Gable end support 2

[rittz]

I have read the posts in Thread #507-240778 ----Which was “Gable End wall support.” It is now closed. There is one post in there that reads in part as follows”

“I have been asked by a contractor to engineer a wood garage. The plan dimensions of the garage are 40'-0" x 60'-0" (clear span) with a required clear height of 16' and a 8:12 roof.

The only problem I can't resolve is how to transfer the loads from the gable ends into the wood roof diaphragms.

I could sheathe the underside of the trusses with plywood (gypsum board is not strong enough) but I don't think the contractor would like that. I could provide kickers at 2'-0" o.c. but I am not sure if this is the best way to go.

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I have used a variety of systems to achieve support for the gable ends of such buildings and I’m not exactly happy with them. I have sometimes strapped the ceiling for light gage metal covering in shops. The strapps but into the gable plate. And sometimes I sheeted the ceiling (when the owner would agree)

I like the strut idea described in several of the posts which uses the Simpson GBC connectors at the double plate of the wall. I am wondering how the top of the strut might be attached to ensure load transfer into roof diaphragm (7/16” OSB). Would it be attached to the upper chord of a single truss? Or may to blocking between several upper chords.

 

[DaveAtkins]

I have attached it to blocking between two roof trusses, with the OSB attached to the top of the blocking.

DaveAtkins

 

[XR250]

You either need to balloon frame the gable end or put a ceiling diaphragm in there. There is no free lunch with the Simpson GBC. The load has to be reacted into the roof trusses and puts a huge up or down load on the truss that it is attached to. This has to be accounted for by the truss manufacturer and your hold-down system. It turns into a big CF. You seem like you are fairly new at this. As someone who has done this many times, balloon framing the gable or a partial ceiling diaphragm is the way to go. Maybe you could talk him into a hip or dutch hip roof - which simplifies things.

 

[msquared48]

You can also install rat runs with horizontal x bracing at the rat run level.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[SteelPE]

I think that was my thread. I never did come up with a suitable connection so I had them sheath the entire ceiling........they did not like that at all but ultimately did it. All I heard was how "they have never done this before" and how I was "being too conservative". Never did do any additional work for the client again.

The problem with balloon framing was that the studs were too large and everyone who I run into want to use a gable truss on the end. The stud at the ridge wold have been over 25 feet tall in this instance. I have asked others about the problem and they seem to use some form of bracing in the gable end.

There garage is still there after a few hurricanes, blizzards and a snowy winter.... that's all I really care about.

 

[rittz]

SteelPe

I know what you mean. I have insisted on sheathing the ceiling a couple of times. And all I hear was how "they have never done this before" and how I was "being too conservative” etc. Contractors all want to use a gable studs on the end. And of course they need to use some form of bracing at the intersection between the gable studs and the regular wall studs below. The roof trusses need to take care of the brace reactions.

I think I will use full length LVL . If we do it the other way it is possible they may have a problem before they get the ceiling sheeted … or maybe even not bother sheeting the ceiling at all.

 

[XR250]

I am currently working on a job where we are balloon framing a gable that peaks at 29 ft. We can get 29' 2x10's here that are finger jointed.
These types of building are always a problem. Trying to get the numbers to work out on adding braces at the ceiling line is tough and expecting it to be built correctly is wishful thinking. Ironically, the buildings, even designed and built poorly, seem to hold up well.

 

[hokie66]

Finger jointed? That is fine for fascias and the like, but is not strong enough structurally, unless you are talking about a different process than the one I am familiar with.

 

[wannabeSE]

Hokie66,
Here is a link to information on structural finger-jointed lumber:

http://www2.wwpa.org/TECHGUIDE/FingerJointed/tabid/861/Default.aspx.

 

[hokie66]

Thanks, wannabe. I was not familiar with that product.

 

[RFreund]

How about creating X type bracing on top of the ceiling joists? Probably hard to do with all the webs and such.

Excel - you seem (maybe not) to be against the use of bracing at the ceiling (kickers up to rafters/roof deck) - have you seen cases where this has caused problems? I feel like I have seen this constructed a few times but don't remember hearing/seeing any issues (disclaimer - I could be wrong here and I don't have a ton of experience). Also no apparent strengthening of the truss that I can recall either. Just curious, Thanks!


EIT

http://www.HowToEngineer.com

 

[XR250]

@RFreund.
If you run the numbers on the uplift loads on the truss it get pretty hard to design. Also, unless you run the kickers at a really steep angle to the first truss, there will always be a web in the way. If you try to run a really steep angle, the numbers get huge. I have never seen one built correctly, even though they seem to work.
No free lunch here. The best way to react these things is horizontal. Even trying to detail a horizontal truss to brace it is tough as the numbers get big and there is a bunch of detailing.

 

[RFreund]

@Excel - I see, makes sense. Thanks for the response!

EIT

http://www.HowToEngineer.com

 

[rittz]

Bottom line. Convince the client Sheet the ceiling. Every other method is less effective. And often an imperical design. And not that much cheeper.

 

[dhoward26]

I have used a combination of the ceiling sheathing and diagonals before. I have also just used the diagonals in the past.

As a side note, an agricultural barn I designed a couple years back I used sheathing 8 feet into the building on the bottom chord with blocking and diagonals. We had an extremely large wind load come up during construction. The neighboring farmer was having a similar structure being built but apparently wasn't engineered (not sure, I wasn't around to verify) and didn't have the bracing. The building I designed survived, the other guys ended up being a pile of tooth picks.

It seams it is a toss up whether doing all the bracing, or increasing the size of your studs, is the most cost effective option. I've done both.