AISI-S213 & ASCE 7-10

[cpp11]

Shot in the dark: Anyone here proficient in the application of AISI-S213 (or AISI-S400, since the cold-form Code has recently been updated) with respect to the seismic design coefficients and provisions in Chapter 12 of ASCE 7-10?

ASCE says to use an R value of 6.5 for wood-sheathed cold-form walls, which is similar to stick framed shear walls, but AISI-S213 states that using an R value greater than 3 means that all collectors, chord splices, etc. need to be designed for "amplified" seismic loads (ie., Overstrength). Chapter 14 of ASCE 7 points to AISI-S213 for design detailing of seismic forces, which looks to be pointing me towards desiging my connections with a rho of 2.5.

This, quite frankly, seems ridiculous, and I've gone ahead and designed my chord splices without the use of the overstrength factor, but I'm wondering/hoping someone here has had an issue with this before and can maybe lend me a hand.

Thanks, all!

 

[Andy Lin]

I remember doing this back in 2010 -- don't know if the current code has new exceptions or not. I recall doing some digging and found an explanation for using overstrength in cold-formed steel but I am drawing a blank right now.

We ended up having to splice the top track (18 ga) with 20 #10 SMS (5 each flange and 10 on the web). At some locations where splice won't work, we just provided steel beams or HSS tubes.

Similarly, all jambs at the end of shearwalls were double 12 ga studs or HSS at some locations.

For the anchors though, I think because of the way Appendix D was written at the time, we may have ended up using the minimum of "maximum load that can be developed" and "amplified seismic load"... I can't remember specifically.

 

[cpp11]

What bugs me is that these sorts of connections aren't usually subject to overstrength/"amplified" design in the AWFPA wood shear wall design provisions, and the AISI-S213/S400 codes were (allegedly) written to mirror typical wood design requirements.

I'm currently specifying (12)-#10 SMS at the lapped connection in the top track, with all screws though the web. This is what my boss specified for an older project, and while there were a few changes I made to my detail set, I stuck with this spec because the numbers seem to work, and it's similar to the strength at which we spec our wood top plate splices.

For this particular project, the difference between an R of 3.0 and 6.5 is either installing (1)- or (2)-CMST12 straps at the splice. We'll see what the plan checker has to say about my work.