Large Garages
Large Garages
(OP)
I'm feeling pretty comfortable with conventionally framed structures as of late and most of my residential work falls with typical parameters that I've dealt with on similar projects.
Today a large garage landed on my desk, conventional light wood frame construction. The only thing that really jumps out at me is the size of this structure. 40'x60' rectangle with 40' trusses on 15' high 2x6 walls. I haven't ran all of the numbers yet but I'm sure I can get the stud walls to work with a minor upgrade as well as the shear walls, roof diaphragm and garage door header. The stemwall foundation and slab have been upgraded by the owner and my experience tells me already that bearing loads won't be a problem either.
Nothing really special going on here other than size which causes me to wonder if at some level I may be overlooking something with respect to a structure of this size. As we begin to scale things up are there other codes or factors that come into play that would not otherwise with a smaller structure. There are no internal walls, just the 4 exterior walls with a 18' wide garage door at one of the gable ends and a 3' man door. From a prescriptive standpoint I know this structure breaks all of the IRC braced wall line rules so the IRC is out of the question on this one.
The reason I have a concern here is based on a conversation I had with an architect on a personal project about 10 years ago. At the time I was involved with my brother in a roofing materials distribution business. Being very young and inexperienced I figured I would design our next warehouse. Ultimately we had to have a architect take it over after my initial attempts. His first comment at my conventially light woof framed structure (100'x60'x20' box) was that it was simply too flimsy at that size and we ended up going with CMU for the 20' high walls.
Also in a recent thread on tall walls I am left wondering if an upgraded wall is necessary on the side walls of this structure what would be easier and more "contractor friendly", 2x6 walls spaced at 12" o/c or 2x8 walls at 16" o/c. I typically don't try and specify over DF No. 2 for studs since I think the expense of No. 1 or SS would be unwarranted, easier to bump up to more studs or deeper studs, at least this is my current thinking which may or may not be correct.
Today a large garage landed on my desk, conventional light wood frame construction. The only thing that really jumps out at me is the size of this structure. 40'x60' rectangle with 40' trusses on 15' high 2x6 walls. I haven't ran all of the numbers yet but I'm sure I can get the stud walls to work with a minor upgrade as well as the shear walls, roof diaphragm and garage door header. The stemwall foundation and slab have been upgraded by the owner and my experience tells me already that bearing loads won't be a problem either.
Nothing really special going on here other than size which causes me to wonder if at some level I may be overlooking something with respect to a structure of this size. As we begin to scale things up are there other codes or factors that come into play that would not otherwise with a smaller structure. There are no internal walls, just the 4 exterior walls with a 18' wide garage door at one of the gable ends and a 3' man door. From a prescriptive standpoint I know this structure breaks all of the IRC braced wall line rules so the IRC is out of the question on this one.
The reason I have a concern here is based on a conversation I had with an architect on a personal project about 10 years ago. At the time I was involved with my brother in a roofing materials distribution business. Being very young and inexperienced I figured I would design our next warehouse. Ultimately we had to have a architect take it over after my initial attempts. His first comment at my conventially light woof framed structure (100'x60'x20' box) was that it was simply too flimsy at that size and we ended up going with CMU for the 20' high walls.
Also in a recent thread on tall walls I am left wondering if an upgraded wall is necessary on the side walls of this structure what would be easier and more "contractor friendly", 2x6 walls spaced at 12" o/c or 2x8 walls at 16" o/c. I typically don't try and specify over DF No. 2 for studs since I think the expense of No. 1 or SS would be unwarranted, easier to bump up to more studs or deeper studs, at least this is my current thinking which may or may not be correct.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com






RE: Large Garages
In Canada I think that span of roof trusses triggers commercial loading over the residential loading, might want to check that with your local code.
As far as lumber grades I would specify what you need, get on the phone with a local supplier and get some price lists for different lumber at different grades. IF going to D.Fir No. 1 or SS is less than 30% more expensive but will allow you to go at 16" instead of 12" then I would do it in a heartbeat. Less plywood nailing, less insulation batts (same square footage but less to handle) etc.
Here we spec SPF No1/2 for most stuff. They are the same grade, there's also SS and stud grade. The stud grade is normally such garbage that the contractors don't even want to use it.
RE: Large Garages
RE: Large Garages
One other issue that I deal with on these large clear span buildings with tall walls is the tension transfer from the roof to the base requires additional detailing.
RE: Large Garages
With the snow load and dead load I've got 790 plf at the top of the side walls. I've read through some discussions about top plate bending before in other posts but I can't remember if one should consider both or only one of the top plates due to splices. I'll have to search back through some of the posts. To align the studs and trusses would require moving the truss spacing to 16" o/c or moving the studs to 12" o/c.
I have never called out DF No. 1 or SS for studs but it seems it may not be out of the question.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Yes I was referring to net uplift from wind loads applied to the top plate. My most recent building (60' clear span 4/12 roof ASCE 7-05 Exp. C) had approximately 335 plf of net uplift at the truss/plate interface. I ended up blocking all of the splices per SDPWS requirements and used APA SR-101C for guidelines on nailing and anchorage requirements. Initially, I required A LOT of nails at my splices/plates, but due to the relatively low base shear (~50 plf) I "re-purposed" some of the shear nailing for uplift nailing. A good conversation with an APA engineer put my mind at ease that this was an appropriate method.
RE: Large Garages
I think BadgerPE might have been referring to wind uplift on the trusses and their connection to the studs and, subsequently, the foundation. A stronger Simpson hurricane strap may be required at that span.
RE: Large Garages
My point--make sure it is clear these are 15' stud walls, not 7' stud walls on top of 8' stud walls.
DaveAtkins
RE: Large Garages
I now specifically put full height studs directly on the framing plans as I got bitten by this twice on gable end walls and vaulted ceilings.
The fix ended up being steel columns at a spacing to make horizontal wind beams at the 8' mark work out.
RE: Large Garages
I'm going to give this a pass, for a number of reasons:
1.) I'm treating this as simple supported, in reality it is more like a continuous beam so bending moments would be less.
2.) I'm not considering any additional stiffness from wall sheathing or gypsum wall board.
3.) If you consider a partial composite action of the two top plates the section modulus would be greater than simply adding the section modulus of two 2x6 plates.
4.) In my notes I specify that all top plate splices be positioned over a stud.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Might be better to go 2x8's @ 24" o.c. - stiffer wall, less material and the ability to tie the trusses directly to the studs for uplift.
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
With regards to strength it will work but what I am not liking is the 1.02 in deflection at 70% C&C wind loads. Even though the IRC gives you a pass at L/120 for flexible finishes and L/180 for exterior walls with gypsum on the interior side it seems to me that a deflection exceeding 0.5"- 0.75" is excessive. Does anyone else consider a hard cut off in this respect?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
With a DF No. 2 2x6 stud @ 16" o/c = 1.02"
With a DF No. 2 2x6 stud @ 12" o/c = 0.77"
Interesting how the 2x8 does so much better in bending, the depth squared in the section modulus is to blame of course.
I don't know if the customer can return all of those 2x6 studs but it makes me wonder if I shouldn't present him with the option to go with the 2x8 studs. 24" o/c is a lot less nailing of sheathing.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
I was talking with a Huttig rep yesterday about a lumber package for a previous job and she mentioned that the max. deflection they like to see is 0.5" (above and beyond the code require L/360, L/240 etc...). I'm guessing this hard cutoff for a deflection is somewhat arbitrary. One of my mentors suggested .75" for the wall of windows I previously posted about. With these tall walls I'm seeing a trend where the strength is not the governing factor but the deflection is.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
RE: Large Garages
Interestingly with the one gable wall of this structure I only had 12' of shearwall. Given the deflections and the eccentricity of rigidity of the structure I opted for a rigid diaphragm analysis and distributed the shear wall loads accordingly. Even with that the load to the garage door wall was approximately 6432 lbs (ASD wind), with a unit shear of 539 plf and uplift of 8080 lbs. I always conservatively neglect the counteracting dead loads because I don't think you can rely too much on a distributed dead load to fully counteract a single "point" upload.
The 8" x 24" stemwall below this wall required two #6 rebar top and bottom to deal with the bending moment imparted into the stemwall foundation and footing. I'm not very experienced with concrete so I'm not entirely confident that my calculator for this portion of the design is not too conservative but there will be a significant moment at the edge of the shear panel as shown below:
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
If you have gyp on the inside, do you still need blocked sheathing on the outside? I would think the contribution from the gyp might be enough to allow unblocked shear walls. For studs at 12
o/c and minimum plywood nailing it's only a 20% reduction for unblocked walls. if you tighten up the spacing to 6" everywhere there's no reduction.
Alternately you could show strapping at 24" o/c on the inside face, I would then consider the studs braced at 24" for suction as you won't have all of the studs roll over at the same time when there's sheathing on the tension face.
RE: Large Garages
RE: Large Garages
I still like the idea of some midspan blocking, I think I'll call out mid span blocking at 8' o/c if gyp board is applied or 4' o/c if no gyp is applied. There needs to be a penalty without the gyp.
I also think grouping the studs into doubles and then putting them at 24" o/c would probably be easier to build but either way it is the same amount of wood .
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I generally do this kind of thing for the out of plane forces: Link
Having a gypsum ceiling in addition to the discrete bracing feels good from a belt and suspenders standpoint but I never count on it. Unless you detail it carefully -- and atypically -- it's unlikely to be a complete / competent diaphragm.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
RE: Large Garages
Being that the span and size of these gable end trusses are so large it is something requiring a second look.
The SBC summary sheet (B3) has a very brief treatment of the subject:
http://support.sbcindustry.com/images/publication_...
I contacted the owner and requested a copy of all truss documents that will come from the truss manufacturer. If I do not see a bracing method specified within these construction documents that is satisfactory I will create a detail specifically for this bracing situation.
This PDF provides more samples of bracing details:
http://support.sbcindustry.com/docs/06_BCSI_bookle...
This document utilizes a horizontal truss to transfer the gable out of plane loads to the sidewalls:
http://support.sbcindustry.com/images/publication_...
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
http://www.strongtie.com/products/connectors/gbc_p...
Does anyone have any experience using these?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
This detail is usually overlooked by most engineers (in my state anyhow)
That is why is makes sense to balloon frame it. There is no free lunch. You will need at least 2x8's if not more to do that.
I have tried the GBC's, but it is about impossible to get the kickers fed thru the trusses - much easier if it is stick framed. They also put a huge uplift on the end wall and the truss that they connect to (depending on the wind direction) This load is also about impossible to deal with.
Might want to try a plywood ceiling for the first 12 ft or so.
I have done this by specifying that the first 6 trusses be made 1/2" shorter in height than the rest. Then they can sit on top of the plywood and you still have a smooth GYP ceiling.
The contractor hated it!
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
WA = 40.6 psf
WB = (38.7 x 6 + 40.6 x 1.5)/7.5 = 39.1 psf
AreaA = 83.3 sqft
AreaB = 300 sqft
Wtotal = (40.6 x 83.3 + 39.1 x 300) x 0.6 = 9,067 lbs (ASD)
wavg = 9,067 lbs / 40 ft = 227 plf (ASD)
That is a substantial load that needs to be transferred into the roof diaphragm, Wow.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Z = 141
Z' = 141 x 1.6 = 225 lbs
Capacity = N x Z' = 2 x 225 lbs = 450 lbs -----> OK
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
https://www.youtube.com/watch?v=9FnB5Y0qgHw
The uplift on the roof diaphragm is not very desirable but I suppose the trusses can resist that load in some fashion or another since this seems to be the common method handling this.
I do like the horizontal truss and ceiling diaphragm method however both of these method are not transferring the load into the roof diaphragm but rather directly into the sidewalls and bypassing the roof diaphragm altogether. My roof diaphragm in this direction is very strong (60 ft deep), to not tie into it and replace it with a partial ceiling diaphragm 12 ft deep and 40 ft in length is hardly a optimal solution either. There is also the issue of the diaphragm aspect ratio limits of SDPWS Table 4.2.4, for an unblocked diaphragm I technically need 13'-4" of OSB/PLY on the ceiling.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
How are you going to get those kickers threaded thru the common trusses? Also, that is a substantial uplift of the trusses that the truss mfg. has to deal with and you have to deal with at the ends.
RE: Large Garages
I usually spec bottom chord blocking in the first few spaces and the way I detail the drywall nailer at the perimeter provides shear transfer into the shear walls.
RE: Large Garages
1) If your blocking only goes two trusses deep then your diaphragm is only 4' deep at the side walls where you dump the reactions.
2) If there's an interior partition in the vacinity of your diaphragm, you'll lose sheathing continuity unless some rather unconventional detailing is provided.
3) Layfolk think that they can mess with drywall at will. This doesn't prevent us from using gyp shear walls however.
As far as I can tell, there are only two mechanical clean options:
1) Full height wall.
2) Horizontal truss.
And neither of those is generally acceptable to builders/developers.
A while back, in a Meedek thread, I proposed a horizontal truss that was actually a pre-eng truss in place of XR250's plywood. That gets around the aspect ratio limits but would be even less popular with builders because the truss heights wod need to be trimmed 1.5".
@XR250: good on you for even attempting the horizontal diaphragm in the real world, yet alone actually getting one built. You're a structural engineering martyr!
@Medeek: keen observation on the hip roof comparison. That had never occurred to me.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
I don't see too many people in residential applications removing the ceiling gyp without replacing it. I guess it depends on the level of resistance you need, I have put in kickers up to the top chords on a few projects they're a bitch to get in but it's generally doable.
I am with XR250 though, my standard gable end detail is balloon framed so the ceiling is a moot point.
RE: Large Garages
As much as I would like to use a horizontal truss or a 14' deep ceiling diaphragam (324 plf unit shear) I don't know that either option would gather much support from the owner or builder.
Also looking at the unit shear this would have to be a blocked diaphragm at this depth (324 plf > 237.5 plf). To get the unit shear in the ceiling diaphragm below 237.5 would require 20 ft. of sheathing coming in from each end wall. That is 40 ft. of the 60 ft, might as well sheath the entire ceiling. I don't know maybe my wind forces are too high or my wind trib. exercise above is somehow awry, but this is a lot of force to get into each sidewall (4534 lbs).
I just did a sanity check on those shearwall forces and my numbers coming straight out of Woodworks is 6569 lbs per Wall A and Wall B (sidewalls), this of course does not include the internal pressures and does include the leeward wall pressures. My total windward force if I include the tributary area going straight to the roof diaphragm is approx. 5548 lbs per shear wall. The ratio of the leeward + windward to windward w/ neg. int. pressure is approximately 5:4 so my numbers are not too far off. The Woodworks software also uses a less conservative and more accurate method of trapezoidal wind pressure loading for the windward side, which explains why my numbers will be slightly (10%) higher.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I've also seen some details with an X-brace configurations and a C-Brace configuration, not sure what is going there but I'm looking at all possible solutions right now and trying to develop an appropriate solution not only for this job but a standard detail I can utilize for future work as well.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I agree that people generally restore gypsum that is removed but real trick is whether or not Johnny DIY reno guy will restore it using the special details required to maintain diaphragm continuity.
Because of the manner in which the diaphragm load is delivered (diaphragm edge tension/compression rather than shear), I don't think that unblocked gypsum diaphragm capacities will allow the effective diaphragm depth to be extended any further than the blocking extends.
The relationship between the extent of the blocking and the effective depth of diaphragm is really the unspoken Achille's heel of all of the systems that we've discussed, even the balloon framing option.
I believe this statement to be incorrect for the reasons mentioned above. Unless you extend blocking into the diaphragm over the entire 60' length, which would get you shot, I think that the effective diaphragm length is only 40'/2 = 20'.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Do I need blocking between the truss bottom chords? Wouldn't a CLR (2 16d nails per truss) do the trick?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
RE: Large Garages
Having been a truss manufacturer in a past life, I know that the hang-up with the horizontal would be the loss of repetition in the trusses and the need to possibly increase all of the truss heel heights to accommodate the handful that would sit on top of the floppy horizontal truss.
I've heard of the LVL method, love it and was thinking of proposing it. Is it a problem that it's 24" rather than 22.5"? If one could get their hands on a 22.5" LVL, they could infill two truss spaces and shear connect the two LVL's across the intermediate truss with Simpson connector plates to form a composite, 48" beam.
Another alternative that I've considered is an extension of your plywood suggestion. One could build plywood box beams 22.5" wide and fit them between the trusses just like the LVL concept. You could make them as deep as needed.
@Medeek: I'm not sure that you need the ceiling blocking unless you're counting on load transfer to both diaphragms.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
RE: Large Garages
If the garage is in seismic design category C or higher, the diaphragm to wall detailing requirements in ASCE 7 §12.11 should be met. This includes continuous ties between diaphragm chords and restrictions on using toenails and nails subject to withdrawal.
RE: Large Garages
This is related to my point above. I've always found it strange that it's not required in low seismic areas. Obviously, it's more important in high seismic zones but, at the end of the day, load is load. Do people actually follow that requirement for houses in California? It's hard to imagine.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
Double kickers in three places (where roof height exceeds 6'), with a horizontal brace attached to the gable truss at 4' height.
The question: Will they build this as I draw it up? I'm going to put a note somewhere stating that the EOR is required to inspect the installation of the kickers and blocking prior to them closing up the ceiling with gypsum. I love to do on site inspections but so far my clients that I have had the opportunity to inspect their work have not been very pleased with my findings or some of my comments.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Consider using Simpson S/PAHD & S/HPAHD Strap Tie Holdowns at the garage door openings. I found they are easier to fit in and install.
http://www.strongtie.com/products/CFS/S_PAHD-S_HPA...
RE: Large Garages
RE: Large Garages
At the garage door in the SWL2 detail (sheet 2) I don't show any holdowns. I'm actually more worried about lateral here since the garage doors will transfer all of their out of plane wind load directly to the two trimmers on each side, half of that force needs to be resisted at the trimmer/stemwall connection. Currently I have a 5/8" anchor bolt there, probably not enough considering my lateral load is about 1250 lbs.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
My idea with the blocking is not to really treat the ceiling as a diaphragm but to prevent localized cracking and buckling, whether this actually does what I intend is currently in question.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
But then in section 2508.3.1 it appears that blocking/nailing at all panel edges is required but this particular sections wording is confusing to me.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
EIT
www.HowToEngineer.com
RE: Large Garages
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
There are two distinct kinds of blocking in my opinion. The first kind improves shear transfer between sheathing units and is optional. The second kind transfers the applied load into the diaphragm and is not optional. It's this later kind of blocking that I'm getting at.
The sketch that I'll post for Medeek will deal with this too. Stay tuned.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
I think I will continue to develop the bracing solution using kickers and blocking similar to what is shown above but I will also include the option to sheath the entire ceiling with OSB if that is easier.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I'm assuming, based on my most recent interpretation of IBC 2508.5, that I can use the gypsum ceiling diaphragm as unblocked diaphragm. Given that I'm in seismic D cat. my max. shear capacity will be 50% of the 70 plf allowable => 35 plf.
My ceiling diaphragm load that I'm allowed would be wD = 2vB/L = 105 plf
I have a diaphragm load at the top plt. of 226.6 plf, if the ceiling diaphragm takes its share of 105 plf I am left with 121.6 plf to be picked up by the kickers.
At 48" o/c that would be 486 lbs per kicker, the center ones would be a little more since the loading is actually trapezoidal but this would be averaged out since the three central kickers utilize a two brace method shown above.
At 486 lbs I am overloaded by 14% when the brace is in tension, however based on footnote 1 of the Simpson GBC connector and also on the fact that the loading is trapezoidal and will diminish as the braces approach the sidewalls I can probably give this a pass.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
The secondary kickers will connect to the gable truss at 4' above the bottom chord as previously noted.
The only problem with the GBC bracket is that it gets in the way of any blocking I may want to insert between the gable truss and the next common truss.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Also, are you sure the trusses have vertical webs at 48" o.c.?
RE: Large Garages
105 plf of the diaphragm load will be picked up by the ceiling diaphragm.
122 plf of the diaphragm load will be picked up by the kickers and transferred to the roof diaphragm.
Of course the problem with all of this is I don't really know how the load will really be shared between the two elements so I'm kind of stuck. If I design the kickers as if they take all of the load then I'm probably at 24" o/c with them which is absurd.
I could theoretically create 2 ply kickers (sister two 2x6 or two 2x4) together, but the problem really is the connection capacity on each end. If I want to connect directly to the top plate of the wall I don't really see any other option except to utilize a Simpson GBC.
I really don't want to go to a balloon framed wall since the client has already purchased his studs and he is pretty dead set on using them. Also for reasons given above some bracing at the ceiling line will be required either way.
I've added in the holdowns at the garage door at least, as you can see from the updated image above. At least I can figure that much out.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
As far as the load sharing - who knows. Make sure the truss designer knows about the new loads.
You are lucky people use concrete foundation walls in your area. In my area, they would have built a 4" brick/4" CMU wall and expect me to do something with it.
RE: Large Garages
Available vertical webs are going to be a problem though. The center brace will probably have a center web to brace against (assuming Howe truss and not a Fink) but the next one will not. I can see why people shy away from kickers, its messy. By the time they are finishing installing the diagonal braces (kickers) and the braces for the braces this whole thing is going to look like a rats nest up in the ends of the attic.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
https://www.youtube.com/watch?v=N-jog8SrDpg
The kickers appear to eliminate the hinging but there is still some pinching in of the space between the gable truss and the next truss:
https://www.youtube.com/watch?v=jtlBB-kPqz4
https://www.youtube.com/watch?v=FWAh5OVmqyc
Without any secondary kickers (those above the main kickers tying into the wall top plate) my calculated lateral force to each kicker is 226 plf x 4 ft = 904 lbs, if the diagonal is 45 degrees the compression force in the brace is then 904 lbs x 1.41 = 1278 lbs
The axial loads in the kickers given by RISA3D:
The wall studs loads are:
The RISA Model:
Closeup of the gable truss with kickers:
Planview:
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
RE: Large Garages
To get any load spread at all within the diaphragm, the plywood sheets require some internal tension capacity. That tension capacity would be unreliable in gypsum sheathing which is why I'm even more skeptical of diaphragm load distribution with ceiling assemblies in the absence of chord to chord drag struts.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
I wish I knew more about FEA and plate modeling. I think if one could establish a realistic model that accounts for various factors such as nail slip and tension etc... it would be interesting to see really how accurate our simplistic assumptions are.
Here is the Von Mises Plate Stress from the model above:
I never did take an FEA class in school, wish I had. My other electives (robotics, jet engine design, aerodynamics etc...) are pretty much useless to me now. I guess it is time to find a good text book on FEA and understand plates a little better. I would also like to utilize some FEA models to validate my new FTAO and Portal Frame calculator that I'm working on.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
https://www.youtube.com/watch?v=uc3WAWo3WV8
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
I like your shear model. I imagine a significant amount of tension does occur at the plywood butt joints in reality even if the edge distances are small. I have seen too many instances in practice of plywood acting in pure tension in this manner without failure.
RE: Large Garages
EIT
www.HowToEngineer.com
RE: Large Garages
RE: Large Garages
1) I attached a gable end wall brace detail. I have others that utilize (2) 2x6 diagonals up to the roof with upside down LU26 hangers connecting the blocking to the trusses. You really only need to figure out the force on the brace and then detail your connections to take the force. Sometimes the Simp. Gable End Wall connectors don't work and you need to use steel angles.
2) The hold-downs at your garage opening will more than likely cause spawling in the concrete. I would recommend using an HDU or something along those lines to avoid the splitting. I have seen many, many straps installed at angles, missing studs when nailing to the studs etc to the point that I don't even look at including them in my drawings any more as well.
3) How are you transferring the out-of-plane force from your garage opening king studs into the roof diaphragm and the stem wall? This can be a critical connection that is generally missed and should be looked at...just like the gable end wall braces.
RE: Large Garages
My next best option is to simply require braces at 24" o/c, this will get my forces down to more manageable levels.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
The overall structural plan for reference:
I've decided to try 36" on center spacing since 48" on center has to high of point loads at the connections to the top plate and also at the connection to the roof diaphragm
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Take a flat ceiling diaphragm, flip it up vertical, support it at both ends and you have a really tall, thin beam. However the way I see it is that the direction of the rafters or girts play into it. From my recent work on the pole frame structures it can be shown that the diaphragm chord forces are not just at the perimeter as is typically assumed with wood framed diaphragms but rather shared by the internal girts as well.
I would be really interested to read more on the methods used to come up with the diaphragm allowables found in the SDPWS and what their assumptions and simplifications were. Are these numbers from purely empirical testing?
The to further complicate the matter you pitch the roof. Low slope roofs are probably pretty close to the classic diaphragm but what about a 12/12 pitch roof. Does the higher pitch make the diaphragm stronger or weaker? Where does this change in pitch show up in the SDPWS tables? Maybe it is a insignificant factor.
My thinking with the cross grain splitting is what is the failure mode. Will the nails heads pull through the panel first or through the edge before the framing splits. My suspicion is that the nails will pull through the edge of the panel before the framing members splits when the nails are not closely spaced (ie. 6" o/c at edges).
I actually think modeling diaphragm action, nails included would be a good candidate for FEA. I'm just not sure how to model the nails and sheathing effectively. What I am interested in visualizing is how the nails load up in a diaphragm. Do the nail loads mirror the classic diaphragm shear diagram (zero load at the middle) or are there other effects or factors at play that are overlooked by the classical diaphragm model?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Note that I'm just having fun with this as an arcane technical discussion. I'm still handling this as everyone else does: full diaphragm engagement, blinders up.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Large Garages
RE: Large Garages
You have a potential career as an artist :>
RE: Large Garages
EIT
www.HowToEngineer.com
RE: Large Garages
Picture of the framing of the shearwall next to the man door:
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
Are truss straps correct?
Can't see the outlooker straps/clips.
Is the exterior water drainage being followed? tall exposed OSB sheathed walls needs more then 15# roofing paper
Consider checking the nailing of the 2x8 on the inside of the garage door opening.
The garage door track attached to it and is a critical elopement we have seen failures during high wind events of the door blowing in.
RE: Large Garages
@boo1
The exterior cladding will be hardiplank over the felt. What is your thinking on the 15# felt, what do you suggest?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Large Garages
The 15# felt paper does not last (or met code), the tall exposed wall will get wet.
review some of the stuff from Joseph Lstiburek, or Matt Resinger on drainage plane and weather proofing
http://buildingscience.com/documents/digests/bsd-1...
http://buildingscience.com/documents/insights/bsi-...
http://mattrisinger.com/category/exteriors-siding-...
RE: Large Garages