I've been thinking about site built trusses some more and trying to apply some rational thought to how best to nail together a WGC truss.  If you consider nails in single shear, 8d nails spaced at 4" between fasteners with a row spacing of 1" and and end spacing of 1.5" you end up with something like this.



Those are 8d common nails so they aren't very big but spaced at 2" between nails in a row I would be afraid of splitting that bottom chord. 

Looking at this I'm fairly convinced that going with longer nails that are in double shear and clinched give more bang for the buck, allow less nails and thereby less chance of splitting the truss members.  Thoughts?

Lightweight version of a Simpson Strong-Tie HDU8 Holdown.

View model here:

https://3dwarehouse.sketchup.com/model/ce77385b-5873-48b1-ba1a-a37c2ac58294/HDU8

Its about 1/10th the weight of the official holdown in the 3D Warehouse and 118 polygons vs. 3,109 polygons. 

I will plan on using these lightweight versions in the upcoming wall and structural plugin.

If you overlay the simplified version on top of the official version you will see how closely they match up.  The critical dimensions are primarily accounted for.

Version 1.1.4 - 06.11.2017
- Added pre-drawn face outline tool for stemwall and slab-on-grade foundations and slabs.

You can now click on a face (any closed polygon shape) and the plugin will generate the appropriate stemwall, SOG or slab.

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:

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. 

By default the foundation vents are placed a fixed distance (user driven) from the foundation corners.  Once the stemwall is created it is not very hard to move the vent manually if required.

Tutorial 1:

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.

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.

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.

Added "FPSF" option to polygon stemwall foundations.



Now I've thoroughly beaten the FPSF option to death, the only thing I might add in later is a global setting to change the insulation color to pink, blue or white.

An octagon slab on grade (FPSF).  Note that the angle of the corners is 225 degrees, any less and the corner treatment would go away. 

Added "FPSF" option to polygon slab-on-grade foundations:

I haven't enabled it for polygon shaped stemwall and slabs yet, that is still a work in progress.  Too much to do and not enough time to do it all.

Working on the square/rectangle spread footing tool:

I will start with wood posts as an option with the following sub-options for the wood post:

Post Size:  4x4, 4x6, 6x6, 6x8, 8x8
Post Height (in.)
Post Base:  None, ABA, ABU, ABW, CBSQ
Post Cap:  None, CCQ, ECCQ
Post Rotation:  0, 90, 180, 270

I also plan on having the option for steel posts with the following sub-options:

Post Size:  HSS4x4x1/2, HSS4x4x3/8, HSS 4x4x1/4, HSS3x3x3/8 etc...  (round and square tube)
Post Height (in.)
Base Plate Size (in.) - square shape L x L
Base Plate Thickness (in.)
Base Plate Hole Dia. (in.): 1/4, 3/8, 1/2, 5/8 (4 bolts per baseplate)
Vert. Offset (in.)  - for non-shrink grout
Post Cap:  Not sure what to do with this yet.
Post Rotation:  0, 90, 180, 270





I've been contemplating using the Simpson Strong-Tie post caps and bases as provide in the warehouse but I'm worried that the polygon count is too high.  I may have to generate my own dumbed down versions.

- Added "FPSF" option to rectangular stemwall foundations.