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Author Topic: Clear Span Roof Truss Calculator  (Read 6906 times)

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Offline Sedgehammer

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Clear Span Roof Truss Calculator
« on: February 05, 2019, 12:00:58 PM »
Searched the site and interwebs, hadn't had much luck in finding. If anyone has one or has a link, would be much appreciated.

Thanks

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #1 on: February 05, 2019, 06:37:57 PM »
I was playing around with this several years ago, there are so many truss configurations it I don't know if this was along the lines of what you are looking for.
http://forestryforum.com/members/donp/vectormath.htm

Then I started to try to make it check members;
http://forestryforum.com/members/donp/trusswbending.htm

Ok, looking at it, I'm remembering, I sort of abandoned it about 10 years ago. IIRC it is based on "the method of joints", one way of analyzing a truss. google will probably have reading material on truss design. It was becoming a monster of inputs and results and stops short of giving all the info you would need. What is it you are trying to do?
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Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #2 on: February 06, 2019, 12:57:01 AM »
Thanks for your reply Don.
.
We've been working on this project for about a year now. Had an architect working with us. He wasn't cheap, but an acquaintance recommended him. Every time we'd give him what to do, he'd do a few of the changes/corrections, then we'd get the plan back and we'd have to tell him what he forgot. So I said I'd email him all the changes, so he could 'remember' them. Was good for a bit, then his self showed up again. We reminded him to look at the email on corrections and he got mad and said he didn't want to do emails anymore, just to call him. So I did one last time and he 'forgot' some more, so I called him out on it. He of course got mad, adjusted his bill and we parted ways. So I have a set of prints that I cannot get any info off of, so I am trying to find where I can get dimensions for the spans we have with the pitch we have. 
.
We have 3 spans that we are dealing with. 2 are easier, as they are over the rooms with the RCDF ceiling joists with the wood decking for the ceiling. They are 20' & 24'. We are in the 3-4 range on roof pitch. All roof trusses will be hand framed with a 2x12 ridge board. I can put supports in these where needed, so should be able to use 2x8's, but don't know where for sure to support them, as I cannot find a truss design aid with a ridge board that are hand framed.
.
The last one is harder. Span is 36'x16' depth. It comes off of the house dining/living room areas. Would have 12"x12" RCDF as posts at 8' & 16'. Would have a tie at these locations based on somewhat you have shown. Then would just have roof trusses/joists either 2' or 32" OC. Was going with 2x12 since had no idea and nailed to a ridge board. Ridge board probably a 2x16, but would need to check the length of the angle cut first. Roof trusses/joists would be resting on a RCDF 4x12x16' with an 8" heel. End truss would have a post at 18' to support the ridge board. Not sure what to make the 2 rafter tie trusses out of either yet.
.
Hopefully my carpenter lingo isn't too messed up for you and you can figure out what I'm doing. I'm not stuck with any particular sizeof anything, so what I listed was just what I was thinking.
.
Thanks

Offline LeeB

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Re: Clear Span Roof Truss Calculator
« Reply #3 on: February 06, 2019, 05:24:07 AM »
https://www.blocklayer.com/calculatordirectory.aspx

Not actually what you are looking for, but a neat site and might help you with the lingo.
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #4 on: February 06, 2019, 07:29:53 AM »
Some things to think about.
Those trusses could come from a truss manufacturer. The engineering would be already done and would be correct. The 20 and 24' 4/12's would be built out of 2x4's and are pretty much a stock item. They would go up in a day. The 36' would be larger dimension members but would still be a good bit smaller than what you would be site building. That is more than likely the best path forward.

If we come up with something here you should have an engineer review and seal it whether it is required locally or not. I have done 24' site built trusses from sealed plans and in the end I said never again, it was a lot of work for no real gain. Your 36' span you are probably looking at 24' top chord stock, that isn't going to be cheap or easy to handle, bottom chords 20' material, ridge in heavy LVL, you get the idea. 

You were talking about supporting the materials in the previous thread from some these trusses, you're getting out into the land of pure ... magic :D.

Based on the little bit I'm understanding of what you've described, if you're open to some design ideas I'd like to see a sketch of the plan and elevations. His work is copyright so just a napkin sketch.
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Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #5 on: February 06, 2019, 12:29:42 PM »












Yes, have thought about buying them from a truss manufacturer. Nearly everything built here is hand framed with ridge board. I am exposing the ridge board 2' at the ridge, so would have to cut into the first 2 to support it. 

I'll post some more in a bit.

Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #6 on: February 06, 2019, 01:13:12 PM »



.
This is what the gable end looks like on the pump house. House will look same.
.
Cut back on 2x12's if we'd use them for the truss on the porch end is 3.75". The length if the angle cut is just a little over 12", so a 2x14 or a 3x14 would suffice for the ridge board I would think. It'll only be 18' long with 2' soffits.
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I'm thinking that we'd only need the end gable truss. I could use 1" threaded rod to tie the 8' posts together.  These would be supported from rods from roof trusses in 3 places, so wouldn't sag.
.
As far as magic stuff goes. The 24' ceiling joists span on their own. I was just planning on helping them only so much as to be a stiffener to help  minimize twisting & warping.

Offline Den-Den

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Re: Clear Span Roof Truss Calculator
« Reply #7 on: February 06, 2019, 07:43:47 PM »
Designing or modifying trusses are things you should not do.  If you ignore this advise, and anything goes wrong, you will likely lose any lawsuit that occurs whether it is your fault or not.
You may think that you can or may think you can't; either way, you are right.

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Re: Clear Span Roof Truss Calculator
« Reply #8 on: February 06, 2019, 08:32:58 PM »
Designing or modifying trusses are things you should not do.  If you ignore this advise, and anything goes wrong, you will likely lose any lawsuit that occurs whether it is your fault or not.
It happens all the time. Prints nor engineered products are fail safe. 

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #9 on: February 06, 2019, 09:58:10 PM »
I take it the rear elevation is 36' wide where the chimney is. Looking thru the window upstairs and at the exposed tails it looks like the intention is a cathedral ceiling, probably a glulam ridgebeam with an exposed rafter ceiling rather than trusses and a level ceiling. The left wing looks the same based on the elevation and that would be nice looking. Is it the 20 or 24' width and where is the other width roof? Are you sure you want to truss this roof? I'd lean towards framing it all in heavy timber in that style.
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Re: Clear Span Roof Truss Calculator
« Reply #10 on: February 06, 2019, 11:05:13 PM »
Correct
.
Correct and no glulam. What plan doesn't show is I am going to make 4 metal 3 piece trusses that will attach to the top of the sill plates and inside of the wall at every 4'. These will be 1' deep where they attach to the wall and arching to 3'6" at the top. Will weld in 3/16 laser cut panels made to show outdoor pictures like deer, horses and maybe an Indian. Might just clean and clearcoat, but the wife will prolly make me sandblast and put black primer. Will prolly install these before the t&g ceiling wood. Could either be hardwood or 6" t&g car siding. Ridge board will be 2x12 df.
.
Left wing is 20' wide. Will have exposed ceiling joists and wood ceiling as well.
.
Back behind the 36' is a 24'. The 24' is above the kitchen. Will have same ceiling as the left/north wing. Rendering doesn't show 24' roof correctly. It shows it as 36'.




.
Am having a hard time in justifying the expense for what little eye candy it gives off. If you can show me where I'm goofy, I'm in a disney show...... 8)

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #11 on: February 07, 2019, 07:19:46 AM »
Start drawing the roof structural framing, I'm not following yet.
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Re: Clear Span Roof Truss Calculator
« Reply #12 on: February 07, 2019, 09:05:34 AM »
I'll try and get something today. 
.
Oh, the cathedral in living dining you were talking about with exposed trusses. This won't be I don't think. I think I'm going with 2x12's with 8" heel, so I can put on the 2' rafter tails. Decked in 5/8 osb 2' oc. Then insulation R38. Then either sheeting it fully with 6" t&g pine or if my hardwoods (gum, oak & hickory) come through at price point, I'll prolly use them. But I'm not sure if I'll sheet it fully then install the metal trusses or install the metal trusses and then sheet it in between them.

Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #13 on: February 07, 2019, 03:22:55 PM »
Here ya go
.
Posts are 36' os to os, forgot to show
.
Could go with 2 angled timbers also with the 4/12 pitch
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2x12's are 2' oc to the house. Then either 6" pine t&g or various rabbited (ship lap) hardwoods 3/4"x 8' to 16' on top of and clear coated. Will deck over with 5/8's osb regardless so roofing metal screws don't show through
.
I don't show it, but could cut the rafter tails out of the 2x12 itself. Just rip them at 8x21". The reason I wasn't, anything over 20' is priced in BF vs LF. That 1' extra = $36, but I might anyways.
.
There is also another set of outside posts @ 8'. It is at the point where i'd run the 1" metal cross tie with a turn buckle or use some actual threaded rod and ends 
.
Have a huge bobcat to lift any timbers in place, so size of them isn't really an issue
.




Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #14 on: February 08, 2019, 07:49:03 AM »
OK I'm just starting to get a little traction. Let's take it one section at a time. This appears to be the back porch.
36' wide x 16' deep. There are 2' overhangs on everything. This is not the metal and laser cut trusses, I'm assuming that is inside, later. I can't make out the labeling on the sketch, esp what is written in the gap between the kingposts?

What I'm looking at is not a truss. It would work for a gable end but the tie is connected to a post and we don't have a post centered under the ridge at 8'. You can add the posts at the outside/front edge, I'm really looking more at the internal truss as clearspan, supporting a structural ridge with common rafters hanging from it, common rafters between trusses, is this what you are describing?  

See if we're on the same page;




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Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #15 on: February 08, 2019, 09:00:11 AM »
Bingo

Yes, metal trusses are inside

"Open" is what is written there. Just like you have it, but there'd be a post right under it on the end gable under the ridge at 18'. I don't have a second one built like you show in the middle, as there will be no post in the center. Here is where I was going to use the threaded rod as the cross tie. I can buy 36' long material, but that gets pretty spendy. I was planning on using metal plates to bolt together the 2, 18' beams on the front gable along with the king posts tying it all together.

Not sure what you mean "we don't have a post centered under the ridge at 8' ". Ridge center is 18' and there is a post under it on the gable end.

I am not married to any specific size, so I had written different sizes.

I did have the sill beam as a 4x12. Ridge beam as a 2x14. Posts either 12x12 rc df or 6x12 hard wood.
Thanks for all your inputs thus far, most appreciative!  smiley_beertoast

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #16 on: February 08, 2019, 07:21:59 PM »
OK, let's try to size some members and connections.
I'm calling your area 20 psf live load (wind)+10 psf dead load(material weight)=30 psf total load.
The plates (what you called sills) are spanning ~8' and supporting half the roof width on each side, 18'. 8'x18'x30psf=4320lbs
Run the calc, you'll be doing the next one.
http://forestryforum.com/members/donp/ddsimplebeam.html
I'm getting a pass at 4x10 (3.5x9.25 not sure of your finish dimensions)

The ridge, I can see this one of two ways and am going to be conservative. I'm going to say it will carry 8'x18' of roof, the distance between gable and mid truss and the distance from mid truss to wall, two 8' spans. Load is the same then 4320 lbs, try your 2x14, I get a pass at full 2x14 or at 1.5x13.5 if duration is wind, pushing it there.

Rafters 18' span, use this calc;
https://awc.org/codes-standards/calculators-software/spancalc
2x12 I get max allowable 21'4"

The threaded rod tie, what is the tension on the tie and end connections;
Build that as a rigidly connected truss to support the ridge. Tributary area is 4' on each side of that truss, halfway to the gable, halfway to the wall, so 8'x36'x30psf=8640 lbs gravity;
http://forestryforum.com/members/donp/vectormath.htm
enter 8640 and 4 pitch
tie tension is 9720lbs
https://awc.org/codes-standards/calculators-software/connectioncalc
double shear, wood main member 1.5 thick, DF-L, 18 degree angle to main member, 1" bolt, 1/4" plate U shaped threaded rod connector wrapping the rafter... 1751 lbs, nope need 9720, try 3.5" main member, 4086 lbs. Hmm, 3 would work but the wood's gone, that's not working, need something serious there. Bob the tail and completely strap the rafter end in steel and hook up to the steel rod. The lower compressive strength of DF is 625 psi. 9720/625= the strap needs to wrap around at least 16 square inches of rafter end grain and you need a rod capable of 10,000 lbs or more.

That was stream of consciousness, check it and redirect.
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Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #17 on: February 08, 2019, 10:40:06 PM »
Original thought was 4x12 for the plates

2x14 for ridge passes, but barely, so 2x16

2x12 for rafters works

Boring through the 4x12 and through the 12x12 and putting a 11x11x1" thick  plate on the back side. 1" threaded (fine thread) rod would stick through the center and I would tighten it until everything remained just a little off plumb to the inside

https://stockcarsteel.com/cold-rolled-steel-bar/cold-rolled-1018-steel-round-bar

https://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm

Thoughts?

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #18 on: February 09, 2019, 12:02:40 AM »
I'd lean to 4x for the ridge myself.
You need to hook up to the rafter with the threaded rod rather than just the plate or post. It needs to create a rigid triangle, rafters and rod. You're going through another set of connections your way. My concern would be the rafter to plate connection simply shearing if you tie below the rafter, that 10 kips is still there at that connection needing to be resisted. If the rod is right at the top of the plate and your steel plate hooks over the backside of the top plate and also extends up and grabs 15.5 square inches of the rafter end grain, a groove up from the birdsmouth notch, that would probably work. you would be weakening the overhanging tail but there is one 2' away in either direction, I'm less concerned about that. You're getting my thoughts though, I'd want to start slightly inboard of plumb with the ridge slightly humped, force it to take load as the sheathing weight is applied. The rod is nice in that you can adjust it. Whatcha think?
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Offline Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #19 on: February 09, 2019, 08:50:59 AM »
That's a big piece of meat for the ridge board, but you're prolly right. I usually overbuild stuff and my overall design wasn't too far off.

I see your point clearly and agree, but I'll most likely directly fasten the rafter to the 4x12 with a plate on the inboard side of the 12x12 oppisite of the outside plate and weld on a bracket that goes up the side of the 2x12 rafter and bolt it there.

Thoughts?


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