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RE: 2007 CBC special seismic load combinations

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Glen,

Let me quote one more section from Breyer’s “Design of Wood Structures” 6th edition on page 2.43 last paragraph:

 

“ASCE 7 Sec. 12.14 is titled Simplified Alternative Structural Design Criteria for Simple Bearing Wall or Building Frame Systems. This section provides a simplified version of the equivalent lateral force procedure, for use on a limited scope of buildings. Use of the simplified procedure should result in roughly equivalent results. Because the scope of the  buildings is limited, there are a number of checks in the general procedure, which do not need to be considered in the simplified procedure. ASCE 7 Sec. 12.14.1.1 provides a list of 12 scoping criteria that the building must meet in order to be designed using the simplified procedure. Among the 12 there is one that will be problematic for a number of wood-frame buildings. Item 11 says the simplified approach is not permitted in structures with system irregularities due to in-plane or out-of-plane offsets of lateral force resisting elements. An exception permits offsets in shearwalls in two story buildings of light-frame construction, provided detailing requirements are met. Because offsets in shearwalls from story to story are so common in wood-frame buildings, there are likely to be a good number that do not qualify for this procedure. For this reason this book addresses the equivalent lateral force procedure instead. “

 

So, not only did the article you noted below verify that the Overstrength Factor needs to be considered, the use of this procedure is very limited and still somewhat confusing J

 

Dennis

 

From: Glen Underwood [mailto:gunderwood(--nospam--at)clarkpac.com]
Sent: Wednesday, May 28, 2008 8:22 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: 2007 CBC special seismic load combinations

 

Here is a good "Code Simple" segment by SK Ghosh and Susan Dowty published in the Feb 2008 edition of Structural Engineer Magazine.

 

It discusses the conflicts between the standard (ASCE 7) and the Code (IBC) as well as the supplement to the IBC that clarifies - and the fact that supplements are not usually adopted by jurisdictions.

 

In CA, we would have to wait for a supplement to the CBC (technically).

 

Link:   http://www.gostructural.com/article.asp?id=2605

 

 

Glen A. Underwood