Design of Coped Gusset Plates 6

[jochav5280]

I would greatly appreciate any advice or incite into what additional limit states I would need to check for a coped gusset plate. Our fabricator recently sent us the attached shop drawing; however, I am not sure what else I would need to check other than the tensile/compressive capacity of the gusset plate using the Whitmore Section.

Also, the attached shop drawing implies that this gusset plate will probably introduce a moment into the connection joint, since the the connection centroids do not intersect at the same point on the braces line of action (according to the AISC's Uniform Force Method).

Any advice, incite or direction in design such a gusset plate would be greatly appreciated.

Thank you in advance,

jochav5280

 

[GoBizon]

Ugly, I guess that mechanical duct has to go somewhere!!!

Seems like the plate would transfer the force in the brace to the connecting members (each member would have an axial load and lateral point load due to the plate) as opposed to the centroid of the connection.

 

[jochav5280]

GoBizon,

Yeah, I know how the load is going to transfer; I was more wondering if there are any additional design checks I should carry out on the gusset plate besides checking the Whitmore Section's tensile/compressive capacity.

Thanks,

jochav5280

 

[Gumpmaster]

Run far away if there's any seismic forces involved!!

Draw your free body diagrams like in the AISC examples and make sure all of your forces are accounted for. Draw a free body diagram through the re-entrant corner and see what's happening there. Probably some moments in the plate.

Round off the re-entrant corner to a minimum radius of 3xplate thickness.

 

[jochav5280]

Gumpmaster,

This project is actually in Seismic Zone 4 in South America; so that is a big concern.

Just looking at the connection you can tell that there are moments invovled at the connection interface, since the two connection interfaces do not line up orthogonally at the same point on the brace's line of action.

I have several of these ugly looking connections that I just received from the fabricator. They appeared to connect the gusset plate in whatever fashion they wanted, paying no attention to the Uniform Force Method requirements. Our structural models assume zero moment at the connection interfaces. That said, I am going to reject these designs and have them re-design them so that the moment is eliminated.

Since both bolted connections frame into a beam web, the Uniform Force Method says that there will only be shear at these connection interfaces. That said, maybe all I need to check is the shear capacity of the gusset legs?

Thanks,

jochav5280

 

[nutte]

I would say there is only shear at the interfaces. Working backwards from the supporting beam web, this shear will create a moment on the gusset plate that needs to be checked.

Are you worried about the moment from the single clip angle connecting the gusset to the supporting beam web? This is addressed in the single clip angle calculations, so it shouldn't be a cause for concern.

Right now, the "hole" in the gusset is cut like a rectangle. Is it to get past a column? Can it be shaped like a triangle instead?

 

[hokie66]

Your sections are reversed. Weak axis bending of the plate also needs to be considered because of the way it is connected with clip angles.

 

[weab]

Agree with nutte. This detail looks pretty standard at a column. Design for shear and sleep well.

Check the gusset for weak axis if you'd like, but as a 12mm plate with just 4- 20mm bolts it should be fine.

I assume you are using 20mm bolts, but the work I do overseas calls for 22mm holes for 20mm bolts. Holes that are just 1mm larger must be tougher to install.

 

[hokie66]

If those clip angles are 80 x 6 as I read it, they are the weak link.

 

[Grizzman]

I always boggles my mind when engineers leave one of the most critical links of the structural system up to someone else to design. Often that other person is not an engineer or is an engineer with very limited knowledge of all the forces going into the connection.
I'm not saying you shouldn't let fabricators design some connections. I just don't believe you should let them design critical lateral system connections.
If you reject there design, I suggest you send them a drawing of what you want, so there is no misunderstanding.

 

[ToadJones]

We used to do a lot of work in the power industry and avoided these boomerangs wherever possible by laying out bracing to avoid columns.
Just looking quickly, it looks like all the work-points line up to me.
Agree with Grizzman here.
Leaving anything but simple shear connections up to the fabricator is questionable. They don't have your structural models and can only go by the forces you provide them. I have seen times when the fabricator completely disregarded transfer forces in their connection designs even though they were provided to them.