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Author Topic: Clear Span Roof Truss Calculator  (Read 8572 times)

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Online Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #40 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


Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #41 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.
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Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #42 on: February 13, 2019, 11:00:32 PM »
 Actually midheight is about the bottom of the circle.

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Online Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #43 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. 

Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #44 on: February 15, 2019, 07:24:06 PM »
Break out your pencil and sketchpad, you've lost me again :).
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Online Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #45 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




Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #46 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.
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Re: Clear Span Roof Truss Calculator
« Reply #47 on: February 16, 2019, 12:43:47 AM »
Here ya is





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


Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #48 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.
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Re: Clear Span Roof Truss Calculator
« Reply #49 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°





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....






Offline Don P

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Re: Clear Span Roof Truss Calculator
« Reply #50 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

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Online Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #51 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

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Re: Clear Span Roof Truss Calculator
« Reply #52 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.
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Re: Clear Span Roof Truss Calculator
« Reply #53 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 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

Online Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #54 on: February 17, 2019, 03:15:36 PM »
Build a truss similar to these 2;





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





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

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Re: Clear Span Roof Truss Calculator
« Reply #55 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.
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Re: Clear Span Roof Truss Calculator
« Reply #56 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. 

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Re: Clear Span Roof Truss Calculator
« Reply #57 on: February 17, 2019, 07:14:09 PM »
That one link to a 40' tube steel truss... was it local? that was cheap
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Re: Clear Span Roof Truss Calculator
« Reply #58 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. 


Online Sedgehammer

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Re: Clear Span Roof Truss Calculator
« Reply #59 on: February 17, 2019, 10:47:34 PM »
What kind of loads you think we're looking at?

Thanks


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