Seismic Design Category D Immediate Occupancy

[siuceric21]

I have a structure I am laying out that is approximately 200' tall, in Seismic Design Category D, & has an "immediate occupancy requirement". The immediate occupancy criteria defines the structure shall retain pre-earthquake design strength and stiffness. To me, this means not of the structural elements can not go into a yielding condition. My question is regarding the system and R factors that should be assigned to this structure. My thought is a follows:

1) The structure must remain complaint w/ ASCE 7-10 Table 12.2-1. Thinking the structure will be D.2 (Steel Special Concentrically Braced Frame) and all of the special detailing requirements involved.

2) Loads applied to the Lateral Force Resisting System must be applied using an R=3 to keep the structure compliant with the immediate occupancy criteria.

Any issues with this design approach? I realize this will result in very high lateral loads, but it is required to keep the structure from the yielding condition.

Thanks in advance for any help.

 

[azcats]

Any consideration or Risk Category and the Seismic Importance factor? Using category IV would increase seismic loads by 50%. But that's still somewhat less than your proposed R reduction.

Yeah - I don't know what I'm talking about on this subject...

 

[structSU10]

It sounds like using the principles of ASCE 41 for performance based design could get you what you want, but its hard to relate it to ASCE 7 level loading / R factors. I think the ASCE 7 risk category is supposed to enhance to post-EQ performance criteria.

 

[siuceric21]

azcats - The risk category, in my mind, reduces the probability of collapse, not limit the yielding.
structSU10 - I will look into the ASCE 41 a little more and see if I can find anything that defines the performance I need. ASCE 7 risk category certainly enhances EQ performance, but I do not believe it is to the point I am looking for.

Thanks for the input!

 

[sticksandtriangles]

Terms like "immediate occupancy" are explicitly defined in ASCE 41 as structSU10 mentioned.

There is no need to use engineering judgement to assess immediate occupancy if you are using ASCE 41.

Hopefully the means in which you are evaluating the "immediate occupancy requirement" is explicitly outlined in your contract.



S&T