Seismic detailing of existing buildings

[goodriws]

Our firm has been awarded a new hospital addition in a high seismic area. Governing code is IBC 2009. Site Class is D, spectral accelerations are high, so the SDC is D and by a mile. The structural narrative of the RFP lays this out and I have verified. However, the structural narrative of the RFP indicates use of R=3 steel moment frames per provisions of the International Existing Building Code. I am not aware of such provisions and have been unable to find them in my research. So:

1) Where are these provisions?
2) What are the ethics involved here? In such a high-risk area, should I even consider R=3 if the IEBC does indeed allow it? (The existing building is old and probably is detailed equivalent to R<3. The addition will be independent.)

Thanks in advance for your help.

 

[msquared48]

If you are keeping the addition separate, and no structural work is being done in the original structure, it does not have to be upgraded.

However, after talking with your superiors, if they agree, it would be prudent to write a letter to the hospital administrators informing them of your concern.

Mike McCann
MMC Engineering

 

[goodriws]

Thanks Mike. Sorry about the confusion, but my question is related to the SLRS of the new, independent addition. Not the existing structure. The existing structure won't be touched, that is fairly clear. But the addition - I just can't see how it can be an R=3 system.

 

[OHIOMatt]

I guess I am not quite sure what the question is. Are you retrofitting the existing structure? Is your concern for seismic separation?

 

[goodriws]

The existing building is load-bearing CMU with steel joists, built decades ago. The addition is adjacent to existing, but independent (horizontal addition, not vertical). The existing building, its required upgrade, etc. is NOT the question.

The question is related to the NEW construction (the addition which is not attached to existing). The structural narrative indicated R=3 system was possible per provisions of the IEBC. Everything I am reading says that the new work must conform to the current building code, which would be IBC 2009, which would require R>3.

My question is: where in the IEBC does it allow for an independent addition to be R=3, even though the SDC is D?

 

[OHIOMatt]

The addition needs to be designed per the current building code (IBC), not the existing building code (IEBC). Perhaps you should simply call the engineer that put the narrative together to discuss this provision.

A system were R=3 most likely will not result in a very economical design. In addition, I am not even sure what system would qualify for use in this scenario.