hybrid steel/CLT structure

[JMASE]

All,
I'm looking to get a better understanding of using CLT deck with gyp concrete topping, supported by steel beams and columns for a five story institutional building. Specifically, what to pay attention to when using the CLT as a floor diaphragm sending lateral forces to concrete shear walls or braced frames for the LFRS. Wind will control this design. Any guidance? Related: any info on floor vibration performance of CLT on steel floors?
Thanks

 

[phamENG]

Best guidance I can give you is to remove the phrase "Wind will control this design" from your vocabulary.

Just because W>E for base shear doesn't mean you can ignore earthquake detailing. Sure, you could use R=3, but that doesn't get you completely off the hook. Last 5 story building I did (exposure D at the beach with winds above 120, concrete and wood), I had several locations in the building where seismic loading and/or minimum detailing was the controlling case for this or that connection or member, even if the total base shear was greater for the wind loading.

CLT hasn't caught on in my area yet, so I haven't had to look into this exact construction type, so I'm afraid I don't have anything for you on specific details.

 

[Eng16080]

I agree with phamENG regarding wind versus seismic. The only way to know which "controls" is to design the entire structure for each. In particular, when you have horizontal and/or vertical irregularities in the LFRS and are required to use the overstrength factor, the seismic forces can easily become much worse than wind.

Aside from that, I have almost zero experience with this particular type of construction. I am aware of a design guide which might help though: AISC DG 37: Hybrid Steel Frames with Wood Floors.

Good luck!

 

[jayrod12]

The couple of CLT diaphragm designs I have done we have ran then as both rigid and flexible and envelope designed it.

Pay attention to the connections to your LFRS, depending what that is, sometimes the anchorage is a bear to get to work, especially into masonry.

Otherwise it is governed by plywood spline shear capacity and fastening. The through panel shear strength and stiffness is astronomically high compared to the connections.