Gusset Plate Design
Gusset Plate Design
(OP)
I am designing connections of a Special Truss Moment Frame. The top and bottom chords are continuous while the web members are connected by welding to the gusset plates. The joint is treated as rigid. As a result, the web members will carry axial force, shear force and moment. I can't find any book or anything on the net that tells me how to design the gusset plate of this type. Help me please.






RE: Gusset Plate Design
RE: Gusset Plate Design
RE: Gusset Plate Design
ConnectEngr, where you been?
This seems to be your area of expertise.
RE: Gusset Plate Design
RE: Gusset Plate Design
With trusses I have dealt with (mill building type trusses and the like) the flexural stiffness of the web members and connections is so low that I never thought modeling them as rigid was appropriate.
RE: Gusset Plate Design
There has been papers written on this subject going all the way back to the early 1900's.
see attached....this is very old....probably outdated
RE: Gusset Plate Design
We are Virginia Tech
Go HOKIES
RE: Gusset Plate Design
http://www.FerrellEngineering.com
RE: Gusset Plate Design
But, I do recommend releasing shear and moment in the panel points.
http://www.FerrellEngineering.com
RE: Gusset Plate Design
In this case I felt it made more sense given the high stiffness of the web members and their overall flexural rigidity.
For web members life small HSS or small pairs of angles I feel those are generally best suited as axially loaded members.
RE: Gusset Plate Design
http://www.FerrellEngineering.com
RE: Gusset Plate Design
Thank you.
RE: Gusset Plate Design
With back to back channels I don't have any suggestions for the force combinations in the connections. Typically the channels are bolted through the web and gusset plate, or welded to the gusset plate. These connections are for axial force only.
http://www.FerrellEngineering.com
RE: Gusset Plate Design
Connect-
Would you agree that with connections where the work points offer no eccentricity that there is no reason to design for moment?
My intuition tells me that the only moments on these connections will be secondary or the result of deflections?
RE: Gusset Plate Design
I don't think the moment in Chad73's panel point is due to workpoint eccentricity. He is modeling the truss as a rigid frame, with the diagonals and verticals fixed at the truss chords. In the model, this works fine. And in your example of a welded wide-flange truss, it can work. But in a double channel truss the forces must transfer through a single gusset plate at the centerline of the cross section. Some moment can be taken in the channel web to the gusset. But the majority of the moment is in the flanges. The model sees lines with given properties and nodes. The actual shapes and load local stresses are not considered.
http://www.FerrellEngineering.com
RE: Gusset Plate Design
I see.
I have done a fair amount of trusses made up of WT top and bottom chords with double angle webs. I always modeled the top and bottom chord continuous and the web members as "truss" or axial members.
Usually I did not need gussets at all as the top and bottom WT stems were large enough to make the connections. When I did need a gusset to extend the web I had the fabricator full pen weld a plate to the stem and grind it flush. I only considered axial force on this plate and I only make the plate as big as necessary to accommodate the welding or bolting of the web members.
RE: Gusset Plate Design
RE: Gusset Plate Design
Is it really required?
We are Virginia Tech
Go HOKIES
RE: Gusset Plate Design
RE: Gusset Plate Design
However, I still think the remaining portions of the truss should have joints that are pinned.
RE: Gusset Plate Design
http://www.FerrellEngineering.com
RE: Gusset Plate Design
I think you are getting at the point I am trying to make (albeit poorly so). Even if modeling members like double angles as pins, they probably in reality do develop some secondary moment but since their moment capacity is so low it can be ignored in design.
RE: Gusset Plate Design
Back to the original question. I believe that if you size the gussets as required by AISC 341, the gussets will end up being sufficiently stiff to be considered moment connections.
Chad73 you did mention above that you are using C shapes for all memmbers. AISC 341 requires that the webs in the special section be constructed of flat bars. If you follow this, there it the webs would likely not have much moment capacity.
RE: Gusset Plate Design
Good luck.
RE: Gusset Plate Design
RE: Gusset Plate Design
Agree with your assumptions about pinned connections for trusses and everyone else's comments about how to model the chords, but this discussion has raised another question that I have always struggled with. Would you still assume pinned connections if you are designing a HSS truss with all-around welded connections? I don't want to hijack this thread, but I thought it might be an appropriate question given the theme of this thread.
Thanks!
JWB
RE: Gusset Plate Design
Yes. HSS welded panel point is a pinned connection. Similar to a bracing connection with gusset on top an bottom flange. The beam is still considered a simple beam. But ductility limits on endplate or angle thinks would not apply.
http://www.FerrellEngineering.com
RE: Gusset Plate Design
My initial answer was brief, because I was typing on my cellphone.
IMHO
Welded HSS trusses with staggered member sizes have pinned panel point connections. As an example of staggered, I mean 10" chords, 8" verticals, and 6" diagonals. Unless the walls are extremely thick, the connection flexibility is found in the ductility of the HSS walls.
If the members are all the same width, so the welds are directly in alignment with the supporting HSS wall...
The connections have less flexibility. But, you cannot obtain the full strength of the walls with the welds. An AWS BTC-P10 (J-Grove PJP) has a maximum effective size of 5/8 x the wall thickness. And there is still ductility in the walls along the fillet welded sides.
This is another case, where the modeling software has no problem analyzing these rigid panel points. But, developing the welds and checking the HSS walls may be impractical. And may require backing up and changing the model or member sizes.
http://www.FerrellEngineering.com
RE: Gusset Plate Design
That is exactly what I thought, but recently there has been a discussion at the office, debating whether truss connections in general behave as "pinned" or "fixed". I have always thought, in reality, truss connection behavior was somewhere between pinned and fixed, but everyone assumes pinned for the reasons previously stated. Once again, thanks for the prompt responses.
RE: Gusset Plate Design
When you look at the actual requirements for the design of the joints and web members in the special segment of the truss you will see that the gusset plates and connections will be large enough to transfer moment. Since the web members must be flat bars, they have very little bending capacity. Thus, for the truss specifically asked about by the OP, it is more accurate to model the joint as fixed.
Since the intent of the truss is to allow for significant elastic deformation in the special segment, moments created at the joint due to the webs should not be discounted.
RE: Gusset Plate Design
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Near the end of the page there is a discussion of the consideration of moments at truss joints with the opinions of several experts listed.