Author Topic: Truss Calculators  (Read 376509 times)

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Offline Medeek

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Re: Truss Calculators
« Reply #425 on: June 09, 2016, 12:19:30 AM »
Various configurations of a 16' King Post Truss:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=d38c0061-b812-499a-b02a-70c43148d958

With a raised heel note the use of either a wedge, slider or vertical web with strut.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #426 on: June 11, 2016, 12:52:02 PM »
Version 1.6.1 - 06.11.2016
- Added Coffer truss type, configurations: (AUTO).
- Metric input enabled for coffer truss type.
- Added gable end trusses for coffer truss type.
- Structural outlookers (vert. & horz.) enabled under advanced roof options for Coffer truss type.
- Building parameter menu (2nd) and advanced options menu for trusses now default to last picked options of the session for that sub-menu item.


Various configurations of a 40' coffer truss shown below:



The web triangulation algorithm automatically determines which configuration is appropriate based on the span between panel points.  This simplifies the geometry input menu but does take some control from the user.

View model here:

https://3dwarehouse.sketchup.com/model.html?id=a9f2e281-557d-4d13-a9ad-64bdfdd078f4
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Medeek

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Re: Truss Calculators
« Reply #427 on: June 14, 2016, 12:42:18 AM »
Version 1.6.2 - 06.14.2016
- Added Symmetric Cathedral truss type, configurations: (AUTO).
- Metric input enabled for symmetric cathedral truss type.
- Added gable end trusses for symmetric cathedral truss type.
- Structural outlookers (vert. & horz.) enabled under advanced roof options for Symmetric Cathedral truss type.

Various sizes and configurations of a symmetric cathedral truss:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=2755897d-3855-447a-bc13-d4478cf99355
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #428 on: June 14, 2016, 10:03:20 PM »
Modified an existing truss roof to make it a half hip truss set:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=6e2633ca-ebb2-4597-87e9-ba41b47a636f

This will be my first venture into more complex truss systems.  I figured I would cut my teeth on the half hip (Jerkin Head, Tudor Hip) truss set first before attacking the more complex full hip variants of which there are many.

After sketching this model up and examining the geometry I now have a number of questions:

1.  Are my roof planes correct?  Note that I have drawn the apex of the hip roofs at the edge of the last full truss and not at its centerline.  Not entirely sure what is common practice in this regard.

2.  I've shown some non-structural outlookers along the rake.  What would the outlookers along the half hip portion look like?

3.  If I use structural outlookers how would those be framed in over the hip section?

4.  Does the apex of the half hip typically coincide with the next truss or could it land somewhere between trusses?  ie. the half hip length is some multiple of the truss spacing.

5.  Is the hip section usually the same pitch as the rest of the roof?  There is really no reason why it has to be.

6.  As the length of the half hip increases the depth of the gable end truss decreases as does the first inboard truss.  What is the practical limit for the minimum depth of the first inboard truss?

7.  Does anyone have some shop drawings of this type of truss set that I can study?
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #429 on: June 15, 2016, 10:48:44 AM »
As previously noted the web dialog from the plugin can actually be used external to SketchUp to explore gambrel attic geometry:



Imperial Units:

http://design.medeek.com/resources/gambrel/web_dialog_gambrel_attic.html

Metric Units:

http://design.medeek.com/resources/gambrel/web_dialog_gambrel_attic_metric.html

I might develop this into a web based app which would allow one to generate 2D AutoCAD geometry (.dwg) of the truss profile.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Medeek

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Re: Truss Calculators
« Reply #430 on: June 15, 2016, 03:35:38 PM »
With non-structural lookouts would you frame them something like this?  This question is mostly directed at the contractors and carpenters out in the field who actually have to build these roofs.  Typically as an engineer I never worry about these details especially when they are non-structural.



In my opinion they aren't really doing a whole lot, much better to drop the gable truss and then cantilever them from the first in board truss (ie. structural outlookers).
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #431 on: June 15, 2016, 06:00:27 PM »
Hip Truss Algorithm:

Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #432 on: June 16, 2016, 02:16:36 AM »
On the jerkinhead I would step back inside and make the lookouts structural. I've only framed one, I think the style has largely passed. That one was a homeowner afterthought. I was installing piggybacks and he shouted up asking if I could leave off the last couple of piggybacks and clip the gable. I cobbled something together that passed his muster but when I came down and looked at it I would prefer the pitch match the main I think. I was in the neighborhood playing with what the truss was allowing, but not matching.

From an engineering standpoint we wing it on overhangs very often, and very often they are the leading edge of a roof failure in high wind. I was the only carpenter in a room full of engineers when we were talking about this. The professor commented that we do a lousy job nailing the bottom corners of roof sheathing off. I asked if any of them had ever been staring at the roof of their truck far below while holding on with one hand and nailing with the other. The room glowed for a second, but I do hang there for longer now, man I really need to repaint that sucker  :D

Offline Medeek

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Re: Truss Calculators
« Reply #433 on: June 17, 2016, 04:57:55 PM »
Outlookers oriented horizontally with gable end truss top chord dropped:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=9f3dd430-1b90-435a-bfa6-f2bbe4d3e553
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Medeek

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Re: Truss Calculators
« Reply #434 on: June 19, 2016, 05:00:51 PM »
Version 1.6.3 - 06.19.2016
- Added Gable Dormers to the Minor Roof Sub-Menu (dormer walls only).

For now only the walls of the dormer are created:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=e17866e5-2e1d-4fb7-8203-fcb6484e8f08

I am still ironing out the details on how to best model the roof geometry.  I will probably offer either a rafter or truss option.  Other details such as multiple windows will also come later.

For now please test the metric and imperial wall creation.  I will probably need to post a tutorial video on how to use this feature since it involves selecting the main roof plane (top of a rafter or truss) and then two points that define the width/exterior corners of the dormer.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #435 on: June 20, 2016, 07:29:35 AM »
Testing the dormer (wall) feature out with a gambrel attic truss:



These dormers have a typical gable profile but it might be useful to have a gambrel dormer option as well to match with a gambrel style roof.  Note that I have not shown all of the ladder framing in the model.  On a roof like this it could get quite extensive.

To generate the dormer roof I just used my rafter roof feature and then trimmed the elements back manually. 

View model here:

https://3dwarehouse.sketchup.com/model.html?id=315004e6-6c2e-427e-981e-dc891371c77c

https://www.kubity.com/p/uCN2F6
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #436 on: June 20, 2016, 10:27:27 AM »
Same barn with a few more details.  For gambrel attic advanced options I should also include the option for a crow's beak as shown in this model and the option to set the extension.



View model here:

https://3dwarehouse.sketchup.com/model.html?id=1d1a6c57-08c4-46a4-a93e-9ae28b9f477e

https://www.kubity.com/p/uraGAJ
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #437 on: June 25, 2016, 07:37:20 AM »
Under advanced options for gable roofs (truss and rafter) I am thinking about adding a "roof return" option.  Any thoughts on "greek returns":





The images above shows a roof return with a gable termination, alternatively this could end with a hip termination as in below:



Or with a full greek which stretches across the entire span:



Does anyone have any specific framing details on how best to frame these roof elements?

As far as the logic to add them into the plugin it won't be a big deal, just an additional module that plugs into the advanced roof module.

To simplify things I would used the same pitch on the returns as on the main roof.  The three variables would be:

1.)  Return Type: Gable, Hip, Full
2.)  Length of the Return
3.)  Extension beyond Rake
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #438 on: June 25, 2016, 09:53:31 AM »
A quick study of a hip return:



Notice the inboard hip rafter does not terminate at the gable wall when the return length is too short.  This poses some interesting framing given this situation, note the return on the right side of the roof is this case, not entirely sure how one would support/terminate the hip rafter in this situation.

When the return length allows the hip rafter to terminate at the gable wall then the framing is fairly straightforward.

The hip rafter will terminate at the gable wall when the return length is greater than or equal to twice the total return extension (Rakeboard Width + Gable Overhang + Return Extension).

The other question that I have is how to apply the sheathing to these small odd shaped roof segments.  How far up under the overhang should the sheathing extend?

View model here:

https://3dwarehouse.sketchup.com/model.html?id=482d84f7-52a6-4b56-bf7d-4f373d825ec0

https://www.kubity.com/p/ytJPd4
« Last Edit: June 25, 2016, 10:11:07 AM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #439 on: June 25, 2016, 05:35:25 PM »
The sheathing needs to get up far enough to close it up, the full returns on this house were full of nests and poop, hopefully I've left no way in now. another renovation I'm involved with has flat topped returns.. go figure, they are slightly pitched now, but, I don't think the pitch needs to be the same, these look better somewhat flatter as the main pitch increases IMO. They can also tuck behind the main rake as in your full greek return sketch.

When I frame a long "faker" either across a gable like that or across a shed dormer bottom, I'll make plywood templates out of scraps that are the shape of that section. These have a notch out of the bottom edge for a 2x4 wall ledger. 2x blocking is nailed to opposite faces the ply to give nailing for roof, wall, soffit and subfascia. This goes faster and straighter than trying to assemble sticks in the air.

Offline Medeek

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Re: Truss Calculators
« Reply #440 on: June 25, 2016, 09:47:47 PM »
I have problems with birds nesting, nothing worse than waking up one morning and being covered in bird mites.

I'm looking for more pictures of actual framing of different styles of returns.  I think your right on the pitch, I should probably make that another input so that the user can control the return pitch independent of the roof pitch.

Here is a good picture of some typical greek returns (hip), just wish they showed the framing:

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #441 on: June 25, 2016, 10:18:45 PM »
This is an excellent link:

http://spot.pcc.edu/~rsteele/BCT122_123/return_eave.pdf

They run the outside hip rafter back to the gable wall and don't run the barge rafter (rake board) to the fascia like I've shown, maybe I've got this wrong...

This method would allow for sheathing of the return without having to notch around the barge rafter.  I call this the floating barge rafter method:



Compare with extending the barge rafter all the way to the fascia board:

« Last Edit: June 25, 2016, 11:13:53 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #442 on: June 27, 2016, 05:08:51 AM »
Version 1.6.4 - 06.27.2016
- Added roof return option within the advanced options menu for common, scissor and vaulted trusses, configurations: (HIP).



View model here:

https://3dwarehouse.sketchup.com/model.html?id=790b256d-72fe-46c9-b49c-dd7da0209a02

This option is available for most typical triangular shaped trusses.

I will be adding the gable and full return at a later date, currently only the hip return is available.  Another limitation is that the return roof pitches currently default to the main roof pitch.  I need to add some additional code that will allow the pitch of the return portions to be set independent of the main roof pitch.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #443 on: June 27, 2016, 07:34:57 PM »
12:12 main roof with a 8:12 hip roof return.  The interesting part is the hip rafter
where the return meets the main roof plane.  The dropped hip rafter is off center so that it supports the sheathing from both planes.  The calculations might prove challenging.

Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #444 on: June 29, 2016, 10:36:04 PM »
Roof return pitch can now be set independent of main roof pitch:



The calculations for a hip rafter that handles two pitches was insane as expected.  I've also made some other minor adjustments and bug fixes related to the sheathing and rake board when the roof return extension equals the gable overhang.

I've set it up so that the return pitch can also be greater than the main roof pitch but its doubtful if this will find any usage.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Medeek

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Re: Truss Calculators
« Reply #445 on: July 02, 2016, 12:04:53 PM »
Looking at the lumber and I-Joist floor module this morning and thinking it might be nice to make an option that allows one to specify something other than a rectangle for the floor outline.  For example an L-shaped floor outline:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=f44c5189-df6e-4178-9bf1-47e7cb74e0c5

https://www.qrvr.io/p/HlnqPF

Or even more exotic shapes with non-orthogonal corners.  I'll be giving this some thought over the weekend.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #446 on: July 07, 2016, 08:23:59 AM »
Version 1.6.5 - 07.07.2016
- Added energy/raised heels for polynesian truss type (1 variant: vertical w/ strut).
- Fixed HTML truss selector menu so that window size no longer truncates truss images.



View model here:

https://3dwarehouse.sketchup.com/model.html?id=c4ecc314-9702-4c99-9148-ca0790178583
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #447 on: July 11, 2016, 05:54:34 PM »
This is an example of a 24' x 24' garage that I would like to build on my property this summer or the next. 



View model here:

https://3dwarehouse.sketchup.com/model.html?id=77329ddc-a170-4dde-945e-4e413304f620

I created the foundation and roof with minimal effort using my own plugins.  The walls were created initially with the housebuilder plugin however I then manually edited the walls.  Note that the top plates overlap properly as they should.

Also note that the garage door wall is a double portal frame.  I would like for my wall plugin to automatically create this standard type of portal frame (PFH) both single and double (ie. Garage Door Option). Notice the embedded Simpson Strong-Tie STHD14 holdowns.

I like to use 2x jamb boards around the door perimeters when the stem wall projects above the concrete slab, this may be atypical constructon for others.  Local contractors like to embed a pressure treated nailer into the concrete.

In theory I should be able to create this exact model using the Foundation, Wall and Truss Plugin and do it all within 5 minutes or less.  That is the goal.

With the wall plugin I will have the standard linear wall tool but I would also like to have a rectangle wall tool that will immediately throw up 4 walls given three user selected points, similar to the truss and roof plugins.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #448 on: July 12, 2016, 01:45:45 AM »
That would be cool. Aligning studs and rafters/joists? One thing I run into often is the walls are laid out to efficiently use sheets but the efficiency falls off with the roof due to overhangs and alignment of framing members.

Have you seen the article on dropped vs raised portal beams and wall bowing, I have it here somewhere if not. Also some fairly specific nailing callouts in a portal frame, can it kick out something in a comment or detail?

I like the jamb down low for something to nail to. Superior walls, precast foundations, uses borate treated 2x in those locations. Listen for comments from the deep south though, that is a common termite problem area. If they can hide they will tunnel over treated.
« Last Edit: July 12, 2016, 02:04:31 AM by Don_P »

Offline Medeek

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Re: Truss Calculators
« Reply #449 on: July 12, 2016, 09:08:37 AM »
The one flaw with portal framed walls is the hinge created at the header and pony wall, that is the reason for the limitation on the pony wall height.  Other engineers hate these things and strongly prefer a conventional shear wall (segmented) design.  Moving the header to the underside of the top plate certainly helps but there is still a hinge issue between the header and the portal frame shear panel.

In this particular case I would probably not portal frame it since my aspect ratio is 3.33 and is less than the 3.5 maximum requirement by the SDPWS.

The only way to align studs and trusses would be to run them at the same spacing however the studs are usually 16" o/c and the trusses are 24" o/c.  With a 24' span the individual load per truss is not going to be egregious and the double top plate in bending should be fine.  However, with a large structure (ie. trusses with spans exceeding 40 ft) this can become a problem and recently on a large garage I had to call out a triple top plate.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer