## Truss Calculators

Started by Medeek, March 12, 2013, 06:33:08 AM

0 Members and 2 Guests are viewing this topic.

#### Medeek

Hip roofs are quite the head scratchers.  Its hard enough trying to figure out the math I can only imagine actually trying to build these things.  A couple other people I have consulted with basically said the same thing about the common against the transition, just scab on a nailer and then apply sheathing etc...
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

Version 1.4.2 - 03.19.2016
- Added energy/raised heels for attic trusses (1 variant: vertical w/ strut).
- Addressed some minor usability issues with the attic truss menu and options.

View model here:

https://3dwarehouse.sketchup.com/model.html?id=u4f64fd8b-160f-49ce-815d-a66991527cdb

I've had quite a few people asking for this update so stayed up most of the night and knocked it out.  Note, that the raised heel option is currently limited to attic trusses with a span of 24 ft. or greater.  The reason for this is the way my logic currently works with spliced top chords.  If this becomes an issue I will spend some more time on it to encompass attic trusses with a lesser span.  I still do not have the gable truss, metric input or structural outlookers for this truss type, yet more items for the "todo" list.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

Thinking about dormers today and attic trusses:

View model here:

https://3dwarehouse.sketchup.com/model.html?id=ud50cb83e-54fc-42b0-9b57-0a5691b1c678

2-ply girder trusses on each side of the dormer with ladder framing between.  I haven't bothered to show all of the main floor framing geometry (doors, windows, stairs etc...)  My question is what would be the best route for the infill framing above the dormers.

1.)  Ladder frame perpendicular to trusses.
2.)  Install a ridgeboard hangered between the girder trusses and a lower header and install rafters parallel to the trusses?

Note that the manual creation of the dormers took about an hour whereas the attic truss main roof and dormer roof were created with the plugin and only took about 5-10 minutes.  A dormer routine would be useful.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Don_P

I would do #2 with a plumb 2 ply header, although I don't see enough meat on the girder trusses to attach to  ... I'd probably fill the truss area with deadwood and plate with ply then attach the header hangers. Seek other advice.

I'm not sure if we've talked about it, as the "hat" gets wider on a 2 piece truss that level deck needs permanent lateral bracing as well. The only collapse I've seen was in a church where that level got quite wide, and then being unbraced, twisted and collapsed. Dr Woeste wrote an article on that in JLC, I think in the 90's. With all the dormers' folded plates it isn't happening here, just a FYI.

#### Medeek

Quote from: Don_P on March 20, 2016, 08:53:58 AM
I'm not sure if we've talked about it, as the "hat" gets wider on a 2 piece truss that level deck needs permanent lateral bracing as well. The only collapse I've seen was in a church where that level got quite wide, and then being unbraced, twisted and collapsed. Dr Woeste wrote an article on that in JLC, I think in the 90's. With all the dormers' folded plates it isn't happening here, just a FYI.

I'm assuming you are describing the continuous lateral bracing (CLR) between the piggyback truss and the main attic truss?

I have not shown all of the bracing, but you will note that the attic truss created by the plugin leaves a 1.5" gap between the trusses for this bracing requirement.

A couple years ago I helped on a similar design but I did not get any pictures of the roof framing, I'll have to get back out there and take a look at how we framed up those roof sections between the girder trusses.

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

#### Medeek

A basic algorithm to convert a common gable truss into a transition truss should not be to much problem.  However, to make it handle all cases would become difficult if you include raised energy heels, drop top chords and scissor trusses in the mix.  Consider the two examples below:

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

#### Medeek

Version 1.4.3 - 03.20.2016
- Added Scissor truss type, configuration: (6/6).
- Added energy/raised heels for scissor trusses (2 variants: wedge and vertical w/ strut).
- Addressed some minor usability issues with the scissor truss menu and options.

View model here:

https://3dwarehouse.sketchup.com/model.html?id=u8ca4bf44-f28a-481e-8c1e-b53de30e3696
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

Polynesian 4/4 truss is working:

However, I haven't released this latest update yet, I still need to enable gable end trusses and advanced options for this truss type before it is ready for prime time.

The inputs are similar to all other truss types except you have two top chord pitches and a pitch break length measured from the left butt cut of the truss.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

Version 1.4.4 - 03.21.2016
- Added Polynesian truss type, configurations: (4/4).
- Metric input enabled for polynesian truss type.
- Added gable end trusses for polynesian truss type.

I'm not sure where this type of truss is commonly used but whenever I see one I think of a bus stop or train station:

Advanced options are not yet enabled for this truss type yet, so sheathing, fascia, rake will have to come later.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

After adding Bowstring and Bow Barrel trusses the only common other round truss type is the Barrel Vault.  The problem with this type of truss is the webs get messy or at least hard to predicate because of the interplay between the vault and the pitched roof above it.  In an effort to better understand this type of roof/ceiling configuration I've created the matrix below:

High Res. PDF copy here:

http://design.medeek.com/resources/truss/BARREL_VAULT/BARRELVAULT_STUDY1.pdf

I am trying to predict the max. height of the vault given a specific roof pitch and and vault width to span ratio.  Perhaps I am recreating the wheel and some architect or designer has devised a method to create the perfect barrel vault given a roof pitch and other criteria.

I would be interested in what other opinions are on this matter.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### ChugiakTinkerer

Thanks so much for the scissor truss with energy heel.  Will definitely have to update the plugin.  Any chance the menu changes included an arbitrary overhang?  For my example a 19.25" overhang allows me to use a precisely 12' metal roofing panel.  I imagine being able to input an overhang other than 2" increments would be useful in a lot of other instances too.

The progress on your updates is impressive, if not downright amazing.  Where's that We're Not Worthy animated smiley icon?
My cabin build thread: Alaskan remote 16x28 1.5 story

#### Medeek

The latest version has switched to an arbitrary overhang for most if not all truss types and rafter roofs, see changelog notes for Version 1.3.8 (03/10/2016).  The development has been very rapid the last few days as I have come upon some time to work on it and a serious push over the weekend to get some updates accomplished that were long outstanding.

I'm just amazed at the SketchUp API that allows me to script all of this.  I've always like the free form feel of SketchUp but never took it very seriously as a design or drafting tool.  With the ability to program extensions/plugins I think that changes the equation slightly.  I can now generate an entire structure in 3D in about 4 hours that would take me over 2 weeks to accomplish in Solidworks.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

Using a typical Barrel Vault 8/7+4 or 8/7+2 configuration I come up with the following triangulations.  I'm sure there are other methods of configuring these webs but for the purposes of the plugin I think these solutions will suffice for now:

High Resolution PDF copy here:

http://design.medeek.com/resources/truss/BARREL_VAULT/BARRELVAULT_STUDY1_REVA2.pdf

Based on this matrix I've been able to come up with a simple algorithm for the triangulation of this truss type.  I'll admit the barrel vault truss is one handsome devil.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

A 9:12 barrel vault truss with a 16' wide barrel:

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

#### Don_P

Quote from: Medeek on March 22, 2016, 07:53:56 PM
I'll admit the barrel vault truss is one handsome devil.

I think we need to do an intervention
I'm curious, what is the bottom chord tension like in one of the deep barrels as compared to a straight bottom chord?

#### Medeek

#365
I don't know, I've never actually analyzed a truss like this.  I suppose I could put the exact same size of truss with identical loads into RISA and compare the two, that would be interesting.

Has anyone ever seen a gable end version of this truss type?  My thinking is that it might make more sense to just use a common gable truss otherwise you would be looking at some very complicated wall framing below the truss.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

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

#### Medeek

Version 1.4.5 - 03.24.2016
- Structural outlookers (vert. & horz.) enabled under advanced roof options for Scissor (4/4) truss type.

I guess I somehow missed enabling structural outlookers for scissor trusses.  Anyhow this issue was brought to my attention this evening so I've tried to rectify it as much as possible.  After delving into the code I realized that the scissor truss module needs a major rewrite and cleanup so I was only able to get structural outlookers enabled for the 4/4 configuration.  Later next week I will jump back into this module and work on the 2/2 and 6/6 configuration.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

#368
I had someone ask me if it would be possible to create a small house or cabin based entirely on a raised heel attic truss profile, probably with some skylights for light.  I've never seen this type of design before but I don't see why it might not work.  Has anyone ever seen something like this done?  Basically an attic truss with a raised heel (48') resting directly on a stem wall foundation with post and beams or something similar.

The one issue I could see is if there were no windows for a bedroom (no egress) that was midway the length of the structure.  The design shown is 36' wide, 42' long with a 21' wide attic room.  6"x24" stemwall foundation, with a 12"x6" footing.

Typically large attic trusses are quite expensive so it would seem that this would be an expensive way to build a house perhaps there is some other reason that makes this method of construction viable?

Also note how much of the square footage is dead space (630 sqft) vs. the total area (1512 sqft).

View model here:

https://3dwarehouse.sketchup.com/model.html?id=u88dea626-2d7e-45cb-8751-6f2f3b101fc5
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Don_P

I fail to see an advantage with that,15' of the footprint is unuseable and then a premium for the floor space. Replace the foundation with superior or similar precast full height walls on a gravel foundation and you can have a very fast build.

#### Medeek

Another look at the cambered truss:

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

#### Medeek

Version 1.4.6 - 03.26.2016
- Added Cambered truss type, configurations: (6/X).
- Metric input enabled for cambered truss type.
- Added gable end trusses for cambered truss type.

Six variants of the (6/X) configuration dependent on the ratio of the camber width to span.  Notice that in all cases the top chord has six panels, the bottom chord varies from 4, 5 and 6 panels.

View model here:

https://3dwarehouse.sketchup.com/model.html?id=ued7e0d19-2843-4b3a-9786-3c15cf876fdf
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

Second look at cathedral trusses (6/X) family:

The logic required to triangulate these type of trusses becomes tedious.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

I've been meaning to add in cathedral trusses for quite some time and I finally had the chance last night.  Configuration (3) shown below for a catheral 6/X truss:

Now I only need to code in the other six configurations and its ready to release as a new update.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

#### Medeek

A breakdown of the configurations for the Cathedral 4/X family:

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