Author Topic: Truss Calculators  (Read 369593 times)

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Offline Don_P

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Re: Truss Calculators
« Reply #200 on: December 09, 2015, 04:01:18 AM »
Bingo, that is how the framing looks above the top plate once blocked.

I agree with just having it throw a warning up when the birdsmouth exceeds 1/4 depth. I've spoken with the engineering folks at AWC and several others about this change and feel it is incorrect but it is code now. When you get into complex hips and valleys you need room at the HAP, the height above plate, the distance above the birdsmouth, to get things to plane correctly. Often with a hip you'll be pushing the minimum notch on the commons in order to keep an acceptable notch and bearing on the hip.

Roofs can get very complex and trying to include too much could lose most users in the weeds, I'm not sure where that point is though because capability also fosters neat stuff.

Offline Medeek

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Re: Truss Calculators
« Reply #201 on: December 10, 2015, 08:41:06 AM »
Version 1.1.9 - 12.10.2015
- Added Gable Rafter Roof with Glulam Beam (all advanced options enabled).

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


Offline Medeek

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Re: Truss Calculators
« Reply #202 on: December 10, 2015, 07:57:56 PM »
Here is quick model of the wall framing associated with a gable roof with a glulam beam:


Beam Pocket with 6x6 post:




Gable wall and eave wall intersection:




Overview of Model:

Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #203 on: December 11, 2015, 03:20:40 AM »
Looking good. My lookouts are normally the same dimension as the fly rafter to provide soffit nailing as well as sheathing nailing.

And a pet peeve, a glulam end out in the weather. I prefer to run the fly or at least the finished fascia over the end and tuck the glulam under the overhang.

Offline Medeek

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Re: Truss Calculators
« Reply #204 on: December 11, 2015, 05:43:20 AM »
I've added an extra input for the beam which allows ones to specify the overhang of the beam from the outside of the wall.  With zero overhang the beam will be flush with the wall framing and not exposed.  If the beam overhang is less than the gable overhang, the fly will be as shown below (up to the roof peak).  If the beam overhang is greater than the gable overhang it will project past and the fly will adjust accordingly.  The beam overhang is not restricted in any manner.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #205 on: December 11, 2015, 06:06:14 AM »
I remember a few years back when I was in college and working a side job as a construction laborer we framed up a roof similar to this.  The rafters were large I-Joists (TJI 560 equiv.) and were hangered from the glulam beam.  The beam was probably almost 2 feet deep.  I just remember I was glad I was cutting the blocking on the miter saw and not the one at the peak of the roof setting the rafters into the hangers. 

With that being said I am wondering how often I-Joists are used in this type of application versus common lumber.  I can probably add in an option to use them instead of common lumber.  One question I have though is what to do at the other end, where they bear at the wall.  I would need to study this further.

On a slightly different note.  Since Don_P and others on this board have helped with the development of this plugin and given graciously of their time, energy and knowledge I would like to offer the full (not trial) plugin to all those members of the board who are interested, free of charge.  Send me an email or message me with your board name and I will provide you the link to download the plugin.  All that I ask is you provide me with feedback on how to further improve and refine it if you find something that needs attention.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #206 on: December 11, 2015, 03:47:11 PM »
Early on I asked for a raise, next thing I knew I was 30 feet in the air and the boss asked if I wanted another  :D.

I was going to say I know how much work you've put into this, but I think you've put in more than that. Thank you.

I've used TJI's for rafters once and swore I'd never do it again. It has been, holy cow, 21 years ago. The top end was no big deal, the bottom required squash blocks and a proprietary lateral strap that went from plate over top of rafter and back to plate. The tails required more deadwood. Basically they were light and easy in one regard but the detailing ate up an inordinate amount of time. But they have less thermal bridging and can be deeper to hold more insulation, can span further and are straight. I've detailed sawn rafters by applying 2x2's under or over the rafters on different jobs for insulation, that sure wasn't fast, so part of my objection is probably just whining. That detailing is in each manufacturers product guides.

AITC, glulam.org, has a good series of details as well, they are in the manual but I believe that section is one of their free downloads. Another way to draw that is with a dropped ridge that has a beveled cant strip on top that the rafters bear on with a gusset across the rafter couple.

Offline Medeek

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Re: Truss Calculators
« Reply #207 on: December 11, 2015, 04:46:14 PM »
I have some designer friends in Colorado and they suggested I add the I-joist option for rafter roofs since in their neck of the woods the snow loads usually require them to go to I-joists except for small spans.

All of the pertinent details for typical I-Joists can be found here:

http://www.woodbywy.com/document/tj-4000/

The problem with I-joists is the bevel cuts are more difficult since it requires more operations to model, but I think I can do it. The outlookers at the gable ends would need to notch around the top flange of the I-joist. A double or single bearing plate is required at the ridge or hangers from the beam, notching at the high end of the roof joist is not allowed. Birdsmouth cut at the low end of the joist is allowed but requires web stiffeners on both sides of the joist.

I don't think I would model in any of the web stiffeners, otherwise the model gets too heavy, same goes for small fasteners and hangers. 

I haven't even considered the option yet with the rafters resting on top of the beam (dropped ridge).  As you suggested they (TJI manufacturer) do not allow notching at the top end and therefore a beveled bearing plate or strip is required with web stiffeners on both sides of the I-joist.  Their detail shows a strap across the tops of the I-joists tying them together across the beam, I'm pretty familiar with this detail from some local jobs. I'm also wondering about the beveled strip, how is it made, thickness at the butt etc...

With common sawn rafters how would you typically handle a dropped beam?  Would you use a beveled strip or would you apply a  birdsmouth cut at the ridge?

The problem is I'm not out in the field enough so I never get to see this stuff actually go together.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #208 on: December 11, 2015, 08:54:10 PM »
When the plugin is loaded in a metric template it will now utilize a web dialog with metric sizes for glulam beams.  The menu and glulam beam sizes are currently listed at the following link:

http://design.medeek.com/calculator/sketchup/html/web_dialog_glulam_metric.html

I probably don't list every combination possible or manufactured in each respective country or jurisdiction but hopefully I list the most common sizes.  So far I have entered in data for the United Kingdom (Great Britain), South Africa, and Australia (and New Zealand). 

I can enter in more countries if provided the data (width, depth, locale name and ply thickness).  Now that I have the web dialogs and html files setup it is not a big deal to add more entries.

When the plugin is loaded in inches or feet then the US sizes or AWC NDS tables are loaded.  So far I have only found one country that still uses the old units.

http://design.medeek.com/calculator/sketchup/html/web_dialog_glulam.html
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Medeek

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Re: Truss Calculators
« Reply #209 on: December 13, 2015, 02:17:22 AM »
Added dropped beam options for Gable Rafter Roof with Glulam Beam: Notched rafter and Bevelled plate.



Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #210 on: December 13, 2015, 03:58:32 AM »

The problem with I-joists is the bevel cuts are more difficult since it requires more operations to model, but I think I can do it. The outlookers at the gable ends would need to notch around the top flange of the I-joist.

This one has been nagging in the back of my mind, the CO designers would be a better resource. As the outlooker is loaded outboard, wind down or unbalanced snow, if it is notched around the flange does it put an unallowable tension on the flange/web connection?

Offline Medeek

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Re: Truss Calculators
« Reply #211 on: December 13, 2015, 06:26:16 PM »
Version 1.2.0 - 12.13.2015
- Added ceiling joist option for Gable Rafter Roof.



Note: In the image shown I have raised the ceiling joist 24", the default is zero, or resting on the top plate of the wall.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #212 on: December 13, 2015, 10:11:43 PM »
This one has been nagging in the back of my mind, the CO designers would be a better resource. As the outlooker is loaded outboard, wind down or unbalanced snow, if it is notched around the flange does it put an unallowable tension on the flange/web connection?

If the outlooker is nailed into the web of the TJI (vertical outlookers) then I think it would probably be okay, since a fraction of the load would be transfered directly into the web through fastener shear.  I guess the question really is what is the point load at that location.  The worst case loading situation (for most locales) would probably be a (+ 200 lbs) construction worker installing trim or shingles at the gable with all of his weight concentrated at or near the end of the outlooker.  Assuming a worst case 2 ft overhang with I-joist rafters at 2ft on center you have a 200 lbs point load at the end of this outlooker.  Theoretically the sheathing would distribute some of the load into the other outlookers but lets assume the full load for argument sake.  According to Weyerhaeuser's technical bulletin (TB-808) the max. allowable load (hanging from the bottom flange) is 500 lbs every 5 feet (250 lbs each side of the flange).  Probably any more than this and you run the risk of ripping the web out of the flange (localized failure of the I-joist). 

So if we put a 300 lbs guy out there I would say things get a little dicey.  In areas with exceptional snow loads this could also become a consideration.  My first thought would be to limit the overhang allowed for such regions and of course metal, high pitched roofs help considerably.

I also noticed in the TJ-4000 (Detail O) they only show the outlookers in a vertical orientation.  Are we allowed to do a horizontal orientation (outlookers laid flat)?  And if so how do we make that attachment?

You will also notice in this same detail that they suggest doubling the joist adjacent to the gable wall when the overhang exceeds the joist spacing.  This will help to prevent excessive load and deflection to this joist but it doesn't decrease the point load to the flange/web interface unless you drive fasteners through both I-joists and into the outlooker and provide blocking between the I-joists webs.

Locally here in Ocean Shores WA the high wind loads are the main factor and the sheathing loads at the overhang necessitate outlookers at 24" o/c, even though every one around here seems to like to run them at 48" o/c.
« Last Edit: December 13, 2015, 10:27:37 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #213 on: December 14, 2015, 03:02:47 PM »
Various configurations of a cambered truss:

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Offline Medeek

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Re: Truss Calculators
« Reply #214 on: December 16, 2015, 09:42:01 PM »
Version 1.2.1 - 12.16.2015
- Added gable end trusses (ladders) and ribbon boards to the floor truss type (Warren - System 42).
- Sheathing option enabled under advanced floor options for floor trusses.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #215 on: December 21, 2015, 11:23:10 PM »
Version 1.2.2 - 12.21.2015
- Added TJI Rafter Roof with Glulam Beam (all advanced options enabled).
- Added dropped beam option for TJI Rafter Roof with Glulam Beam: Bevelled plate






Note, the birdsmouth cut at the lower bearing point.  What I am not showing is the additional web blocking (stiffeners) required at this bearing point and at the ridge beam, see TJI-4000 for more details.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #216 on: December 23, 2015, 01:58:09 PM »
Version 1.2.2 - 12.23.2015
- Structural outlookers notched around TJI top flange when oriented vertically, as per TJI manufacturer's structural details.



The tails of the TJI joists at the overhangs is left untrimmed however it is very easy to trim the tail of the rafters as shown below to customize to your particular roof requirements.

Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #217 on: December 25, 2015, 01:17:42 PM »
Check detail O on pg 15 of TJI4000 a rake wall with blocking between outlookers, for the rbz. I think you can simply make that solid sawn rafter the same depth as the outlookers to show the blocking and the rake wall would be drawn in the wall layer. I would only nail the outlooker end through the web, I believe on a laminated flange a horizontal nail is not allowed I'm not sure about a solid sawn flange. Anyway, if so, that would also mean the non structural outlookers in the previous post need some connection detailing

Offline Medeek

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Re: Truss Calculators
« Reply #218 on: December 25, 2015, 02:23:55 PM »
You have the option of making the the solid sawn gable end rafter as deep as the outlookers or deeper.  I'm trying to make the plugin as realistic as possible but also give plenty of latitude for the designer to configure things as they choose, probably in some cases constructing things incorrectly. 

With the outlookers oriented horizontally I'm not sure how one would actually make that work, it probably does not since the TJI4000 does not give a detail showing that orientation.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #219 on: December 29, 2015, 05:24:30 AM »
Version 1.2.3 - 12.29.2015
- Added Hip Rafter Roof.



A square hip roof (pyramid):



I still need to add in the advanced options for this roof type (sheathing, fascia etc...)  I'm also thinking about ceiling joists and how best to configure them.  For low pitch hip roofs the ceiling joists near the hip ends will clash with the hip jack rafters unless they are oriented parallel to the jack rafters.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #220 on: December 29, 2015, 07:12:19 PM »
A more complex hip roof combined with some trusses.  Note I have not trimmed back all of the rafters in the top image.



I initially generated the hip roofs (two rectangles) and then deleted the appropriate members and trimmed the common rafters to create the valley jack rafters and cripple jack rafters.  The valley rafter was created by copying an instance of one of the hip rafters and moving it into place.  The end result is:



Overall the process has been simplified by having the hip roof feature in the plugin.  Trimming the members is the most time consuming, perhaps a more efficient trim tool can be devised so that intersecting members can be easily trimmed back to clean up a complex roof.  Ultimately it would be cool to have the plugin automatically handle even more complex roofs such as this but that would take some serious programming.

Also note that I used a raised heel for the trusses so that the heel height and gutter line of the trusses matches that of the rafters.
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #221 on: December 30, 2015, 01:57:19 AM »
Wow!
I was still working on a response to the previous post. I believe the correct way to frame the ceiling joists would be to use common ceiling joists until you bump the underside of the hip. Then from that last cj turn short cripple cj's from the last common ceiling joist onto the adjacent wall alongside those rafters, again until you bump the underside of the hip. Then double up that last common cj (I left it off until now to facilitate nailing) Then from the lower end of hip at the wall corner to the corner formed by the last cjs there is a diagonal cj, a dragon. Then hip cj's into it... being short spans these can all usually drop to 2x4's.

Then, technically a hip needs to be tied in both directions (or propped). I've gone the one way with ceiling joists and the other way with simpson straps into the diaphragm or until I can get to a "hard" place.

Offline Medeek

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Re: Truss Calculators
« Reply #222 on: December 30, 2015, 12:09:45 PM »
So theoretically the ceiling joists can get a little crazy as well.   

In the sample residence shown below the pitch is 7:12 so in this case the CJ's could run all the way up to the last jack rafter and there would be no need to have cripple cj's, or maybe it would be reasonable to have a few to tie the whole ceiling together?  I'm not real familiar with "old school" framing since I never see any of it locally, most jobs use trusses with the occasional framed over section but rarely do I see entire roofs, stick framed, like shown below.

I get the bracing of the roof with the ceiling joists but I'm not understanding the other way with the straps.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #223 on: December 30, 2015, 05:49:53 PM »
Note the cripple or stub ceiling joists in this picture:



and the doubled ceiling joist in this picture:

« Last Edit: December 30, 2015, 06:06:42 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #224 on: December 30, 2015, 07:07:50 PM »
Testing out the hip roof feature with some more complex roof lines:







The thing that jumps out at me right away is the ease with which I can generate the basic roof lines and most of the rafters.  This particular roof required (4) rectangular roofs to generate all of the lines.  The only thing that is missing is the valley rafters.  To make this feature more functional for complex roofs I only need to have a tool that can generate valley rafters and trim back members to create the cripple rafters.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer