INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Transition Truss with Dropped Top Chord

Transition Truss with Dropped Top Chord

(OP)
Has anyone ever seen a transition truss with a dropped top chord? If such a thing exists and you have a drawing or pictures please post.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

I don't have a pic but I've built a few before. Do you have a particular question regarding them?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Transition Truss with Dropped Top Chord

The term "transition truss" must be regional. I've never heard it before.

What exactly are you referring to?

RE: Transition Truss with Dropped Top Chord

(OP)
The transition trusses are where two dissimilar roofs meet:



A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

Around here (central Illinois) those are referred to as a "partial gable".

I've done a DTC one one side of such trusses. But not too often. DTC gables aren't common in this area.

RE: Transition Truss with Dropped Top Chord

(OP)
I think it would look something like this:

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

(OP)
However I think the framing at the lower peak would be more correct if the top chord members abut like this:

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

Medeek,

I will bite and ask the question. Why is the top chord of the higher ridge in your last two examples dropped approximately 1 inch.

Jim

RE: Transition Truss with Dropped Top Chord

(OP)
A raised heel truss?



The perspective in this screenshot makes the heel webs look out of plumb, they are actually plumb.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

(OP)
The dropped top chord is for the structural outlookers (2x4 flatwise).

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

I've also seen it done like this:

1) Make the structural truss match the larger profile.

2) Drop the top chord and install the outlookers the whole way.

3) Build in some gable verts where you need 'em.

4) Maybe drop a web to the new interior bearing.

5) If you're a P.Eng/hardass, give some thought to how you transfer diaphragm shear across the transition.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Transition Truss with Dropped Top Chord

(OP)
Two scissor truss roofs:

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

Nate:
The left most gable truss (grid A), with the vert. nailers in place of diag. members should have the top chord dropped 3.5" measured perpendicular to the slope, so that standing 2x4 outriggers can span over it, from the first interior truss top chord out to the sub-rake 2x. The normal top chord tails are cutoff at the outside of the top pls. and the bot. chord end there too. Then a short standing 2x4 tail is plated to the top of the normal top chord, in the same truss plane, with several feet of back span, up to the first outrigger. The framing in the lower corner btwn. the sub-rake and the eave sub- fascia, is just stick framed fill-in. You can nail those outrigger ladders together on the ground if you wish, with the sub-rake, and some blocking over the gable truss and btwn. some of the (or all of the) outriggers, and install the whole half of the rake at one lift.

Then there are a group of std. king post trusses moving to the right and upward toward grid B. This same truss is used over grid B, and you have the truss guys build a short vert. gable wall on top of it, with vert. nailer studs and the top chord held down 3.5", and the other normal top chord extended to meet. Again, the outriggers are about 4' long and canti. over this transition truss and back to the next first interior std. truss. The outriggers get end nailed at the first interior truss top chord, and you might add light joist hangers up-side-down at these joints. Same thing toward and at grid C. Depending on what the truss guys want for these transition trusses, you might stick frame the funny dropped vert. gable walls on top of the std. trusses.

The gable trusses in the cathedral/vaulted ceiling area are done about as you show them, with a 3.5" dropped top chord. The builder will bitch, but it’s probably best that these gable walls be framed full height to the under side of the truss, the bracing area and ceiling diaphragm. The upper most, right most end, of the right gable truss, out over grid F, should have a standing 2x4 on top of the normal top chord. It will have a longer back span going back toward the ridge btwn. grids E & F. That’s kinda a nasty transition btwn. those two vaulted ceiling areas. You gotta study that a little more, as to interior ceiling planes and ridge lines, etc. I’d either stick frame a sloped ledger to the main gable truss from the main room, or put a std. small scissors truss right against the main gable truss.

Your sketches at 20MAR16, 18:18 & 19:30 look like real abortions, you better study them a little more. What’s with the out sloping (not plumb) raised heels? Making two vaulted ceilings of different spans or pitches meet end to end is almost always difficult. Draw cross sections through the two rooms at that meeting wall, and then you have to study how to make it work. What ceiling planes match and differ and which wall face will show the vert. transition, and then how to frame the roof in that immediate area.

RE: Transition Truss with Dropped Top Chord

(OP)
Locally I see a lot of outlookers oriented flatwise:



By the way you can download any of these SketchUp models if you want to rotate them in 3D or zoom in to a particular spot:

https://3dwarehouse.sketchup.com/by/medeek

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Transition Truss with Dropped Top Chord

You name - it I got an example of it.

______________
MAP

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close