Author Topic: Truss Calculators  (Read 145649 times)

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Offline Medeek

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Re: Truss Calculators
« Reply #575 on: April 15, 2017, 08:28:25 AM »
Then of course to further complicate matters there is the double bobtail truss which is really nothing more than a raised heel truss with unequal heel heights



So rather than add in a completely new category of trusses I suppose I could just allow the user to specify a heel height for both the left and right side of the common truss.  Currently the first menu has the option for a raised heel which is then applied to both sides of the truss.  I think I could just update to be:

Raised Heel Left: YES/NO "Defaults to NO"
Height Height Left (in.): "Defaults to 12" if no user entry"
Raised Heel Right: YES/NO "Defaults to NO"
Heel Height Right (in.):  "Defaults to SAME AS LEFT"
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #576 on: April 27, 2017, 10:06:24 PM »
Version 1.8.8 - 04.28.2017
- Added energy/raised heels for mod fan truss (3 variant: wedge, slider and vertical w/ strut).
- Metal plate connectors now enabled for mod fan trusses.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #577 on: April 29, 2017, 01:50:10 PM »
**Fun with Roofs - Episode 1**

My 9 year old son took one look at this roof and then said "Don't build this in Florida, you'll create a sink hole".











View model here:

https://3dwarehouse.sketchup.com/model/2032fed3-cb9b-40c4-80b1-be1009b3f022/Residence-8
« Last Edit: April 30, 2017, 11:01:40 AM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Adam Roby

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Re: Truss Calculators
« Reply #578 on: April 29, 2017, 07:10:57 PM »
The center would make for a great water catchment through....   :)

Offline ChugiakTinkerer

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Re: Truss Calculators
« Reply #579 on: April 30, 2017, 12:00:51 AM »
I'm thinking a koi pond would go perfectly there.
My cabin build thread: Alaskan remote 16x28 1.5 story

Offline Medeek

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Re: Truss Calculators
« Reply #580 on: April 30, 2017, 09:53:57 PM »
Version 1.8.9 - 05.01.2017
- Added energy/raised heels for triple fink truss (3 variant: wedge, slider and vertical w/ strut).
- Metal plate connectors now enabled for triple fink trusses.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #581 on: May 13, 2017, 09:15:33 AM »
I'm trying to figure out the correct way to frame the stairwell as it joins up with the floor diaphragm above. 



It's hard to show exactly what I mean with sectional views, the best thing is to view the 3D model and you will see what I am talking about.


https://3dwarehouse.sketchup.com/model/c44b3423-611d-4dac-be93-4cf1cc072891/Stairs-1

I am working on the polygon and hole tool for I-Joist and Solid Sawn floors.  When you actually frame out this opening would you just use rimboard around the perimeter as I have shown?
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #582 on: May 13, 2017, 12:51:13 PM »
I've got to fix my wife's computer today so that will probably stop me from getting any real meaningful work done on the plugins but at least I've been able to throw together a first draft for the office I want to build.  Any thoughts on improving the design, sometimes once you get an idea in your head it is hard to see outside the box.











I haven't shown the doors or the front porch which will probably be quite small and pressure treated lumber.

- 32'x24'
- 5:12 or 6:12 roof with asphalt shingles
- two rooms
- 9' ceilings
- stemwall foundation with crawlspace
- carpet throughout
- 5/8" wallboard
- 3068 doors, (1) 4040XO, (3) 5040XO
- 11-7/8" I-Joists at 16" o/c
- studs DF No. 2, 2x6 @ 16" o/c
- sheathing will probably be 1/2" plywood, I don't like OSB in our climate.
- Siding Hardiplank or cedar siding, my budget may call for T11 though.
- Electric wall cadet heaters
- 50 AMP sub-panel from house
- 16" overhangs at eaves and gables with gutters and downspouts and 4" drain lines away from building.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #583 on: May 13, 2017, 02:31:05 PM »
Just some quick view observations. I would try to set the rimboard at the top of the stairs on the cross wall containing the doorway underneath. Is there a reason not to? At the foot of the stairs I would use an lvl... all that means is I don't know the design values for rimboard and am conservative though. Fine with it otherwise.

The door rough opening is 36" which corresponds to a 2-10 door, non existent size, drop to a 2-8 door and a 34" RO and the framing should work better.

In the office I'd move the vent by the door. A kitchenette (sink, micro and coffeepot space) and bath would be nice but drives up cost.

Offline Medeek

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Re: Truss Calculators
« Reply #584 on: May 22, 2017, 11:54:52 PM »
All the end details are working.  This is an example of a Mansard Parapet truss with 5 panels and different overhangs:



Now I just need to work on the plates and advanced options.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #585 on: May 27, 2017, 02:30:36 PM »
Version 1.9.0 - 05.27.2017
- Added flat truss type, configurations: flat, monopitch, pitched.
- Metric input enabled for flat truss types.
- Added gable end trusses for flat truss types.
- Enabled the following end details for all flat truss types: None, Overhang, Cantilever, Mansard, Parapet, Mansard w/ Parapet.



Plates and advanced options are still in progress.  With the amount of configurations available with this truss type it will probably be a while before these next elements are in place.

The flat truss type is very configurable and with a little adjustment of parameters you can also easily create a (non-attic) gambrel truss using the flat pitched option.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #586 on: May 27, 2017, 04:44:07 PM »
Here is an example of a small commercial building with a flat truss roof (parapet):



Download model here:

https://3dwarehouse.sketchup.com/model/d8413377-4287-4fb3-99b9-3d200441a2fe/Commercial-Building
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #587 on: May 28, 2017, 02:35:42 AM »
The flat double pitched truss allows for a user driven asymmetric ridge location as well as differing left and right heel heights.  This opens up virtually any possible truss geometry even a negative pitch if one is so inclined:



Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #588 on: May 28, 2017, 12:08:57 PM »
I thought I was done with flat trusses but it was pointed out to me that I also need to consider top chord bearing configurations for this truss type.

I've created a simple matrix below with top and bottom chord bearing flat trusses.  I'm not sure if these make sense, please review and feel free to comment.



The model can be downloaded here:

https://3dwarehouse.sketchup.com/model/acee31ef-9e54-4eca-83d7-02747815ed29/Flat-Truss-End-Details-3

Top chord bearing usually involves the following steps:

1.)  Trimming the heel web up a specific vertical amount (vertical offset).
2.)  Insertion of a secondary heel web next to the trimmed (bearing) heel web.
3.)  Trimming the bottom chord back to the secondary heel web.
4.)  The diagonal web next to the heel is slightly altered by the addition of a secondary heel web.
5.)  Certain configs require an additional heel web on the outside of the trimmed heel web:  Mansard, Cantilever, Mansard w/ Parapet.

I can easily make this all happen and open up the option for top chord bearing flat roof trusses however I want to make sure it is right first.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #589 on: May 29, 2017, 02:41:05 AM »
The top chord bearing option is almost complete for the flat trusses.  Here is a preview with a Mansard /w Parapet on the left side and a cantilever on the right side.  The bearing widths can be set independently as can the parapets heights now.



I'm not entirely satisfied with the UI for this truss type, a proper html UI would be much more intuitive but time consuming to create.  Yet another important item on the todo list.

The plugin is starting to stray into some fairly exotic truss territory.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #590 on: May 29, 2017, 09:57:17 AM »
Wood Gusset plates are on my mind this morning (for those of us crazy enough to build or own trusses):



Of course this option would be pretty much useless without the engineering to size the plates and check the fasteners.  I will be giving this some more thought in the near future.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline MountainDon

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Re: Truss Calculators
« Reply #591 on: May 29, 2017, 11:48:03 AM »
There are some who would like to build their own I'm sure.

Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline Medeek

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Re: Truss Calculators
« Reply #592 on: May 30, 2017, 08:48:02 AM »
I think I've beaten the flat truss to death but I noticed after perusing through a number of flat truss shop drawings that the modified warren is also a popular web configuration.  Its not too big of a deal to enable this configuration.  The flat truss will then have the option between a pratt or mod warren web configuration.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #593 on: May 30, 2017, 08:39:32 PM »
Enabled mod warren webs for the double pitched flat truss configuration:



The truss shown above is an asymmetric double pitched top chord bearing flat truss with a mod warren web configuration and cantilever ends.  That is quite a mouthful.

I have not added the top chord bearing option and the mod warren webs to the other flat truss configurations yet (flat, monopitch, pitched), however I will if specifically requested. There a much hotter items on the plate.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #594 on: June 08, 2017, 07:09:40 AM »
In the global settings I've added a setting to switch between metal and wood connector plates.  Initially I will only enable wood plates for some of the more typical common trusses (ie. fink, howe, queen and king), if this feature proves to be popular I may enable it for more truss types.


Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #595 on: June 09, 2017, 11:33:39 PM »
Version 1.9.1 - 06.09.2017
- Added plywood gusset plates for common fink trusses.
- Enabled a "WOOD" plate type option in the global settings.



*Note that the wood gussets are currently only available for the Fink truss, if anyone needs them enabled for a different truss please let me know.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #596 on: June 10, 2017, 12:08:55 AM »
For the truss DIYer, would you rather drive a 3-1/2" nail through both gusset plates and the truss member and then clinch it on the other side or use smaller nails and not have to clinch?  From an engineering standpoint I know what I prefer but I am curious what the actual builder would prefer.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #597 on: June 10, 2017, 05:24:19 PM »
Added plywood gusset plates for raised heel common fink trusses.



View model here:

https://3dwarehouse.sketchup.com/model/b21431bc-c3b6-4038-a81e-f27fc78f69b1/WGC-Truss

Note that there are currently no calcs associated with these WGC trusses.  If you are going to build your own trusses I would strongly suggest you find a local structural engineer to assist in specifying the plates sizes and fasteners, especially if the truss span is greater than 16 feet and your snow loads are greater than 25 psf in your region. 

When I engineer WGC trusses I will also call out a waterproof glue as well however I don't take the glue's strength into the calculations.  This provides another margin of safety and also the rigidity of a glued and nailed gusset plated truss is superior in my opinion to your typical MPC truss. 

Every member is critical in a truss, however some are more stressed than others.  Your top and bottom chords should never be anything less than a No. 2 DF.  I would suggest No. 1, No. 1 & Btr. or Select Structural.  The webs of a typical truss are usually stressed quite a bit less than the chords and sometimes you can get away with stud grade lumber but I would suggest DF No. 2 on all webs as well.  A strategically placed knot can easily ruin an entire truss.

Just as important as the materials is the level of care taken in cutting the members and assembling the truss.  All joints should fit tightly together so that members in compression can bear directly on their adjacent members.  Also realize that tension members may experience load reversals in high wind or seismic events so even tension members are no exception to the rule.

The correct fasteners and fastener size is critical.  The nails will be in single or double shear and the joint connection is relying entirely on this shear strength of the fasteners to hold together.  Fasteners too close to the edge or ends of a member are not as effective, so fastener placement is also critical.

I am curious how the two truss types would compare in a burn test, which one would stay intact longer.  My suspicion is that the plywood gussets would char and slowly burn however the metal plates would heat up and loose their strength quickly and fail.

I know most people don't do this but I would personally stress test each truss before installing it on the intended structure.  Mostly what you are looking for is a uniform deflection across all the trusses so that they can load balance properly.  If a truss is defective this test should help ferret out this data even though visually the truss may look acceptable.
« Last Edit: June 10, 2017, 06:28:48 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #598 on: June 11, 2017, 08:25:34 AM »
I would prefer to shoot ring shank 8d's from each face. Yup, I know what you want, I doubt it would happen in the field is my logic. I agree any field glue is gravy not to be used in the calcs. My understanding from a truss guy I was sitting beside in one seminar is that the metal plate protects the joint area, the wood burns through before the joints fail... still not sure I buy that but what do I know  :D. Is ply orientation critical? Would you test to design load or beyond?

Offline Medeek

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Re: Truss Calculators
« Reply #599 on: June 11, 2017, 01:23:19 PM »
Just for the record the algorithm to size and position the mid top chord to web plate (Plate 2) is a real piece of work:

Code: [Select]
gamma2 = 3.14159265358979 * 0.5 - @Phi
length2 = @Pldim2 * 0.5 -1
p3x = @Swx4 + length2 * (cos(@Theta2) / cos(gamma2 - @Theta2))
p3y = @Swy4 - length2 * (sin(@Theta2) / cos(gamma2 - @Theta2))
p2x = p3x - (@Tcd + length2) * cos(gamma2)
p2y = p3y + (@Tcd + length2) * sin(gamma2)
p1x = p2x - @Pldim2 * cos(@Phi)
p1y = p2y - @Pldim2 * sin(@Phi)
length4 = sqrt((@Strx4 - p1x)*(@Strx4 - p1x) + (@Stry4 - p1y)*(@Stry4 - p1y))
zeta2 = atan((p1y - @Stry4)/(@Strx4 - p1x))
length3 = length4 * sin(zeta2 + @Theta3) / sin(3.14159265358979 * 0.5 + @Phi - @Theta3)
p4x = p1x + length3 * cos(gamma2)
p4y = p1y - length3 * sin(gamma2)

if @Theta2 > gamma2
  p2x = p3x - ((@Tcd + length2) / (cos(@Theta2 - gamma2))) * cos(@Theta2)
  p2y = p3y + ((@Tcd + length2) / (cos(@Theta2 - gamma2))) * sin(@Theta2)
end

Actually had to use the Sine Law:  https://en.wikipedia.org/wiki/Law_of_sines

Its funny because my 15 year old daughter just covered trigonometry in her math class and she told me she would never use this stuff so why learn it. 
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer