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Seismic Bracing

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Dormer1975

Mechanical
Aug 31, 2007
25
Ok, I wanted to get a thread going on this topic. This thread is about 2 things: 1)Determination of whether you have to seismically brace and 2)Seismic bracing in 13R systems. I have done a decent amount of research on this subject but please correct me if I'm wrong on any of this.

The owner of the company that I work for has been in the fire sprinkler industry for over 35 years. In his experience, seismic bracing of 13R systems has not been done predominately. I know in our region at least it hasn't been enforced. I believe this is due to the Uniform Building Codes that had been the authority prior to 2002. In the UBC, the country had been separated into "seismic zones". In the part of the country and state that we are in, those zones indicated we did not have to seismically brace, period. We seismically braced all of our NFPA 13 systems anyways, as a company policy. Then, the International Building Code was adopted in our state in 2004. We currently use the 2006 International Building Code and things have changed. In the IBC, if I understand it correctly, determination of whether to seismically brace depends on what the building site "Seismic Design Category" is. This is a letter range from A to F. This was similar to the seismic zones of the UBC. The way you get your seismic design category depends on the site class (soil composition) and the spectral response accelerations, Ss or S1 (0.2 and 1.0 second - still researching exactly what these are and which we use). Needless to say, on a project, the structural engineer should provide either the seismic design category, or the Ss values to determine the seismic design category which in turn indicates whether seismic bracing is required. I'm still searching for the literature in the IBC that dictates if your site is in a Seismic Design Category A, B, C, D, E, or F, you will or will not seismically brace. If anyone knows where this is please let me know.

Ok, regarding seismic bracing of 13R systems. I recently did a project for a 5-building 2-story housing development in which the AHJ asked about seismic bracing (13R systems). It's stick frame construction and we use Blazemaster CPVC with "no block", "stand-off", and "pipe strap" hanging methods. In addition, we drill through TJIs in accordance with truss manufacturer specifications. All said and done, the installation is going to move with the building in the event of an earthquake. I went ahead and installed sway bracing as the project was moving forward but am looking for clarification for future 13R projects.

The way I understand it though, NFPA 13R defers to NFPA 13 on sway bracing. (NFPA 13R 6.7.6) So, sway bracing 13R systems differs in no way to 13 systems. Is this correct?
 
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Ixaon,

Answers to your questions in no particular order.

You must follow NFPA 13 rules for 13R installations.

You will use the Ss (0.2) spectral accelleration value, and obtain it from the USGS web site based on latitude and longitude coordinates of the site.

As far as the specifics of the seismic bracing referred to in IBC 2006, you may have missed it, but the reference document is ASCE 7, 2005 edition. You will need to look at a copy of this document to understand where everything comes from.

Hope this helps.
 
Thank you much for the responses. Actually, I did see the reference to ASCE 7. I'll have to obtain a copy of it to further educate myself. I wasn't sure if all my answers could be found in the IBC.

I'd be interested to hear from other fire sprinkler contractors on their practices regarding seismic bracing of 13R systems.
 
For new builds, the project's main construction documents should have most of the seismic information you may need in them, usually done by the structural engineer of record following IBC Chapter 16.

Don Phillips
 
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