Stiffener Plate Design

[RDMESH]

I had a client who wants to offset beams from the stud wall line so he can run his steel studs to parapet. My boss wants to create a seat angle to bear the beam on top of it. The seat angle we used is angle8x8x3/4" with 1/4" stiffener plate welded to steel column of Hss6X6X3/8". I designed the 1/4" stiffener plate and it can carry only 13 kips of load. The applied load from beam ranges from 30 kips to 80 kips. If I assume the angle is stiffened then it can safely handle the load. But if i check the stiffener plate then it has to be 1 1/4" to carry the maximum 80 kips of load. Is this correct? I believe the plate will buckle before the failure of seat angle. But my boss thinks seat angle with 1/4" stiffener plate can easily handle the applied load of 80kips. Please help if i am incorrect. I am also attaching the scenario of calculation that i am running.

Thanks....please comment...

RD

 

[KootK]

The Canadian steel manual has some tabulated stiffened seat connection capacities which are similar, but not identical, to your detail. Using those tables, you'd need a stiffener at least 7/8" thick. Using that as a basis for comparison, I'd say that the 1/4" stiffener is dubious. It's also kind of disproportionate for use with a 3/4" think

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.

 

[KootK]

...It's also kind of disproportionate for use with a 3/4" thick angle.

Take care to ensure that your column can handle the applied moment as well. It will be significant.

Another detail to consider might be a pair of brackets either side of the columns with a seat plate spanning between them.

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.

 

[RDMESH]

Thak you Koot K... The column works fine for the moment...I am still not sure about the failure mechanism....I am debating that the 1/4" stiffener plate will buckle before the failure of angle seat..is that correct?...do you agree?...My boss disagrees that 1/4" stiffener plate wont work....I am trying to see if i am doing something wrong?...

 

[KootK]

I haven't checked you calculations in any detail but, as I mentioned above, I suspect that the stiffener is too thin.

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.

 

[jayrod12]

It seems thin to me as well.

The angle thickness may get a laugh from the steel fab guys as well. I've been told that they don't tend to stock the thicker angles so unless you need a lot of it then you're better off making a welded plate bracket.

 

[Tomfh]

Stiffener is too thin, and the stiffener thickness and angle thickness are out of proportion.

The connection to the column, and the column bending capacity (including local buckling capacity) also appears potentially problematic.

 

[RDMESH]

Than you jayrod12...

 

[RDMESH]

Thank you Tomfh...

 

[BadgerPE]

Section 5.3 in Blodgett's "Design of Welded Structures" deals with this topic if you are looking for more literature.

 

[Hokie93]

I believe your boss is out to lunch on this one. The only issue I see with your calculations is that the "allowable" load of 12.85 kips is actually a factored load (P[sub]u[/sub]), not a service-level load. It is unclear to me if the 30 kip to 80 kip loads are factored or service. My point is, be careful not to mix allowable loads with ultimate strength capacity and vice versa.

 

[RDMESH]

Hokie93..the loads i mentioned are 30 to 80kips are factored loads...Thank you for your comment...

 

[Lesali]

Not running any numbers but start here: Stiffen the stiffer plate by adding a "flange" on the outer edge and try material sizes commensurate with the beam it is to carry. You might even consider fabricating this "corbel" out of a piece of the that WF size.