Truss connection 2

[BAGW]

Hi,

See image below. The diagonals are in compression and vertical is in tension. When I sum up all the components for the gusset to chord design, the forces adds up to be zero. This does not make sense. How do you come up with the forces for the gusset to chord design? I dont think splitting the plate into half and checking for the local forces is correct.

Any thoughts. Can I just design for 140k of vertical force?

Thanks

 

[rb1957]

surely there's a bunch of load transferred into the upper chord ?

I picture this as part of a larger truss beam, carrying the load in bending (between the upper and lower chord).

another day in paradise, or is paradise one day closer ?

 

[KootK]

surely there's a bunch of load transferred into the upper chord ?

Maybe, but there are certainly other possibilities and OP has yet to share the requested, additional details.

With that monster point load and no horizontal shear in the joint, I feel that the two strongest candidates are:

1) A big transfer truss with a monster point load landing at dead center as you and DaveAtkins hypothesize OR;

2) The dirt simple transfer strut system that I mentioned above and have repeated below. That would have no axial in the top member.

I feel that my call is actually the more probable but who knows. If it's drawn to scale, this thing's not got a huge chord for such a hard working truss. W8? W10?

 

[rb1957]

true, if it's a single bay then the top chord isn't highly loaded, the moment is between the diagonal and the lower chord.



another day in paradise, or is paradise one day closer ?

 

[BAGW]

I missed all the above conversation..

Ktook your assumption is absolutely correct. The forces in chord is minimal and its a W8 member.

The weld between the gusset and the top chord is checked for both ways proposed by Ktook (designing for 140kips tension, this is what I was leaning towards if you look at the first few discussion) and also the way BAretired has suggested (70kips of shear with half the guesset length). It did not make a difference both ways. The plate is 1/2" thick with 1/4" weld to the chord.

The below path as Ktook has mentioned is something which I was thinking aswell. Decided not to get into that and designed the weld to top chord as explained above.

 

[r13]

The stresses at the chord-gusset plate interface is depending on the work point. Another perspectives for thought.

 

[BAretired]

The stresses at the chord-gusset plate interface is depending on the work point. Another perspectives for thought.

Not true. Suppose there is no chord and the geometry remains the same.

Edit: Well, okay there would be no stress in that case, whereas there would be some stress if the chord is present. I take it all back. Sorry!!!

BA

 

[KootK]

I agree with retired13 on that point, particularly if one considers some extreme examples. Just because there's no tension on the weld when the chord is deleted, that doesn't mean that there's no tension on the weld when the chord remains in play.

 

[rb1957]

is this a single bay, or part of a larger (beam) truss ?

another day in paradise, or is paradise one day closer ?

 

[r13]

BA,

You are correct - there is no boundary stress if no chord, also when the plate is perfectly rigid without distortion.

 

[BAretired]

retired13,

Yes, but if the chord is present, it will be stressed to accommodate plate distortion.

BA

 

[r13]

We are essentially on the same page. Without the chord, the connection by itself is stable under condition of force equilibrium. When attaching to the chord, the localized stresses tends to cause distortion, thus a straighten force is required, and will be provided by the chord through weld. This force shouldn't be too significant for this case though.