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by conqueso
996 days ago
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Great story, and LeMessurier is certainly deserving of praise. I'm curious about his initial mistake. The article mentions that he placed the pillars at the middle edges, as opposed to corners, because this is beter for resisting the quarterly winds. So he clearly knew they were a thing. Why then did he not do the calculations for how they would effect the chevon braces until the call from the student? That seems like a pretty huge lack of oversight. Was it pride? The moment of inspiration is described romantically, sprawling designs on the back of a napkin and such, and he was disappointed that the chevrons would be hidden behind the aluminum skin/facade - consoling himself with the thought "It'd be there for God to see". The article describes the whole situation as a perfect storm of sorts (no violation of building code, industry standard of bolts instead of welding, etc), but I can't get past how he didn't crunch the numbers for something that seems like it should go without saying. |
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Basically, I'm surprised that no one did the basic worst case sigma=MY/I for the side and quartering loads. The old grizzled supervising engineer generally will run through a bunch of ballpark estimates to see if the designer has actually checked all the worst case combinations.
I don't really buy the article's factor of safety discussion -- the factor of safety is for uncertainty, not blunders. I _might_ save you from a blunder, but that's not what it's for. It's for variation in material dimension, quality, and loading variation.
As for the bolts vs welding, There's definitely scope for changes at the shop drawing stage. When an engineering firm designs a building, they'll generally design a set of typical connections, but when the shop goes to build them, they have to take this column:floor beam connection and actually turn it into "cut this cope, drill here, ..." and they'll generally do the simplest, cheapest thing they can.
The engineers have to review the shop drawings, and if they don't have a good set of calcs for what the loads are in that particular bit, then they aren't going to necessarily see that this substitution of bolts won't work. (Note -- bolts can be just as good, and potentially better than welds, depending on what you're doing, how you're erecting, and the space you have available. Full Penetration welds are a pain, but they're the easiest way to specify a full strength join. But doing them on site, in the air, when you're putting the thing together is not something that you'd generally want to spec.)
There have been a significant number of historical disasters connected to shop drawing changes that the engineers didn't pick up. (e.g., the Hyatt Regency walkway collapse).
Also remember, this was done in the 70's, so they wouldn't have had Finite element models of the building where it's super easy to just run a couple more loads. Everything there would have been indeterminate elastic analysis, so it's not quick to run an accurate calculation if you're trying to find beam sizes.