Seismic deck diaphragm?

[SteelPE]

I am in the process of looking at designing a large warehouse in accordance with IBC2009. I am currently using a R=3 and I am getting some rather large loads built up in the diaphragm (nothing that falls outside of the diaphragm values listed in your standard deck catalog). My question is in reference to the diaphragm load built up under seismic loads. Since this load is calculated at the strength level and the diaphragm tables are calculated at the allowable level, am I allowed to use 0.7E when figuring the diaphragm requirements?

 

[structSU10]

Not looking at IBC,

ASCE 7-05 12.10.1.1 Diaphragm Design Force

Floor and roof diaphragms shal be designed to resist seismic forces from structural analysis, but shall not be less than that determined in accordance with Eq. 12.10-1.

This section further discusses limitations.

I use this value unreduced. I figure during an earthquake you do not want your deck to yield/plasticize, you want your LFRS to yield and dissapate the energy - If the deck were to plasticize and such your load transfer would change to your LFRS. So this force should be high compared to LFRS.

 

[jittles]

I would disagree with structSU10. Allowable level indicates you use ASD load combinations, i.e. .7E. Similarly, you would use ASD load combinations to determine the area loading before you go to the vertical loading tables for the same steel deck.

 

[MrHershey]

Generally steel deck catalogs list everything for allowable stress design, so you'd use 0.7E. You'd have to verify with whatever deck you're using, but I haven't seen one where that wasn't the case.

 

[JAE]

I've always used .7E for deck diaphragm - when working off allowable deck diaphragm tables.

The code has provisions for minimum and maximum diaphragm loads so that is taken care of in the code and you don't need to further use additional loading on it.

However, you can always (and probably should be) a bit conservative with metal deck diaphragms due to large variations in fastener/weld installation quality.

 

[UcfSE]

The safety factors are different for seismic loads. Make sure you're checking those out too to be consistent.

 

[frv]

I was going to mention the same thing UcfSE did. Some manufacturers list their allowable capacities based on wind, as opposed to seismic, so you'll have to adjust the allowable for the lower factor of safety used in seismic.

 

[SteelPE]

After posting, I remembered that I had a SDI manual somewhere. I found the book and figured that the under seismic loading the omega is 3.0 vs wind loading at 2.35. So I am going to figure my deck using an omega of 3.0 with a shear of 0.7E.