Author Topic: Truss Calculators  (Read 369591 times)

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Offline Medeek

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Re: Truss Calculators
« Reply #275 on: January 30, 2016, 12:59:21 PM »
Dutch Gable Rev. 2:

https://3dwarehouse.sketchup.com/model.html?id=u32c4c79d-603a-4363-99db-df726b281151

Same as previous except for doubled up common rafters at dutch gable.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #276 on: January 30, 2016, 04:38:23 PM »
Dutch Gable Rev. 3:

Doubled up gable common rafters with the dutch ridge/ledger is sandwiched between them. Found a paper by Larry Haun, Mar. 1995 "Framing a Dutch Roof" that was published in Fine Homebuilding magazine, that describes a very similar method of framing.



View model here:

https://3dwarehouse.sketchup.com/model.html?id=ude19cd3c-e059-42e0-8e7d-2b0b6b0852a8

Disregard the common rafter sizes they are undersized but look at the method of sandwiching the dutch ridge/ledger between the last common rafters. I would probably also install some blocking between the double gable common rafters. I'm also not showing all of the ceiling joists and bird blocking etc...

If the roof gets large enough then one could go to a double ply dutch ridge, or even a deeper LVL member, assuming there is no internal support available from internal walls.
« Last Edit: January 30, 2016, 04:54:09 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #277 on: January 30, 2016, 06:49:43 PM »
I like that [cool]

Offline Medeek

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Re: Truss Calculators
« Reply #278 on: January 30, 2016, 08:21:57 PM »
I think I'm ready to add the dutch gable into the plugin.  It's only slightly more complicated than the hip roof.

I've also realized that for hip roofs I need an option to set the depth of the hip rafters since they are often larger members than the common or jack rafters.

Here is the new icon for secondary roofs:



This category will contain the following items:

- Gable Roof Minor
- Hip Roof Minor
- Dutch Gable Roof Minor
- Gable Dormer
- Hip Dormer
- Shed Dormer
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #279 on: January 31, 2016, 03:53:33 AM »
Can't remember if it's come up or if there is anything other than operator knowledge required, watch the birdsmouth on the hip over the wall, it needs to stay over support, the birdsmouths on everything are limited to <1/4 member depth.

The passing subfascia detail on the inside corner;
https://3dwarehouse.sketchup.com/model.html?id=u13eb2420-daf2-4d3b-bd87-8297d6fd88ce


Offline Medeek

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Re: Truss Calculators
« Reply #280 on: January 31, 2016, 10:48:46 AM »
I still need to add in a warning about the <1/4 rule.  I'm assuming birdsmouth cuts of the hip rafter and the valley rafters both need to stay over the support, I need to take a look at that.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #281 on: January 31, 2016, 04:48:50 PM »
Yes, full bearing. You can run a dragon beam or a header to support the hip in some times of trouble.

BTW, if you bob the tail the 1/4 depth rule vaporizes, then you can scab on a 2x tail, 2/3 inboard 1/3 extended. This can get you out of some tight spots.

Offline Medeek

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Re: Truss Calculators
« Reply #282 on: January 31, 2016, 07:53:24 PM »
Yes, full bearing. You can run a dragon beam or a header to support the hip in some times of trouble.

BTW, if you bob the tail the 1/4 depth rule vaporizes, then you can scab on a 2x tail, 2/3 inboard 1/3 extended. This can get you out of some tight spots.

Does the 1/4 rule really make sense?  A 2x10 rafter requires a 6.94" depth remaining, whereas a 2x4 extending as the overhang that has no birdsmouth cut would pass?
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #283 on: February 01, 2016, 12:28:49 AM »
edited to southern pc;

Bless their pea pickin hearts, it doesn't make a lick of sense to me. I've been to the top of the ladder with awc before this last code cycle but the porch light has not yet glimmered.

Dimensionally this is short but it's roughly how we've bumped a dormer out before.
https://3dwarehouse.sketchup.com/model.html?id=u926f7220-73e9-424c-82bd-6e44545b7b52



Doodling some more... this is really rough but shows a jerkinhead or clipped gable
https://3dwarehouse.sketchup.com/model.html?id=ufe2a9943-aeee-4457-bbe5-6c4971ce5ee5

« Last Edit: February 01, 2016, 04:01:17 AM by Don_P »


Offline Medeek

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Re: Truss Calculators
« Reply #284 on: February 02, 2016, 12:35:40 AM »
The jerkinhead or half hip is yet another roof type that I need to add. I will be studying your jerkinhead model below.  Interesting how the fascia and rake blend into each other.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #285 on: February 02, 2016, 12:37:50 AM »
Version 1.2.8 - 02.02.2015
- Added Shed Rafter Roof with Ledger (all advanced options enabled).
- Added ceiling joist option for Shed Rafter Roofs.
- New submenu item and toolbar icon added for secondary (minor) roofs.



View model here:

https://3dwarehouse.sketchup.com/model.html?id=u972818f0-96f0-4f85-9781-087a2db95199

I used this option to create a monitor style roof line but it can also be used for porch roofs, carports etc...  I still need to add a standard shed roof with and upper and lower birdsmouth cut.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #286 on: February 02, 2016, 03:48:28 PM »
More "Fun with Roofs".

This roof was generated by first creating a hip roof primitive then deleting all but 3 components which were then copied and rotated into place for the lower roof hip corner.  The shed roof /w ledger component was created with one primitive and then copied and rotated into place.  Overall a fairly painless process now that I am somewhat familiar with navigating my way around SketchUp.  The fascia required a couple of trims.

The pyramid at the top required no manual intervention. Approximately 10-15 minutes of work for a fairly substantial roof.



View model here:

https://3dwarehouse.sketchup.com/model.html?id=ue55bf7ab-c669-4cd7-8f05-305dee4e2519
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Fun with Roofs
« Reply #287 on: February 03, 2016, 07:11:15 PM »
Testing the real world application of the Medeek Truss Plugin.  This model combines a double fink truss, raised heel fink truss, monopitch truss and shed roof with ledger.  While creating the shed roof special attention to the birdsmouth cut was required to ensure that the fascia height of the rafters and trusses lined up.  Also note the use of the raised heel type truss on the upper roof portion.  Structural outlookers were specified for all gable overhangs. 

5:12 pitch roofs with rafters and trusses 24" o/c.  I did not apply a level cut to the rafter overhangs but that would probably be a given.  Span of the double fink is 48 feet with 2x6 top and bottom chords.



Revision 2 shows the 2x6 framed walls with a thickened edge monolithic slab on grade foundation.



View models here:

https://3dwarehouse.sketchup.com/model.html?id=u98040448-af54-4d79-af30-a3aefca9b941

https://3dwarehouse.sketchup.com/model.html?id=ud8f4c186-1836-4d16-928a-2ba8c10c99a9

If anyone has some real world applications using the plugin that they are willing to share I would be very interested to see how it is being used and it would also give me some direction for further development and improvements.
« Last Edit: February 03, 2016, 09:36:54 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Balloon Framing vs. Platform Framing
« Reply #288 on: February 04, 2016, 08:35:32 AM »
I've ran into this structural question before, where you have a stairway next to an exterior wall.  My first thought is to call out a balloon framed wall up to the 2nd story top plate(s) but then that makes the rim board and double top plate of the first story discontinuous. What is the preferred solution or how have you seen this done in similar circumstances.

Here is a quick mock up in SketchUp to better explain what the two options are:





You can also view and download the 3D SketchUp model here:

https://3dwarehouse.sketchup.com/model.html?id=uf979b67e-2755-4981-9bfc-06d20b64d313
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Don_P

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Re: Truss Calculators
« Reply #289 on: February 04, 2016, 07:30:46 PM »
WFCM Fig 2.1k Floor Diaphragm opening limits
Exterior walls adjacent to the opening shall be framed using full height studs where the opening is less than 2' from the exterior wall.

Max opening is 12' or <50% of floor length.
That is from the engineered section, the prescriptive section is silent other than the 12'/50% rule but the fig shows stairs against the exterior wall, platform framed with a double rim, which is how it is normally but incorrectly framed. Those drawings have not been updated in at least 40 years, I remember the prescriptive set from 2nd year drafting. I'll let them know, it'll take till cycle after next if they agree, which I suspect they will.

Offline Medeek

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Re: Truss Calculators
« Reply #290 on: February 04, 2016, 07:43:47 PM »
I'm familiar with Figure 2.1k and the 12'/50% rule but to be honest I never actually noticed the comment to the right of it, funny how that is.  I've run into this same issue before on some of my own garage designs and I've mostly seen it platform framed.  In some situations I've called out that it be balloon framed but I've noticed some opposition from local contractors on this.

I've spoken with a number of other engineers today on the subject and the opinions are about equally split between the two options.

If I am to platform frame it I would probably do something like this:



Essentially creating a box beam that can resist the lateral out-of-plane loads on the wall (wind).  The problem is  if the instructions are not completely followed and a splice is inserted into plates, rim or LVL where is should not be, proper construction is critical.

If one does balloon frame this section of wall it is advisable to block and strap inline with the rim joist to preserve the continuity but there is some disagreement on the effectiveness of this method.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #291 on: February 05, 2016, 04:01:17 AM »
I've been trying to recall but can only remember the situation once. I had attic trusses above, so... I created a hinge there. To box inside and out it does have basically the detail you drew. Have you run the numbers in flatwise bending @12', say with 2x8 sizes? It may be a non issue.

Offline Medeek

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Re: Truss Calculators
« Reply #292 on: February 05, 2016, 10:37:14 AM »
I added the  porch roof using the hip roof and shed roof primitives.  I'm wondering if it might not be worthwhile to add in a feature to create this type of combination roof automatically.  Shed Roof w/ ledger & hip ends.



View updated model here:

https://3dwarehouse.sketchup.com/model.html?id=uf979b67e-2755-4981-9bfc-06d20b64d313

Note, how close the ledger is to the rim joist.  The porch roof diaphragm will actually stiffen up the region of the wall where the stairway is to some extent, in general the use of a "wind beam" is probably advisable if platform framing is used and a quick check of the numbers should be done.

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

Offline Medeek

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Re: Truss Calculators
« Reply #293 on: February 05, 2016, 01:17:37 PM »
I probably should have checked the numbers first.  Given the high wind loads in our area (155 mph ult.) a 3-1/2 x 9-1/2 PSL loaded in the weak axis will deflect almost a full inch with a clear span of 10'-10" and a trib. length of 9'.  However, a 5-1/4" beam will pass with flying colors, so I've updated my detail to:



The eccentricity is small enough that I think it makes sense to just sandwich them together and make sure they act as one unit.  I still like the idea of disallowing any splices in the members in this region of the wall and will keep my notes specifying that.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #294 on: February 05, 2016, 04:34:24 PM »
I had a brain fart on a job with a 2 story cathedraled greatroom. I had gone >18' tall with 2x6's in the exterior wall when an engineer friend dropped by and caught it.  Not that it was part of my plan but the saving grace was the hipped porch roof and ceiling. If the porch carry beam is built up I prefer to keep post spacings under 8' so that 16' lumber can weave that beam together, that is also the prescriptive limit for deck posts in awc's DA6.


Offline Medeek

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Re: Truss Calculators
« Reply #295 on: February 07, 2016, 01:17:40 AM »
Started the manual as a MS Word document however that did't work so well for hyperlinks.  Starting over with an html manual page:

http://design.medeek.com/support/trusspluginmanual/mainpage.html

Couple of pages up, only about 25 more to go...
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #296 on: February 12, 2016, 10:02:43 PM »
Version 1.2.9 - 02.12.2015
- Added Shed Rafter Roof (all advanced options enabled).
- Added ceiling joist option for Shed Rafter Roofs.
- Initial menu now defaults to last picked option of session for that sub-menu item.

A typical application might be a clerestory roof with a upper shed roof and lower shed roof with a ledger board:



View model here:

https://3dwarehouse.sketchup.com/model.html?id=u0b2dd5bc-605d-467c-a6bb-449bb54e76e6
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #297 on: February 13, 2016, 04:29:03 AM »
LOL. lose the cj's and gable the upper and you just drew my house.

Offline Medeek

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Re: Truss Calculators
« Reply #298 on: February 13, 2016, 10:37:07 AM »
LOL. lose the cj's and gable the upper and you just drew my house.

Upper roof rafter or truss?  Beam or ridgeboard?
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #299 on: February 13, 2016, 02:59:23 PM »
Upper is ridgebeam/ common rafter 2x10's on 2' 4/12, lower is shed off a ledger same stock and pitch. 28x36' in 14x36' modules, 3 clerestoy windows (bedroom, stairway wrapping woodstove alcove, and office), they were going to be horizontal sliders till I felt the heat rolling up that south facing roof and made them fixed. Lower front is 2 sets of French doors flanked by 2 6'wide horizontal sliders. There is the same window in the east and west ends and east downstairs bedroom in the 2 story section with another above in the upper bedroom. I can blow doors out any of those openings but likely never will. It could also be expanded as a monitor with a matching shed on the back (with window changes). It started as a HS drafting project, took me a semester, Mr Mac kept copies of the codebook in the front of the class and part of our grade was to detail to code. It was a passive solar design, I now call it solar tempered as we never drop the cellular blinds and I didn't put in the insulated shoji on that lower south wall. Passive solar takes active people, but it does warm up the dark tile floor and has decent overhang shading in summer. I finished drawing it for construction about 10 years later.