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RE: IBC2003 for single family

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I don't design with the IRC. I only refer to it if there's a special issue I am required to address which mentions the code.  I find many of the charts and tables less conservative than my own calculations and experience.

My favorite examples come from the foundations section:

6" x 6" footings are allowable for single story residences, as are 7" wide footings for 8" hollow cmu walls.  "Luckily", these are unreinforced, or you'd have a mighty hard time getting a 3" clear cover on your rebar in a 6" footing. (Yes, yes, you can form, but if you're putting in a 6" footing, are you really going to use a form?)

6" solid units (not grouted) or 8" hollow units are allowable for basement walls with up to 6' of fill (for a 6' tall wall), and 10" solid (not grouted) blocks are okay for 8' of backfill with an 8' wall. The thought makes me shiver.

These fine examples of living on the hairy edge are, admittedly, under the best of circumstances (4000psf bearing / gravel/sand soils). Nonetheless, after all the residential basements I've been in with clean horizontal cracks running the entire width of the wall, I just don't put a whole lot of trust in unreinforced masonry.

At 03:08 PM 8/5/2004 -0400, you wrote:

Eli- It looks as though you need to read section 2308 carefully to see what it specifies for your structure.  I don t think that section 1614.1 exception #2 relieves you from all seismic requirements it simply says the structure isn t required to be analyzed per section 1616.1. 

As far as the IRC goes, we use it for single family structures. Of course, for lateral analysis you re referred to ASCE 7-98 and IBC2000

 

Jen

 

-----Original Message-----
From: Eli Grassley [mailto:elig(--nospam--at)psm-engineers.com]
Sent: Thursday, August 05, 2004 2:42 PM
To: seaint(--nospam--at)seaint.org
Subject: IBC2003 for single family

 

List:

We are taking the leap into IBC world up here in Washington, and I m hashing through the lateral force provisions for design of an engineered single family home.  I ve noticed a tasty exemption in IBC2003 section 1614.1, exemption 2&basically stating that single family light frame designs in seismic design category A, B or C are exempt from ALL of the earthquake design sections (i.e. just design for wind).  Is this wishful thinking, or am I missing something here? 

 

As a related question, has anyone delved into the IRC??  Does this code apply to engineered single family structures, or only to prescriptive design?  In other words, is the IRC only intended for architects and builders to use?  I have heard of a case where a structural engineer was sued because they used the prescriptive design procedures in their design of a wood framed house.  I guess the courts want to be sure us engineers actually use all those fancy buttons on our calculators.

 

Eli Grassley

PSM Engineers

Seattle

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