4 ms·

Why would the strength requirement for a 5 story building be different from a 50 story building? Do the building materials behave differently when you increase

by abduhl 9y ago

Why would the strength requirement for a 5 story building be different from a 50 story building? Do the building materials behave differently when you increase a number? The Millennium Tower is not a "counter proof" to my argument, although it has become a bellwether for exactly the kind of posters I call out in my original post. My argument is that people on here who do armchair structural engineer and make comments like "the building code is too lax" are ignorant and full of shit. All the Millenium Tower proves is that, even with a building code, it is still possible to get unintended consequences. To the rest of your post about skyscrapers getting a lot of leeway - they don't get any more leeway than any other structure, they just have the money it takes to invoke portions of the code that allow alternative analysis methods. It just doesn't make sense financially to do some of the complex modeling for a 3 story building to shave 5% of material costs. If anything, the building code is more stringent on skyscrapers because it does require more advanced analysis. This analysis is NOT precluded for smaller buildings, it is just not worth the money.

wpietri 9y ago
> Why would the strength requirement for a 5 story building be different from a 50 story building? Because if it falls over it won't just kill 5 stories worth of people, but 50 stories plus an unknown number of people in the building it falls on, as well as creating a giant civic problem? > ignorant and full of shit Oooohkay, buddy. At best you are playing semantic games here. If your theory is that the building code is just fine when things like the Millennium Tower can happen, then we disagree on what "fine" means.
- ggcdn 9y ago
  > If your theory is that the building code is just fine when things like the Millennium Tower can happen, then we disagree on what "fine" means. What portion of the building code do you think needs to be updated in response to the Millennium situation? In reality, the building code achieves a success rate far in excess of what engineers deem acceptable. It is unfortunate that the Millennium is a big glaring exception, but the fact remains. Geotechnical engineering (the cause of the Millennium lean) remains a highly empirical field of engineering with uncertainties that dwarf structural ones. Hence there is a lot of built-in conservatism in design parameters like bearing pressures. But there are limits to the amount of information you can ascertain of what's below you that you cannot see. Looking back in retrospect and saying "well obviously they should have had longer piles" like many people have on the various threads about the tower is a pretty ignorant thing to say, and it shows that they do not have an appreciation of the engineering behind the decision. There a tens of thousands of examples of friction piles that have worked flawlessly. The engineering evidence appears to have supported the decision, but the in-situ soil conditions varied from their design model. This, in my opinion, is not a failure of codes, but an unfortunate, statistically rare outcome.
  - wpietri 9y ago
    Engineers may deem this acceptable, but given that San Francisco taxpayers may end up footing the bill, I doubt the rest of us do. I understand that the people who built it believed that they were doing just fine. But I also understand that there are enormous pressures to keep costs low on a project like this. The notion that for this building those enormous pressures had exactly zero contribution to this outcome is a claim I certainly wouldn't accept without evidence. If this were really in the range of statistically expected outcomes, then a) there should have been a plan in place to fix it before the structure went up, and b) they would have had sufficient insurance coverage to pay for the fix. Neither is true. The ongoing gosh-golly-who-cooda-node routine plus the simultaneous festival of blame-shifting suggests to me that, at best, the business side of the operation went well beyond what an engineer would have done in the same place. The correct fix to the building code here I'm happy to leave to the experts, just as long as they eliminate outcomes like this. If that ends up raising the costs for other fancy buildings stuffed with pied-a-terres for the wealthy even to prohibitive levels, I am entirely fine with that. Erring on the side of of earthquake safety while building near major faults in major metropolitan areas seems like a great choice to me.
    - ggcdn 9y ago
      > just as long as they eliminate outcomes like this I guess the point I'm trying to make is that complete elimination isn't possible in a long tail statistical distribution. There will always be a point where we have to draw the line, and there will always be freak occurrences of undesirable outcomes. This is the crux of engineering - finding the correct balance between cost and safety. Perhaps the current state is not enough, but the wildly disproportionate amount of structures that are working just fine tells me we are close. > If that ends up raising the costs for other fancy buildings stuffed with pied-a-terres for the wealthy even to prohibitive levels, I am entirely fine with that. Building codes aren't only applied to high end buildings. Any changes affect the (badly needed) low end housing just as much as high end buildings. Just another thing to consider. > Erring on the side of of earthquake safety while building near major faults in major metropolitan areas seems like a great choice to me. No disagreement there ;)

by abduhl 9y ago

wpietri 9y ago

> Why would the strength requirement for a 5 story building be different from a 50 story building? Because if it falls over it won't just kill 5 stories worth of people, but 50 stories plus an unknown number of people in the building it falls on, as well as creating a giant civic problem? > ignorant and full of shit Oooohkay, buddy. At best you are playing semantic games here. If your theory is that the building code is just fine when things like the Millennium Tower can happen, then we disagree on what "fine" means.

ggcdn 9y ago
> If your theory is that the building code is just fine when things like the Millennium Tower can happen, then we disagree on what "fine" means. What portion of the building code do you think needs to be updated in response to the Millennium situation? In reality, the building code achieves a success rate far in excess of what engineers deem acceptable. It is unfortunate that the Millennium is a big glaring exception, but the fact remains. Geotechnical engineering (the cause of the Millennium lean) remains a highly empirical field of engineering with uncertainties that dwarf structural ones. Hence there is a lot of built-in conservatism in design parameters like bearing pressures. But there are limits to the amount of information you can ascertain of what's below you that you cannot see. Looking back in retrospect and saying "well obviously they should have had longer piles" like many people have on the various threads about the tower is a pretty ignorant thing to say, and it shows that they do not have an appreciation of the engineering behind the decision. There a tens of thousands of examples of friction piles that have worked flawlessly. The engineering evidence appears to have supported the decision, but the in-situ soil conditions varied from their design model. This, in my opinion, is not a failure of codes, but an unfortunate, statistically rare outcome.
- wpietri 9y ago
  Engineers may deem this acceptable, but given that San Francisco taxpayers may end up footing the bill, I doubt the rest of us do. I understand that the people who built it believed that they were doing just fine. But I also understand that there are enormous pressures to keep costs low on a project like this. The notion that for this building those enormous pressures had exactly zero contribution to this outcome is a claim I certainly wouldn't accept without evidence. If this were really in the range of statistically expected outcomes, then a) there should have been a plan in place to fix it before the structure went up, and b) they would have had sufficient insurance coverage to pay for the fix. Neither is true. The ongoing gosh-golly-who-cooda-node routine plus the simultaneous festival of blame-shifting suggests to me that, at best, the business side of the operation went well beyond what an engineer would have done in the same place. The correct fix to the building code here I'm happy to leave to the experts, just as long as they eliminate outcomes like this. If that ends up raising the costs for other fancy buildings stuffed with pied-a-terres for the wealthy even to prohibitive levels, I am entirely fine with that. Erring on the side of of earthquake safety while building near major faults in major metropolitan areas seems like a great choice to me.
  - ggcdn 9y ago
    > just as long as they eliminate outcomes like this I guess the point I'm trying to make is that complete elimination isn't possible in a long tail statistical distribution. There will always be a point where we have to draw the line, and there will always be freak occurrences of undesirable outcomes. This is the crux of engineering - finding the correct balance between cost and safety. Perhaps the current state is not enough, but the wildly disproportionate amount of structures that are working just fine tells me we are close. > If that ends up raising the costs for other fancy buildings stuffed with pied-a-terres for the wealthy even to prohibitive levels, I am entirely fine with that. Building codes aren't only applied to high end buildings. Any changes affect the (badly needed) low end housing just as much as high end buildings. Just another thing to consider. > Erring on the side of of earthquake safety while building near major faults in major metropolitan areas seems like a great choice to me. No disagreement there ;)