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RE: Load Paths

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No, not if the top is at the top plate. The way you were explaining your
solution number 3. I guess I didn't understand your definition of "quasi".
But, if you're intending on putting a hinge in the wall then, yes, I think
there's a stability problem.
	
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 4:03 PM
||To: seaint(--nospam--at)seaint.org
||Subject: Re: Load Paths
||
||Bill-
||Are you suggesting that the Simpson Portal frames have some hitherto
||undetected lateral stability problem?
||I aplogize for not following the previous thread of Dennis' more
||closely. It went through at a time when I was too busy (& Dennis can be
||a little prolix sometimes :o)  I'll try the archives if someone
||remembers the topic heading (searching under Dennis Wish isn't practical
||:o)
||Chuck Utzman, P.E.
||
||Bill Allen, S.E. wrote:
||
||>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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