Truss Calculators

[Don_P]

Going back to the straps, a hip roof is considered to thrust both ways. Where the ceiling joists tie from side to side unbroken we've got it tied. In the direction across the short tail joists the roof is not tied yet. If there is adequate sheathing nailing on the attic floor across the tails and to a floor diaphragm that would work. I've blocked deep into the room to develop a tie there. I ran about half a spool of simpson strap last year on a house that had a floor under a diamond hip with the tail joists untied, the wall had been thrust outward at the top.

There was a common thought in that time that still persists, and there is merit, that a hip roof is self supporting. The roof was a flexible diaphragm and even now is unblocked, although fully sheathed it is too flexible to count on calling that some form of folded plate. The hips back then were often 2x4 or 2x6. I've removed them broken, scabbed and propped, and with 4" of permanent deflection as well.

R802-803 touches on it;
http://codes.iccsafe.org/app/book/content/VA/2012_VA_Residential_HTML/Chapter%208.html
I prefer to have the hips, valleys, and any ridge designed as beams and supported as such if at all possible. I would check those members on your hipped ranch, smile and build. Since you have it on structural beams I wouldn't be concerned with the tail joists (although I'd probably wrap a strap on the center tail joist and over the double common cj)

JLC had an article some years ago, a small hipped building with LVL hips bearing on welded steel top plate angles, feet long out of each corner and with clips to rigidly hold the hips, that was a nice looking self supporting hip.

The complex roof even untrimmed sure helps with visualization. By hand that would have taken me many walks out in the yard 

[Medeek]

Looks like JLC has a lot of good articles on a number of things even beyond conventional roof framing, I'm going to have to spend a day just looking through their site.

[Medeek]

Looking at cantilevered trusses tonight.  The use of a wedge, slider or strut depends on the amount of the overhang and in some cases if the overhang (cantilever) is within the scarf cut of the top chord no additional member is required, see image below:



Notice how the web strut is centered over the point of bearing with the long cantilever.  Also notice that the panel point placement of this fink truss was not altered with the addition of the cantilever.

Basically this will be a new truss family and I'll start with the fink truss and take it from there.  If anyone has shop drawing from truss plants they are willing to share that show different configurations of a cantilever truss, that would be very helpful.

[Don_P]

Found the JLC article I was thinking of here;
http://www.mvconstruction.com/roof_article.pdf

[Medeek]

Version 1.2.4 - 01.08.2016
- Plugin integrated with the Medeek Truss Designer.
- Engineering of common fink truss enabled.



When a new truss is created (common truss types only for now) the parameters are specified within the dynamic component attribute library.  Opening the component options allows one to change some of these values.

The new engineering icon allows one to automatically transfer all of the truss design parameters directly from SketchUp to the Truss Designer for engineering checks. 

[Medeek]

The current Medeek Truss Plugin menu now has 5 icons:



The available items are the following:

1.) Draw Roof Truss:
  - Common
  - Attic
  - Monopitch
  - Scissor
 
2.) Draw Floor Truss:
  - Floor Truss
  - TJI Joist

3.) Draw Truss Set:
  - Valley Set

4.) Draw Roof Rafters:
  - Gable Roof
  - Gable Roof w/ GLB
  - TJI Roof w/ GLB
  - Hip Roof

5.) Engineering Calculations:
  - Truss (common truss types only)

Note that the menus show additional items that are either being worked on or are planned for future releases.

[Don_P]

I've banged around on it some, awesome work.
Is there a way to get back to the options boxes and change a setting after the truss has been drawn which would then modify the drawing to reflect the change? I've been "undoing" the truss in sketchup and trying again. 

[Medeek]

You make a good point.  The truss component in SketchUp is not fully dynamic yet, however if you right click on the actual truss component and open the Dynamic Component -> Component Options dialog box you will see that you can change some options associated with the truss.  The items grayed out you cannot currently change but I would like to try and make some of them dynamic as well.

if you make a change here and then proceed with the engineering you will notice the new values are then sent to the calculator.  The dynamic attributes revealed in this dialog are what is being sent to the calculator for engineering.

For most people engineering a truss will probably not be particularly useful (truss plant usually takes care of these details) however if I add engineering for rafters, beams, ceiling joists, and floor joists etc... I think that would make this plugin significantly more of a value add. 

[Don_P]

If you can work in plywood gusset design at some point then truss design becomes quite useful. In my state and a number of others we have an ag exemption from inspection, we can design and build our own, I can also use native lumber... hmm allow me to enter design values?

For rafters, we did have a request on the forum last week for an A frame design. The concept pic looked like quite long rafters, so would probably be better in I joists, and looked to be a bit steeper than 24/12. Can the pitch be a type in input? When a roof starts to get cut up the pitches can be X.xxx/12

[Medeek]

A couple months ago I was working on the engineering of the plywood gusset plates.  I really should re-focus back on to that and get it going.  There is definitely a nitch market there that no one has seemed to fill just yet. 

If I remember correctly I was pondering the exact nature of a heel joint and the proper treatment of the gusset plate (shear, tension or both) in this situation.

[Medeek]

I've done some maintenance on the beam calculator in preparation for integration with the Truss Plugin:

Version 1.0.1 - 01.10.2016
- Updated javascript front end so that selected options are properly retained.
- Updated total load (reactions) to include applied load and selfweight over total span. Results now more closely agree with WoodWorks Sizer Software.
- Inputs now include option for Total Span and Clear Span.
- Removed beam configurations that are not yet complete.
- Beam graphic now shows span geometry with supports.

http://design.medeek.com/resources/beam/beam_calculator.pl

At some point I need to come up with a slicker interface that allows for multiple point loads and supports but that is a job for another day.

[Medeek]

Version 1.2.5 - 01.10.2016
- Plugin integrated with the Medeek Beam Calculator.
- Engineering of North American glulam beam sizes enabled (Western, Southern Pine).

Also note that the Beam Calculator has a very nice PDF report output than can include client and job information.

[Medeek]

Screenshot of the Beam Calculator that will pop up when called from the plugin:



So far I only have glulam beams as an option in the plugin but I will probably add LVL, LSL, PSL and Solid Sawn and those can also be analyzed with this same interface.

[Medeek]

First tutorial video:

https://youtu.be/1WqGkK15zYA

[Medeek]

Engineering Video:

https://youtu.be/f0y7y8WtjDw



The SketchUp model used in the video can be found here:

https://3dwarehouse.sketchup.com/model.html?id=u6c602b47-40bb-4349-9e0e-0917746ab90a

[Medeek]

Valley Truss Set:

https://youtu.be/CrI7pdEfb1o

[Medeek]

Hip Roof Framing:

https://youtu.be/zyHuGR6nwpg

SketchUp model used in the video can be found here:

https://3dwarehouse.sketchup.com/model.html?id=u53e50317-d46f-40dd-a95f-c50b1d51302d

I think you are going to be hard pressed to find something that can frame up a hip roof faster than this thing can.  I just keep coming back to it trying to create even more cut up roofs just for fun. 

[Medeek]

Testing the limits of the Medeek Truss Plugin with complex hip roofs. Note that the roof primitives have not been trimmed back. This is primarily a study to determine what additional programming would be required to generate this type of roof automatically:



This for me would be the holy grail of hip roof framing...

[Medeek]

As you can see there is still a tremendous amount of work that can be done here.  To that end I've started a KickStarter project which if successful would allow me to devote at least 4-5 months of my undivided attention on the programming of this plugin:

https://www.kickstarter.com/projects/128644708/medeek-truss-plugin

[Medeek]

I have been giving some thought to dormers and how to specify them.  Below is a dormer design I framed in Solidworks a few years back for a garage design:





Of course the numerous ways in which one could frame a dormer is probably beyond the scope of this discussion but I would like to consider what geometry needs to be determined in order to orient and size the dormer.

After some thought I think the following points, planes and lengths would define the geometry of a typical dormer:

1.) Main Roof Plane
2.) Attic Floor Plane
3.) Offset from exterior wall below (how far the dormer is out of plane from the ext. wall below).
4.) Pitch of Dormer roof
5.) Dormer width
6.) Dormer height (distance from attic floor plane to top plate of dormer wall)
7.) Window width, height, and header depth
8.) Dormer wall thickness (2x4 or 2x6)
9.) Dormer rafter depth
10.) Position of Dormer along length of building

Items 2,3 and 10 can be combined into a single point selection.

[Medeek]

Pondering complex hip roofs this afternoon and considering the graphic below:



A few rules seem to emerge:

1.) An outside corner will always create a hip that is 45 deg. from each leg of the corner.
2.) An inside corner will likewise always create a valley 135 deg. from each leg of the corner.
3.) Where two hips or flying hips meet a ridge will extend 135 deg. from each hip.
4.) When two valleys meet at 90 deg. they will terminate and a ridge will extend at 45 deg. from each valley.
5.) With a building with walls only running north-south or east-west all ridge lines will always be north-south or east-west.
6.) Likewise all hips, valleys and flying hips will be oriented northwest, northeast, southwest, or southeast.
7.) When a valley meets a ridge, (they will always meet at 45 deg) a flying hip is generated that is 90 deg. from the valley and 135 deg from the ridge. 
8.) When two valleys meet at 180 deg. from each other, the result will be either to flying hips perp. to the valleys or the degenerate case of 4 valleys and 4 ridges.
9.) When a valley and a hip meet each other at 180 deg. then two ridges that are 45 deg from the valley will be the result (typical L shaped roof).
10.) When 4 hips meet the result is a pyramid.

There may be a few other degenerate cases I'm missing but I think that covers it.

[Medeek]

Variation in plate heights, pitches, overhangs and even mixing hip and gable (half hip, dutch gable) further complicate the matter.  To begin with I need a algorithm to generate the roof planes, then the framing just falls out from there.  To create the roof planes I need a fairly robust straight skeleton implementation.

[Don_P]

The rules apply if the pitches are the same, as soon as you go to a split pitch the hip in plan changes. You can draw a right triangle with the inches of pitch of one side on one leg, the pitch of the other side on the adjacent leg and the hypotenuse connecting them will be the hip angle in plan.
Draw a 4/12 end meeting an 8/12 main roof and the hip angle change from 45* to around 65*. To keep the overhangs the same, the hip moves out of the corner at the building line to the steeper side.

I was hoping for more response on the kickstarter, it is amazing to see what you are doing. I'd really like to see what you can do with more time dedicated to developing this.

[Don_P]

Here's an irregular hip, a 4/12 meeting an 8/12 main roof superimposed over the building line.

there used to be an article online by Joe Fusco that did a good job of walking through it with a calculator.

[Medeek]

Version 1.2.6 - 01.18.2016
- Sill plate option (advanced) enabled for top and bottom bearing floor trusses.




https://3dwarehouse.sketchup.com/model.html?id=u98d5f3e7-8cab-4acc-8160-7e20617e1814

Work on the manual is progressing however for those interested the red colored boards in the image are called  "ribbon boards".  This is fairly typical for floor trusses.  The notch purposely left in the truss to accommodate the ribbon board is called the ribbon cut or ribbon notch.  Continuous ribbons provide stability for installed trusses, and also provide a solid nailing surface for the edge nailing of floor sheathing. This eliminates the need for larger and more expensive “rimboard” solutions required by dimensional lumber and other engineered wood products.  2x4 lumber is common, but any dimension of 2x lumber can be used for the ribbon board.

Similar to the complex hip roofs I need to program the floor truss module so that it can automatically frame out any non-rectangular floor plan.