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RE: Load Paths

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Chuck -

My opinions on the four options you presented are:
1. I don't think that would be very popular but may be an option after
reviewing my opinions on the remaining options.
2. I don't think this is any better than what is shown in the jpg. IMO,
there is still a lateral stability issue.
3. If this solution includes a horizontal top plate at the location shown in
the jpg, I don't see any improvement. The 4x top plate is an intuitive
provision to provide an adequately stiff spring support at the top of the
wall. I don't know if a 4x plate would be adequate until I solved the
buckling problem.
4. The full height posts is a solution similar to Dennis' problem a few
months ago and, IMO, requires the same buckling solution.

What I would do (in order):
5. Ask the architect to change the aspect ratio of the windows. In the past
and in my practice, this has been 100% successful because the alternatives
(I present) are much more expensive. After all, the architect is usually
accountable to the owner in controlling costs. In this case, it would
require changing the pier to 2'-6" and a 4'-0" opening. As one of my female
architectural clients used to say "What's 6 inches between friends"? :o).
6. If the opening was *really* that important and a steel, 2 story frame was
out of the question, then I would be forced to find the solution to the
buckling problem and then provide the elements which would provide the
lateral stability.

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: chuck utzman [mailto:chuckuc(--nospam--at)pacbell.net]
||Sent: Thursday, February 03, 2005 9:53 AM
||To: seaint(--nospam--at)seaint.org
||Subject: Re: Load Paths
||
||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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