4 ms·

I'll go out on a pretty small limb and say that the vast majority of Civil Engineering failings are not a matter of an incorrect safety factor, but are things t

I'll go out on a pretty small limb and say that the vast majority of Civil Engineering failings are not a matter of an incorrect safety factor, but are things that are explicitly not part of it. 1) Blunders. (Many places. You do the math wrong, or approve the wrong shop drawing, and no factor of safety is going to save you). (See the Hyatt Regency Walkway Failure) 2) Inadequate Geotech Info. (Basically every dam failure ever) 3) Genuinely new behavior. (Tacoma Narrows) 4) Contractors. (I-90 Bridge Sinking) 5) Deferred Maintenance. (Fatigue on bridges, Minneapolis)

ghaff 5y ago
Agreed. Although I'd probably also argue that a safety factor probably papers over those kind of problems in many many cases.
- londons_explore 5y ago
  But the question is, if you used a probabilistic approach, and tried to model, even very roughly, those things (probability contractor bodges the job in a way inspection doesn't notice: 10%), then would you end up with a safer bridge for the same money spent?
  - ghaff 5y ago
    It feels like you're picking numbers out of the air (or basing them on historical experience) either way. Unless you actually have historical data on certain types of problems--but then it seems like you're pretty much back to a safety/fudge factor.
    - londons_explore 5y ago
      But a large number of guestimated fudge factors all added up will approach the true value as long as there is no bias. The same does not apply for factors of safety - a 1.5 FoS is always between 0 and 50% too much.
      - deleted 5y ago
        [deleted]
  - wiredfool 5y ago
    That can be an unbounded black swan event. There are distributions where there is no mean value. The difference between a square section and welded channels. The difference between 53F and 27F. The difference between putting the waterproofing on before or after the post tensioning anchors. Leaving watertight doors open during a storm.
kortex 5y ago
6. Corner-cutting. I consider that distinct from blunders or bad contractors. See: the Pal-Kal construction method. I consider that not part of the safety factor because IIRC it was basically fudged or outright ignored, often times with building inspectors paid off. https://en.m.wikipedia.org/wiki/Versailles_wedding_hall_disaster https://en.m.wikipedia.org/wiki/Versailles_wedding_hall_disa...
chipsa 5y ago
I suppose a subset of 1 is: failure to consider stresses during construction, and only doing the calculations on the final product (FIU pedestrian bridge failure).

ghaff 5y ago

Agreed. Although I'd probably also argue that a safety factor probably papers over those kind of problems in many many cases.

londons_explore 5y ago
But the question is, if you used a probabilistic approach, and tried to model, even very roughly, those things (probability contractor bodges the job in a way inspection doesn't notice: 10%), then would you end up with a safer bridge for the same money spent?
- ghaff 5y ago
  It feels like you're picking numbers out of the air (or basing them on historical experience) either way. Unless you actually have historical data on certain types of problems--but then it seems like you're pretty much back to a safety/fudge factor.
  - londons_explore 5y ago
    But a large number of guestimated fudge factors all added up will approach the true value as long as there is no bias. The same does not apply for factors of safety - a 1.5 FoS is always between 0 and 50% too much.
    - deleted 5y ago
      [deleted]
- wiredfool 5y ago
  That can be an unbounded black swan event. There are distributions where there is no mean value. The difference between a square section and welded channels. The difference between 53F and 27F. The difference between putting the waterproofing on before or after the post tensioning anchors. Leaving watertight doors open during a storm.

kortex 5y ago

6. Corner-cutting. I consider that distinct from blunders or bad contractors. See: the Pal-Kal construction method. I consider that not part of the safety factor because IIRC it was basically fudged or outright ignored, often times with building inspectors paid off. https://en.m.wikipedia.org/wiki/Versailles_wedding_hall_disaster https://en.m.wikipedia.org/wiki/Versailles_wedding_hall_disa...

chipsa 5y ago

I suppose a subset of 1 is: failure to consider stresses during construction, and only doing the calculations on the final product (FIU pedestrian bridge failure).