After Corbu » engineering

Damage is a feature not a bug

Quixote — Fri, 02 Apr 2010 06:18:52 +0000

Disaster porn for engineers:

Click here to view the embedded video.

This seemed like a good opportunity to point out that while that video makes the damage look pretty bad and cause youtube commenters to call for the designers heads, this is an example of a building behaving well. The concrete outside the wall rebar cage spalled off, which looks like failure, but is predictable and intentional – you need a layer of concrete outside the cage for corrosion protection that you plan on being sacrificed during an earthquake. The rest of the wall remained confined and was able to cycle through major inelastic deformations to dissipate energy and prevent the rest of the building from collapsing. They were so effective that the owners are planning on repairing the damaged shear walls and finishes and reopening, which is pretty impressive.

Thank you RISA

Quixote — Thu, 17 Sep 2009 05:46:19 +0000

Because of you, when the boss catches us having rubber band fights we can always just say: ”I’m iterating for p-delta.”

Similar to coders really.

Update: It’s embarrassing when you misspell the punchline.

Grade Beams FTW

Quixote — Thu, 27 Aug 2009 02:16:52 +0000

They are just really fucking awesome at reducing moment frame deflection.

That is all.

Column Drop Caps Done Right

Quixote — Fri, 21 Aug 2009 10:25:44 +0000

A beautiful way to limiting punching shear problems. Radial control joints along the bottom of the drop are a nice accent.

National Technical Library Prague photo by vtr do

You can’t change gridlines in midspan

Quixote — Fri, 21 Aug 2009 10:06:48 +0000

Click here to view the embedded video.

While I agree with Archidose that this video is a wonderful way of presenting the design concept and understand that this house is just a study in the use of wood structural panels and not intended for construction, the engineer in me groaned at the way in which the walls were completely discontinuous across the 2nd floor. Modular prefab construction in wood and concrete is often unfairly maligned as cheap or ugly and there’s certainly ample ability to attain architecturally compelling forms with prefab materials.

But know your material. You’re going to have a hard time using one replicable panel design if every panel is loaded differently by the floor above. If you’re using an off-the-shelf panel, it almost certainly will not have been engineered to recieve the large point loads caused by upper walls framing orthogonally past lower walls. Or to cantilever. Or to be a floor system subject to a highly irregular load patterm.

All this means multiple custom panels are required, which is very doable, but as each piece becomes specialized you’re getting less and less value out of the prefab system you’ve adopted. Of course you can treat the panels as mere partitions and provide a separate system of columns and beams, but at that point the prefab panels are an aesthetic gimmick rather than a structural system, and you’ve abandoned the study’s premise of building out of one sustainable material as well as the authors fealty to Miesish “honest express of materials.”

Typically I’m completely for untethering conceptual models from practical constraints in order to move the creative process forward, but simply using materials in ways they weren’t intended and in ways they work poorly is not a creative achievement; you also must arrive at elegant ways to make the novel applications work.

Martian Wordle

Quixote — Fri, 03 Oct 2008 11:47:24 +0000

So, despite my general tendency to find all internet traditions lame, I think these wordles are pretty awesome and I made one for my Mars structural design project (and lo and behold, those are amongst the most common words). Impressively, the script processed my 100+ page paper in a scant few seconds. I am overwhelmed with coder envy.

this is really what I do every day

Quixote — Thu, 28 Aug 2008 02:27:46 +0000

No joke: this is Joe living my life.

(h/t: Lewism)

Add Another to the Black List

Quixote — Sat, 12 Apr 2008 02:57:48 +0000

See Ezra try to take food out of my (hypothetical) child’s mouth by downplaying the very real danger of the earthquake menace with his “Robots! Robots!” flimflam. In reality these things are not competitive, as the worst robots are brought by quake.

But really: setting most of the snark aside, unless you live or work in an unreinforced masonry building, you don’t have much to fear from earthquakes. Codes now require buildings to be able to dissipate a lot of kinetic energy (read: break) in the event of the Big One, and they definately probably won’t fall on your head most of the time. Of course seismic engineering is largely empirical so it suffers from all the usual problems of trying to extrapolate from a curve set to a small historical data set, meaning it’s predicitive value is something less than awesome.

There’s a reason they write a new building code after every major earthquake…

Architectural Bling

Quixote — Sat, 23 Feb 2008 09:41:36 +0000

Even though I was told recently that real engineers design buildings not bridges (the view a side effect of the long standing structures vs. civil schism) — and I have a strong disdain for Dubai’s nouveau riche gaudiness — it would be a fun to work on one of these super-bridges. Long-span structures make it economical to use curvilinear members, which are a nice challenge to engineer — we get to break out our calculus (otherwise rarely used) and tailor members very specifically to the loads involved.

However, the real travesty of Fxfowle’s design is that its’ pretty derivative. This is Dubai! They’re supposed to be crazy! Why not commission Soleri to build his twisted tubular bridge that also contains apartments, retail, and offices in it’s skin. The first (and therefore biggest!) mixed use bridge seems more in Dubai’s style than settling for a Calatrava B-side.

The Swiss Seismic System

Quixote — Fri, 22 Feb 2008 09:02:28 +0000

Not Switzerland, as that country is known for its superior engineering*, and they’d probably scoff at this kind of patchwork, but Swiss Cheese. Below you see a beautiful concrete shear wall, essential for taking wind and earthquake loads from one level of a building to the next — helpful for people not dying! — punched through with one big hole and a couple small ones.

Ideally you reinforce these things beforehand vertically, horizontally, and at 45 degrees at each corner (even more ideally you do a finite element analysis — lots of computer modeling and numerical methods to go gaga over — but that’s let’s not let the perfect be the enemy of the good). Here, reinforcing beforehand clearly didn’t happen and the fix was to bolt plates to the wall — the technical term is “band-aids.”

It’s a valiant effort, but if originally you were going to reinforce the opening in three directions, and now you’re only doing it in one, that’s a problem. Presumably, some engineer modeled the above reinforcing situation and decided it was okay, but the point remains that you’re not really replacing the lost capacity of the wall; it’s weaker and going to behave differently. More specifically it’s going to crack through the weakest cross-section — in a line running through all those holes.

Cracking itself isn’t inherently a problem — it dissipates energy in a quake, keeping other parts of the building from collapsing — but now it will happen at lower magnitudes, meaning the building is damaged more easily and has a shorter lifespan. Which is why these holes piss the hell out of me. Buildings cost a huge amount in nonrenewable resources and construction waste is a significant percentage of landfill wastes. They are only useful for a small amount of years (averages I’ve seen thrown around: 50-80). When you weaken the seismic system you take years off the building’s lifespan.

Yet contractors go around drilling like a gang of drunk yahoos prospecting for oil. Afterwards, they send you pictures like the above and ask if it’s okay. Dudes: you already demolished the wall! I guess it’s going to have to be. They explain that their schedule dictated they had to have the hole immediately. Which makes sense. The schedule ($$$) is definitely more important than life safety; definitely more important than the long-term value of the building. Assholes.

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*Plus I’m not really sure they have an earthquake problem — they’re pretty far from a plate boundary — and hence might have no need for a seismic system. Normally that would mean I would sneer at the “engineering,” but oh! The bridges!