Truss Gusset Inducing Moment Into Chord
Truss Gusset Inducing Moment Into Chord
(OP)
I am designing truss web connections for a 10' deep, 70' long truss with wide flange parallel chords and double angle web connections. The configuration is similar to a warren truss with verticals at the "V"s.
The question I have is in regards to the braces inducing a moment into the truss chords. In order to develop enough weld from the gusset plate to the beam, alpha bar for the connection becomes larger than alpha. This appears to induce a moment in the chord in accordance with the uniform force method special case 3. I do not think the EOR designed the chords for this moment.
I would appreciate any advice or insight into whether this moment is truly induced into the beam. And also, if there is a better way to make this connection.
Thanks!
The question I have is in regards to the braces inducing a moment into the truss chords. In order to develop enough weld from the gusset plate to the beam, alpha bar for the connection becomes larger than alpha. This appears to induce a moment in the chord in accordance with the uniform force method special case 3. I do not think the EOR designed the chords for this moment.
I would appreciate any advice or insight into whether this moment is truly induced into the beam. And also, if there is a better way to make this connection.
Thanks!






RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
Yes, the workpoints coincide at the neutral axis'. This makes me think that there should be no moment applied to the chord. And I agree that this is an internal connection moment. However, looking at the beam free body diagram in the AISC steel manual UFM special case 3, there is a moment, Mb, from the gusset interface that appears to apply to the beam. If the connection is relatively small, this moment should be small. However, if the connection is sufficiently large, this moment could be fairly large and it appears that it needs to be considered.
@MiketheEngineer - I assume you are referencing a better way to make the connection. If so, would you please elaborate?
I appreciate all of the excellent feedback and I apologize if this is a trivial problem... All of my training tells me that if the braces are coincident through the neutral axis then no moment is applied to the chord. But something is just not "clicking" as far as the gusset/chord interface moment.
Thanks!
RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
RE: Truss Gusset Inducing Moment Into Chord
Another way to look at it is using KISS method, or simple vector analysis. Consider the appropriate eccentricities in the welds and/or bolts, and prying and bending in the connection material. And provided the work point is at the neutral axis of the truss chord, there is no moment induced in the chord.
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