Tension-Only Bracing in Seismic Zones

[SmithJ]

Hello All,

I know that one is not supposed to use tension-only bracing in seismic zones D and above (4 and above in the UBC). However, I can not seem to find the particular section of the code where this is addressed.

Does anyone have a reference to this? And also what portion of the bracing force needs to be resisted by compression in the bracing members?

I believe the rational behind this is related to the Northridge earthquake and its after effects but any light that can be shed here would be much appreciated also.

Thanks in advance,
JS.

 

[JAE]

IBC via AISC Seismic Provisions for structural steel -

In the AISC document - under the various types of braces, there is language dealing with limiting the max. "all compression" or "all tension" braces to between 30% and 70% of the seismic demand.

 

[SmithJ]

JAE,

Thanks for your response. When you refer to AISC document, I am assuming you mean the ninth edition of the Steel Construction Manual. Could you verify this and also what section you are speaking about?

Thanks,
JS.

 

[swearingen]

Don't rely on the 9th edition of the Steel Manual for earthquake information. It is way behind the times - it was written before Northridge - many updates to the research have been done since then.

 

[JAE]

Not the Steel Manual, rather, the AISC "Seismic Provisions for Structural Steel Buildings". This is referenced in the IBC (2000) in section 2212.

The latest Seismic Specification is here:

New AISC Seismic Spec

The 1997 versions here:

1997 AISC Seismic Provisions

 

[SmithJ]

I believe I found the link to the document JAE was referring to:

http://www.aisc.org/Content/ContentGroups/Documents/2005_seismic_provisions/SeismicProv_web.pdf

I am still trying to find the exact section that makes reference to what we are discussing here.

Thanks.
JS.

 

[SmithJ]

Sorry, I posted the above before reading JAE's response.