Column size governed by thickness of weld required at baseplate?

[Psymiun]

Hello everyone,

I've got a situation where my column requires a 3/16" weld to its baseplate which is anchored into the foundation.

Beacuse a 3/16" weld is needed I have to use a column at least 1/4" thick per AISC (3/16"+ 1/16"= 1/4")

This leads to VERY low d/c ratios in the column (axial, bending, shear).

The problem is the column weight is killing the budget for this relatively small structure (cantelevered steel canopy). It seems silly to have the increased thickness over the entire length of the column, when its only needed at the base. Is it possible to have a column 1/4" just at the base to satisfy the minimum thickness of material for the weld, then have the remaining portion of the column smaller? What are my options here? I would imagine there is some sort of go to column splice or column type that varies thickness for this type of stuation.

Any information on this would be much appreciated. thanks!

 

[jayrod12]

Is this an exterior application? If so, I'd be inclined to leave it at 1/4" thick, leaves some meat there for when it inevitably corrodes. I usually don't go thinner than 5/16" for anything exterior even when specified as hot-dipped galvanized.

 

[phamENG]

I agree with jayrod regarding resiliency of the structure.

I disagree with Psyiun's interpretation of AISC 360. The t-1/16" is for lap joints, not T-joints. Take a look at the manual, page 8-36 if you have the 14th edition.

 

[Agent666]

Agree with phamENG.

.... And I believe you should interpret the t plate thickness as more like t-1/16=max weld size you can apply for a given t. Its to do with ensuring you can determine there has been no undercutting of the plate edge leading to less throat thickness in the weld.

For tee joint you can have a 1" fillet weld if you like, the incoming plate thickness has no bearing on any max size in that configuration.

 

[dauwerda]

For what it is worth regarding the thickness, 3/16 is usually the minimum allowed in the utility industry (transmission poles and substations). Sometimes I see a requirement for minimum of 1/4". I wouldn't (and don't) have any issues using a 3/16" thick sidewall that is galvanized in most locations - coastal regions may warrant a second look.

I agree that you are misapplying the weld requirement in this case.