-laminat...
- lightedman 7y agoCLT is literally plywood with thicker lamellae. I use this stuff when I design and build LEED-Gold certified hydroponic food production buildings. CLT is made out to panels and then cut to customer specifications. It has the same construction (including 90-degree off-orientation of each layer) and pretty much the exact same manufacturing process. Glue Laminated Timber has the same orientation all the way through. It is meant specifically for one-direction loading (primarily structural support beam but can be done for joisting as well) whereas plywood and MDF and CLT will handle multi-directional loads (and is why it gets used for the outside skin of buildings framed with wood.)
- coryrc 7y agoYour post shouldn't have been killed. Your comment is the same as the last sentence in the summary on wikipedia: "It is similar to plywood but with distinctively thicker laminations (or lamellae)."
- aidenn0 7y agoI can see CLT replacing steel, and possibly CMUs, but concrete in general? - It can't be poured into arbitrary shapes. - Much lower acoustic isolation
- SamBam 7y agoI would expect that the vast majority of concrete used in construction isn't poured into "arbitrary shapes," but flat walls. Even if only 50% of concrete is pored as flat walls, that would still be a huge market for this.
- bch 7y agoRe: acoustic isolation - having recently dealt w acoustics/concrete (laying a floor in a concrete apartment), I found out there’s not necessarily “concrete in general” so acoustic (and other) properties can vary from concrete to concrete.
- deleted 7y ago[deleted]
- floatingatoll 7y ago99pi episode "Built on Sand" talks about mass timber aka CLT: https://99percentinvisible.org/episode/built-on-sand/ https://99percentinvisible.org/episode/built-on-sand/
- danans 7y agoMy house has some LSL (Laminated Strand Lumber) beams which, like CLT, are engineered, but are built up from wood strands of and a lot of glue instead of from boards like CLT. As a result, they can be made from the remainder products of milling lumber. They can even be made from rapidly harvestable plans like bamboo: https://www.sciencedirect.com/science/article/pii/S0950061815001117 https://www.sciencedirect.com/science/article/pii/S095006181... This company appears to be making them: https://www.moso.eu/en/products/bamboo-beam-panel-veneer/bamboo-beams https://www.moso.eu/en/products/bamboo-beam-panel-veneer/bam...
- hammock 7y agoWhere does that glue come from and how good is it for humans/the environment?
- jpollock 7y agoa more important question is what happens when it's exposed to water, either through flooding or a leaky building.
- bdamm 7y agoThere are many forms of fungi (mold, various rot) that can feed on wet wood. There are not many forms of fungi that can feed on cured adhesive, which also functions to prevent the wood that is there from getting wet. Thus, I'd expect engineered/laminated timber to be better at repelling rot than standard untreated timber. Done well, it could last longer than steel.
- ethbro 7y agoIf anyone on HN has never hoisted an LVL beam (or even glulam), I would highly recommend it. Suffice to say they're 'quite a bit' heavier than wood. That weight is the adhesive and/or compression. So we're very much not talking about 'tree wood' at this point.
- analog31 7y ago
- newnewpdro 7y agoSince this is basically plywood++, does it have similar failure modes? Like what happens when there's a leaky tub frequently wetting a structural piece of CLT?
- edaemon 7y agoI don't know about all of CLT's failure modes, but Oregon State University is building a structure (for their College of Forestry) out of CLT and had some delamination issues: https://www.oregonlive.com/news/erry-2018/08/4965f0c7df3495/problems-at-peavy-faulty-timbe.html https://www.oregonlive.com/news/erry-2018/08/4965f0c7df3495/... That's just like plywood. I have to imagine other similar problems affect CLT. Your example of moisture damage essentially has to affect wood, though there are ways to engineer the CLT that will mitigate moisture damage.
- buss 7y agoHere in San Francisco, CLT won't be legal for buildings over six floors until about 2023 because of dumb policies. California uses the International Building Code as its base building code and then modifies it based on particular laws we have here. This modification & ratification process takes about two years. Then San Francisco does the same thing, adding another two to three years (because surely _our_ engineers are better than a consortium of the world's best structural engineers...) The 2018 International Building Code provides codes for tall CLT structures, which won't get adopted in the CA code until late 2020, which won't get adopted in the SF code until late 2022 or 2023. At that point, developers can start applying for permits for CLT buildings, which takes about four to five years. Then add two years of construction. So SF won't see CLT structures over six floors until about 2030. Makes you realize how unseriously we're taking climate change when the only carbon-negative structural building material in existence won't exist here for another decade.
- watersb 7y agoI am guessing some of this delay springs from the Loma Prieta Earthquake (1989). Lots of structural retrofit there. Yet I also guess that lessons from big quakes have been a part of the IBC review process. For decades. ??
- Gibbon1 7y agoYeah every time there is an earthquake they learn how new modern materials and construction techniques fail and perform worse than the previous ones. Kinda of like how joints in steel frame buildings held together with stupid janky rivets would shift and creek during earthquakes while strong modern welded ones wouldn't . Progress! No wait that last bit is bad. The steel at the welded joint buckles unless carefully designed. Which they weren't for the first 30-40 years.
- rayiner 7y ago> At that point, developers can start applying for permits for CLT buildings, which takes about four to five years. Then add two years of construction. Permits take longer than the building?!
- maelito 7y agoI'm looking for a model of the carbon emissions of a concrete house vs a mostly timber house. That is, a program writen in code or text with parameters such as : square meters, number of floors, wood species, distance travelled. It looks like open source carbon models are almost unheard of yet.
- cmutel 7y agoWe looked into this with a completely open toolchain [0]. You could email either of the two first authors to get the code (not sure why it wasn't in the paper supporting information). Building open carbon models isn't difficult, it's the input data that normally require licenses. I have built an open source life cycle assessment (LCA) software which has some traction [1], and there are alternatives for LCA [2] and integrated assessment models [3, 4]. However, data availability, especially on the level of completeness and detail you need to answer a specific question like carbon performance of a structure over a given period of time is a challenge. We are working on building a large open database to answer these kinds of questions[5], and Hacker News readers are welcome. Happy to chat via email if you want more info! [0] https://pubs.acs.org/doi/abs/10.1021/acs.est.5b01735 https://pubs.acs.org/doi/abs/10.1021/acs.est.5b01735 [1] https://brightwaylca.org/ https://brightwaylca.org/ [2] http://www.openlca.org/ http://www.openlca.org/ [3] https://github.com/JGCRI/gcam-core https://github.com/JGCRI/gcam-core [4] https://github.com/iiasa/message_ix https://github.com/iiasa/message_ix [5] https://bonsai.uno/ https://bonsai.uno/
- maelito 7y agoThanks for these great resources. What I'm trying to do is, I believe, complementary to these LCA tools. I'm building a website https://futur.eco https://futur.eco that bridges carbon models with our every day life as citizens. Sorry, it's in french for now, but I have some hopes that you read french :-) Behind the website is a database of open source and extremely simple LCA models, expressed in a new redable programming language. All of it resides in this single file : https://github.com/laem/futureco-data/blob/master/co2.yaml https://github.com/laem/futureco-data/blob/master/co2.yaml.
- sjg007 7y ago
- kimburgess 7y agoWell this is timely. In case anyone else is from Brisbane, Australia - we're home to the world's largest CLT building: 25 King St. It's open to the public this weekend as part of BNE Open House: https://brisbaneopenhouse.com.au/building/25-king-street/ https://brisbaneopenhouse.com.au/building/25-king-street/. There's also a talk this evening: https://www.eventbrite.com.au/e/brisbane-open-house-tall-timber-buildings-taking-on-climate-change-tickets-70864384281 https://www.eventbrite.com.au/e/brisbane-open-house-tall-tim....