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General Forestry => Timber Framing/Log construction => Topic started by: Sedgehammer on February 05, 2019, 12:00:58 PM

Title: Clear Span Roof Truss Calculator
Post by: Sedgehammer 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
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P 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 (http://forestryforum.com/members/donp/vectormath.htm)

Then I started to try to make it check members;
http://forestryforum.com/members/donp/trusswbending.htm (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?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 06, 2019, 12:57:01 AM
Thanks for your reply Don.
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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. 
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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.
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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.
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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.
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Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: LeeB 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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P 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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 06, 2019, 12:29:42 PM

(http://forestryforum.com/gallery/albums/userpics/53840/20190206_105652.jpg?easyrotate_cache=1549472903)



(http://forestryforum.com/gallery/albums/userpics/53840/20190206_102231.jpg?easyrotate_cache=1549471725)



(http://forestryforum.com/gallery/albums/userpics/53840/20190206_102131.jpg?easyrotate_cache=1549471722)


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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 06, 2019, 01:13:12 PM

(http://forestryforum.com/gallery/albums/userpics/53840/20190206_084008.jpg?easyrotate_cache=1549473410)

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This is what the gable end looks like on the pump house. House will look same.
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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.
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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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Den-Den 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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer 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. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P 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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 06, 2019, 11:05:13 PM
Correct
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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.
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Left wing is 20' wide. Will have exposed ceiling joists and wood ceiling as well.
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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'.


(http://forestryforum.com/gallery/albums/userpics/53840/20190206_214634.jpg?easyrotate_cache=1549511976)

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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)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 07, 2019, 07:19:46 AM
Start drawing the roof structural framing, I'm not following yet.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 07, 2019, 09:05:34 AM
I'll try and get something today. 
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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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 07, 2019, 03:22:55 PM
Here ya go
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Posts are 36' os to os, forgot to show
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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
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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.
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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 
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Have a huge bobcat to lift any timbers in place, so size of them isn't really an issue
.

(http://forestryforum.com/gallery/albums/userpics/53840/20190207_140157.jpg?easyrotate_cache=1549570466)

Title: Re: Clear Span Roof Truss Calculator
Post by: Don P 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;


(http://forestryforum.com/gallery/albums/userpics/10017/36_porch.jpg?easyrotate_cache=1549629821)

Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer 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
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P 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 (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 (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 (http://forestryforum.com/members/donp/vectormath.htm)
enter 8640 and 4 pitch
tie tension is 9720lbs
https://awc.org/codes-standards/calculators-software/connectioncalc (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.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer 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://stockcarsteel.com/cold-rolled-steel-bar/cold-rolled-1018-steel-round-bar)

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

Thoughts?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P 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?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer 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?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 09, 2019, 06:07:22 PM
I'm thinking a 4x12 ridge, align the rafter bottoms with the bottom of the ridge, the tops will poke up about 5/8" over the top, if that's objectionable a beveled 2x4 cant strip could fill the gap.

If you run the plates up the sides of the rafter and weld a cap plate over the top, better yet inset it flush, you've trapped it. Weld fast and douse it quick. The connection is eccentric but if the steel is heavy enough to not twist. Ben Brungraber at Firetower handed out some pics of historic iron "shoes" for restraining that connection, I'll see if I can dig something up. In old timberframe buildings and bridges it was very common to have steel or iron in high tension places like this. At that time he was working on a large truss that had over 70,000lbs of thrust at the heel. His comment was that if you can resolve the heeljoint the truss is usually buildable.

Here we go, this was just a quick google 
@TimberHawg1 (http://forestryforum.com/board/index.php?action=profile;u=44080) might enjoy these as well, first 2 are old engineering texts the third is a current company but there are pics of new and old work, Greenoak uses stainless nowadays for their steel work;
truss heels (https://books.google.com/books?id=3CA0AQAAMAAJ&pg=RA6-PA51&lpg=RA6-PA51&dq=timber+truss+heel+joint+iron+shoes&source=bl&ots=Ic5dcQB9SW&sig=ACfU3U02b27gajuBTiKK4-E-O6X3MGjh7w&hl=en&sa=X&ved=2ahUKEwiqpdrG6K_gAhWFj4MKHTkBDpIQ6AEwB3oECAcQAQ#v=onepage&q=timber%20truss%20heel%20joint%20iron%20shoes&f=false)
timber roof construction (https://books.google.com/books?id=i_VZAAAAYAAJ&pg=PA21-IA1&lpg=PA21-IA1&dq=timber+truss+heel+joint+iron+shoes&source=bl&ots=m-n26Yc57t&sig=ACfU3U0H-iO_5uRUp8xS5r0FwbFWbgmD0w&hl=en&sa=X&ved=2ahUKEwiqpdrG6K_gAhWFj4MKHTkBDpIQ6AEwCXoECAkQAQ#v=onepage&q=timber%20truss%20heel%20joint%20iron%20shoes&f=true)
Hit around pgs 15-20 here for some interesting trusses;
https://www.greenoakcarpentry.co.uk/wp-content/uploads/2016/09/What-Designers-Need-to-Know-about-Oak-Framing.pdf (https://www.greenoakcarpentry.co.uk/wp-content/uploads/2016/09/What-Designers-Need-to-Know-about-Oak-Framing.pdf)



Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 09, 2019, 08:40:22 PM
If one was going to use 10x10's or 12x12's for doorways or openings/archways, what can one expect for end and width shrinkage?

Thanks

Your post didn't show up on my phone, I'll check out what you linked and post on it later tonight or tomorrow. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 09, 2019, 10:03:21 PM
In length normal wood doesn't shrink appreciably. In width 1/4 to 3/8" from green to in service moisture content, that varies considerably. Where you chose to fix the connection plays a large role in the direction the shrinkage moves things. For instance with the post at a door if you pin the post closer to the jamb the post will stay tight to the jamb but the opposite face will move towards the pin. In the case of your plates pin them low, close to the bearing notch so that the notch will carry the load rather than the pin. When bolting, bolt low, near the bearing and do not space bolts more than about 5" apart across the face width of a piece of wood to avoid drawing the wood apart and splitting it between bolts.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 10, 2019, 03:04:09 AM
Can do both

Yes, he's pretty much correct. The thing we need to remember is that there are 8 other rafters that are all carrying the same load more or less, so while it's important to lock them down, I don't think the 'one' needs to be overly worried about. I was planning on some serious metal to keep everything lined up and secure. With that said, I kinda like the u-bolt approach. I think it adds some 'look' to it, plus making it very secure.

Some of that in those diagrams/pictures is just crazy.... Way above my pay grade that's for sure..... I do marvel in how things were made pre-powered tool era. Museums can be a favorite of mine.

Quote
In length normal wood doesn't shrink appreciably. In width 1/4 to 3/8" from green to in service moisture content, that varies considerably. Where you chose to fix the connection plays a large role in the direction the shrinkage moves things. For instance with the post at a door if you pin the post closer to the jamb the post will stay tight to the jamb but the opposite face will move towards the pin. In the case of your plates pin them low, close to the bearing notch so that the notch will carry the load rather than the pin. When bolting, bolt low, near the bearing and do not space bolts more than about 5" apart across the face width of a piece of wood to avoid drawing the wood apart and splitting it between bolts.
Gotchya on the shrink

Ya kinda lost me on the rest  ??? Remember I ain't a timber framing guy  ;D
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 10, 2019, 08:25:29 AM
Well you hopped into the pool, start paddling :D
I'm just messing with you, holler whenever I lose you :)

The tie is what makes that one rafter couple critical, it supports the ridge and the adjoining common rafters then hang from the ridge. It is a "post" supporting the ridge at midspan, the rest hang from the ridge. Load goes to stiffness, this is our hard point. If you are looking at them all contributing equally than you would look at the plate stiffness in bending across the 8' spans between tie points against the horizontal thrust load, that would be the stiffness, we haven't done that. Another way of doing it is to size the ridge so that it can support the roof from wall to outer gable with the rafters hanging from it and calling the steel tie gravy, or eliminating it. Double the ridge load above and 16' span in the calc. What you just described is kind of getting into hope or unconservative thinking, it might work but is not a good way to go unchecked.

For post and beam, steel connected heavy timber, the glulam folks are the standards writers. This is their main publications page;
http://www.aitc-glulam.org/Shopcart/index.asp (http://www.aitc-glulam.org/Shopcart/index.asp) The Timber Construction Manual is the standards reference. I have a copy here, you can probably get it through interlibrary loan and it does detail truss construction but kind of at a deep end of the pool level. Still might be worth checking out. "Design of Building Trusses" James Ambrose, is another good reference at more of a builder's level. "Simplified Engineering for Architects and Builders" Parker and Ambrose, has a very good section on truss design.

This detail excerpt from the AITC manual shows some of what I was talking about above as far as good and bad connection methods, click it and roll through the pics to see best practices;
http://www.aitc-glulam.org/Shopcart/Pdf/aitc_104_2003.pdf (http://www.aitc-glulam.org/Shopcart/Pdf/aitc_104_2003.pdf)
Think about how, where and why they connect where they do, especially go to pg 27 and read those prohibited connections and understand them.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 10, 2019, 09:46:34 AM
No, no, I got all that 8)

It's this part 
Quote
Where you chose to fix the connection plays a large role in the direction the shrinkage moves things. For instance with the post at a door if you pin the post closer to the jamb the post will stay tight to the jamb but the opposite face will move towards the pin. In the case of your plates pin them low, close to the bearing notch so that the notch will carry the load rather than the pin. When bolting, bolt low, near the bearing and do not space bolts more than about 5" apart across the face width of a piece of wood to avoid drawing the wood apart and splitting it between bolts.

I have an idea'r  ;D But not more than 21.9%......  :D
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 10, 2019, 06:46:08 PM
Don, while you're replying on the door/archway posts I thought I'd post on the interior stuff & anyone else with idea's, please chime in

The idea is to have a cathedral ceiling with exposed rafters preferred. Of course by doing that, it requires another roof to be built on top of it, so we can achieve R38 insulating value. We would prefer to have the 6" t&g pine or the 8" t&g hardwood as the ceiling vs rocking it. Don, on the exterior roof system you had said 2x12's work on 24" oc. I am wondering if 3x12's work on 32" oc.....

32" oc would be 7 rafters plus a half. This could be made up on the interior wall side of the house a few different ways, so for now lets say 7 rafters. Was thinking of something like this, with the 3x12 piggy backing the metal truss on truss 2, 4 & 6 or replacing 2, 4 & 6 entirely. Would need to still have a piece of rough cut on top of metal truss for ceiling to attache too though.  


(http://forestryforum.com/gallery/albums/userpics/53840/20190208_102736.jpg?easyrotate_cache=1549837480)


If 32" oc doesn't work, could do something like this on 24" oc. 20'x6" c-channel with 24"x12"x1/4" plates welded to both ends and either 1/2 chain with a threaded eye bolt for tension bolted through and to the exterior wall with a plate on the exterior side and/or to the end of the rafter heel or 2"x2" sq tubing welded under the c-channel to the outside wall plate and/or to the rafter heel


(http://forestryforum.com/gallery/albums/userpics/53840/20190210_161224.jpg?easyrotate_cache=1549837220)


With all that, we are not 'married' to any single idea, but we are trying to do something different without getting too exotic though. I can build pretty much anything metal and can work with wood, but am not a timber finisher by any means. Worst come to worst we could build a "pole barn" type RC truss, but really do not like the look all that much.

Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 10, 2019, 06:51:50 PM
Whoops, we're on top of each other but I'll post the reply to the post Q and then read this latest post.

If I'm understanding the question right. Imagine a 12x12 post standing on a slab. If I bolt a piece of angle iron to the floor on the door jamb side of the post and bolt the upright leg of the angle to the post, as the post shrinks the door jamb side of the post will not move. As the post shrinks the far side will move towards the point of attachment, the angle clip.

Same thing if you bolt a horizontal beam to a notched post. If I put the bolt or peg through the beam into the post down low on the beam, close to the notch the beam will bear on the notch as it shrinks. If I put the pin at the top of the beam and into the post, as the beam shrinks it will lift off the notch and hang from the bolt. The beam will likely split at the bolt. That is shown in pics in the second link in my post above. Scroll through that and think about what they are showing, good stuff for post and beam or timberframe builders.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 10, 2019, 07:36:48 PM
I'll let you walk through the rafter check, talk me through it like I did above and I'll spot you.
Also try 3.5x11.25 dougfir @4' oc.

The easiest way to do a cathedral ceiling is a structural ridgebeam with rafters hanging from it.
Sounds like a 20' span? 18' tributary width... half of each rafter is bearing on the eave wall, half is bearing on the ridge x 30 psf=540 lbs per lineal foot on the ridge. Glulam table here;
http://www.aitc-glulam.org/pdf/Capacity/DF_26.PDF (http://www.aitc-glulam.org/pdf/Capacity/DF_26.PDF)
Looks like a 5-1/8x13.5 would work.

Then 2x T&G decking. That looks good, is readily available and pretty fast to dry in. Does that solve it or do you want to keep going with the above?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 10, 2019, 10:00:43 PM
Whoops, we're on top of each other but I'll post the reply to the post Q and then read this latest post.

If I'm understanding the question right. Imagine a 12x12 post standing on a slab. If I bolt a piece of angle iron to the floor on the door jamb side of the post and bolt the upright leg of the angle to the post, as the post shrinks the door jamb side of the post will not move. As the post shrinks the far side will move towards the point of attachment, the angle clip.

Same thing if you bolt a horizontal beam to a notched post. If I put the bolt or peg through the beam into the post down low on the beam, close to the notch the beam will bear on the notch as it shrinks. If I put the pin at the top of the beam and into the post, as the beam shrinks it will lift off the notch and hang from the bolt. The beam will likely split at the bolt. That is shown in pics in the second link in my post above. Scroll through that and think about what they are showing, good stuff for post and beam or timberframe builders.
Okay, got it. 
Was planning on overhang the horizontal beam 3 " on each side. Then notching them as wide as the studs. Fastening the stud to the vertical beam and 'now' only down low to the horizontal beam. The floor joists would rest on the horizontal beam. 6' opening with 12x12 rc df & 3' opening with 9x9 rc df no floor joists above it.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 10, 2019, 10:19:52 PM
I'll let you walk through the rafter check, talk me through it like I did above and I'll spot you.
Also try 3.5x11.25 dougfir @4' oc.

The easiest way to do a cathedral ceiling is a structural ridgebeam with rafters hanging from it.
Sounds like a 20' span? 18' tributary width... half of each rafter is bearing on the eave wall, half is bearing on the ridge x 30 psf=540 lbs per lineal foot on the ridge. Glulam table here;
http://www.aitc-glulam.org/pdf/Capacity/DF_26.PDF (http://www.aitc-glulam.org/pdf/Capacity/DF_26.PDF)
Looks like a 5-1/8x13.5 would work.

Then 2x T&G decking. That looks good, is readily available and pretty fast to dry in. Does that solve it or do you want to keep going with the above?
I cannot figure out how to change spacing unless I got the wrong link, but I looked at 3 of them

Prefer to run the ceiling parallel with the house walls, but I guess that's possible with 2' DF on 4' oc. I don't know where that's available right at the moment though or price point

Since I have to build another roof on top of it, would the live load be double?

No glulam and I cannot put that much weight on the interior wall end, as no direct post/wall underneath. It's offset about 18". Could put a double floor joist right there though. The other end is the fire place, but that most likely will be built later. Not going block all the way. Am leaning towards using a stainless chimney and using steel primed black on the inside above the mantle to ceiling tapering and angling as it goes the entire 27'. Would have a riveted look, but just with 5/16 square headed bolts
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 10, 2019, 10:41:02 PM
Gotcha, no bearings for a structural ridge beam, trusses it is. Getting to be bedtime for me and I have welding class tomorrow nite, might be a couple of days before I can look hard at it. I'm not meaning to hog all the fun, you other guys can chime in.

Rather than overframing the roof another idea, 6" of foam, three layers of 2" thick 4x8 sheets would perform better than fiberglass, polyiso is around R7 per inch, XPS is R5 but either will perform better than glass.  This is along the lines of what I was thinking, these were 4x10 DF at 4' oc (narrower room and a little steeper pitch) 2x6 T&G, foam, 2x4 sleepers at 2' oc, ply and then shingles.

(http://forestryforum.com/gallery/albums/userpics/10017/biltuproof2.jpg?easyrotate_cache=1192055654)


(http://forestryforum.com/gallery/albums/userpics/10017/biltuproof3.jpg?easyrotate_cache=1192055654)


(http://forestryforum.com/gallery/albums/userpics/10017/biltuproof1.jpg?easyrotate_cache=1192055654)
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 10, 2019, 11:29:59 PM
No probs, have fun, see ya later and many thanks!

Nice work! 

I'm at a 4/12 due to the fact the existing is 4/12 and I can do the roof steel myself. Plus I don't think a steeper roof would look as nice with this style of a home. What do you think?

Polyiso

6" @ R39 as 2" = R13 x $30 per sheet or about $2,100. Depending on how it's laid out, it might not be that much higher than glass over all.

5" @ R33 = $1,824

Could one screw the 19/32 osb directly to the decking if 2" df t&g with 7" screws?

Purlins vs sleepers.... After thinking on it, it's about a horse apiece I guess. One could go with 4" and then sleeper/purlin it, then go with 1.5" in between purlins since 24" oc if one needed to save the 1.5". It'd be a R33 @ $2,064.

Okay, I am on board with the polyiso. Now the easy part...... :D
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 11, 2019, 12:11:16 PM
Ok, have a little conflict. If we go with the 5 or 6" polyiso, how do we do an exposed soffit with 8" rafter tails. 

I suppose one could nail/screw the rafter tail to the sleeper and decking below and just put the 5/8 car siding on whats exposed and run the 5/8 osb on the rest? 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 11, 2019, 07:35:07 PM
Decking

2x8 T&G YP @ $1.64 sq ft

or

2x6 T&G DF @ $2.60 sq ft

Besides the obvious price point difference and wider wood, any advantages in using DF over YP?

Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 11, 2019, 10:57:32 PM
I'd roll through some of the syp and see if the quality is acceptable, if so and if you like the look seems like a no brainer.

If you don't mind a fascia above the exposed tails that will cover the depth required for the foam sleepers and ply then that would solve it. I prefer having that vented channel created by the sleepers, your call there.

I like playing with this truss design tool;
http://pages.jh.edu/~virtlab/bridge/bridge.htm (http://pages.jh.edu/~virtlab/bridge/bridge.htm)

Here's a quick one I did to show how it works, add a 0 to every number to get the approximate forces, These are axial (along the length, axis) forces acting on the truss members. So those forces would be checked as columns. The top chord also acts as a beam supporting the live and dead loads distributed along the members between the nodes. They are designed as "beam columns" or in the NDS "Combined Bending and Axial Loading" we can preliminarily size this but your engineer will do the actual final calcs and design.


(http://forestryforum.com/gallery/albums/userpics/10017/36truss.jpg?easyrotate_cache=1549943311)


Welded up 50 coupons tonight, something smells like burnt metal and burnt fur... off to the showers :D
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 12, 2019, 12:51:46 AM
That's what I was thinking

think_not.....;D Have to figure a way to frame in the rafter tails.... I could rip the 2' that'll go on the roof out of the 2x8 and that won't be much if I use 6" polyiso with sleeper. Then screw through the 8" of the 2x8 into the decking and then screw it to the sleeper

I hear ya on the venting part. I might have to drop down the freeze board a bit for air, and screen it for bees or drill some holes and screen them.  smiley_devil_trident

Hmmm. My computer doesn't like it. Just a blank page with a small square box in the middle at the top of the page. Tried going to the school itself and it's website is fine all the way up to the truss builder  smiley_furious3

That's kinda how I was thinking, but out at the edges would be 1' deep and at the mid points in between it, would be the web to the lower truss. Then I would weld in plasma cut designs in the 11 gauge panels.Weld them in between all the truss openings. Could maybe even go to 12 gauge.

Working on a acrylic circle LED 30" design for the middle at the peak, so would want the center to be that large clean through. Supports would have to go around it.

Coupons  smiley_clapping You trying to be a certified welder?

Burnt fur just mean you was being busy..... splitwood_smiley

Could either go 40" center and have 3 metal ones with 3 wood ones or got to 4" oc and have just the 4 metal ones. Would have a 3x6 screwed to the top of the truss with the width being the 6", so as to have 3" to nail the syp into.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 12, 2019, 06:50:26 AM
Try internet explorer browser and update your java with Oracle.com and see if that gets it.
The circle in the center top reminds me of the Iron Bridge in Britain, nice detail, way above my pay grade. If the truss is top chord bearing on the wall and the 2x or 3x6 on top of the steel projects out to support the tail, the tail could be applied under that, outboard of the wall, then the buildup of T&G, just brainstorming there.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 12, 2019, 10:12:52 AM
no dice....... :o
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 12, 2019, 10:15:34 PM
Not a big problem, you are way out of my league, this is deep into engineer land.
Here's a sketch of what I think you are talking about for a truss;

(http://forestryforum.com/gallery/albums/userpics/10017/36porch1.jpg?easyrotate_cache=1550026696)

I think it is quite do-able. As I look at it the bottom arc of the circle wants to straighten out under load and let the truss flatten, the strength of that circle is critical. The exposed tails could be attached to the extended top chord, grooved around the steel. Top chord is the bearing at the walls, the bottom chord drops down inside the walls. A nailer on top of the top chord to attach the T&G to. Is this pretty much what you are envisioning so far?

I am going for structural certification. We got a steel lintel in at work today where somebody decided to knock holes in the block walls years ago where it suited them, the inspector called for engineering and repair now that we are remodelling. We dry fitted the built up parts a few weeks ago and tacked it, then dropped them off at the welding shop, paid good money and waited and hauled. Then back to work, we dry fitted, played with them a little more, jacked into place, then put posts and post bases under them and tacked. I'll call the welder out to do the final welds then a certified welding inspector. It would go smoother if I can do the welding on site myself next time. Looks like the weather breaks tomorrow so back up top to strip more roof and do repairs then class tomorrow nite, I was getting into a groove towards the end last time so hopefully it will start to be like riding a bike soon.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 12, 2019, 11:13:38 PM
Hot *DanG! Your pretty handy yes sir you is!

The circle would also have a plasma cut design welded into it or if we go with an LED there, it would be a 24" opening cut into the 12 gauge. I'm working with a couple custom LED makers right now, so depending what they can come up with. It might me flat on the bottom and then made to match the top cord though 

There would be a web tie at the midpoint between the wall and the circle

There would be no metal outside the walls like you're showing on the rafter tails

Top cord is either bearing on the walls if the walls are the thickness of the roof system shorter or the top cord is welded to a plate that is sitting on the top plate

Yes, was thinking of a 3x6. Give it some bulk in the looks department. Drill tap it onto the top cord with 4" drill tap screws

Wow, good for you! You're a man of many talents I see. If I may, what type of stuff do you normally work on? This job doesn't sound like a log cabin

Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 13, 2019, 07:51:21 AM
 With a tie lower down the full circle is fine, the lower tie is taking the spreading force.

You would be looking at the entire section I drew last night then as the top chord, a combination section sort of like a plate girder and the tie is the bottom chord, an interesting problem. Let's keep playing with it a little while but this will need to go upstairs for final design.

You'll need to find withdrawal specs on the 4" screws for uplift later in the design.

I'm just a carpenter in a small rural community, so many hats, like many of the guys here. The current project is remodeling an old concrete and masonry 1940's Shell gas station into an office and coffee shop. On the last log barn repair we actually got into sort of a similar tie to what you have been talking about. The log plate at the top of the walls was being pushed off the walls by the spreading rafters. We recovered the wooden silo rods and put them through the 9x11 plate log with steel plates on the outside to act as big washers. The rods spanned across he building as rafter/plate ties. We welded in turnbuckles in the center of the rods as well as the threaded ends under our washers, then began cranking the rods tight and pulled a good bit of the bow out. Since the plates had taken a permanent bow, yup even at that dimension! We got out what we could and restrained them from further thrust, picking the happy point but preventing progressive collapse. If you look at the barn pic Brad posted on TimberHawg1's thread you can see a neat bowstring reinforcing the near tie from plate, down under the unposted tie and back up to far plate. Whoop off to the races. Tell me about yourself.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 13, 2019, 11:00:32 PM
 Actually midheight is about the bottom of the circle.

<br
>(http://forestryforum.com/gallery/albums/userpics/10017/36porch1b.jpg?easyrotate_cache=1550116676)
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 14, 2019, 12:47:00 AM
Just spoke with the designers on the LED and the biggest they can make is 24", but the image is only 18"..... think_not

So then I asked what is the biggest they can make and he said 32"x17"  8) so...... The circle will be a rectangle, which will raise the bottom cord a far amount

It will be a bottom cord bearing if the wall is the thickness of the roof system shorter as you are showing it in the latest rendition

If not the 4" (5/16") screws, how about welding a piece of 1/4"x2"x2" angle to the top cord on both sides every 2' and them either drill and lag screw it down with 3/8" or 1/2" bolts or drill all the way through and bolt it down? I like bolts better, but I'd prolly use some home made square washers bent in on the edges and weld the head of the bolt to the washer and then counter sink them into the beam. This way it could be tightened and the bolt head wouldn't move

Don't say you're just..... You're a pretty talented guy. Plus you spend a lot of time here helping people like me out.... smiley_clapping

Sounds like it might be an interesting project. I like how some of them old buildings are rebuilt to keep their charm, yet are fitted to work well with today's technology.

Me? Hmm.... Retired medically I guess best describes me right now. Had a heart attack in October, but that's all fine now, but I fell backwards out of a cab over truck and bounced my head and my back off of the pavement back in 15. Messed be up real bad and still. Before that worked with my wife in her trucking business. Had 4 quad axle dump trucks. Done a lot of things over the years. Built my own house back in 98 in WI. 4,400 sq ft. 2 stories. Walkout basement. In floor heat. Framed houses in the 89 for a bit. I can work wood fairly well. Can weld pretty good. No training in either though. Had a dairy service business and designed some specialty equipment that was sold globally. Grew up on a dairy. Have a 5 & 6 year old, so they keep us busy with all their activities. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 15, 2019, 07:24:06 PM
Break out your pencil and sketchpad, you've lost me again :).
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 15, 2019, 08:24:48 PM
Yeah, my wife says I have a tendency to do that. Sorry

Can do either or or another idea. I welcome any design inputs from anyone

Bottom one thinking of putting some wood in it for a 'warming' effect, plus it adds some depth to it

Can either do the 12 gauge plasma cut in's or just go with some webbing


(http://forestryforum.com/gallery/albums/userpics/53840/20190215_191007~0.jpg?easyrotate_cache=1550279956)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 15, 2019, 10:18:47 PM
Now show me how you are sitting on the wall and your bearing on it, the plasma cut art, the tie rod, the 3x6 plate, ceiling, insulation, overhang and fascia, in other words bring it all together in a section cut of what you are thinking.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 16, 2019, 12:43:47 AM
Here ya is


(http://forestryforum.com/gallery/albums/userpics/53840/20190215_233243.jpg?easyrotate_cache=1550295896)


Ya made me think.....  electricuted-smiley

Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 16, 2019, 08:55:24 AM
Cool, getting there. Go right and figure out the overhang, we have exposed polyiso right now, figure out that part of the detail to the fascia and tails.

The 2x12 bolted to the face of the post is a no go. It would need at a minimum to be notched into the post, cant hang from bolts.

We were up on the roof till dark, off to see if it survived the rain, or sucking up water :-\. I'll check in on you later.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 16, 2019, 11:28:06 AM
2x10 ripped down to 18.5 on both edges to roof angle for the freeze boards, which will cover up the polyiso. The cement board will butt up to the freeze boards and the rafter tails. Same as on the pump house pictures, except on the rafter end they are cut to fit. Rafter tail itself is 21.5" with a 2x6 and then a 2x4 fascia. Both being ripped to the angle of the roof at 18.5


(http://forestryforum.com/gallery/albums/userpics/53840/20190206_084008.jpg?easyrotate_cache=1549473410)


It's top cord bearing, so should be fine. Actually I don't think the ends bolts are even needed, as there should be almost zero wall push out. The other reason for the 2x12 is so sheet rock an run up to it, leaving a bit of it and all the metal for a plate type look. Might do the same for the exterior, but the cement board is only 3/8, so the 1/2 plate would still be exposed

The above is based if i leave the wall at the same height as the rest. If I drop the wall 3", the top cord is welded to the top of the 1/2" angle

Drawing didn't show the angle tabs welded to the top cord of the truss in which the 6x3 would be bolted to, but thinkin on drilling through top cord and bolt directly through it with 1/2" bolts every 2'

Fun, fun.... Got any pics? Cold and damp here. Got Jack frost hangin from the trees here....


(http://forestryforum.com/gallery/albums/userpics/53840/20190216_120834.jpg?easyrotate_cache=1550346194)


Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 16, 2019, 10:42:47 PM
Happily we were above freezing, hmm, that could go either way... mud :D

Hanging the overhangs, not a good idea, it's gonna sag over time or depart in high wind, keep thinking on that.

On steel trusses, I'm just reading one chapter ahead of you, in other words keep tuning the design but it does need to go to an engineer. I've been reading through the steel construction manual and really the way to design this is not as a truss but as a tapered plate girder. This is an older stand alone section which no longer appears in the manual but is more in line with what you are wanting to do, also notice the section and examples on access holes;
https://www.aisc.org/globalassets/aisc/publications/out-of-print/welded-tapered-girders.pdf (https://www.aisc.org/globalassets/aisc/publications/out-of-print/welded-tapered-girders.pdf)

Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 17, 2019, 12:59:24 AM
It made the table on the compound miter saw really slippery today. Them 2x4x12's moved like they was on ice......  smiley_headscratch

Yup, I would generally concur

Yap, that would describe it better, but the manual it's got lots of funny looking characters along with numbers in it......  electricuted-smiley

What's the loads we're looking at for it do you figure :P
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 17, 2019, 09:12:24 AM
It looks to me like the web works at the quarter point but is possibly in buckling trouble at the midpoint at 11 gauge. What you are really doing is marrying 2 tapered plate girders at the ridge with a hole in the spliced section. There is a rotational moment connection at the peak right there that needs serious consideration. I believe it is quite do-able, the loads are light, the details are up to the engineer. Work out the parts of the design that you can do before going there though, the overhangs still need work. I understand that you would like to avoid that cost but it is money well spent... the role of the engineer is to do with one dollar what any damfool could do with two. The shop where I buy steel and have fabrication done has a couple of engineers they like to work with who do good work at reasonable prices.

 What I would try is lifting up the section you drew and extend the top chord out to support the eave overhang and bury it in a notched out rafter tail. The 2x8 T&G then forms the soffit. On the gable ends also extend the T&G out to support those overhangs. One way to lower the overall height is to try an upturned channel as the top chord with a 2x T&G nailer laying flat in the channel, if that works that would lower the overall overhang thickness about 3". Then remember that is just an idea, don't become too invested in it. The engineer might come in out of left field with a better idea.

I'll tell a little story from this week as to why I like to consider things before bringing in the design professional. We had thought through several options for plumbing and HVAC with those trades before bringing in the architect's engineer. The ideas coming out of that engineer, well, sucked. Because we had other ideas to offer the ideas were out there for all the parties to consider. I think we redirected what would have been an ill considered plan, and if not I will listen and possibly redirect again. Hopefully it saved the time of going down an undesired path. On our own projects we have more time to do some of the legwork and time to consider things.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 17, 2019, 11:55:17 AM
Any idea on what an engineer would charge?

The place you work with, even though I'm out of state, you think they'd be usable?

Notched rafter tail......... They's only gonna be 2x8's. Not much meat to be anotchin on.....

Thought about the upturned channel. Abandoned it for the look of the beam. Removing it still leaves me short of going over the plate with any metal to extend out for the rafter tail. I'd still need to make that wall shorter. Looks like 6.5" total. Then there's the roof thickness issue. We're still at a thickness of 9". Plus the thickness of the T&G is about 1.125" thicker, soooooooooo electricuted-smiley

A few thoughtin's.....

1. Make girder deeper. Bolt 3x3 wood to both sides down 7.5" to the top of the 3x3. Nail T&G to top of the 3x3 and then polyiso on top of that. Have truss/girder 7.5" above the wall. Bolt 2x8x4' rafter tail 2' up onto the girder

2. Build webbed truss and put cut outs into it or just leave them as is or redesign it to look more rugged/deco/I don't know what to call it. These here are very popular here, but too pole barnish looking. 10' oc and span 40'.
https://wheelermetals.com/store/products/d/19948/trusses/40-truss (https://wheelermetals.com/store/products/d/19948/trusses/40-truss) Drop the T&G down same as above

3. Scrap metal truss and figure something else out. Any idea's  ;D

4. Build a tipi and convince the wife we're the long last tribe of the Mohicans  smiley_indianchief

Update; Had an epiphany at church smiley_angel02_wings
Developing pc_smiley
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 17, 2019, 03:15:36 PM
Build a truss similar to these 2;


(http://forestryforum.com/gallery/albums/userpics/53840/polebarnlt.jpg?easyrotate_cache=1550432510)


The above is how it will fit on the wall with modifications. 

Will be 7.5" above the wall, which is like the rest of the house

Plate on the wall will be 12" wide x 1/4" plate and 32" deep and will extend over to the top plate 8". Will bolt through the top like in my previous drawing and through the wall with corresponding plate on the exterior


(http://forestryforum.com/gallery/albums/userpics/53840/Pole_Barn_Truss_Clear_Span.jpg?easyrotate_cache=1550432648)


It will be a web truss, but made with 2.5"x1/8" sq tubing

Depth will be 38"

Will use 8" syp t&g for the entire roof system, so as all roofs will match. Will add approximately $1,300 to budget, but makes layout simpler, thus faster, so a savings there

From the top of the truss will drop down 13.5" and weld a 2x3x1/4" angle ledge on both sides for 3x6 timber to set on. 3x6 timber will be bolted to & through the truss and to each other. 8" t&g will nail to top of 3x6 and 6" of polyiso on top of that, which will be to the top of the truss. Screw 8" t&g to the truss. At rafter tails, bolt 2x8x4' rafter tail to truss

Between truss at ridge place a 7x7 timber cut to fit between trusses. Will sit on 2x3x1/4" ledge welded to both sides of each truss and will weld to the angle that is welded on for the 3x6. Will cut 18.5 angle on edge of the 7x7 timber to match roof slope. Will bolt to the 3x6 timber where they meet with a 6x6x1/4" angle

I think this is a good blend of both metal and wood. If we want we can add a collar brace and add the arsty fartsy stuff there, but collar brace won't be needed
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 17, 2019, 06:44:37 PM
The shop that makes those trusses more than likely has an engineer on staff that can design and fabricate what we were talking about earlier.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 17, 2019, 06:56:37 PM
Going to build it ourselves or if not, have a guy locally that's only $25 an hour in his shop. Just depends how busy we are and how I feel. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 17, 2019, 07:14:09 PM
That one link to a 40' tube steel truss... was it local? that was cheap
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 17, 2019, 07:25:32 PM
104 minutes 

That's a standard size, so they build a gazillion of them, but I will give them a look see. Not sure if they do custom or not. 

Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 17, 2019, 10:47:34 PM
What kind of loads you think we're looking at?

Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 18, 2019, 07:04:06 AM
What I drew above, the trusses were on 4' centers x 36' span x 30 psf=4320lbs each. Need to keep an eye on the actual dead weight of the steel though, it might be worth bumping that up to 35 psf.

For the bar joist "trusses" you showed, here's how I'm thinking about them and maybe one of the engineers will help me out here. They are designed as parallel chord trussed half beams, each one 18' long. Then at the peak the two halves are connected by a rigid moment resisting connection. If that is the case the stress on that peak connection, where you want the hole, is something like (4320lbs/2)x 18'=38,880 ft-lbs. Think about it just like a pair of torque wrenches, the handle is 18' long and you are pulling down with 2160 lbs of force, the "bolt"(connection) is seeing that torque (rotational moment). If you've ever tried to torque up to a few hundred ft-lbs and broken bolts you understand my concern with rednecking this. All that is simply my read of how that is working, not saying I'm reading the problem right, that is why I kick it upstairs.

I'm also wondering about the roof construction beyond this room, you've mentioned 2x8's. If 2x8 rafters are spanning 18' we need to talk about that :P.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 18, 2019, 09:19:11 AM
Yeah, prolly right

Canceled the hole. If we add the LED, it'll be below the truss. Some of the manufacturers of those trusses bolt together at the ridge and these are just made from angle. Pretty sure these are just 2.5x2.5x3/16


(http://forestryforum.com/gallery/albums/userpics/53840/Pole_barn_truss_2~0.jpg?easyrotate_cache=1550498735)


What would you put under the plate for studs. Will be 2x8. I am thinking at least 3

Spans are 24' and 20'. Was going to add webs where needed, but hadn't really looked at it yet and since we're going with the 8" syp t&g for the wooden trusses now instead of 5/8 osb, there'll be more weight to consider
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 18, 2019, 09:47:23 PM
Quote
What would you put under the plate for studs. Will be 2x8. I am thinking at least 3

Spans are 24' and 20'. Was going to add webs where needed, but hadn't really looked at it yet and since we're going with the 8" syp t&g for the wooden trusses now instead of 5/8 osb, there'll be more weight to consider
Lost me again :D. Draw me sumthin, I don't know where we are.
Title: Re: Clear Span Roof Truss Calculator
Post by: Hilltop366 on February 18, 2019, 10:26:35 PM
Been following along but out of my league to comment on design but I'd price the weight of the same kind of steel out and compare it to the cost of the truss from the company in the link.

I'm thinking that if you can make a stock pre-made truss work for you verses a diy that the pre-made with engineering, cutting, welding, and priming all done might be a good deal.  
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 19, 2019, 01:33:54 AM
Lost me again :D. Draw me sumthin, I don't know where we are.
Hopefully tomorrow, but it's just a vaulted parallel truss with a modified top plate mount
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 19, 2019, 01:43:48 AM
Been following along but out of my league to comment on design but I'd price the weight of the same kind of steel out and compare it to the cost of the truss from the company in the link.

I'm thinking that if you can make a stock pre-made truss work for you verses a diy that the pre-made with engineering, cutting, welding, and priming all done might be a good deal.  
I know where you're coming from and I wish that'd work, but several issues
1. Those truss are made to standard specs and they build a ton of them, so costs are very low because of
2. Those are pole barn style trusses and while they would get the job done, doesn't look very nice and this is going in a house
3. Since we're making a known truss, engineering won't be much. Most likely not even needed
4. Can't be red primered anyways, so bare metal would be preferred
5. Sure I could buy those and then cut them to fit and re-fab them, but then we'd really have no idea where we were, as it has to be a vaulted parallel truss
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 19, 2019, 05:23:48 PM
Decided to go with blown in fiberglass since I have the room with making a vaulted parallel truss as deep as I want basically. A fair amount cheaper than the polyiso


(http://forestryforum.com/gallery/albums/userpics/53840/20190219_160728.jpg?easyrotate_cache=1550614483)


What I'm not showing is the 1/2 wall plate that goes under the 7" top cord to give me the 7 1/2" needed for the rafter tails

Also not showing the 3/8 wall plate that will go from the bottom of the beam down to 1/2" past the bottom cord


(http://forestryforum.com/gallery/albums/userpics/53840/20190219_160930.jpg?easyrotate_cache=1550614654)


We could make the truss only 22.5" deep and run the 3x6 flush to the bottom cord. Trying to get some pictures to weight both options

Was thinking if we leave the 16" exposed, was to make some faux bolted plates at every exposed web connection that would look like it was bolted together. Kinda like bridges were built years ago

A friend just suggested to make the beams a bit bigger like a 3x10 and drop it down below the truss 2" or leave the truss only exposed it 2", so the truss would only be about 24.5" deep

Which ya guys think......teeter_totter

I also am wondering how far that 2x8 syp t&g (1.5x7.25 actual) could span? If 60" for the roof deck and 52" ceiling, we could lose 1 truss
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 19, 2019, 08:47:35 PM
Interesting. My first thought was that would be tough to insulate between and around the web work. Then the thought of lumber bolted to the sides of the flat plate girder type truss would help resolve the buckling issue and make a smooth easily air sealed ceiling plane. Then listening to your friends suggestion and combining that it sounds like a flitch plate beam, the beams made by sandwiching lumber on each side of steel plate. Some neat ideas floating around.

Looking at it like a flitch plate with the rest of the steel just dangling below. The arched tie is a piece of something like 4" wide flat plate welded to the bottom. Just throwing the thought of the night out there, if the flitch plate passes and the tie is there, poke the rest as full of holes as you want.

(http://forestryforum.com/gallery/albums/userpics/10017/AutoSave_36porch2.jpg?easyrotate_cache=1550631539)
 

From the building code (table R803.1) #2 syp in 2x material would be good up to 72" span for roof sheathing.

Ever wander around under the bridges in San Antonio?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 19, 2019, 10:06:16 PM
If the beam mid truss, would just weld a plate between webs flush with beam bottom

Would still set a beam at least 1 size deeper than beams sandwiching truss, between trusses at ridge. Would give impression that the 3x10's and 12x12's are doing the work. Would need to come up with a way to bolt angle on 3x10 ends at ridge where butts to the 12x12 though. Would a 6x6 angle work drilled at the 1.5" point from edge on both sides of the angle and bolted with 4,  1" bolts or would it put to much stress pulling in different directions

If the beam below truss, could weld 18" or so of the plasma cutouts to the bottom with round stock, small pipe or ? for a stiffener. Then could still add the circle at ridge

So the 60" works,  smiley_safety_glasses smiley_bandana 

Been there 10 years ago, walked along the river and had dinner I guess, but don't remember much (from accident). Wife said we're going again this summer, so   digin1 smiley_beertoast

So which ya guys think 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 19, 2019, 10:20:26 PM
Interesting. My first thought was that would be tough to insulate between and around the web work. Then the thought of lumber bolted to the sides of the flat plate girder type truss would help resolve the buckling issue

Looking at it like a flitch plate with the rest of the steel just dangling below. The arched tie is a piece of something like 4" wide flat plate welded to the bottom. Just throwing the thought of the night out there, if the flitch plate passes and the tie is there, poke the rest as full of holes as you want.

(http://forestryforum.com/gallery/albums/userpics/10017/AutoSave_36porch2.jpg?easyrotate_cache=1550631539)
 
Just saw this after I posted, thanks!
If midtruss beam, just weld a plate between beams in between webs to seal 
Per your picture. Need area for insulation, so metal would need to extend 15" above beam. Then someway to fasten decking to the truss. I guess a 2x4 could be bolted to each side and then could screw decking into it
Kinda kool idea....... 🤔🤔🤔
The 4" is how thick, .375"? 
With plate being so deep, could be fairly thin I would think
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 19, 2019, 10:46:06 PM
3/8 would be more than enough structurally for a tie, gotta think about stiffening side to side which is as much about width as thickness but it is a tension element in my way of thinking.

Here's what I was thinking, the wood on the sides of the steel is hidden, it can be local framing stock, I've got a 2x12 and a 2x4 drawn. Bolt through the lumber and steel sammich in a W pattern to form the flitch plate beam. The roof deck goes on top, the ceiling goes underneath and the insulation is in between.


(http://forestryforum.com/gallery/albums/userpics/10017/36porch1insul.jpg?easyrotate_cache=1550634332)


Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 19, 2019, 11:52:14 PM
Kinda liking this curved thin design.

Curveball......smile_juggle

Show the beam and screw 2x8 t&g to the top of it like before. Bolt a 2x6 on top of the upper tie to screw the decking to.

The metal that is sammiched can be just regular plate to cut down on cost, but a question on the beam to metal. Beam is may be wet (still waiting on kiln drying guy), does there need to be some separation between beam and metal? If so, prolly just an area 2"x3/16 wide where bolted to beam would suffice. There would be gap if I put the angle ledge to hold beam.

Just weld the deco metal to the bottom of the regular plate (but above beam line) with the deco circle in it to get desired depth and run down the wall about a 1' or so with a plate that bolts to the wall.

I guess this same curved deco idea could be also welded to the bottom of the tube truss.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 07:53:10 AM
Yup, the way I'm looking at that is the upper section is designed as a rafter pair. The rafter pair can be wood, steel, bar joist, flitch plate, etc as long as it can take the load and deflection. The lower arched plate is the tie across the rafter bottom to restrain the rafter pair from spreading, that removes that peak moment resisting connection. The deco plate in between is just keeping that bottom chord from changing length. So it is really at its heart just a typical pair of rafters with a ceiling joist.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 20, 2019, 08:57:41 AM
Question, if we put a top tie on it, why the 2, 2x12's & 2x4's?

Also, one could actually just use a 27" deep vaulted parallel I-beams and put the 3x10 on top of the bottom flange and a 2x6 lying flat on top of the top flange. Then once one knows what that thickness is, don't put the lower flange on at 27" point, put it on the bottom of the curved part. 

In this way one could get design values fairly easily I would think, but I haven't had any luck finding a calculator yet.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 09:38:12 AM
I'm not following all of that but here is my thinking, the 2x12's are common rafters, there is our easy design value. They would pass as 2 #2 syp or dougfir 2x12 rafters spaced at up to 5' apart, I drew them at 4'9" spacing above.  The 2x4's were packed on just to give that 15" depth for blown in insulation. The top edge of the 2x12's is the nailing surface for the roof T&G decking. The bottom edge of the 2x4 is the nailing edge for the ceiling T&G. The other structural element needed in that is a bottom rafter tie to keep the rafters from spreading. The arched plate. It's length is fixed by the deco metal. By having the rafters bolted through the deep decorative plate, it is increasing the rafter strength and stiffness, I haven't counted that in the above. If the rafters deflect they may put some amount of buckle into that thin unstiffened plate, that is cosmetic not structural. If you want to add decorative beam work below the ceiling plane that is fine. If it begins to add up to much load then the # 2 rafters should be bumped up to #1, SS or LVL. The 2x12 or both 2x12's are ripped down to 2x8 as tails that extend over the wall.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 20, 2019, 01:16:18 PM
Kind like this


(http://forestryforum.com/gallery/albums/userpics/53840/20190220_121235.jpg?easyrotate_cache=1550686484)


This way don't need to double up on joists & timbers

and spacing I think is 60" based on 20' with 3 trusses
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 01:40:41 PM
The section where you have the arrow that says 12 gauge will buckle from the roof load, it can't handle the compression. That is where the structural 2x12's and any 2x spacing you need go, which renders that flat 2x6 and welding up top unnecessary... more good for less work and cost. the 3x12's under that are not a bad thing atall, they stiffen the plate but are part of the trim.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 20, 2019, 03:06:27 PM
I gotcha.

Could we use 2, 2x8's instead of a 2x12 and a 2x4? Part of the reason is the 2x8 can go right out for the rafter tail

Also, what does eastern red cedar compare to in using a span calculation 

Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 04:15:19 PM
No it has to be a pair of nice 2x12's, rip the 2x12 down to 2x8 as it passes over the wall, make sure there are no other defects in that ripped down area.
ERC is not really a good structural wood which is why you don't see it listed in span tables and in the design value tables. It is very nice for paneling and trim.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 20, 2019, 05:45:20 PM
🤔 won't the metal also be picking up some of the load since it's sammiched and can't buckle?

It might not matter, just not sure what I'll be using fir rafter tails yet. Waiting on the RCDF sample  

On the erc (eastern red cedar), before you posted i remembered about the wood website wood database and it lists it stronger than western red cedar https://www.wood-database.com/western-red-cedar/ (https://www.wood-database.com/western-red-cedar/)  and https://www.wood-database.com/aromatic-red-cedar/ (https://www.wood-database.com/aromatic-red-cedar/)

With that said,  can it be used for porch rafters. 2x8x10' (1.5x7.5 actual) with a 8' span, 2' tail 2' oc. Will have the 2x8 t&g fir decking. Metal roof. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 06:32:05 PM
I'm using the KISS method there, 2x12's work, 2x8's is an engineer's playground.

Wood database is reprinting data from the USFPL's "Wood Handbook". Those are ultimate average strengths based on break tests of small clear samples. Go carefully trying to apply that to allowables. WRC has different growth characteristics and so a higher likelihood of getting higher grade material in the field. That said, for small short spans, pay attention to grade. ERC is slightly stronger than northern white cedar which is in the drop down calc in the toolbox.



Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 20, 2019, 08:22:16 PM
I hear ya on ther KISS method.

ERC passes at 1.5x7.5x8' actual at 15lbs per sq ft = 240 lbs.

Would you have an issue using ERC 1.5x7.5x4', 21" (exposed) for the rafter tails?

I can get it cheaper than the WRC and don't know how the RCDF will stain, as to match all the porches using ERC.

Don't really want to use RCDF fir the porches due to shrinkage, but if I dried it first and it stained well, it's a duh.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 09:05:18 PM
Run it again. We've been using 30 psf for total roof load 20LL+10DL Even if snow is below 20 psf wind then controls, never use less than 20psf Live Load, about never use less than 10 psf Dead Load. IF you do a skip sheathing and tin pole barn maybe, but even then I don't. Be conservative.

Not really a problem IMO on the tails however the usual rule of thumb on something like that is 2/3 inboard 1/3 outboard and nail the heck out of it.
The real issue is going to be finding enough 2x8 ERC that makes #2 unless there are much better trees out there than here, it is a small very knotty tree to me, most would be in the #3 category, porch roof sheathing maybe.

The shrinkage on a 2x8 is not a problem IMO... really if it's stickered under tin by the time you get to framing porches it'll be dry. West coast framers have put up a lot of green DF.

The poplar I'm sawing for framing now, well, whenever this ice and sleet stops, I can about guarantee by the time he gets the site and foundation ready its going to be mighty close to lumber store KD. We'll plane and straight line it right before use. The heavy timber is the slow poke and if anything, on something like an exposed heavy timber porch post, I'll put an oil type finish on it to slow down the surface drying to try to reduce checking in the sun and wind. That outer shell is drying and shrinking way faster than the fat green core, it wants to pop its buttons.

I saw a comment you made on borate and I'll give you a heads up there. If I treat green right off the saw, above fiber saturation point, when you can see the wet in the wood, Timbor or Solubor gives penetration as deep as Bora-care or Solubor + antifreeze. If the wood is dry, below FSP, then use Bora-care or add glycol to Solubor. The only difference there is Bora-care has ethylene glycol, antifreeze, in it, glycol dries very slowly, borate diffuses in on the wet.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 20, 2019, 10:00:01 PM
Yeah, I messed up. The 15 lbs psf was the ceiling load. It passes at 30 lbs psf

Ok, so  5' one is pretty close. 

Can get 12x12 timbers here.

🤔🤔🤔  So maybe only dry the 3x timbers and just air dry the 2x8 stuff. That's a thought, would there be a price break for getting them kiln dried or not? They quoted $0.35 a BF.

So would you oil coat the big stuff as soon as we get it to slow drying?

Gotcha on the Timbor. I'm thinking that once we get the wood, we'll coat it as we unload what isn't getting kilned

Speaking of big stuff, have you used big timbers for door framing on a stick frame and if so, how'd you do the timbers and the door?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 20, 2019, 10:44:18 PM
There would be a price increase for having someone kiln dry, not sure I'm understanding the question, either way .35 for material or drying sounds too cheap.

I've used Seasonite in the past with really good results, it came from Flood back then, it looks to be a Spanish company now. Other than that I've used boiled linseed oil or even just a first coat of the final finish if breathable with the understanding it will fail quickly on green wood. Never use Sikkens or a film forming finish on green wood. Borate before any finish. Price Solubor at the local real farm supply against Timbor, they are chemically identical down to the same CAS number.

I can't recall setting a door directly in between large vertical timbers although, probably have, lotsa houses and oldtimers :D. We talked about shrinkage movement and how to do it earlier.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on February 21, 2019, 06:14:40 AM
Thinking about what I think you are asking re the door. If you are proposing having the timbers extend through the wall with the stick framing infilling between timbers, that is a very tough detail. As the timbers shrink it is difficult to maintain air seal. What I've seen happen is warmer moist air begins to pass out through the shrinkage gap, hits the cold dew point in the gap and drops its moisture in that zone between timber and stud, rot begins. Try to detail with the timbers either inside or outside of the envelope.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on February 21, 2019, 10:25:05 AM
Yeah, been thinking the same thing. I was just tossing the idea around and was coming up with the same reasons why it won't work.

On those timbers used inside, would you rabbit them at floor level to tuck tile under them or would you just run the tile and other flooring up to and then trim on top of the flooring to cover any gap?

The $0.35 is the price per board ft to dry the df, so is that cheap enough that you'd dry the 2x8 also instead of air drying them. I didn't word it very well in my previous post. 

The stain we are planning on using is ready seal and here is from their website;

Quote
Conventional wood stains typically form a rigid film on the surface of wood, rather than penetrating into the wood fibers themselves. This rigid film cannot flex with the expansion and contraction of the wood through the seasons and is prone to cracking, and peeling which eventually leads to coating failures.


All Ready Seal wood stain and sealers penetrate deep into wood fibers, moisturizing the wood with water-proofing oils and creating a flexible barrier that keeps moisture out. Because no rigid film is formed on the surface, our wood stains can flex with the woods' expansion and contraction and will never crack, chip, flake or peel, another reason Ready Seal wood stain is the best stain!

Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 04, 2019, 02:02:06 PM
Interesting. My first thought was that would be tough to insulate between and around the web work. Then the thought of lumber bolted to the sides of the flat plate girder type truss would help resolve the buckling issue and make a smooth easily air sealed ceiling plane. Then listening to your friends suggestion and combining that it sounds like a flitch plate beam, the beams made by sandwiching lumber on each side of steel plate. Some neat ideas floating around.

Looking at it like a flitch plate with the rest of the steel just dangling below. The arched tie is a piece of something like 4" wide flat plate welded to the bottom. Just throwing the thought of the night out there, if the flitch plate passes and the tie is there, poke the rest as full of holes as you want.

(http://forestryforum.com/gallery/albums/userpics/10017/AutoSave_36porch2.jpg?easyrotate_cache=1550631539)
 

From the building code (table R803.1) #2 syp in 2x material would be good up to 72" span for roof sheathing.

Ever wander around under the bridges in San Antonio?
I have changed this up a little. Please look at my drawing. 

Drawing is incorrect. There will not be a 2x8 that runs the full length plus the rafter tail. The trusses do not come out in place to do this. I'll put a cross nailer in place to attach it to 3' up from outside edge that attaches to the 3x10 and I'll weld a bracket on the C purlin. I'll now be putting a 3x10 for the nailer and to help support truss. 3x10 will be bolted through metal for truss and the 12" C purlin. This 3x10 could be a 3x12 if needed.

I'm also attaching the load carrying of the 12" purlin. Can either get 12 gauge or 14 gauge.

(http://forestryforum.com/gallery/albums/userpics/53840/20190304_122858.jpg?easyrotate_cache=1551725526)


(http://forestryforum.com/gallery/albums/userpics/53840/20190304_125052.jpg?easyrotate_cache=1551726073)

what you think?
Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 05, 2019, 07:38:23 AM
Draw a plan view of the roof... in something darker. Maybe it will start to click.
I'm assuming the C channel is to create insulation space?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 05, 2019, 12:16:04 PM
I'll try and draw something later today. not feeling good right now.

The C purlin replaces the2, 2x12's & the 2, 2x4's that you had sammiching the top of the metal arch in your sketch up picture. Then i added back a 3x for the nailer for the roof. I just didn't know how deep of a nailer i needed if we need more strength.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 05, 2019, 05:05:31 PM
I think I'm following now. The trusses are on 5' centers, so 5'x30 psf= 150 lbs per foot. Try sending the manufacturer a sketch and see if they can provide any assistance, some of the engineered products will help with design and I think you've just come up with something they might want to showcase in one of their trade magazines. I've run into a truss guide for cold formed steel online before as well but this is outside of what they were doing, there are always details worth noting in those though.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 07, 2019, 10:38:11 PM
Just getting the c purlins from our steel supplier that we use for some other projects. They get it straight from the mill. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 10, 2019, 02:38:55 PM
Here's a truss that my brother drew up. What do you think of it?

The metal legs would bolt to the wall and the plate between them would extend up and over the top plate of the wall. 

Since it's green wood and will shrink, one cannot box in the wood in the bottoms and sides and then bolt through the beam and the 2 opposing metal sides?


(http://forestryforum.com/gallery/albums/userpics/53840/IMG-20190309-WA0000.jpg?easyrotate_cache=1552243010)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 10, 2019, 07:58:05 PM
Technically that is not a truss since it has a tie that is raised and puts the rafters into bending.
Take a look at this calc,
http://forestryforum.com/members/donp/raisedtiethrust.htm (http://forestryforum.com/members/donp/raisedtiethrust.htm)
Play with lowering the tie as much as possible to lower the thrust but also bear in mind as you lower the thrust you are also lowering the bending point load on the rafters caused by the raised tie. I do like it just drop the tie as much as possible.
Also go to the rafter span tables in chapter 8 of the codebook here;
https://codes.iccsafe.org/content/VRC2012/chapter-8-roof-ceiling-construction (https://codes.iccsafe.org/content/VRC2012/chapter-8-roof-ceiling-construction)
This is for dimensional lumber but gives a sense of what you are dealing with. Read the footnotes and notice the rafter span reduction as the tie is raised, this is due to that tie bending moment. Then go to the end of the span tables and read the heel joint connection table footnotes, that is the connections required to resist the thrust you figured in my calc above.

Backing up to the last design. I had a pm conversation with a forum member and he made a comment that bears bringing up. Unprotected steel does not perform well in a fire. I did a little checking in the code, you can scroll through that rafter chapter above and get to the cold formed steel laws. They don't specifically prohibit exposed steel there but it is clear they are assuming it is protected. In the main building code book it does call for 1 hr protection in the roof assembly. Then I walk into a walmart or Lowes and look up at exposed steel, hmmm. If you or anyone reading is considering this method it needs more fleshing out, engineering and a conversation with the insurance company would be good.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 10, 2019, 09:32:32 PM
Yup, already discussed it with him before that it needs to be lowered all the way. he's working on a new one

If we go this route, it'll be 6x12's

I'll look through that code book

Once he's done with the changed design and you see it, I have questions about bolting the plates and timbers together that I raised earlier

Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 10, 2019, 10:44:38 PM
Make it easier, post his sketchup file, its the tab right above the "add photos to post" tab. I'll be out late again tomorrow nite, but the welds are consistently looking about ready to test 8). Can you get 32' material for the tie?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 11, 2019, 12:32:33 AM
If I can copy it from what he sends me, you betchya

Awesome! Being a craftsman with wood is harder I think and you seem like you are all of that and more, so you should do fine..... boxingsmiley

It'd be 36' 5.5"....... Maybe, I'll check.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 11, 2019, 10:38:13 PM
The truss is then dropped down enough to get the ceiling deck on top of the trusses, then the 12" insulation space and 8" tails out. The bottom chord extends into the walls for support.


(http://forestryforum.com/gallery/albums/userpics/10017/36porchTrussheel.jpg?easyrotate_cache=1552358263)
 

The heel joint is the only tough joint here, it needs to resist a lot of toggle, thrust, from the rafters as they try to slide outward. This is sort of what I've done before, plenty of ways to play with it. Basically capture the end of the rafter chords and hold that well and bolt a strap to the tie with enough connection capacity in shear to resist the thrust. That could also be your threaded rod running from heel to heel buried in the upper surface of the bottom chord. There is a timberframe pavilion nearby that has that detail. The rest of the metal plating the sides of that joint is for pretty or doesn't need to be there structurally, you'll still need something top and bottom of the kingpost to make those tension connections. Something along these lines secures the heel better than side plates IMO.


(http://forestryforum.com/gallery/albums/userpics/10017/rafterfoot2.jpg?easyrotate_cache=1192055721)
 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 13, 2019, 09:29:23 PM
The mill got back to me today. Can get a 38' pine. No DF. Longest they can get a DF is 24'. The pine is stable. It's beetle kill. 

If the bottom cord is of in pine, I'm assuming the top cords should also be pine?

Here is the truss wall metal bracket drawing I sent my brother. Red is the metal. It has a 1/2" welded in heel stop. The sections will be laser cut and the heel plate will go through each side plate and will be welded on the outside. He's working on it now. Any suggestions on it? 

The wall section isn't correct, as these will go in between the studs, so it will vary in exact location. I do plan on putting at least 4 studs under each and might even go with 5. What do you think?


(http://forestryforum.com/gallery/albums/userpics/53840/Truss_metal_wall_brackets_.jpeg?easyrotate_cache=1552526406)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 13, 2019, 10:19:49 PM
That looks fine. The pine would work for the bottom chord that is in tension, The top chord I'd keep in DF if possible, it'll be stronger and stiffer.
Getting 6x6 post material from them might be worth thinking about, then the thickness under the truss will be the sam as the truss thickness and the studs up either side will be tight to the sides of the truss and can be nailed in easily. You might have to plane down the 5.5" dimension to match your 2x6's if you go that route, there's several ways to skin that detail.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 13, 2019, 11:31:54 PM
Can do DF, but it would be green and the pine is dry. What concerns me if we tighten the side plates we are starting the same, but the DF will shrink more, where as the pine won't much.

I am thinking of using metal for the middle webs instead of any wood. I was having it come back down the ridge 6' on each side, plus in the middle.

The 1/2" metal plates extend over the top plate of the shorter studs, so the width would be 7". Can add in some OSB to make the difference to, and make it tight though.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 14, 2019, 07:54:19 AM
The brits sometimes call the kingpost a kingrod which is a better description. It is a tension rod hanging from the peak, dangling down and holding the tie up from sagging. Then the web struts are posts in compression jacking up under the rafter chords supporting them from bending so think about their size in terms of keeping them from buckling as the rafters bend down onto them.

The DF at 6" thick won't shrink more than about 1/8" in thickness, tighten the bolts when dry, the heel stop is what is doing the work, the beetle kill has unknown degrade. Wood is pretty strong in tension so if you inspect it, it is probably fine in the bottom chord, bending in the rafter chord is real work and degrade is very unpredictable in terms of strength loss. In all of this remember a truss is a pretty high performance building element.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 15, 2019, 12:04:58 AM
Thinking something on these lines.

1/2" metal. Each piece is laser cut and snaps together like a puzzle. Then once the 1" bolts are all tightened, the pieces of the web that sticks out from the flange will be welded onsite.

The web portions of the ibeams are 1/4" narrower than between the flanges. this will allow movement and compression before welding. Could even wait for a year, then weld, but will be tightening with a 1" impact, so will compress the wood some.  

Considering having bottom plates designed like the ibeam webs and they would be welded in after it's bolted tight. If I do that then the plates would extend 1.25" below the wood so there would be material under the piece that sticks through the side plates.

I'm also adding a decorative bottom plate of the bottom cord. Forgot to show it.


(http://forestryforum.com/gallery/albums/userpics/53840/20190314_224948.jpg?easyrotate_cache=1552622066)


Hows the welding comin along?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 15, 2019, 07:48:19 AM
Correctly a truss has pinned connections free to rotate at each panel point. What you have drawn is rigid. As the truss deflects it can put tearing stresses into the wood. For instance look at the web 2 pin upper connections and think about the stress on the wood as the truss deflects vs if one pin were used there. At the junction on the lower chord same kind of rigid connection. Ideally if you draw a line down the center of each member they should all line up concentrically about the pins to avoid eccentricity, that was obviously not done in one of the bar joist trusses you showed earlier, I didn't comment on it then but it was pretty obviously not well designed, that point was outside of the trusses which put eccentricity into the connections to the chords of the truss. Here if the webs were pinned to the top chord and pinned to the king which was then pinned to the bottom chord it would solve that in my mind. Anyway, this is technically a frame. All that said a modern lightweight metal connected wood truss is basically the same, really a frame rather than a true truss. Those are just general comments, that stuff is getting deep into an engineers playground, I can't say whether it will work or not just more info.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 15, 2019, 10:33:20 AM
 ???

How can it rotate if bolted? I know you mentioned pinned, but that's how it would be made if all out of wood, but how does one use pins if using metal?

I've done several searches and I see them braced off of the king rod and in the web and some even down to the bottom cord, near the king rod. Some all wood and some with metal connectors.

If you were designing it, how would you lay it out?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 15, 2019, 12:09:13 PM
Here's a new one. Not like you were talking really, but I think better that the earlier one. Still would like to see what you are thinking.


(http://forestryforum.com/gallery/albums/userpics/53840/20190315_105342.jpg?easyrotate_cache=1552665461)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 15, 2019, 09:11:53 PM
Sorry, I was geeking out, pinned is a non rigid connection that is free to rotate, it can be a bolt, nail, screw, steel pin, wooden peg. To keep the confusion rolling, those are all referred to as dowel type connectors. Ideally a truss would be pinned in that the connections are restrained in space but free to rotate. I think I'm probably deep in the land of navel staring there :D. My point was think of the prying action of the bolts on the wood as the truss is loaded, you don't want them to cause it to split down the grain.

Back in the real world. Here's a scan from "Design of Building Trusses" I think this short excerpt would be considered fair use in light of our discussion. If you hit ctrl and scroll your mouse wheel it should zoom and be readable, that's how I'm reading your pics. I'll post this one and dig in another manual for something I think I remember there that might be pertinent.

(http://forestryforum.com/gallery/albums/userpics/10017/heavy_timber_001.jpg?easyrotate_cache=1552698003)<br
Next page;
...steel members.
4. Maximum diameter of bolts <1/4 width of wood and <1/3 width of steel plates. (they mean total of all the bolts in that section of the member, in other words don't compromise more than 1/4 of the net section. Another caveat don't use a bolt larger than 1" dia in wood, chances are you are outside of the wood's strength)
5. A minimum of 2 bolts should be used in each member at a joint.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 15, 2019, 10:19:07 PM
Now for a slightly different point of view, this is from "Wood Engineering and Construction Handbook" Dr Woeste at Va Tech suggested I get this and it is a good one to have on the bookshelf. There's a good chapter on trusses and in fact, there's about 11 pages detailing the engineering of a very similar truss to yours as a design example. Check interlibrary loan in your neighborhood (there's really lots there you should probably study) or PM me your email if you want a scan of those pages.

Anyway from earlier in that chapter just basic info;
Quote
Heavy Timber Truss Joints. The most common type of joint used in heavy timber trusses is a bolted connection using steel side plates. A number of pitfalls related to this type of joint can be avoided by remembering the principles of consistent deformation for all components and materials and for all conditions to which the connection may be subjected. The use of steel side plates, while common, economical, and practical, can lead to in service problems. The thermal characteristics and dimensional changes  of wood with moisture change are greatly dissimilar to to those of steel. Large steel side plates and multiple connector rows of fig 9.18a can lead to splitting of the truss member as cross grain tension is induced by shrinkage with moisture change. This can be avoided by the use of multiple straps as fig 6.18b. In all wood truss connections, it must be recognized that moisture content at the time of fabrication may be quite different from that in use.
...
A single large connector plate, as shown in 6.19a, while commonly used, should be avoided. A degree of fixity occurs, and the couple generated between the two web connectors produces cross grain tension which may split the web end. Also differential stiffness between the chord and side plates can induce unanticipated stress in the chord connectors. Fig 6.19b shows one possible arrangement to avoid these potential problems.

Both recommended connections at first seem more complicated than their single member counterparts. However, the multiple strap details typically use less steel and fabrication tolerances are less critical because of the lesser number of connectors in a given component.. Of course, steel side plates must be designed in accordance with appropriate standards, with checks made on bolt bearing, net section tension, end and edge distance, and stability in compression members.

The preceding discussions make reference to cross grain tension stresses. These are the lowest strength characteristics of wood and should be avoided whenever possible. The eccentric connection of fig 6.20 induces very complex tension and shear stresses and secondary bending moments and must be expected to perform very poorly unless the stresses are very low.

 
(http://forestryforum.com/gallery/albums/userpics/10017/6_18a_001.jpg?easyrotate_cache=1552702492)
 
 
(http://forestryforum.com/gallery/albums/userpics/10017/6_19_001.jpg?easyrotate_cache=1552702629)
 
 
(http://forestryforum.com/gallery/albums/userpics/10017/6_20_001.jpg?easyrotate_cache=1552702687)
  
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 16, 2019, 12:02:13 PM
Sorry, I was geeking out, pinned is a non rigid connection that is free to rotate, it can be a bolt, nail, screw, steel pin, wooden peg. To keep the confusion rolling, those are all referred to as dowel type connectors. Ideally a truss would be pinned in that the connections are restrained in space but free to rotate. I think I'm probably deep in the land of navel staring there :D. My point was think of the prying action of the bolts on the wood as the truss is loaded, you don't want them to cause it to split down the grain.

Back in the real world. Here's a scan from "Design of Building Trusses" I think this short excerpt would be considered fair use in light of our discussion. If you hit ctrl and scroll your mouse wheel it should zoom and be readable, that's how I'm reading your pics. I'll post this one and dig in another manual for something I think I remember there that might be pertinent.

(http://forestryforum.com/gallery/albums/userpics/10017/heavy_timber_001.jpg?easyrotate_cache=1552698003)<br
Next page;
...steel members.
4. Maximum diameter of bolts <1/4 width of wood and <1/3 width of steel plates. (they mean total of all the bolts in that section of the member, in other words don't compromise more than 1/4 of the net section. Another caveat don't use a bolt larger than 1" dia in wood, chances are you are outside of the wood's strength)
5. A minimum of 2 bolts should be used in each member at a joint.
On the bolts. Since 6" thick wood, then that would be 4, 3/4" bolts or 3, 1" ones, right? And how big is a 'section'?

On the steel plates. Don't follow  that one.

Do you prefer this style truss or one with a single king rod based on how we are using the steel for webbing?
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 17, 2019, 01:52:11 AM
Can't sleep, so i thought i'd draw up a quick one. I'm not showing any web detail, but I think I followed what I was able to pick up for this design except for the king rod. I just thought it added some look to the design..... Not sure i like the design yet though.


(http://forestryforum.com/gallery/albums/userpics/53840/20190317_001220~0.jpg?easyrotate_cache=1552801623)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 17, 2019, 08:38:58 AM
With the exception of the king rod you have drawn a Fink truss (Albert Fink first patented it). It is a good solution. As mentioned in one of those articles it is not a bad thing to reduce the number of members coming together at any one point. This brings 2 web members together in a place instead of 3 as in your kingpost design. I was actually thinking of moving the web struts up onto your kingpost in that design. Anyway, this is a good truss, normally it divides the bottom chord into thirds and the top chords into halves as you have done.

For more exploring another variant on the kingpost model is a Howe truss. With your kingrod in this model you are heading towards a Pratt truss. Keep exploring, looks like you are having fun working through the possibilities.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 17, 2019, 07:34:19 PM
Don't really care for the fink truss. If it's a lot better or we need to use, sure, but would rather not if at all possible, but I can see the advantage of reducing the number of members coming together in 1 point with it.

Have a question. If I'm connecting everything by metal plates, what's the difference between the 2 designs really? I know the top cord web is further down the top cord on the second one and a few too many bolts, but besides that since it's all metal to metal.


(http://forestryforum.com/gallery/albums/userpics/53840/20190314_224948.jpg?easyrotate_cache=1552622066)



(http://forestryforum.com/gallery/albums/userpics/53840/20190317_104249.jpg?easyrotate_cache=1552837500)
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 17, 2019, 10:43:23 PM
In my opinion, and that's all it is, the upper drawing has the webs torqueing on the bottom chord under load and in the second drawing they are not, the web struts can rotate easier as the truss deflects. Is it enough to matter, above my pay grade. I can help rough you in and am happy to share what I know however I am a carpenter not an engineer. Hopefully after wading through those 11 pages of equations it becomes clearer, an engineer is a good idea and earns his pay.

This is the article on kingposts from the TF Guild and the NPS I was thinking of, good to read through, notice the truss on Mt Sinai, pretty cool they understood it that well back then.
https://www.ncptt.nps.gov/blog/timber-framing-no-72-june-2004-2004-12/ (https://www.ncptt.nps.gov/blog/timber-framing-no-72-june-2004-2004-12/)

Another neat graphic on bridge trusses while I was googling the above;
https://www.nps.gov/hdp/samples/haer/truss%20poster.pdf (https://www.nps.gov/hdp/samples/haer/truss%20poster.pdf)
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 18, 2019, 12:51:32 AM
When you said that I looked at the truss again and I could see it plain as day, err I mean night......smiley_brick hits_hardhat  Thanks! smiley_beertoast  Even though it would be bolted and how, it would still move some overtime.

Ok, so now we are on the bottom truss design. In your opine, how far down from the ridge would you bring those webs? 1/3? 7' 8" is where it's at now roughly in that drawing. The length of the top cord is roughly 19' 7 1/2". 6' 6" is about 1/3.

In the old ways all that knowledge would get passed down from master to apprentice who then became a master and on and on with new knowledge added in. Pretty neat when you think about it.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 18, 2019, 07:30:14 AM
Or as one contractor says "They don't build them like they used to, we have laws against that now :D" There is not a master/ apprentice program in the states. In the first half of the 19th century "rational design" began replacing empirical design, that is using science and mathematics to design rather than experience alone. The industrial age and more modern loadings along with increasing failures in empirically designed structures were driving forces in that change. I'm a bit nostalgic as well, I think we would do better with more mentoring such as the internship that engineers do have to go through for craftsmen as well but do understand where it all comes from and can't disagree.

I like to see the web struts at around a 45 or steeper but you can calculate the forces as the angle changes. That works well with a steeper roof as far as keeping the chord sections equal, less so with a shallower pitch and a kingpost design, that is when the Fink or one of the other trusses begins to shine.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 19, 2019, 01:03:05 AM
Sadly that's about how it is. 

Yes, i agree, but we both know that just because ones an engineer on paper doesn't mean they know how to actually engineer.......

Do you have an engineering firm that you use for this types of things? I looked around here and couldn't find anyone today. All those that are here that I could find are for large commercial projects.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 19, 2019, 08:43:10 AM
That is the truth of it, every person is an individual, so I've dealt with... am dealing with, all kinds. I'll obey Mama's rules and hush there :D. Engineers, like contractors, are licensed at the state level. The local guys I like here are only licensed in my state, well one goes down into Carolina as well, but they aren't licensed out there. Many folks here use Firetower for timberframe work, they do work nationwide or at least substantially so, I imagine they could take care of you or would know someone. I've spoken with those guys a few times and they are very knowledgeable, a fair amount of what I've been pontificating here comes from listening to them.

If you are pretty well settled on a basic design, then it is time to retain an engineer and have it detailed. At that point I do not drive the bus, I listen, maybe redirect, my design might end up not being the best way to go, it is still just an idea. The good ones give me the closest to what I want while satisfying the laws of nature. As coach Hilton said while getting ready to give us driver's ed,"Now boys, there's some laws that a man cannot break, two vehicles cannot occupy the same place at the same time" He later jammed his brake when I punched it at a yellow light, we slid to a halt a little abruptly and sorta sideways "We stop for those things :D" That's the kind of thing the engineer is checking for while giving me the hottest car he can.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 19, 2019, 11:02:29 PM
Oh yeah, I hear ya. I dunno yet if it makes me mad or makes me laugh when people pay for professional help and then don't listen.... I guess it depends on how it effects me....

Agreed on the comment about the hottest car. Funny story also. :D

If they are just designing a truss, why's it matter where they be located? They aren't doing any plans besides it. No site inspection etc.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 20, 2019, 07:32:47 AM
It is frustrating what falls under state control vs federal. States control licensing of professionals and all depending some professions and states have reciprocity and most of the time they do not respect one another's licensure. Back in the day I could travel and build fairly freely, that is a thing of the past now even though for instance when I went next door to work I went for contractor's testing and it was the same group that had tested me here. Oh well, render unto ::). But yes physics is the same each side of the border. Interestingly from welding class, that certification is recognized internationally and most of the structural welds are self certified by the welder, I pointed that out to our building official after he asked for a special inspector to be brought in, he still has power to trump that but AWS pulled some strings.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 20, 2019, 07:24:50 PM
Yeah, makes no sense like most of what government does..... All I need is a design of a truss, not an actual building engineered. Sil no luck finding one here .

From what you wrote, you more partial for the fink truss since it's a 4/12 I take it?

On the 6x12's, they need to be FOHC?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 21, 2019, 08:40:56 AM
Hmm, not real partial to one over another, I also like the Howe designs with timber compression struts and steel rod tension struts, I'll see if I can dig up a pic. We're getting into personal taste there though. I tell my clients "when this is done I go home to my house, this is your house."

FOHC is less prone to checking, that is not structural just aesthetic.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on March 21, 2019, 10:46:52 AM
I meant for the pitch of the roof as to your preference of a truss.

Yes, each house is theirs that they go home to, but sometimes different view points and opines makes one think of something they hadn't and the different ideas can be married into one and it's better overall. 

Ahh k
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on March 21, 2019, 07:24:35 PM
Check out fig 4-25 here;
https://docplayer.net/22941914-Heavy-timber-frame-construction.html (https://docplayer.net/22941914-Heavy-timber-frame-construction.html)

When we came up at 6x12. well going back pages of memory that I'm not going to dig back thru, the timber size was for a truss with no webwork, the top chords spanning 18'. The web members support the top chord so its size can be reduced structurally, but nothing wrong with being larger than structurally necessary if it looks good to your eye.
Title: Re: Clear Span Roof Truss Calculator
Post by: Tam Barron on August 31, 2019, 06:42:05 PM
Sorry, I was geeking out, pinned is a non rigid connection that is free to rotate, it can be a bolt, nail, screw, steel pin, wooden peg. To keep the confusion rolling, those are all referred to as dowel type connectors. Ideally a truss would be pinned in that the connections are restrained in space but free to rotate. I think I'm probably deep in the land of navel staring there :D. My point was think of the prying action of the bolts on the wood as the truss is loaded, you don't want them to cause it to split down the grain.

Back in the real world. Here's a scan from "Design of Building Trusses" I think this short excerpt would be considered fair use in light of our discussion. If you hit ctrl and scroll your mouse wheel it should zoom and be readable, that's how I'm reading your pics. I'll post this one and dig in another manual for something I think I remember there that might be pertinent.

(http://forestryforum.com/gallery/albums/userpics/10017/heavy_timber_001.jpg?easyrotate_cache=1552698003)<br
Next page;
...steel members.
4. Maximum diameter of bolts <1/4 width of wood and <1/3 width of steel plates. (they mean total of all the bolts in that section of the member, in other words don't compromise more than 1/4 of the net section. Another caveat don't use a bolt larger than 1" dia in wood, chances are you are outside of the wood's strength)
5. A minimum of 2 bolts should be used in each member at a joint.
Ok 
First thing is the span of the roof.
Edge to edge. Anything under 5metres  can easily be done with straight timbers, given good footings.
In reasonable conditions 8inch coach bolts, well greased work well.
Use the old square of the hypotenuse equal to the sum of the squares for the other 2 sides. 
A pitched roof needs an apex beam. DO NOT cut into that.cut notches into your side timbers ( I wish I knew the USA words)
Brace timbers may be needed, but depending on span  are usually used for spreading the load of roofing material.
To stop your walls falling outwards!
A proper structural engineer can tell you. But if you are just putting up light stuff, no probs. Thatch, terracota tiles or slate, put in roof brace
I have used coach bolts, but I think proper wood pegs would be better. Metal sweats, does not expand and contract like wood. 
Any way I have 2 wooden barns about 100yos old and still fine. The one I put up 10 years ago is ruddy awful pine and anything exposed to weather just rots!

Help. ta,I am trying to get used sump oil,the old way of doing things.


Title: Re: Clear Span Roof Truss Calculator
Post by: Tam Barron on August 31, 2019, 06:52:05 PM
That is the truth of it, every person is an individual, so I've dealt with... am dealing with, all kinds. I'll obey Mama's rules and hush there :D. Engineers, like contractors, are licensed at the state level. The local guys I like here are only licensed in my state, well one goes down into Carolina as well, but they aren't licensed out there. Many folks here use Firetower for timberframe work, they do work nationwide or at least substantially so, I imagine they could take care of you or would know someone. I've spoken with those guys a few times and they are very knowledgeable, a fair amount of what I've been pontificating here comes from listening to them.

If you are pretty well settled on a basic design, then it is time to retain an engineer and have it detailed. At that point I do not drive the bus, I listen, maybe redirect, my design might end up not being the best way to go, it is still just an idea. The good ones give me the closest to what I want while satisfying the laws of nature. As coach Hilton said while getting ready to give us driver's ed,"Now boys, there's some laws that a man cannot break, two vehicles cannot occupy the same place at the same time" He later jammed his brake when I punched it at a yellow light, we slid to a halt a little abruptly and sorta sideways "We stop for those things :D" That's the kind of thing the engineer is checking for while giving me the hottest car he can.


Oh I do so like that! Thanks made me smile!
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 22, 2019, 08:18:42 AM
Check out fig 4-25 here;
https://docplayer.net/22941914-Heavy-timber-frame-construction.html (https://docplayer.net/22941914-Heavy-timber-frame-construction.html)

When we came up at 6x12. well going back pages of memory that I'm not going to dig back thru, the timber size was for a truss with no webwork, the top chords spanning 18'. The web members support the top chord so its size can be reduced structurally, but nothing wrong with being larger than structurally necessary if it looks good to your eye.
Working w/ Ben and Griff from Fire tower. Good guys. Thanks for the di rection!
6 x 12 w/ web braces are fine
12 x 12 w/ out
Leaning towards 12 x 12 for a cleaner look
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 23, 2019, 09:23:11 AM
 
(http://forestryforum.com/gallery/albums/userpics/53840/Truss_detail_I-joist_side_view~0.jpeg?easyrotate_cache=1571836611)
 
(http://forestryforum.com/gallery/albums/userpics/53840/Truss_detail_half_view~0.jpeg?easyrotate_cache=1571836609)
 
(http://forestryforum.com/gallery/albums/userpics/53840/Truss_detail_end_view_exterior_look~0.jpeg?easyrotate_cache=1571836602)
 
(http://forestryforum.com/gallery/albums/userpics/53840/Truss_detail_end_angle_view~0.jpeg?easyrotate_cache=1571836601)


Here's where we are at
Title: Re: Clear Span Roof Truss Calculator
Post by: cib on October 23, 2019, 10:20:22 PM

Removed comment. I don't want to derail the thread.
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on October 24, 2019, 08:40:39 PM
cib, normally I'm the worlds worst about jumping off topic in a thread, but, I think repost this on the barn thread you started a week or so ago and lets put the evolution of your design there, I think it'll go to more than one Q&A round before you are done.

Title: Re: Clear Span Roof Truss Calculator
Post by: cib on October 24, 2019, 10:28:39 PM
Removed the comment. I don't want to derail the thread. I was thinking this was more of a general question thread than a specific. Sorry for the mix up.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 28, 2019, 07:36:54 PM
Update. 

6 x12s are fine without bracing. Griff had one truss in his calculations instead of 3. 

I do have question though. If one was to use 3 x 12s 24" OC, how big would the ridge beam need to be you figure?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on October 28, 2019, 11:30:19 PM
I am interested in seeing what you and they come up with. I also think it would be inappropriate for us to begin walking you down the path of reworking a design you all have been, and are, working on.  I do want to see it evolve, it is different and cool. I was downright intrigued by the post tie connection details y'all came up with in the last post, that took a few head scratches to figure out :).
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 29, 2019, 12:24:34 AM
I am interested in seeing what you and they come up with. I also think it would be inappropriate for us to begin walking you down the path of reworking a design you all have been, and are, working on.  I do want to see it evolve, it is different and cool. I was downright intrigued by the post tie connection details y'all came up with in the last post, that took a few head scratches to figure out :).
What I posted is what I had my brother draw up and they said it passes loads. Nothing need be changed thus far, but they have asked me have the architect place it in the room just to be sure.

Reason I asked the on the a ridge beam is I want to compare costs. we're gonna have a fair amount of money stuck in the metal/work alone and I just want to make sure we're in the same county as the ball park....... 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 29, 2019, 10:59:32 AM
here's a link Ridge Beam (http://www.southernpine.com/app/uploads/SS_15-20L.pdf) from another thread on ridge beams of SYP. I would think DF would even have better loads, but if this link provides what I was asking about, what size would it need to be based on 36' ft width and a 14' clear span? Would one use 20 psf dead load and 20 psf live load?  
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on October 29, 2019, 04:58:08 PM
That table works for SYP 2x's built up into a beam.
For dougfir 2-4" thick use the dimensional simple beam calc in the toolbox here, if 5x or thicker material use the heavy timber drop down calc.

Scroll back and you'll find the design loads we were using before, It is probably noted on the prelims you are getting from Firetower as well.

For load on the calc, the ridgebeam is carrying half the roof width, 18'. The tributary area bearing on the ridge is 18' x14'=252 sf x 40 psf (if that is the design load) =10080 lbs
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 29, 2019, 06:16:50 PM
That table works for SYP 2x's built up into a beam.
For dougfir 2-4" thick use the dimensional simple beam calc in the toolbox here, if 5x or thicker material use the heavy timber drop down calc.

Scroll back and you'll find the design loads we were using before, It is probably noted on the prelims you are getting from Firetower as well.

For load on the calc, the ridgebeam is carrying half the roof width, 18'. The tributary area bearing on the ridge is 18' x14'=252 sf x 40 psf (if that is the design load) =10080 lbs
no prelims from Ben or Griff yet, but I just emailed Griff and he just answered.
Roof Dead Load = 20psf
Roof Live Load = 20psf
Roof Snow Load = 10psf
So that adds up to 50 psf rather than 40 psf? If so, 252 sf x 50 psf = 12,600

On the DF grade, what's B+S & P+T?

the beam calculator is asking for total and dead loads. We used 20 psf live load and 10 psf dead load, which you said equaled 30 psf total load. You are using 40 psf now, which is fine, but what should go in both boxes?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on October 29, 2019, 08:02:37 PM
Total load is 40 or 50 psf. Live load is never less than 20 psf (wind). Generally if you have design wind load the snow is gone, but, it could be unbalanced collecting on the lee side, this is what the engineers are for.
Dead load is 20 psf
P&T is posts and timbers, roughly square timbers, within 2" on each face
B&S is beams and stringers, rectangular sections, probably what you are using. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on October 30, 2019, 09:22:59 AM
thanks!
6 x 16 passes, would likely go with a 8 x 16 though. I'll price this out. 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 10, 2019, 07:23:23 PM
I am interested in seeing what you and they come up with. I also think it would be inappropriate for us to begin walking you down the path of reworking a design you all have been, and are, working on.  I do want to see it evolve, it is different and cool. I was downright intrigued by the post tie connection details y'all came up with in the last post, that took a few head scratches to figure out :).
Ben's calling me in a lil'bit. He want's to scrap the 3 trusses and go with 2 parallel timbered beams spanning the short way about 10' apart sitting on big timbered posts and then use rafters set on top. Do you know if one can still buy the laminated ceiling/roof decking like your pa used in those beautiful houses he built? thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on November 10, 2019, 08:34:31 PM
I'm right certain he was Solomon's temple engineer, if anyone knows of a supplier it's him.
This is a list of the glulam listed manufacturers, each does a different range of products;
https://aitc-glulam.org/index.php/manufacturers/ (https://aitc-glulam.org/index.php/manufacturers/)
This is one that is relatively close to you, I've linked to their timber decking page,
http://www.glulamstructuralwood.com/products/Disdero.pdf (http://www.glulamstructuralwood.com/products/Disdero.pdf)
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 11, 2019, 12:39:04 AM
Thanks a lot.

Moved ahead on lot's of fronts with Ben this evening. Decided to drop the 3 metal/wood combination trusses for a variety of reasons. Going with large posts that hold the 2 larger timbered purlin beams 10' apart, then running 3x or 4x12 rafters over them. I think 3x12 DF pass @ 4' OC. If not, what's the widest they can go?

Question though. How does one fasten the rafters to the purlin beams typically? Also the rafters will be 3x12s (maybe 4x if that's the width needed to go to 4' OC ) at least. That's what is in the rest of the house and I think it'll not look right if it doesn't match or what do you think?

Also thinking on this roof system. What about running 2x4s as purlins edge up over the ceiling decking, putting in R13 fibergalss batts in, then screw OSB through the 4" polyiso insulation to the 2x4 purlins. That'd be a R 39.6 roof. Bad thing is the 4" polyiso is a $1.81 per sq ft. 3" I can find for $1.48 used, but in Denver or Dallas. R there is about 30. Doing it this way would be a lot more stable in our windy local me thinks.

Just a thopught, if I went with 2x6s instaed, how'd you fasten them besides drill straight done through it and screw it?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on November 11, 2019, 07:12:29 AM
I'm glad you had a good conversation, it sounds like things are settling. If you want to match the rafter sizes with the others in the house let him know, that might play into his dead loads. The connection details are part of what they will be providing. I can't help with the insulation build up, again work with them on those details.  
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 11, 2019, 09:06:53 AM
I emailed him on both topics before i posted, but I was wanting some objectivity if possible. That's how the best idea's usually are formed. The main reason we dropped the other idea was it just was going to look too cluttered, but my layout/design passed there design values all the way around. If my memory serves, didn't/don't you use something similar roofing on some cabins you built? I just cannot remember for sure where I saw that.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 11, 2019, 04:35:34 PM
Here is what i found today. I'm sure you know what it is Don, but in case anyone else doesn't. This gets screwed to the roof decking and then you screw into the roof purlin (?).  Would you fasten it in a different way?


(http://forestryforum.com/gallery/albums/userpics/53840/20191111_153021.jpg?easyrotate_cache=1573507895)
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 12, 2019, 02:50:45 PM
@Don P (http://forestryforum.com/board/index.php?action=profile;u=17) Didn't you have some cabins you used polyiso on the roofs? How'd you build those out? Thanks
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on November 12, 2019, 04:49:25 PM
I'm just back from measuring "granny's house" on this family compound for a remodel. Anyway, this is what we did, 5" of polyiso over the 2x6 T&G roof deck, 2x4 strapping, ply and shingles.

(http://forestryforum.com/gallery/albums/userpics/10017/biltuproof2.jpg?easyrotate_cache=1192055654)
 
(http://forestryforum.com/gallery/albums/userpics/10017/biltuproof3.jpg?easyrotate_cache=1192055654)
 
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 12, 2019, 05:47:28 PM
Looks like you just glued the iso to the decking, then screwed the 2x4s through the iso to the decking, then screwed the ply to the 2x4s. Amiright, amiright.....;D
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on November 12, 2019, 09:54:28 PM
No glue, all screws and nails. Every other 2x4 is over a 4x10 FOHC dougfir rafter so those screws go thru 2x4, foam, decking and into the rafter. every other 2x4 is just screwed into the 2x decking. then the ply is nailed to the 2x4's.

That was the detail on that job, sitting here I can think of a couple of other ways we've done it, just depends on the plan detail provided.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 12, 2019, 10:50:42 PM
Ahh k. Ben didn't specify any certain way to do it just yet, he just told me come up with a couple of different ways and he'd see if it works or not. He liked my 2x6 purlin 2' OC with R23 batts and then 2.5" iso glued to the purlins, then 5/8 OSB screwed thru the iso into the 2x6 purlins. That's why I was looking for ways to fasten the 2x6s to the decking. He suggested just cross screwing, but I'm not a fan, so I will use those clips every 2', then drill and screw into the decking and where there are rafters into them at 4 points in the purlin, plus i'll lay a bead of construction adhesive under the 2x6. That's what I came up with so far. Over kill? 
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on November 13, 2019, 08:55:00 AM
You'll need to attach the edges of the ply on something like 4-6" centers, 12" in the field so think about getting that done effectively, APA's help desk might have some ideas or their site might have some ready details, apawood.org I think. Glueing on the job is considered structurally to be zero, way too wild an environment. For instance its 12 degrees out there right now and we just decided to hold off crawling up on the roof for a couple more hours, so all depending on the work day you can be trying to apply against weather, temp, wet, etc with unknown gaps and clamping efficiency. Make sure your mechanical fastening is up to snuff, we were screwing those 2x's on I think 2' ctrs but your uplift probably controls, and consider glue to be gravy.
Title: Re: Clear Span Roof Truss Calculator
Post by: Sedgehammer on November 13, 2019, 10:25:32 AM
question though. you mentioned 4-6" on the edges and 12" in the field. On a typical house trusses, they are screwed down only where there are the trusses of course, so why all the extra?
Title: Re: Clear Span Roof Truss Calculator
Post by: Don P on November 13, 2019, 10:35:03 AM
On the trusses, purlins or rafters, 4-6" along the sides of the sheet to keep the edges down and transfer racking loads. In the rest of the sheet 8-12" along every rafter to keep the sheet flat when the racking tries to pop the sheet out of plane. For the other 99% of the time it keeps the sheets flat on the roof from warping. The roofs with 8 or 10 nails in them are the ones you see heading cross country in high wind, a roof gets down pressure but also lift and racking as wind passes over it.