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RE: Seismic requirements in NYC

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If they are using the 1990 UBC as stated (should be 1991), then the R of 8 is correct, however it is only correct if the appropriate formulas are used from the 1991 code.  R values were reduced when the seismic base shear formulas were rewritten for the 1997 UBC.  You cannot compare R values from different codes unless you also compare the formulas and results that are derived from their use.


Seismic detailing requirements in the 1991 UBC were based on zone.  Also, even if wind governs design, the structure still has to meet the necessary seismic detailing requirements. 


From: Anantha Narayan C.K. [mailto:anant_27(--nospam--at)]
Sent: Tuesday, September 19, 2006 10:24 AM
To: seaint(--nospam--at)
Subject: Re: Seismic requirements in NYC




For a braced frame with shear walls, R of 8 seems to be high. For a SCBF and a special concrete shear wall, a R of 6 is specified both by IBC and ASCE.


Maybe I am missing something, but R of 8 seems high for the system specified.




Kyle Delabar <kadelabar(--nospam--at)> wrote:

Hello All,


I am designing the bracing connections for a mid-rise (approx. 15-story) residential building in Manhattan, NYC.  The lateral force resisting system consists of braced frames and concrete shear walls. The EOR has indicated an Rw = 8 on the drawings and references the NYC building code.  From what I gather, the NYC building code follows UBC 1990.  I know that if this were somewhere else with IBC as the code, I would be thrown into seismic detailing of connections because R>3, but I do not see this requirement in the NYC code.  The EOR has provided design brace forces on the elevations.  Is there any such seismic detailing requirement or can I just design the bracing connections for the loads given?  I understand that this question might be better directed to the EOR, but I wanted to know the correct answer before asking him. 




K. DeLabar




Structural Engineer

Bliss and Nyitray Inc.

Miami, FL - 33134


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