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Re: Load Paths

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Bill-
I agree with you. But let us assume for the purposes of discussion, that either the small panels immediately adjacent to the windows don't meet the aspect ratio limit (say they are 2' wide with a 5' tall window between them), or that the shears in the perforated wall are too big--what then? Of course the triangular wall segment above would be sheathed & nailed to bring the roof's load into our shearwall (& I suspect nobody is strapping the low end of the rafter down to the outboard corner post as Thor has suggested previously :o)
1. Steel frame
2  Simpson portal frame
3. A quasi portal frame with regular Simpson panels(or Hardy Frames) using some kind of beefed-up top plate like a 4x? PSL 4. Or full height posts (sized for the wind load) adjacent to the Simpson panels

I guess I've used all four, depending on the circumstances. However, I would never try Dennis' suggestion to simple blow off the plain language of the code regarding aspect ratios. "It's as good as/better than conventional framing" would never fly in a litigation, & I don't think it's a rational approach for an engineer to take with these situations. Since there doesn't seem to be much column load, I don't see how to approach it as a buckling problem. Sizing the posts (or header) for wind load usually seems adequate, but maybe I'm getting too adventuresome in my old age.
Chuck Utzman, P.E.

Bill Allen, S.E. wrote:

Dennis -

I'm not sure I ever said the king post wouldn't work, I just wouldn't do it
if I couldn't analytically justify it. In either case (the king post in your
previous problem or the shear wall in the jpg I'm referencing where the top
of the shear wall is laterally supported by a top plate spanning between
cross walls) you've got a column pinned at the bottom and laterally
supported by a spring at the top. I'm sure someone somewhere (maybe even
since Timoshenko) has developed the critical buckling load for a column with
these boundary conditions, but I don't have it in my library. If I did, then
I would possibly have a different conclusion.

More than likely, relative to the jpg I'm referencing, I would have a
tendency to use full height gable studs, run the shear wall up to the
sloping top plate, consider the height of the shear wall segments the
average between the high and low point (of each segment) and provide
strapping around the opening creating a wall frame. To me, that would be
easier and more straightforward than developing the critical buckling load
considering a spring top support, determining the spring stiffness and
distributing (via details) the force in the spring throughout the structure.

With regards to using judgment, sure, that's my first tool in my toolbox.
But I'm not going to use a scoring system based on how often someone (or
some entity) has been right or wrong (I might not ever use myself!). I'm
really impressed that you've never been wrong. Who knows, maybe on my next
project, I'll defend my design by saying "Dennis Wish said it was O.K." :o)

Regarding the conventional construction argument, I never have that debate.
Maybe it's just the clientele I have; I don't know. I just know that I'm on
the side of the debate that a prescriptive method should be more restrictive
than an analytical method.

Regards,
	
T. William (Bill) Allen, S.E. (CA #2607)	
ALLEN DESIGNS	
Consulting Structural Engineers	
http://www.AllenDesigns.com	
V (949) 248-8588	 .	 F (949) 209-2509	

||-----Original Message-----
||From: Dennis S. Wish, PE [mailto:dennis.wish(--nospam--at)verizon.net]
||Sent: Thursday, February 03, 2005 7:19 AM
||To: seaint(--nospam--at)seaint.org
||Subject: Re: Load Paths
||
||Bill,
||I looked at it - it is the old hybrid shearwall. They have just
||introduced a new light-gauge steel panel similar to the Hardy Panel and
||this may resolve your issues related to out-of-plane forces.
||I understand your concern, and you can limit your H/t ratio by trying to
||analysis out-of-plane buckeling - it's just that with few have done a
||sucessful analysis and there is nothing in the ICBO Seismic Design
||Manual that covers this. I just don't have faith in it as our last
||debate suggested that the king-post supporting openings in excess of
||8'-0" won't work in bending. However, there is not recorded information
||of failures even if the numbers in the strong direction don't calculate
||out. I don't have a problem stamping my work as I figure that the
||Seismology committee is anything but an expert on light frame
||construction and has done more harm than good to the methodology. The
||answer is simply to compare prescriptive conventional framing to
||engineered design. The walls can be designed to 10-feet in conventional
||construction but may not calculate in full-compliance. So regardless of
||whether your stamp is on the project or not, there is a strong argument
||probably coming from NAHB-RC to support taller walls subject to
||out-of-plane forces.
||Go figure - I trust my judgement first before I trust the opinion of the
||Seismology committee on out of plane forces - they have been known to be
||wrong :>)
||As to potential liability, one way or another you end up fighting them
||using the conventional construction argument in your favor. The issue is
||life safety and major structural damage - the same prevention that is
||suppose to be protected by conventional construction.
||Dennis
||
||
||Bill Allen, S.E. wrote:
||
||>Dennis -
||>
||>There was no attachment to the message but a link to a jpg file on my
||>website. Don't worry, it's safe to open a jpg as you know.
||>
||>Here's the link again: http://www.allendesigns.com/images/strongwall.jpg
||>
||>I understand your argument about items in a wood framed structure which
||adds
||>to the stability and are not usually considered in the analysis, I'm just
||>not willing to put my stamp on that kind of detailing. After all, if
||>something does fail, what's my defensible position?
||>
||>Anyway, look at the picture and we can talk more.
||>
||>Regards,
||>
||>T. William (Bill) Allen, S.E. (CA #2607)
||>ALLEN DESIGNS
||>Consulting Structural Engineers
||>http://www.AllenDesigns.com
||>V (949) 248-8588	 .	 F (949) 209-2509
||>
||>
||>
||>
||
||
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