Gusset plate in truss 1

[BAGW]

Hi,

Is it necessary to keep all gusset plates the same thickness for all connection along length of the truss? Web member are double angles and top and bottom chord are wide flanges. Sometimes it becomes impossible to do this. If the gusset thickness varies over the truss length, how is the double angle welded to the connection. Say one end of the angle has 1/2" plate and the other end 1/4" plate, there is a difference of 1/4" between the two ends.

 

[skeletron]

I think you've highlighted the key challenge: the CL workpoint will vary if you have different sized gussets.

There are limitations to how much you can skew your vertical braces, but it is not ideal. You can also add shims or spacers, but again it is not ideal. You would be concerned with keeping the gusset on center to the W-chord so as not to introduce additional eccentricity.

If this is new construction: KISS. Given that the difference is 1/4", I believe this might be a case of practicality overriding precise analytical results. Design one plate. Specify one plate. Cut one plate thickness from a sheet, allowing better nesting and less material loss. Weld/attach one piece to the truss and avoid manual error.

If this is existing construction: I don't understand why/how the force changes enough along a truss web member to necessitate a smaller plate.

 

[Lomarandil]

If your web members are long enough, you can probably deal with bending each of them 1/8" to work.

If not, fill/shim plates are not too bad, but the additional weld time might offset any material savings.

But in modern North american one-off construction, I agree, use a single plate thickness and call it a day.

----
just call me Lo.

 

[BAGW]

Thank you.

Wont Bending of angle induce additional stresses in angle which would not have been accommodated in the member design? Or will it be small that it can be neglected?

 

[skeletron]

That's kind of what Lo is hinting at. The ironworker will bend the angle up to about 1/8" to make it fit. If your design relies on 1/8" of tolerance, then bump up the thickness.

 

[JAE]

KISS
Not sure why you wouldn't just use a common thickness throughout.

 

[DrZoidberWoop]

Your question is very general. The appropriate answer can vary depending on the details you left out.

I assumed you were talking about structural steel when I wrote the following:

You haven't specified the angle orientation or the magnitude/size of steel you're working with. Is the toe of the angle pointed towards the truss chords or out-of-plane? It might seem obvious to you which is better, but I've seen both. If the toe is toward the truss chord and you're working with traditional steel sizes, you will need to specify stitch/fill plates along the brace w/ spacing per AISC Spec E6.2, which is: max fastener spacing = 0.75*[(brace Length)/(min(r_x,r_y)]*r_z. where r_x and r_y are for double angles and r_z is a single angle (see Table 1-15 for common values). Industry practice is to make the stitch/fill plates 1/8" thicker than the gusset, which improves erectability.

You should try to make the gusset thicknesses the same, especially if the brace-to-gusset connections are to be welded. If they were bolted, you could just spec a shim plate or 2 as req'd.

 

[r13]

Same question here. What is your justification/reason to change gusset thickness? Uniform thickness may add a little steel weight, but the cost is offset by ease of construction and fewer mistakes. Keep the design simple.

 

[BAGW]

Seems like keeping the gusset plate the same thickness is a good practice. Thanks

 

[ldeem]

This must be a huge truss to have W shape top and bottom chords. Personally I would take a second look at trying to get WT chords to work and eliminate a whole lot of gusset plate welding.

 

[TrussBridgeboy]

Many good comments here. You should spend some time in the field. Regarding the 1/8" difference mentioned, you'd be surprised at how much beating, bending, warping and who knows what else happens to steel by the time it gets put to bed.