- Back of the Envelope
- Posts
- Envelope #32: Overstrength for diaphragm forces?
Envelope #32: Overstrength for diaphragm forces?
Andy Lin
October 26, 2023
Happy Thursday! Andy from Back of the Envelope here – this is where I share fun-ish SE-related things (plus a dad joke), all in 5 minutes or less.
Today’s email is going to be about “diaphragm design forces for structures with out-of-plane offset irregularity” (and as you can probably guess from the title, it has something to do with overstrength, aka amplified forces).
If you have been practicing for a while, you are probably familiar with the diaphragm design force equation from ASCE 7 in section 12.10.1.1, which shows the Fpx and all that good stuff.
And because you’ve seen it a million times, you may have missed (speaking from experience…) a new sentence that was added to the end of the section in ASCE 7-16:
(blurred out for fun – don’t open your book/pdf yet!)
(Side note: the gray bar on the right indicates that the section had substantive changes from the previous edition. i.e., from ASCE 7-10 to ASCE 7-16. So generally, we should pay more attention to those at each code cycle to find out what’s new.)
If you already know what this is, you can skip to the bottom and read the dad joke. If not, read on to find out more. Let’s dive in!
(Estimated reading time = 3 minutes & 15 seconds)