Roof Gable drag truss with no diagonals

[msdmoney]

Reviewing a shop drawing for a drag truss that I specified at the gable end. Therefore it has the verticals, but I am accustomed to seeing diagonals as well to transfer the horizontal component, otherwise assuming the verticals as two force members, all the horizontal load has to go through the end connection between top and bottom chord. Or alternatively the truss needs to be properly sheathed.

Is this a common application for a drag truss with no internal diagonals?

 

[DaveAtkins]

If the gable end truss has proper sheathing (which it generally does), this should be no problem.

Just make sure the lateral load gets transferred from roof diaphragm to gable end truss, and from gable end truss to shear wall (in other words, verify the load path).

DaveAtkins

 

[msdmoney]

Yep, I can provide the sheathing in lieu of the truss diagonals, was just surprised their drawings and response indicate is is fine as a drag truss with just the verticals, top & bottom chord.

 

[KootK]

Yeah, as a non-sheathed for shear thing, I find the lack of diagonals pretty questionable (I used to be the truss guy). Some likely problems:

1) You'd need to accomplish 100% of your truss tie down at the heel.

2) The diaphragm shears result in some flexural bending in the truss. No diagonals = little bending resistance.

3) At the heel joint at the upstream end, the plated connection between chords would induce tension perpendicular to grain the bottom chord. It can be done but it don't work real great.

My money says that the truss guys:

a) intend for the gable to be sheathed.
b) don't know what they're talking about.
c) are bullshitting you.

Frankly, I'd place my bet on B. I claim special license to be shitty about these things because I'm an ex-industry insider.



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.