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Re: Seismic Joints

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Great, thanks Doug...good to know.


On Thu, Sep 10, 2009 at 2:56 PM, Doug Mayer <doug.mayer(--nospam--at)> wrote:



As Gary mentioned, the SRSS for building separation will be back in the 2009 IBC and hopefully in the CBC soon thereafter.  Luckily, I found out about this early on when I had to deal with a seismic separation and I was told on good authority that it should still be calculated using SRSS.  I’ve done a couple of buildings with separation since then using SRSS and I haven’t been called on it yet.


Doug Mayer, SE

Structural Engineer


From: Ehrlich, Gary [mailto:gehrlich(--nospam--at)]
Sent: Thursday, September 10, 2009 10:48 AM
To: seaint(--nospam--at)
Subject: RE: Seismic Joints




Don’t know if this helps any, but the SRSS method was reintroduced into the 2009 IBC. New section 1613.6.7. I believe the SRSS method will also be in ASCE 7-10.



Gary J. Ehrlich, PE
Program Manager, Structural Codes & Standards
National Association of Home Builders (NAHB)
1201 15th Street, NW, Washington, DC 20005
ph: 202-266-8545  or 800-368-5242 x8545
fax: 202-266-8369

Attend the 2010 International Builders' Show
January 19-22, 2010, Las Vegas, NV


From: Gerard Madden, SE [mailto:gmse4603(--nospam--at)]
Sent: Thursday, September 10, 2009 1:09 PM
To: seaint(--nospam--at)
Subject: Seismic Joints


The ASCE 7 makes a very vague statement about building separations in section 12.12.3

In the good old UBC, we were using SRSS to determine the gap to avoid pounding.

The IBC 2006 Design guide volume I indicates that this gap should be the SUM of the inelastic deflections.

So, say for a building with a drift limit of 1% (an essential facility) with 50 feet to the roof, the gap would need to be 8.5" under the SRSS method. Under the IBC example it would need to be 12"

If I had a regular occupancy building and could use 2.5% drift, then I would need a 30" joint

50 feet is about a 4 story building....are we really going into 24 " seismic gaps for 8-9 story buildings now?

Feedback appreciated.