HSS Shear Tab Weld Capacity

[BadgerPE]

Hey all,

I am working on a simple shear tab connection for a W8X18 beam to an HSS 4x4x1/4". Here are the parameters:

Governing Code: AISC 13th Edition
Ru=10 kips
1/4" A36 Plate Material
3/16" Fillet Weld
E70xx Electrodes

My question deals with HSS shear rupture and if the weld strength can be reduced to account for a reduced thickness.

Tmin=(6.19*d)/Fu=(6.19*3)/58=0.32"
Thss= 0.233"

Can I reduce the weld capacity by Thss/Tmin=0.72 similar to what it done in the last paragraph on page 10-50? In that paragraph it says "When less than the minimum material thickness is present, the tabulated weld available strength must be reduced by the ratio of the thickness provided to the minimum thickness."

While I appreciate the answer "Just make the column larger" I would rather hear if others feel that this is an acceptable method as steel prices are going to be a huge percentage of this projects cost and I would like to reduce the amount if at all possible.

 

[nutte]

You're using the wrong Tmin equation. Your column size is fine.

Tmin=(3.09*d)/Fu=0.160"

This thread discusses why you use the other Tmin equation:

http://eng-tips.com/viewthread.cfm?qid=312546

 

[BadgerPE]

Nutte,

That makes sense. However, based upon that assumption, since my shear tab is welded down both sides, tmintab=6.19*3/58=.32" so the minimum thickness of my shear tab shold be increased to 3/8", correct?

 

[SteelPE]

No, this is the same mistake that was made in my previous post. The tab sees two welds the column actually only sees one hence the correct equation is Tmin=3.09*d/Fu.

They didn't really do themselves any justice with example K.6.

 

[BadgerPE]

Ok. Now the confusion is building. To clarify:

Shear tab sees welds on both sides therefore the minimum thickness:
tmin(shear tab)=6.19*D/Fu=6.19*3/58=.32"

HSS column only sees 1 weld so minimum wall thickness=

tmin (hss wall)=3.09*D/Fu=3.09*3/58=.16"

Therefore, from my OP, shear plate thickness needs to be increased from 1/4" to 3/8" and my HSS wall thickness (0.233") is acceptable.

Does anyone have any objections to these statements? Trying to avoid any confusion.

 

[nutte]

These provisions (recommendations) drive me crazy. They make sense as guidelines, but when they become hard and fast rules that can't be violated, we lose something.

The shear tab weld is sized to be equal to 5/8 times the plate thickness. 5/8*0.25 = 0.156", so you round up and use a 3/16 fillet weld. Yes, it violates the tmin equation, but that's fine: you're trying to make the weld stronger than the plate.

For the wall of the HSS, you're trying to make the wall stronger than the weld. This is a good practice generally speaking, but we need to have the latitude to determine if it's always appropriate. The tmin equations, when promoted as gospel, take that ability away.