Truss Weld Eccentricities

[Nutrin14]

Hello All,

This is my first post in this forum. Please provide your thoughts on the below issue.

I need to provide welded connections for the W sections of verticals and diagonals to the W chords in a truss. The verticals and diagonals are directly welded on the chords by avoiding any Gusset Plate at top of chord flanges due to limitations. Full depth stiffeners are provided for the vertical and diagonal continuity into the chord member and these stiffeners are designed for the local forces as per AISC 360-10: J-10 provisions.

My question is related to the work point eccentricities for the each member element weld design (flange weld of diagonal and web weld of diagonal etc). Please refer the attachment for sketch.

i. I believe the vertical component horizontal eccentricities (eh1, eh2 etc) from the work point shall be ignored for the weld design since full depth stiffeners provided in the chord.
ii. However, the horizontal component vertical eccentricity (ev1, ev2, etc) from work point to be considered for the weld design.

Any thoughts on this please.Thanks.

 

[KootK]

For the weld designs, I would ignore both horizontal and vertical eccentricities. How do you see the vertical stiffeners factoring into things? I think that, if you FBD the webs individually, you just need a weld distribution capable of resisting the applied loads in a manner concentric to the webs.

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.

 

[Nutrin14]

Diagonal webs and vertical webs alone are not sufficient for transferring all the forces into the chords in my case. Hence flanges need to be welded and they come into picture.

Agree vertical stiffeners will not play a role in avoiding horizontal eccentricities. But there will be eccentricities due to the following. Please correct me if I am wrong.

Normally these truss members are designed as single line elements in the software and all the forces are resolved at the work point. But, in reality, there is an eccentricity considering the chord depth/2 for horizontal component and flange concentrated force locations due to the discontinuity of the vertical and diagonal members at the chord top face. The chord member was not designed for these eccentric moments for this effect. This results in an eccentricity in the force transfer.

I have a doubt about the eccentric moment generated due to vertical components of diagonal and vertical member. For clarity, sketch attached. But I am sure there will be eccentric moment due to horizontal component to prevent additional moment transfer to chord.

By the way, what is FBD Kootk.

Thanks.

 

[KootK]

FBD = Free Body Diagram

My answer remains the same. Yes, considered on its own, the horizontal weld components do induce moment about the connection work point. The idea is that the eccentricity of your vertical components should balance that out perfectly. That's never perfectly true in the real world but that is how the design process generally unfolds.

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.