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Shear Wall Hold Down Distance Apart

Shear Wall Hold Down Distance Apart

Shear Wall Hold Down Distance Apart

(OP)
When designing a wood shear wall with gypsum board or wood diaphragms, is there a maximum distance the hold-downs can be from each other?  If a shear wall is 20' long versus 100' long, the uplift is more for the 20' than the 100' so longer shear walls give you better leverage to prevent overturning.  However, 100' long walls seem more prone to buckling than 20'.

Thans  

RE: Shear Wall Hold Down Distance Apart

Yes, but there is probably a lot more dead load to resist the overturning too.  

Depending on the number of stories, I would be surprised if a Holddown was needed for a 100 foot wall, considering the dead load resisting moment.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Shear Wall Hold Down Distance Apart

(OP)
Thank you msquared48,

For the sake of argument, let's say that the lateral force is greater than or double the dead load resisting moment.  Is there a maximum distance between hold-downs?  I understand that a shear wall has a height:width ratio.  I don't find a length:height ratio.  At what point does a shear wall quit acting as a unit and buckle?  I understand the mechanical advantage of having a longer shear wall but how long can a shear wall be?

If the wall is viewed as a beam; at some point would there not be buckling in the wall or crippling in the web?  I know some perpendicular walls would help prevent this.  What if there are no perpendicular walls?  Mathematically, the wall could be as long as required but at some point the wall has to buckle if loaded, correct?  If so, what controls this?  I'm looking at the wall as being like a web in a beam.

If I also look at the wall in plan and consider it like a column with the lateral load being a vertical load, then l/r controls.  How does the theory of a shear wall control this buckling?

The inverse is understandable, the closer and closer I put the hold-downs, the less chance there is for buckling.  The 'height' of the column becomes less and less and the l/r becomes less and less.  This configuration will have higher overturning moments, yes, but the forces in the hold down and the end posts are purely tensile (compressive on the other end).  A 2x6 shear wall is going to have more stoutness than a 2x4 wall.  What prevents this buckling is lateral support at the floors and the resistance to bending by the studs but, for a high load condition, the studs would have to resist both bending and compression from the dead load at least for part of the wall.

My engineer does not believe in long, 'flimsy', shear walls which supposedly buckle like paper.  Consequently, he designed OSB wall modules 4' long with two hold-down, all-thread rods per panel, virtually doubled every 4', going the full height of a 3-story building.  This is causing much grief with my client.  He also does not believe in gypsum board shear walls which, in mid-Indiana, are used quite often.  I understand his reasoning and I agree that OSB is a better material but gypsum board is part of the cost of a building.  OSB is extra, $160,000 extra!  If I have enough gypsum board walls to handle the shear; then why use OSB if the client doesn't want to pay 'extra' because they 'always use gypsum'?

Design-build, you gotta love it ... or starve.

My question still stands; what controls the distance to hold-downs if anything?

Thank you

RE: Shear Wall Hold Down Distance Apart

I would have to take a close look at any shearwall with a stacked length:height ratio of 2.5/1 that had a uplift over 300#.
As for a single story shearwall 100' long, it is being braced by the diaphragm/foundation top and bottom so buckling due to shear is not a problem IMHO. Hopefully the diaphragm(s) is rigid enough or there are perpendicular shearwalls to maintain a vertical wall for the lateral loads perpendicular to the shearwall.
As for gypsum shearwalls the biggest problem with them IMHO is that in a code event they may crack. But the owner/contractor repairing the cracks will not know which walls are shear/braced walls (unless they review the plans). So they would not know which walls they can putty and tape vs the ones they need to replace the gypsum boards on. This is especially true of residential homes.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Shear Wall Hold Down Distance Apart

(OP)
Thank you woodman88,

Your response focuses more on the problem as I see it.

I'm thinking now that buckling due to uplift is not an issue because, theoretically, the uplift puts the whole wall in tension, correct?

Buckling due to shear or lateral load seems to be more of the issue.  I agree that the diaphragm(s) provide lateral support at the top and bottom.  Can you imagine any situation in which buckling of the shear wall would occur in shear; perhaps a 3.5:1 OSB wall?  Perhaps this is why shear wall diaphragms pull the nails out or the diaphragm pulls out around the nails in test failures.  If the horizontal diaphragm(s) buckle because of shear then they weren't designed properly.

Have you heard or seen or been involved in a design where perpendicular walls are used to laterally brace a shear wall?  What controls this; when are lateral walls required?  To me, that is the equivalent of a web of a beam needing web stiffeners because of high load or point loads.  Am I incorrect in viewing the wall as like a beam?

I view a building as nothing more than a cantilever beam divided into sections resisted by shear walls.  In some sense, the mechanism is either a box beam or series of 'I' beams in plan with flanges loaded and the web being a shear wall.  Doing the math that way is roughly equivalent to the floor+floor method.

Also, my engineer says dead load cannot be considered in resisting wind load.  Yet, I found a calculator that considers the outside perimeter wall weight and foundation for helping to resist or completely negate overturning.  That method seems reasonable but it also seems reasonable that the depth of the building and the associated mechanical leverage would go a long way too.  I've also used other engineers who include the dead weight to offset the overturning and resolve the remaining uplift into a proprietary T-Wall connection that transfers that load back into the foundation using 2x and lots of 16d nails and avoiding 'costly' Simpson hold-downs.  Yet others prefer the hold-down because it's much easier to inspect than counting hundreds of nails.  Which or who is correct?  Perhaps all since we're dealing with forces, code, and the fact that all engineers are different in how they resolve loads.  One shoe does not fit all.

Thank you
 

RE: Shear Wall Hold Down Distance Apart

I can't even imagine how a 100 ft. long shear wall would even need hold downs.

 

RE: Shear Wall Hold Down Distance Apart

CurlyQue
First, I think you are focusing on one element of the building (the shearwalls) without considering the overall structure. I do not see the shearwalls as beams, rather I see the structure as a cantilevered column.
Second, so far most of my long shearwalls have had perpendicular shearwalls attached to them. No I did not analysis where and when they were needed. Since they were there I new I could justify the long shearwall due to them if asked.
Third, whether you can use dead load to resist wind depends on which building code and method you are looking. As you have not given the code/method I can not answer this.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Shear Wall Hold Down Distance Apart

(OP)
I can imagine a vehicle going to Mars.  The question is how to get it there.

If a shear wall is 100' long, 100' tall, and has 100 mph load on a 100' wide wall contributing to it, will it overturn?  I imagine so; I don't have to do the math.  You might want to resolve it into smaller components but the point is still the same.

My point is at what length and or load combination will cause a shear wall to buckle because it's too long.  Maybe this situation will never happen.  Maybe shear walls just don't buckle because the overturning moment causes them to all be in tension.  Could the shear of such a wall cause it to buckle?  At some point it seems you have to consider the thickness and ability not to buckle.

My engineer doesn't want to use long shear walls because he says they will buckle like a piece of paper.  Gypsum board is not paper.  OSB is better than gypsum board.  Multiple layers on two faces or configured for 3 diaphragms of OSB is better than 1.  Masonry is better than OSB.  Concrete is better than masonry.  The thickness and the shear capacity of the material and configuration have some contributing factor.

The Fv of a steel beam is better than wood.  The Sx and I values are better for a beam with a thicker web than for a thinner one.  Yes, most of the work is done at the flanges but that is where the analogy breaks down somewhat.  The question I have regards the web, the thickness or stoutness of the material in the web or its lateral stiffness.  It seems that the depth to thickness ratio is important.  Or, is a piece of super-tough, carbon-fiber paper simply good enough.  It will never buckle when glued to toothpicks at 0.1" oc?  Thickness has to be a consideration, does it not?  Maybe I'm missing something (or a lot of things).

Diagonal bracing is steel frame. Although I can't understand why diagonalized metal straps can't be used to improve shear or get rid of it altogether.  That's what metal stud manufacturers and steel frames do.  Why not wood?  Shear gets resolved at the base and is resisted by anchors or fasteners.  Diagonalizing it all puts all the forces in compression or tension; there is no shear except in the diaphragm except in the deck which has a certain value of shear for members spaced a certain distance.  Wood panels have this requirement too, 16" or 24" center spacing minimum.  If this is true for plywood, then isn't it also true for a 2x4 wall versus a 2x6 wall or a 2x8 wall.

What is the advantage of having a 4', 'panelized', modular system with all-thread tie rods at each corner going completely up through the building.  Sure, it's much more 'stout' and eliminates dead-men at the hold downs but it's tremendously more expensive so I fail to see the economic advantage when enough gypsum board walls will do the same thing at virtually no cost especially for a 3-story building ... for god's sake.

What's the problem?  Code allows gyp but one structural engineer won't and so the building cost goes up $160,000?  For what reason?  So he can sleep better at night.  Why not fire the engineer and spend another $16 or $16,000 for a one who'll use gypsum if the owner only cares about the cost.  The point, I thought, was to optimize; sometimes gilded buildings are better; most times they're not.

I understand the value of having OSB.  If cracks appear in the gypsum board, then someone will stop to think about this wall being a shear wall, an important wall.  Red paint effectively says the same thing or red nails or a big sign: "Shear Wall!  Do not touch without consulting an engineer!".

The value-engineers and their supporting civil engineers are having a hay day with this item; like sharks in chum-filled water.

Thank you,

Thanks

RE: Shear Wall Hold Down Distance Apart

(OP)
Woodman88,

I too see a building as a cantilever structure.  But, in plan, when the shear walls and their contributing load walls are isolated, they do act like separate 'beams' in section; you do have tensile and compressive 'flanges' and a web which is what I see as the shear wall.

I'm interested that you did not analyse the lateral support but 'could justify' long walls because of the same lateral walls.  So, you see that they must or could have some contribution; you just don't feel it's necessary to include them in your calculations.  That's the 'feel' of a structural engineer for the largeness or smallness of a problem; the ability when to say, "nah! simplify, simplify."

The code is IBC.  The Method is ASD or LRFD, I don't know for sure.

I would be interested in your thoughts on the panelized system in my other post.

Thanks

RE: Shear Wall Hold Down Distance Apart

100 ft. long WOOD shearwall - 100 ft tall?  I have no imagination I guess.

RE: Shear Wall Hold Down Distance Apart

(OP)
JAE

I appreciate your input.

I really do.

I imagine you have an imagination, I guess, even if you don't believe you do.  Of course you were being facetious.

I am pursuing a point; not an absolute specific condition.  Obviously a 100' long shear wall 100' tall is a most probable improbability.  Try a 10'x10'x.001' thick shear wall instead with a 26,000 lb lateral load.  Say the dead load counter force is 0 which it is in some municipalities.

Let's do the math:  100 mph = 26psf.  100' high x 100' long load wall x 26 psf = 260,000 lb.  260K x 100'/2 = 13x10^6 lbft overturning moment.  / 100' = 130,000 uplift. / 150pcf = approx 10'x10'x10' chunk-o'- regular weight concrete, a big boat anchor.  Shear = V = 260,000lb / 100' = 2,600 plf.  There, that was fun.  Hedgehogs and Foxes are now both happy or foxes and hedgehogs are now both happy; however you want to put it. winky smile

Back to paragraph 2:  26,000 lb / 10' = 2,600 plf.  26,000 lb x 10'/2 = 130,000 lbft overturning moment.  130,000.00001 lbft / 10' = 13,000 lb uplift. / 150 pcf = approx 4.425381248 chunk-o'-regular weight concrete.

So now we've proven that a 100'x100'shear wall with 100 mph load acting on a 100' wide wall induces the same amount of shear in a 100' wall as a 10'x10' shear wall with 100 mph load acting on a 100' wide wall.  It's all in the width of the load wall; reduce that and you reduce shear; plain and simple.

The overturning moment is obviously 10x less mainly because the load is applied 10x closer.

The uplift is 10x less for the longer wall because it's 10x longer.  That's the mechanical advantage of a longer shear wall.

If the 100' long load wall is unimaginable, reduce it to 10' and chop off another zero (i think) from shear, moment, and overturning, it doesn't matter for my point, my question.

The point is that the shear remains the same for the tall condition versus the 1/10 condition.

The difference is that the load acts on a 100' long section versus a 10' long section.  That is, shear is shear and plf is plf.  Right?

Now, take that same 2600 lb load and apply it to a column 100' tall.  You'd choke on the l/r, right?  But, if you applied it to a 10' tall column you'd sleep at night ... except you'd wake up in a fright when you realize ... :

Now, Woodman says the diaphragm is braced at the floors, which it is.  That's the same as saying the column example immediately above is braced continuously and that column is 10' wide or whatever the floor to floor is.

The problem is we're talking about a wall that is .001' thick or a column that is .001 thick.  You wouldn't put a 2600 lb load on a column that's 3 1/2" thick in one direction and .001' in the other because your radius would be infinitesimally gyrational; rather irrational, right?  I know you can imagine that JAE.

So how come it's okay for a shear wall to be loaded laterally with a large load but not a column with the same proportions?  How come one engineer sees the wall is a piece of paper and another says that's okay?  Who's missing what ... because who's on first and what's on third?

I'm interested in what keeps the .001' shear membrane from buckling.  Is it the toothpicks at .01' o.c. or the thickness of the shear wall or what, the nails or the glue?  The tests and tables and all of that say plf, plf.

I haven't heard a reasonable answer to my question:  "Shear wall hold down distance apart?"  One engineer says 4' max; another says 20' or 50' or JAE says never 100'.  What's the difference and how do you calculate it?  It's got to do with thickness.  Why else would shear panels require 2x versus frames or spacing at 48" o.c.  I think it has to do with the 10' wide column example also being braced 16" oc vertically such that a 2x6 or a 2x8 should give more shear value up to the shear capacity of the panel itself of course.  It also has to do with how much you nail the shear diaphragm to keep that puppy from poppin'.  What if I put studs at 12" o.c. or 6" o.c.; I should get more value, right?  What keeps a 100' wall from buckling (or a 4' vs 40' for JAE winky smile)?

I also think it has to do with l/r, the length of the hundreds of mini-columns 1" wide and .001' thick spanning from stud to stud.  If that's the case, then a 100' shear wall will not buckle any more than a 10' wall.

The problem is, I don't believe that for the same reason I won't balance a book on a straw but I will on a straw/2.

That's why I've asked the question.

A lot of the problem is always in the question, right?  Put another way, a lot of the answer is in the problem.

CQ

 

RE: Shear Wall Hold Down Distance Apart

Well, for a wood stud shearwall with some kind of sheathing there are a couple of checks in the design that would mitigate "buckling" of the shearwall.

Say you have a 20 ft. long (not 100 smile) shear wall that is 10 ft. tall.  Lateral wind/seismic load along the top in plane.  You also perhaps have perpendicular wind occurring with the lateral wind.

Most stud wall shear walls have built-up end posts - say 3 2x studs - and then typical studs between the end posts.  The end posts have hold downs (if needed - as the wall gets longer relative to height the hold down requirements does go away).

With the vertical gravity loads (0.6 x Dead) and the lateral wind load, the wall assembly, in plan, is taking forces similar to a beam/column.  There is axial load (P/A) and axial force due to bending (My/I) where M is the overturning moment equal to the lateral force times the wall height.

y is the distance from the center of the wall (in plan) to the end posts.  I is a moment of inertia of the wall assembly.  This I value can be calculated based on the areas of the studs and end posts relative to the center of the wall.

With P/A +/- My/I you can calculate the maximum tension and compression forces in the end posts and in the individual studs.  Each stud will have a compressive force that begins to diminish as you approach the center of the wall.  The end posts, of course, have the highest.

You can individually check each stud against this compressive force and see if it is capable of resisting that axial load (and perhaps in combination with any perpendicular wind load that would apply).  If the studs all work, I don't see how the wall would ever buckle.

Now most engineers don't do the My/I for the hold downs, or even the end post axial checks, but rather take the overturning moment and force all the load into the end posts alone - ignoring the in-between studs.  

Hope this helps.  

RE: Shear Wall Hold Down Distance Apart

(OP)
JAE,

Yes, your approach helps by considering the assembly, the I value, and the Moment about the centroid of the wall.  These views at least address the bending in the wall due to uplift.

I want to discuss why an engineer who sees long sheer walls as 'flimsy' which would crumple 'like a piece of paper' would design a 4' panelized system with hold-downs at the corners of each panel.  How is this method stronger?

That's what generated my initial question.  If hold-downs at 4' is stronger, then, conversely, aren't hold-downs at 10' or 20' or (god forbid winky smile) 100' weaker?

I'll get back to you when I get a little more time.

Thanks again.

RE: Shear Wall Hold Down Distance Apart

A 3-story building with shear panels only 4' long will have very large uplift or compressive forces due to overturn at the end of the panels, and the tension rods will go slack over the years as the studs shrink slightly.

I have never heard of any limitation of maximum distance between hold downs, or the concept of long shear walls being "flimsy" and prone to buckling.

For a multistory, mutifamily wood structure in a low seismic, non-tornado nor hurricane-prone area, usually the endwalls are fully sheathed with OSB, the front and rear elevation walls have OSB walls as long as possible using perforated shear wall design around the windows, and the center long wall(s) (party or common wall - there may be 2 depending on fire rating requirements) are gypsum shear walls the full length of the structure, with few or no hold downs specified.

RE: Shear Wall Hold Down Distance Apart

I should amend my above post by adding that there would also be interior shear walls at certain partition walls aligned front to back, usually gypsum both sides of the wall, and perhaps OSB in some rare cases on the bottom story.

RE: Shear Wall Hold Down Distance Apart

(OP)
AELLC

Thank you for your post.

Your description (in two posts) is the design I think most were anticipating; especially the design-builder and the sub-contractor.  The owner is kind of hidden behind the design-builder.

I'm not sure if I made clear that the design has 4' panels at 4' oc.  There are several walls but the one I have calculations for is 48' with (12) 4' panels.  The configuration of the building is somewhat convoluted (architects winky smile) but these shear walls basically occur every 40' so one wall that jogs would be about 24' long with 6x4=24 all-thread locations, 2 per 4'.

The original design had the same configuration with 1 layer OSB on each side of double stud walls (4 total layers) which is mostly problematic for construction but can be done.  That got changed to a few more walls (in the long direction which makes no sense) with 1 layer each side of each double stud (2 layers) but with all-threads completely up through the building, 2 per panel at each corner or basically (2) every 4'.  There is no accommodation for shrinkage.  Now the design has anchor bolts at the corners of the 1st floor panels with 3"x4" square washers and straps at the 1-2 and 2-3 floor boundaries with A23 hold downs at 2' oc for the trusses all due to contractor budget who freaked when he saw the first design which cost $160K more (for 10 buildings)!  All panels are sheathed in OSB at 2" o.c. perimeter and 4" in field; basically maxed out all the way up.  

This design all seems a bit cobbled but my main focus is on why one would design a 4' panelized system if it's not any stronger or cost effective since you've never heard of such.  I have pictures of test panels with all-thread but never in a multiple-panel configuration like I'm saying.

Thanks

RE: Shear Wall Hold Down Distance Apart

In cases like this, usually the Owner or Builder submits the finished structural plans to a second, independent SE for value engineering.

RE: Shear Wall Hold Down Distance Apart

I did some research and found that the Simpson Strong-Tie people have something called the ATS system, and it does compensate for wood shrinkage. Is your SE spec-ing this? Maybe he had such a difficulty in this case he felt it was necessary.

Ar eyou saying the buildiong is very long, but the exterior walls are jogged every few feet? Maybe your SE is saying he doesn't believe a long, jogged shear wall is effective without buckling. I am not sure how the Code addresses jogged shear walls.

 

RE: Shear Wall Hold Down Distance Apart

(OP)
Yes,

In this case the project was on a tight timeline, foundations are in, and framing has begun.  The design-builder is getting letter from another engineer which they're going to wave in front of the inspector.  That won't do much good because the inspector won't say anything if it's not in the code or on the drawings.  I don't think the design-builder is going to get very far in trying to change anything because the engineer has to sign-off and, since the foundations are in, it's kind of late.

RE: Shear Wall Hold Down Distance Apart

I see a few problems with how your engineer is seeing this.

First, he is saying that the wood shearwall will buckle because it is "too long." That assumes that wood shearwalls act as units. They don't. Each individual panel acts as an individual resisting element with its own buckling capacity included into its listed capacity.

Second, the "too long" theory is viewing the shearwall like it is a column with a point load at the top. It isn't. It is being loaded along its length, and it is being unloaded along its length.

Third, by basically installing holdowns every 4 ft., the engineer is trying to resist the uplift each panel has to individually resist. This is understandable, except he is missing the other half of the equation. The panel "upstream" of the shear force provides the compression force needed to do this.

The three points above basically suggest that he is being extremely conservative by saying wood shearwalls act as a unit when it might be to their disadvantage but they also act as individual panels, without the influence of neighboring panels, when it might be to their disadvantage.

Lastly, how does he explain how having more holddowns will prevent buckling? If viewed in plan, holddowns resit forces in and out of the page, not in plane with the paper, which I assume is the direction you are talking about buckling.

If what you have presented and I understood it correctly, the engineer does not understand wood design and should not be doing this.

RE: Shear Wall Hold Down Distance Apart

(OP)
AELLC per 'did some research' ...

I'm aware of the ATS system that compensates for wood shrinkage; the  SE is not specifying this, just a standard all thread.  He objected to the contractor even using straps instead because he said the straps would pop when the wood shrinks.  So, he's aware of wood shrinking but doesn't accommodate it in the design of the all threads.  I did put a note on the drawings I prepared for him to tighten the nuts before putting on gypsum board.  That's the best I could do.

I'm saying the multi-family building is long, 150'x72' with exterior jogs every 12-20' and jogs at the midpoints interior to offset differences in units along a common-wall spine.

I see jogged shear walls as just being some walls oriented for wind in one direction and some for wind in the other.  Offset shear walls aren't necessarily a problem, you just can't get as much length as ones that don't so the uplift is going to be higher.  Some are only 8' long.

Thanks for your input.

RE: Shear Wall Hold Down Distance Apart

Well in that case the shear walls should have been in the range of 8' to 20' long.

Since the foundation is already in, why wasn't any red flag raised earlier?

RE: Shear Wall Hold Down Distance Apart

(OP)
Cadair,

Thanks for your post.

I agree with a lot of what you're saying but ...

To your fist point"  If they don't act as a unit then how can the overturning moment be resisted by two hold downs, one at each end of a 'long' wall.  You wouldn't be able to use the lever arm of the entire length so your point supports the engineer's position to panelize  You can sheathe shear walls in different ways: vertical, horizontal, or running bond.  The panels are also nailed to common studs, sometimes two where nail spacing requires.  As such, the wall does act as a unit although this specific engineer sees them as individual panels too.

To the second point:  From a structural viewpoint, the wall is being loaded along it's length but you can also view it as a column laterally loaded from floor to floor, having a width of floor to floor, but having a depth of the thickness of the wall.  Viewing it this way just means you're turning the problem on it's head (really on it's side) and viewing like it's a column to address the buckling issue.  As far as I know, this is acceptable in structures.  For example, a grade beam or footing when turned upside down structurally is like a uniformly loaded beam.  That's not saying I'm going to turn it upside down when it's built, of course not, but you can analyze it that way.  So too with this problem as I'm seeing it.  Forces are forces and you can view them as if they're floating in space.  Gravity is another force.

To your third point:  You're point is will taken.  It would seem as if the down force of the adjacent panel does counter the up force of the other.  If so, then the two negate so the resultant is zero.  How then is the overturning moment resolved; at the end points of a long wall as is traditionally viewed?  The endmost panels have no negating force so, according to your viewpoint, the first panel loaded would bear the entire overturning moment and the uplift would be that force divided by the width of the panel which is what, a 4' panel?  To follow your load trail then, the the force is sent from panel to panel and the downward force is taken up at the end panel, whatever it's 'width'.

To your last point:  I agree.  The hold-down forces are into the 'page', the foundation, the ground.  I am talking about looking at a shear wall as if it is a column on it's side with the lateral force acting as if it's loading the top of a column on it's side as I said in point two.

Thank you for your thoughts.

 

RE: Shear Wall Hold Down Distance Apart

(OP)
AELLC per 'well in that case':

I don't follow how you get to a range.  Some are 24' long, some are 48' long, some are 8' long depending on the wall layout by the architect.  There was no real thought about structure from the architect's position so the shear walls got shoe-horned.

Actually, the owner 'purchased' a design from an architectural firm in Texas to build in Indiana and the design-builder bid the project without structural drains.  They ball-parked a figure then came to us (me) and said we need a structural design ASAP.  We contacted an engineer who designed what we (I) documented.  The design-builder then screamed at the size of the foundations saying, after 2 hours of review, that they were 'too-beefy'.  They then screamed when the framing drawings and the infamous shear wall strategy came to light saying it's costing $160K more than their budget, whatever that is.

Isn't this how design-build works in your neighborhood?

The red flags weren't thrown because the foundation design and construction somewhat followed the framing design.

I think they call this SNAFU in army speak.  The design-builder was expecting gypsum board shear walls but did not make this expectation known in advance; they assumed all shear wall are done this way.  The engineer we hired apparently doesn't do those nor does he do 'long' walls.  So, this project has been sort of a perfect storm and I'm in my dingy between calamitous waves.

So now you know the rest of the story.


 

RE: Shear Wall Hold Down Distance Apart

OK I see. I never was involved in design-build for wood MFH.

Then the shearwalls should have been 8', 24', or 48' long maximum, maybe shorter.

Is it understood that a jogged walls cannot be counted as one shearwall? Every shearwall needs to be one straight panel, with or without a window opening. One strap or hold down at each end. The straps dont buckle due to shrinkage because they "grab" onto the end of studs only the distance required for nails to transfer the load, say 12" to 24", and the strap passes over the floor truss depth with minimal nailing.

If it dodn't cost much to temporarily stop the construction, I would guess it a possibility to re-engineer this whole mess with epoxied-in hold downs to the foundations, but that may snag because of high forces at each hold down makes your SE nervous about the regular continuous wall footing wasn't designed for those forces.

RE: Shear Wall Hold Down Distance Apart

CurlyQue,

They don't act as a unit. The overturning moment can be resisted by two holdowns because the middle panels cancel each other out. It doesn't matter if the panels are vertical, horizontal, running bond, whatever. They are units. They will be stronger if they share a common stud as that is how the compression in one resists the tension in the other.

Second point. Okay, I think I'm seeing what you are talking about in the right orientation. Now how does a longer (as in longer wall) mean it is more likely to buckle? I'm assuming stress is constant with varying lengths of wall. How is I varying? Which plane is I in?

Third point. Basically, yes. The holdown is to restrain the first panel. The first panel restrains the next and so on. An easy, conservative way to size holdowns is to take the capacity of the shearwall in plf and multiply it by the height of the wall. The holdown has to be that strong. Notice that it has nothing to do with the length.

Basically, the point is that wood shearwalls don't act as units but rather as individual panels. You don't have to believe me though. Ask the people who write the standard, the American Wood Council. www.awc.org


 

RE: Shear Wall Hold Down Distance Apart

(OP)
AELLC per "OK I see."  (and to JAE)

The shear walls are as you have stated, some short, some long.

It is my understanding that jogged walls cannot be counted as one shear wall as you stated.  Where the wall jogs, that jog takes load from the 90 degree direction whereas the other walls take load from the 0 degree direction.

The straps don't buckle; they can't because they're anly used to resist tension, the uplift force.  When the posts (wherever they are) are in compression then the straps can buckle somewhat due only to the fact that the compression member is compressed.  The nails, in that case, simply keep the straps from buckling.  The main point is that the straps are for tension only as I know you know.

Re-engineering did present itself.  The question became: "Okay, if you only want gypsum, then we'll have to get another engineer."  But the design-builder 'bought' into having OSB because they really didn't have the time to stop construction and wait for re-engineering.  That delay would have killed their schedule.  The owner needs the building done for rent by a certain date ... as usual.

It's all a case of inverse NASCAR: going too fast and slowing down or, how they put it: "You've got to slow down to go fast.  That seems counter-intuitive but it's true even for design-building; things take time and pushing to fast creates all sorts of needless problems.  But that seems to be the design-build industry it seems or, at least, that's been my woeful experience.

It's what I call 'The Conundrum' or, rather, 'The Conumbrain."  Scream and yell but go faster and cheaper, ASAP!

My main reason for the post is to try to determine whether the structural engineer we used for this project has a point.  Are 4', panelized, shear walls stronger than long, 'flimsy' ones.  If so, why?  I believe there is some merit in his approach but I don't agree with his math (divide total overturning moment by 12 panels and then by 4' per panel) because the resulting uplift is the same as if I simply divided by 48' and put two hold downs.  If he were to sum his moments, instead, and do it the way I was taught, then his uplift forces would be on the order of 6.5x less which would be a good reason.  But, if one looks at the panels as being 4' long panels with 12x less force then that's like saying I'm loading up a 4' 'column' with a 'downward' force instead of a 48' 'column' with more force.  From a column perspective that means my L/r is less and the 'column', the wall, is much more 'stout.'  From an axially loaded beam (a column on its side) that means the web is stiffer or has lateral web-stiffeners, the perpendicular walls as was discussed by woodman88.

I wanted to see how others view this engineer's approach.  And, I'm trying to figure out if there is a mathematical approach that verifies this structural approach.

With due respect for everyone's answers and they are all valuable, so far, JAE's My/I and P/A is the closest I've come to what I consider a structural approach.  I haven't made time to analyze it more closely but it's in line with what I was taught too many years ago.

Thanks again.
 

RE: Shear Wall Hold Down Distance Apart

(OP)
Cadair,

Your points are well taken.  I like that you have supported your position again and referenced another source.  I will look at AWC ... again.

Given your position, how is a shear wall with hold-downs at 4' stronger than one with hold-downs at 28'.  I'd say 100' but JAE would grimace.

I (not me) is in the horizontal plane just as you see 'I' <-- here.  That is, look at the wall as being the web of an I beam.  The beam is 10' long in the z axis projecting toward you (the height from floor to floor) the depth of the beam (the length of the shear wall) is say 40'.  The flanges of the 'beam' are the loaded walls, that is, the catchment, the amount of wall receiving wind force.  A building viewed this way, in plan, is nothing more than a bunch of I-beams side by side all 10' or 20' long or however high your building is.  The lateral force applied to the side of the building is the same as the one applied to the 'top' of these beams.  The I value is simply the area of all those walls (flanges and web) times their distances squared (important) from their centroids to a base point, the bottom of the I; how you figure all I values of any cross section square, I-shaped, C-shaped, any shape.  Woodman88 says My/I which is the same as saying Fv=Mc/I, the total overturning Moment times its distance (c or y in My/I)from the centroid of the I value divided by the I value.  You then can calculate what the actual shear force at any point in the I  value which, in this case, is actually shaped like an I beam.  Likewise, F=P/A which is the lateral load / the area of all the walls in the 'I-beam' in plan.

What I'm focusing on is how the wall is like the web of this 'I-beam'.  It is laterally braced at it's ends (the floors)so it is restrained in that respect like a beam cast into a concrete wall.  Apply the forces and you will see that the 'web', the shear-wall, will want to buckle if enough force is applied.  This can be corrected by adding thickness to the web or providing 'web-stiffeners', the walls in the room perpendicular to the shear wall.

You can see all of these mechanisms by playing with a shoe-box.  It is a good model except that your looking at two C shapes rather than one I shape.  Take the lid off (un-restrain the flange), apply a force to one end and you can see how the 'web', the shear-wall, wants to buckle.  What I'm focusing on is the web buckling with the lid still on.  How it will want to bow.  But that's all assuming the wall, the side of the box, wants to act as a unit which you and AWC say it does not because the box side is made of individual units and they 'tranfer' their loads adjacent to each other like soldiers shoulder to shoulder or that thing that has 6 or seven balls suspended and when you lift one and release it, it sends its force through to the unrestrained one at the other end and causes that ball to bounce upward.

This is what I've been taught.

The structural engineer we hired for this project sees things similarly but I haven't quite I haven't quite yet figured out what all is involved in analyzing a shear wall this way.

But, if what you and AWC says is correct then 'my' engineer is missing the point.

Thank you again.

RE: Shear Wall Hold Down Distance Apart

(OP)
Cadair,

Looking at the building as a bunch of I-beams is somewhat misleading because the wind force is transferred through the stud of the side walls up and down to the horizontal floor plates, the plywood deck, and then to the top and bottom of the shear wall.  The load is not transferred laterally along the wall to the end of the shear wall.  I only say the load wall is like a flange of an I beam because it represents that load area; the loads get to the shear wall through the floors, just to be clear that you know I know how the loads get there.

If you look at the 'I' shape as being vertical same as a wall section, the concept is similar because the lateral force would the be applied in the z direction (toward or away from you) but the buckling would be the studs and the panel deflecting in the x direction (left or right).

Why I'm looking at it the other way is that the force is lateral but I'm trying to determine how that affects the length of the wall as if it were a web buckling.

The difference is that I can see the force if the I is in plan view whereas I have to imagine the force coming toward or away from me if the I section is in section view.

The point is that in plan view, the structural engineer is placing  dots that represent hold down locations at 4' in the I section in plan and somehow this configuration is stronger than dots only at the intersection of the I.

What I see is that the dots are closer and that they are resisting lateral load like post-tensioning a concrete beam is stronger than  a beam that is not post-tensioned.  Put another way, the lateral load is divided up among the dots, the hold down locations, such that the force is applied to a 4' 'length' of web versus a 40' length of web; that is, the L/r, the length of the 4' wall has less than for a 40' wall.  It is like a column (the web) is only 4' high versus 40' high so the buckling would be less.

My head is spinning from all this rotating so I'm sure others are quite thoroughly confused.

I'm just trying to understand why a structural engineer considers hold-downs at 4' on center is somehow stronger than one with hold-downs at 40'.  That is all.

Thanks

RE: Shear Wall Hold Down Distance Apart

As for having holdowns spaced 4' oc. He may be considering the shearwall to be acting like a Perforated Shear Wall per the ANSI / AF&PA SDPWS-2008. See section 4.3.6.4.2.1 of it. You can get a free copy of it at http://www.awc.org/Standards/SDPWS.html.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Shear Wall Hold Down Distance Apart

Garth -

Where does it say in the Sect. 4.3.6.4.2.1 that those are hold downs at 4' oc? I interpreted it as anchor bolts at 4' oc and hold downs only at the ends of the entire shear wall, not individual segments (I have been using perforated technology since the APA TR-157 report first came out)

RE: Shear Wall Hold Down Distance Apart

AELLC - What it states is that the length of the full height sections of shear walls must be tied down for a plf uplift force. Do it 1' oc, 2' oc, 4' oc or whatever oc but do it.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Shear Wall Hold Down Distance Apart

i have 3 story wood shear wall with 12'4" total length and it has 6ft opening in center. So fully sheathed wall segment is 3'-2" and 3'-2" each side of opening. total ht is 30ft. Can i still use perforated shear wall approach.  

RE: Shear Wall Hold Down Distance Apart

Regarding, "Given your position, how is a shear wall with hold-downs at 4' stronger than one with hold-downs at 28'.  I'd say 100' but JAE would grimace."

It isn't. All fully restrained shearwalls (of the same material and nailing) are equally strong on a plf basis. Longer walls just have more length, so they can resist more force.

Regarding the I-beam idea. Thanks for the explanation so that I could see clearly. I agree with the other posters that say if the wall is long enough, the diaphragm will brace it via the studs.

Woodman may have a point if it is a perforated shearwall, then additional holdowns will add strength because perforated shearwalls are not technically always fully restrained. 4' o.c. is a little overboard, but if he can't figure out which is or isn't fully restrained...

It still has nothing to do with buckling though.

RE: Shear Wall Hold Down Distance Apart

(OP)
Cadair,

My hat's off to you.

I took your advice and called AWC.  I talked with Loren Ross who was very enlightening.  Wood shear walls are definitely not monolithic.  The forces are in the 'chords' and the panels just keep the rectangles from becoming parallelograms.  

I'm done pursuing bending in long walls.  A wood shear wall will fail before that ever happens.  If a hold-down fails, then the building basically crumples before it ever would overturn.

I asked Loren if this concept is in the AWC standard and he said it's not.  Loren said he's working on a document which describes what he discussed.

Do you know of any document that describes how wood shear walls work using chord forces?

Thank you so much.

And thanks to everyone else too.

 

RE: Shear Wall Hold Down Distance Apart

I haven't read all of the posts above but do have one question.  Is each 4' panel section(either sheathed with sheet rock or OSB) stacked next to each other, but the sheathing does not overlap from panel to panel? What I'm trying to determine is whether you have a line of individual panel sections only connected together by some sort of top plate and either the sill plates at the 1st floor and then either single or double top plates at each floor, but no connection between the panels at the mating studs.

RE: Shear Wall Hold Down Distance Apart

Old runner I'm not sure I understand your question. Typically Shearwall construction is "blocked" so you will have nails around the perimeter of each panel with your edge nailing requirement. Assuming you have an 8' top plate each panel will be nailed to the top plate sole plate and adjacent studs. Where the two panels meet they will be nailed to a common stud to create continuity. If the nailing requirements are low this stud can be a 2x if they are more tightly nailed it's often a 3x.  

RE: Shear Wall Hold Down Distance Apart

(OP)
oldrunner and jdgengineer,

Thank you both for reading through all of the posts.  I apologize for the length.  My main intent was to see how a 4' panel system is stronger than a 'continuous' shear wall; why the first won't 'crumple like a piece of paper' and the second, supposedly, will.

Each 4' panel is sheathed with OSB.  Because each is a panel, there are 2 studs so the panels are fully engaged to studs.  The studs are not, however, necessarily nailed together; the forces aren't negated by each panel.  Each panel works separately.  Each panel has a hold down anchor bolt with a 3" square washer and straps that tie the top of one panel through the floor system above to the next panel above.  Each 'full panel' is essentially 4'x30' which seems to conflict with h:w ratio.

Each panel is constructed in field and the studs are built as a typical wall but with double studs at each panel point.  Structurally, though, the panels are not tied together with 12d or 16d at 4" o.c. or so.

The engineer insists that all panel points have to be double 2x.  I think that's required for high load walls per code table but not for every wall; the code is somewhat ambiguous saying that plywood has to be nailed to a full 2x which to some means 2 edges on 1 stud.

We had another engineer look at the whole design because we were concerned that there might not be adequate hold downs at the ends.  The panels were analysed independently.  The result was that the design works ... a whole lot more than is required.  The design uses 33% of its capacity in wind loading and 66% of its capacity in earthquake loading which in Indy area is very nominal.  The overdesign is really a result of the engineer insisting on carrying the OSB all the way up through a 3 story building.  While I'm not a big fan of gypsum board sheathing for shear walls and other engineers I've talked to have a similar opinion, gypsum board does have some value, approximately 20-25% of OSB.  

The current debate is that the contractor or design-builder is over budget on these walls.  They say they do all of their buildings with gypsum board but I maintain each building is unique. a 50' wide unit (this building) is not the same as a 25' wide one; sometimes gypsum board isn't enough.  We talked about the design at the beginning of the year and gave them full opportunity to go with another engineer but they decided to go forward only to come back 3 months later and bitch about the cost.

So, apparently, you can design the shear walls as independent 4' segments with OSB and anchors at every panel point (netting 2 per 4') and drive up cost.  Or, you can have shear walls acting so the loads are transferred from one to the other per AWC (see Cadair)with the panels 'rotating' about their centroids and keeping the studs aligned.  I've never been able to get a document that shows how this works.  AWC says they're working on it.

Or you can have the latter without what I call boat anchors at each end like the current project I'm working on.  It was designed by the same engineer who reviewed the first project.  Their solution was to use 18"x18" thickened slabs, increase the slab from 4" to 6" and tie the anchors to the intersections and grab some of that 6" of concrete.  I ran some numbers and what I call extra concrete means I could have had twice as many boat anchors at 6'x6'x2' for 25'x30' units.

It seems every engineer looks at each situation slightly differently.  I can see that since forces can be resolved many ways.  But the key, I think, is to optimize; optimize truss layout, optimize materials for shear walls, optimize whether boat anchors are less concrete than a 6" slab for a 12000 sf footprint, optimize the cost to pay for the design.

As an engineer once said, anyone can build a  bridge but it takes and engineer to design one ... just barely.

Anyway, thanks again for your input.

CQ

RE: Shear Wall Hold Down Distance Apart

jdgengineer:  You are right about typical shear wall construction, but CurlyQue answered the question which hadn't been asked.  Basically each four foot panel is a shear wall section in itself - only connected together with top and bottom plates which distribute the lateral loads to each wall individually.  And that's why you would have to have holdowns at each end of the shear wall.   This is similar to tilt-up concrete panels when they are not connected at the vertical joints.

It's kind of an expensive way to this because the sheathing could have been offset at each side so that the vertical edge nailing could have been connected to the adjacent panel.  

As for the issue of buckling the studs, this is a simple calculation using first principles to check out the overturning forces.  I would also be looking at sill crushing as well as stud capacity.   

RE: Shear Wall Hold Down Distance Apart

Why would you want to use this method of separate panels as opposed to on long shear wall? You build the wall on the ground like normal construction and stand it up. Eliminates hold downs and is faster I would think. What is the reasoning for using this panel construction?

As for your analogies of the shearwall being similar to a cantilevered column or beam I'm not so sure about. Here is how I see it:
If you have a 10' tall story height with a 100' long wall your flanges=chords at the end of the wall and the depth of the beam/column is 100 ft however it is braces top and bottom so it is as if you have a plate on the top and bottom of your beam column to help prevent the web from buckling. So really it seems to be this 'weird' plate subject to shear and pinned on all side analogy. Or so I think.

EIT
www.HowToEngineer.com

RE: Shear Wall Hold Down Distance Apart

Seems to me the SE of record used this 4' panel method as a way of simplifying his calculation effort at the cost of construction economy.

RE: Shear Wall Hold Down Distance Apart

(OP)
RFreund and AELLC,

The SE of record maintains that this 4' panel method is stronger than a 30' or 100' long traditional wood shear wall.  Again, his primary statement is that this method won't 'crumple like a piece of paper'.  It is more expensive because of more anchors and because the SE insists on OSB for all shear wall panels.

I am trying to understand why this method is stronger.

When Oldrunner says it is the same as tilt-up or pre-cast concrete, it is.  Pre-cast are typically 8' panels.  Concrete panels are typically 8" thick with 2" of insulation.  Construction would seem to dictate that one would have weld plates at each 4' section if these walls are used in shear.  But one could also have weld plates welded together to take advantage of the moment arm and reduce the uplift too like a traditional shear wall does.  It seems the SE of record is seeing that wood walls could and should be done similarly.

The SE provided a hand calculation sheet for a 40' wide load area.  He calculates the total overturning moment and divides that by the amount of panels (12 for a 48' long shear wall).  He then divides the reduced moment by 4' to get to his uplift.  What I don't understand is why that wouldn't be calculated by summing moments instead.  When I do that calculation , I find that the wall will take 3 times the load which is, curiously, how much the wall is supposedly over-designed according to the second engineer who was enlisted to evaluate the first.  I see that you might also be able to take this one step further and sum moments around one point for every 16" stud space and reduce this overturning to little clips like stitching a pocket rather than having big grommets at the corners of a pocket.  Levi, though, does both.

Then engineer definitely does like to simplify.  I'm not sure earthquake was a consideration given that Indy is in the lowest category.  All drawings were hand sketches and the leasing building utilized 2x8 diagonally at 10' on center to tie down the roof to the shear walls.  The truss manufacturer said he never saw such a solution.  The options were to provide a wood diaphragm on the bottom chords or move the 2x8 to the top of the bottom chord.

The second engineer does forensics and says the first engineer causes all sorts of red flags to be sent up for him.  He then provided a 150 page, computerized report with one leading paragraph of 7 lines that says the design works but is only utilizing 33% of its capacity for wind; 66% for earthquake (apparently earthquake is at least equivalent to wind).  The only recommendation was where the engineer had to use 3/4" plywood.  The second engineer said to use 16d rather 12d at 4" o.c.  The contractor's response was expected; "that's a lot of nails"

One of the advantages to this 4' panel method, as I see it, is that it moves the boat-anchor concrete chunks from the hold-down locations to all along the thickened slab which is the way it was designed.  These thickened slabs are 36" wide by 18" thick with (4)#6 continuous.

What I see is that 8":4' is stronger than 4":4' and 3 1/2":4' with OSB is stronger than with gypsum board.

If the wall is braced laterally top and bottom, then, from a beam-column viewpoint, its L/r would be the same for a 30' or 100' length (in plan) as for a 4' section.  So how does the engineer see his method as being stronger?  If the wall is not braced laterally top and bottom, then I can see how a 4' section is stronger than a 30' or 48' section.  The beam-column 'web' would cripple or 'crumple' like the engineer says.  So, I assume, the engineer sees it this way.

So how is this method stronger?  Or is it?  It apparently works ... even more than it needs.

 

RE: Shear Wall Hold Down Distance Apart

Curlyque:

Your certainly have a unique problem on your hands.  From your descriptions and arguments, it appears that you may have not taken a timber design course when you went to college.  I would suggest that you obtain almost any edition of the Design of  Wood Structures by Breyer and review chapter three (Behavior of Structures under Loads and Forces).  Having a peer review by another firm was a good choice.  I would also wonder if the EOR has previously designed a building similar to what you are building.  

As to the stiffness of 25 - 4 foot wall elements versus 1 - 100 foot long wall element; just considering any thickness of sheathing, the moment of inertia of the 100 foot element is greatly (say massively) greater than the collection of the short width elements.    

Having witnessed panel racking tests of gypsum board panels when I was assigned to the research division of a prestigious structural engineering firm, I personally try to avoid to ever using sheet rock for a shear wall.

Was the design of this building reviewed by the local jurisdiction in order to obtain a building permit?   Recently I worked a case where this wasn't done and only the contractor was provided hand sketches and calculations.  The EOR in this case was found at fault for the subsequent problems.  The structure had to be demolished.
 

RE: Shear Wall Hold Down Distance Apart

(OP)
Oldrunner,

Just for the record, I did take structures in college; otherwise I wouldn't have a clue about what an engineer was talking about.  I am not an engineer, obviously.  I'm trying to understand why this specific engineer considers his design (more expensive, more than required) to be stronger.  It is, but the question is how or whether there is any merit whatsoever to his method (madness).

I will review Breyer.  Thank you.  Perhaps it discusses what the person at AWC talked about with edge forces and what the shear panels actually do.

I understand the I-value is going to be bigger.  That's an argument for the traditional method but yet at some point the 'web' of the beam has to be thick enough or it cripples, right?  You can't have a W section of one size and replace the web with paper (or gyp or osb) and have the same beam.  Yes, in that example, the I value goes down but the buckling is more a matter of the thickness of the web and the length of the web; otherwise what are web stiffeners for?  In fact, the I-value of a gypsum board W shape is the same as one of steel, correct?  The I-value is strictly a function of the geometry and the distance squared of all those pieces, correct?  I understand that shear walls are not true beams.  What the EOR, the designer of this 'masterpiece' is telling me is that a shear wall can be viewed as a beam in section.  I can see how it is like one with the hold down points being like the T and C chords in a W-shape.

OSB is 'extra' cost.  Gypsum board is used in a building anyway so it doesn't add cost and it's allowed by code.

In Indiana, designs are not reviewed by the AHJ.  There are no structural engineers on staff at the State nor the City.  Reviews are not farmed out.  Indiana relies on its design professionals.  Calculations are not required to be submitted.

I appreciate your experience with a prestigious structural engineering firm.  That's the kind of experience I'm trying to tap into in this forum so I can understand this specific engineer's approach. I've talked with two other engineers regarding this design.

That's why I'm questioning.  I want to understand.  I'm doing what I call triangulating the truth.  One person sees an object (design) one way; I see it from another perspective; and yet another views it from a unique perspective.  What the 'truth' is is somewhere in between, the commonality or the common denominator of all the perspectives.

Does anyone know why this Engineer believes his method results in a stronger wall?  It's more expensive, it's much stronger than it needs to be, but is it stronger than a traditional wood shear wall with hold-downs on each end given that OSB is the shear panel material.  It seems like a pipe dream which is costing the owner and the design-builder money and distress and is not reflecting too well on my company.  We chose an engineer and he gave us this design.  Obviously we won't use this engineer anymore.

Thank you

RE: Shear Wall Hold Down Distance Apart

How sad that there is no oversight of the engineering in this state.  Is this why we see so many buildings trashed in the big winds?  My view in the big scale of all things in nature is that wood buildings are assemblies of sticks, pins and paper like panels.

By the way, the modulus of elasticity of sheet rock (gypsum) is hugely smaller than that of the modulus of elasticity of steel.  (sophomore strength of materials course at a really good architectural-engineering school)

RE: Shear Wall Hold Down Distance Apart

I can understand what Engineering #1 is saying. Basically he is saying two things:
1.) Even if you sheathing panels over lap at a stud (typical construction). The panels will still act as separate panels and therefore he is designing them as such.
2.) If you have a very long wall meaning a deep web in the beam/column analogy you could be subject to web-buckling (like paper). To solve for this he is breaking them up into panels.

My thoughts are - if the AWC or APA was worried about this there would be something in the NDS or similar publications. I think that the diaphragm above and below as well as the studs which are acting like web stiffeners will brace the wall.
Although it seems like the engineer has put some thought into this and maybe he knows better than I do. Also with all the holddowns you have many points slip although small they may add up. As far as strength goes - I think they are both equally strong if you consider that the code lists allowable strength values in terms of sheathing thickness and nail pattern. Length is not a factor. However I would almost prefer the continuity of one long wall....I think.



 

EIT
www.HowToEngineer.com

RE: Shear Wall Hold Down Distance Apart

(OP)
oldrunner

Yes, things can always be better.

However, an AHJ isn't going to care one way or the other whether one's design is too much or too costly; too little, probably.  The problem being discussed isn't whether it's going to blow down; it's been proven it won't by another engineer ... without review.

Thanks for the education.  Yes E is a function of strength of materials.  I-value is not. EI makes you right.  I alone makes me right ... so to speak.  I know that much.  Do I get credit for that, professor?

I see your superior education and experience with a prestigious engineering firm have served you well.  I would expect nothing less from an engineer.

Do you care to humble yourself and put your superior intelligence to the problem?:

Why is a 4' panel system stronger, better than one with hold-downs and boat anchors on each end.

At least one engineer believes so.

Qurly

Sorry, but sometimes egos get my ire.  For an oldrunner, humility is obviously not your strong suit.

I've already admitted that I'm not an engineer.

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