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Clear Span Roof Truss Calculator

Started by Sedgehammer, February 05, 2019, 12:00:58 PM

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Sedgehammer

No, no, I got all that 8)

It's this part 
QuoteWhere 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
Necessity is the engine of drive

Sedgehammer

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.  





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





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
Necessity is the engine of drive

Don P

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.

Don P

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
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?

Sedgehammer

Quote from: 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.
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.
Necessity is the engine of drive

Sedgehammer

Quote from: 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
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
Necessity is the engine of drive

Don P

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.









Sedgehammer

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
Necessity is the engine of drive

Sedgehammer

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? 
Necessity is the engine of drive

Sedgehammer

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
Necessity is the engine of drive

Don P

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

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.





Welded up 50 coupons tonight, something smells like burnt metal and burnt fur... off to the showers :D

Sedgehammer

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.
Necessity is the engine of drive

Don P

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.

Sedgehammer

Necessity is the engine of drive

Don P

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;



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.

Sedgehammer

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

Necessity is the engine of drive

Don P

 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.

Don P

 Actually midheight is about the bottom of the circle.

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Sedgehammer

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. 
Necessity is the engine of drive

Don P

Break out your pencil and sketchpad, you've lost me again :).

Sedgehammer

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



Necessity is the engine of drive

Don P

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.

Sedgehammer

Necessity is the engine of drive

Don P

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.

Sedgehammer

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°





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....





Necessity is the engine of drive

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