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RE: RESIDENTIAL: What A Drag

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Bill,

Get out of residential work now, while you still can and you still have some sense of sanity! 

 

-----Original Message-----
From: Bill Polhemus [mailto:bill(--nospam--at)polhemus.cc]
Sent: Monday, August 30, 2004 8:54 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: RESIDENTIAL: What A Drag

 

The plywood shear panel actually is what I had in mind as a “truss”.

 

Thanks for clarifying that for me.

 

The problem with the “let’s make sure we have a common double-top-plate elevation available throughout” is that home designers (and home buyers) don’t give a rip about it. They want “interesting architecture” (can’t blame ‘em), and so they want ME to make it work.

 

However, since few homes here in our area are engineered, when the typical contractor encounters plans of this type, they make stupid comments to the owner or developer, “I don’ know why this goober of a nengineer is a-doin’ it this way! Ah bin buildin’ houses fer tweny-sumpin’ years and Ah never seen it done like this!”

 

(Of course, the notion that you can do something consistently WRONG for “twenty-sumpin’ years” doesn’t seem to enter their minds).

 

Finally, as I’ve said before, this is NOT “earthquake country,” but it IS high-wind country. It is conceivable that we in Southeast Texas will be enjoying a storm event akin to Hurricane Charley in not so very many years, and as we’ve stated here before, high winds will give a residential structure more of a fit than an earthquake.

 


From: Nels Roselund, SE [mailto:njineer(--nospam--at)att.net]
Sent: Monday, August 30, 2004 10:40 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: RESIDENTIAL: What A Drag

 

Bill,

 

In earthquake country, interconnection of all of the parts of the building is important -- generally requiring "drag struts".  This is especially important in residential buildings in which major components of the mass of the building are not necessarily in the vicinity of available shear walls [or other vertical lateral-load resisting elements].

 

My first goal is to establish a common top-of-double-plate elevation for each story throughout the building, and keep the drag forces in the double plates.  When this goal becomes impractical, some other way of maintaining the interconnection is needed.  Sometimes plywood-sheathed shear panels that reach from the common plate level up to the "roof at some arbitrary elevation above" is needed.  I think that the plywood-sheathed panel serves the function that you had in mind for trusses -- sometimes a steel "column" in flexure can be the element that "reaches up".  You need to provide for overturning resistance for plywood panels.  Residential building designers don't make it easy -- persevere! -- it's important.

 

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net