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Using Zx instead of Sx for Older Structures

Using Zx instead of Sx for Older Structures

Using Zx instead of Sx for Older Structures

(OP)
Do you all use Zx capacity for moment to get a higher capacity of out beams for historical structures that likely used Sx during design? I know case by case basis and connections are often critical, but I'm curious in a general sense. I do a lot of renovation work, and I typically take advantage of it. Especially where there are bearing connections. Any thoughts?

RE: Using Zx instead of Sx for Older Structures

Yes, you should use Zx, and all other modern codes. The change from Sx (stress design) to Zx (strength design) is due to our knowledge of the beam capacity, not the true beam capacity.

RE: Using Zx instead of Sx for Older Structures

X2 for using Zx. Some low probability snags:

1) keep an eye on the LTB unbraced length as it's different for plastic capacity.
2) for very old work, ensure that the steel is ductile enough to go fully plastic.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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