Steel Systems Not Specifically Detail for Seismic Resistance, Excluding Cantilever Column Systems

[zrck99]

I am designing an equipment support mezzanine in Seismic Design Category C. I intend to brace the upper level w/ tension only angle cross bracing and the lower level w/ knee braces made up of hss and gussets between my w beams and w columns. I plan on using the "Steel Systems Not Specifically Detail for Seismic Resistance, Excluding Cantilever Column Systems" in order to determine my shear forces to my beams on all 4 sides of the mezzanine, then using statics to determine my forces to my knee braces/columns. I will size my gussets using uniform force method and size the beam to column connection to handle the shear force at the end of the beam. Does this sound like I am on the right track with my method? I'm in a low seismic area and don't have a ton of experience w/ steel bracing systems. Am I correct that tension only cross bracing and knee braces fall under the "Steel Systems Not Specifically Detail for Seismic Resistance, Excluding Cantilever Column Systems" category?

Thanks for any input.

 

[JAE]

Since this is a mezzanine specifically intended to support only equipment - it seems like Chapter 15 of ASCE 7 would be required here instead of Chapter 12.
With SDC C, Table 15.4-1 requires an R=1.5 for "steel ordinary concentrically braced frames" using AISC 360 (and avoiding AISC 341 with a higher R = 2.5).

If you can justify using Chapter 12 (not sure you can since your mezzanine isn't a building) and with SDC C, you'd have R = 3 from Table 12.2-1.
With that you don't have to enter AISC's seismic provisions (AISC 341).

But I think you are in Chapter 15.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[zrck99]

Thanks for the response.

This mezzanine will have some conveyor system supports and access from the ground for people to be on the platform. I"m going to be inside a different building so I think that you are likely correct that I'm more in the Non-building Structure category.

Follow up question that I'm having trouble putting into words: When I look through the table of contents for AISC 360 I don't see any specific Seismic sections whereas AISC 341 looks to be entirely about seismic. By avoiding AISC 341 does that mean that I only need to determine the member forces/forces to each connection and design them as I would design any other nonseismically loaded member? I've never dug deep into AISC 341 but my understanding is that there are much more strict requirements about ductility, stiffness, over strength factors, etc... I know that was probably kind of hard to follow and apologize.

 

[structSU10]

You should always try to avoid having to follow AISC 341. Connections and such become much more expensive.

 

[JAE]

does that mean that I only need to determine the member forces/forces to each connection and design them as I would design any other nonseismically loaded member?

Yes.

Check out Eng-Tips Forum's Policies here:
faq731-376