Stacked Walls Tall Wall
Stacked Walls Tall Wall
(OP)
Hi,
I have been requested to review a stacked tall wall design. The build has been done as requested from the previous engineer (stamped drawgs), both I and the inspector fail to see how he planned on this working.
Criteria:
It is a 20'-0" tall wall with an additional 7'-0" of Gable on top.
All framing is 2x6 SPF No2.
7'-0" wide stairwell tall wall.
26psf unfactored wind load
Site Conditions:
-Framed with 2-9'6" walls (12" Oc studs) stacked one on top of the other (double top, single bottom plates) for an effective 3-Ply Spf girt across the middle, no continuity between it and the other plates
-No attachment at either end of the wall to the floor platform or surrounding framing.
-a single 2x6 on the flat above the wall, extending 5" on each side and nailed above the top plates and butted to the first roof truss(attempting to act as a wind girt for the gable I think)
-absolutely nothing connecting the wall to the foundation. No nails to the ladder, no bolts to the concrete.
-no shear wall provisions for the stairwell walls (full height stairwell walls on both sides and both floors. Might be my saving grace in making this work
Am I missing something - or is this just shoddy engineering?
I tried to run it using C&C wind loads, and given the hinge point in the wall it really seems to me that this is pretty crappy design?
I have been requested to review a stacked tall wall design. The build has been done as requested from the previous engineer (stamped drawgs), both I and the inspector fail to see how he planned on this working.
Criteria:
It is a 20'-0" tall wall with an additional 7'-0" of Gable on top.
All framing is 2x6 SPF No2.
7'-0" wide stairwell tall wall.
26psf unfactored wind load
Site Conditions:
-Framed with 2-9'6" walls (12" Oc studs) stacked one on top of the other (double top, single bottom plates) for an effective 3-Ply Spf girt across the middle, no continuity between it and the other plates
-No attachment at either end of the wall to the floor platform or surrounding framing.
-a single 2x6 on the flat above the wall, extending 5" on each side and nailed above the top plates and butted to the first roof truss(attempting to act as a wind girt for the gable I think)
-absolutely nothing connecting the wall to the foundation. No nails to the ladder, no bolts to the concrete.
-no shear wall provisions for the stairwell walls (full height stairwell walls on both sides and both floors. Might be my saving grace in making this work
Am I missing something - or is this just shoddy engineering?
I tried to run it using C&C wind loads, and given the hinge point in the wall it really seems to me that this is pretty crappy design?






RE: Stacked Walls Tall Wall
You may be able to add straps at each stud across the hinges to attempt to strengthen it but there is no way you can get 2x6 spf studs to work unless they are spaced ridiculously close.
My bet is he never even considered it.
Did you think to account for some lateral resistance from the stair landings? (provided they actually frame into the wall)
RE: Stacked Walls Tall Wall
These sound like fundamental load path issues, not just capacity issues. Fail by inspection based on the information provided.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stacked Walls Tall Wall
I can't see how it would work unless the (3) 2x6 flat plates at mid-height span across the width and somehow are fastened to the adjacent walls.
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RE: Stacked Walls Tall Wall
Will request calcs from the issuing engineer but I'm not expecting anything in return - it is a standard detail they issue for MANY homes.
I have reviewed 3 of his walls so far out of countless ones the inspector has let slide.
Continuing this discussion - is this something you would take to the professional association? (if he refuses to provide calcs, or they don't pan out)
RE: Stacked Walls Tall Wall
-Clear 1/2" gap between stair landing platform and wall
-On our designs if we are really close for deflection I will give some consideration for landings, but all the stamped designs for landings I've seen specifically state not to use them as lateral support for the walls.
Probably just the stair guys covering their bacon, but I like to play by the rules for the most part.
RE: Stacked Walls Tall Wall
Tension at extreme fibre going to ~3000#, Simpson MSTA36 into each stud centred across the girt should solve that issue, but it is bloody close.
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
Max moment on stud: wl^2/8; 13plf * (20^2) / 8 = 650ft-lb
max tension force on stud: T=m/d where distance from neutral axis = (5.5/12)/2 = .229ft
T = 650(ft-lb) / .229ft = 2838lbf (tens)
If I have made an error please let me know! haha
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
The 2x6 on the flat is overhanging the wall to the inside by the thickness of the truss and is likely there to fasten the ceiling strapping. As you show a 20' span in your calcs, you're considering the ceiling as a lateral support.
An alternative to adding intermediate studs and the tension strap is to cut the 3ply 2x6 at the joint in the 9'6" walls and splice the studs in place.
For the tension strap calcs, I think the strap will be closer to the neutral axis than .229 ft.
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
your right on the money with the description, I'm beefing the ceiling plane up a bit and having them sheet it with type X to get some support out of the ceiling.
I talked to my mentor also and he figures the strap would actually be further from the N.A. given the 5/8 ext. sheathing would act partially as a compression chord for the wall. (my calcs were assuming midpoint of 2x6)
by splicing studs are you saying chop the 3ply up, and sister studs around the hing point? Just clarifying.
RE: Stacked Walls Tall Wall
You may need a 3x stud just to get all the nails in and spaced to prevent splitting. While the strapping might prevent the wall from out-n-out failure, I’ll bet you can expect a fair amount of deflection/movement around the joint/level. Maybe detail a joint and cover trim in any interior sht. rock at the level to tolerate this movement.
RE: Stacked Walls Tall Wall
I guess I was just being picky with your 'd' value...but I would think if you're considering the tension trap, stud, and sheathing to act compositely, the N.A. would be closer to the steel. I haven't run the numbers so I don't know, just my gut feeling.
RE: Stacked Walls Tall Wall
You might want to provide a sketch of the elevation & cross section of this wall to make sure that we are all talking about the same thing.
RE: Stacked Walls Tall Wall
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: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
APEGA Discipline Committee Order Skip to page 94.
Wadavis,
E.I.T.
RE: Stacked Walls Tall Wall
Sorry my bad. I was thinking that to attach the stairs to the walls to creat a brace point may be an option. But my mind and fingers were disconnected.
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: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
Please excuse my stupid question (I have not designed in timber for more than 20 years) - so you have a 20' clear span stud that is 'spliced' mid-height with steel straps? Is this how such studs are typically connected for moment splices in high exterior wall situations?
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
Thanks for the reply. Engineered lumber does indeed make sense for such applications.
For the OP's situation where traditional dimensional lumber is used and it IS spliced somewhere over it height (presumable due to availability of longer studs), how does shear get transferred across the metal straps (assuming that nominal shear capacity is required even at max moment)?
RE: Stacked Walls Tall Wall
It's unconventional and had this thing been designed accordingly in the beginning using dimensional lumber you generally make your sills continuous and turn them into wind beams.
RE: Stacked Walls Tall Wall
DaveAtkins
RE: Stacked Walls Tall Wall
Im not following you with strapping both sides - it is a moment connection, not uplift so I think the strap on the outside face of the stud would only be in tension when there is suction acting on the wall.
I agree the ideal solution would be to tell them to tear the wall down and use engineered lumber - but I have ran the numbers, and ran this solution by my mentor (35+ years in wood design) and he agrees that it is an adequate solution. I would never design this from scratch, just too damned mickey mouse for my tastes.
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
That was a fascinating read about Mr. Gill - naming and shaming.
RE: Stacked Walls Tall Wall
DaveAtkins
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
Im still not following how adding the second strap to the outside face of the wall would increase the moment arm to the full stud depth.
I was always told moment arm is distance from neutral axis to your chosen point, with the opposing force acting on the opposite side of the N.A. (see attachment)
Adding the second strap would bring the N.A. closer to the outside face, but by a fraction of an inch only.
I agree to strap each face in the case of a max suction on the wall.
For anyone interested in a good (yet troubling) read, look at the PEG article on pg. 87 (determining suitability of a slab-on-grade for heavy vehicles by comparing the point loading to the compressive resistance of concrete, no flexural / shear / geotechnical analysis)
RE: Stacked Walls Tall Wall
The moment arm should be the distance from the strap to the centroid of the compression, not the neutral axis (think concrete design). The compression force must equal the tension force (otherwise there is not equilibrium).
If you add a strap on the outside face that can take the entire compressive force, the moment arm would be the distance between the straps (think how you would splice two wide flange beams together).
DaveAtkins
RE: Stacked Walls Tall Wall
That was a troubling read. Damn, $45k Formal Hearing costs!
RE: Stacked Walls Tall Wall
RE: Stacked Walls Tall Wall
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.