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Safety factors account for uncertainty. Uncertainty the quality of materials, of workmanship, of unaccounted-for sources of error. Uncertainty in whether the ma

Safety factors account for uncertainty. Uncertainty the quality of materials, of workmanship, of unaccounted-for sources of error. Uncertainty in whether the maximum load in the spec will actually be followed. Without a safety factor, that uncertainty means that, some of the time, some of your bridge will fall down

irishcoffee 6mo ago
A safety factor of 1.0 means “the structural integrity of this construct will meet the expectations of intended use with no issues.” A safety factor of 1.7 means “if this construct is used in a way that is 70% more abusive than anticipated, the structural integrity should remain in tact.” You’re hand-waving enough here that you have the luxury of agreeing or disagreeing with me, well-played. Your initial response was glib and not terribly productive.
- StevenWaterman 6mo ago
  This thread started because of "the cheapest bridge that just barely won't fail" My point was that safety factors are a part of this. A safety factor of 1.0, designing bridges so that they can perfectly withstand the expectations of intended use, means that some unacceptable % of those bridges will fall down in practice. In other words, it's true that you can explain safety factors as: > Assuming perfect construction, and no defects, under designed maximum load, make sure that this bridge really stays up by a wide margin But that misses the point of why we use safety factors. Nobody is paying for a bridge to really stay up by a wide margin. Because there's no material difference between a bridge that stays up, and a bridge that really stays up, right up until the point that the weaker one falls down due to inevitable over-loading or defects in construction / materials.
  - irishcoffee 6mo ago
    Nobody in the US builds anything (permitted) with a SF factor of 1.0. Doesn't happen.
    - StevenWaterman 6mo ago
      Yes, because it would fall down (sometimes, often enough that regulatory bodies forbid it)

irishcoffee 6mo ago

A safety factor of 1.0 means “the structural integrity of this construct will meet the expectations of intended use with no issues.” A safety factor of 1.7 means “if this construct is used in a way that is 70% more abusive than anticipated, the structural integrity should remain in tact.” You’re hand-waving enough here that you have the luxury of agreeing or disagreeing with me, well-played. Your initial response was glib and not terribly productive.

StevenWaterman 6mo ago
This thread started because of "the cheapest bridge that just barely won't fail" My point was that safety factors are a part of this. A safety factor of 1.0, designing bridges so that they can perfectly withstand the expectations of intended use, means that some unacceptable % of those bridges will fall down in practice. In other words, it's true that you can explain safety factors as: > Assuming perfect construction, and no defects, under designed maximum load, make sure that this bridge really stays up by a wide margin But that misses the point of why we use safety factors. Nobody is paying for a bridge to really stay up by a wide margin. Because there's no material difference between a bridge that stays up, and a bridge that really stays up, right up until the point that the weaker one falls down due to inevitable over-loading or defects in construction / materials.
- irishcoffee 6mo ago
  Nobody in the US builds anything (permitted) with a SF factor of 1.0. Doesn't happen.
  - StevenWaterman 6mo ago
    Yes, because it would fall down (sometimes, often enough that regulatory bodies forbid it)