Ragnarok.Ghishlain said:
»Well, that's nice peace of mind there at least.
Do steel and concrete frames get the same level of scrutiny? I imagine that's more of a commercial / industrial application question versus residential application.
Steel is by far the most consistent material. I'd check my Steel Design Manual, but I'm pretty sure the factor for steel is as high as 0.90. Concrete is somewhere around the 0.80 range if it's cast in a controlled environment (pre-cast) and only about 0.65 or so if it's cast-in-place.
Wood starts out at 0.90 or something as well, but has about a dozen other factors which reduce it to about 0.20 for most applications, such as the duration of the load, how moist its environment is, etc.
And then when you're loading the material, you assume every couple of square feet has a 200lb person standing on it, and before any loads are calculated you factor the dead load (self-weight of permanently fixed materials) by 1.25 and the live load (everything else) by 1.50.
Panta is also correct about concrete showing signs of failure looong before it fails structurally. But all building materials are treated like that. If you ever notice a big crack in your residential drywall or the concrete face of a building, an inspector should be notified. That's why I was so surprised when that apartment in Florida collapsed a little while ago, knowing that there should have been signs of failure. In fact, that was the case -- apparently people had been complaining for years about pipes bursting and giant cracks forming. Just nobody did anything about it... :/