FILLET WELDS IN BENDING 1

[RANMAN3]

Can smene tell me if I should put tha NA at the center or somewhat lower say 1/3 up frm the bottom surface when calculating S from stress = M/S. It seams the compression side has more area than the tensin side due to the base material thickness plus the fillet weld area. I just think it should be lower than the 1/2 point. For example, lets say I have a 2x2 square tube with wall thickness of 1/4". I put a 1/4" fillet weld all around. The load is 500 lbs at a distance of 10".
Also, do I use the throat area to calculate S? And do I consider this load to be shear acting on throat area so use .3UTS of weld material to determine safety factor. And what SF is typical? I'm thinking of 2.5 to 1. Is this reasonable?

Thanks

 

[desertfox]

Try this link

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html#Design_St

 

[chicopee]

Show us a sketch of the weld configuration in relation to the load. Two views may be necessary so as not to misunderstand the relationship between welds and load, or you could show us an isometric view.

 

[RANMAN3]

I'll take a look at the site.I don't have any drawing tools as I am currently unemployedand my home computer crashed. I'm on my laptop sitting at Mcdonalds. Life is tough right now but I'm trying to gain knowledge.
Anyway, The load is vertical and the tube is horizontal. Its cantilevered with max moment at welded end, 5,000 in-lbs.
The basis question is, would you calculate I at the throat assuming its vertical? And, on the compression side, would you add area to the weld for the 1/4" tube wall thickness? I dont care about the numerical answer, only approach.

 

[grego50]

where can i found information for a moment resisting weld design?

i think my units doesn't work;
i have fv+fb=45 ksi
and i need to found out if a 6" sq. tube with weld all around will work!
do i need to use C=T= ? OR Fb allow. = 0.3x70x0.707x0.25 = 3.71 k/in
IF I PROVIDE 6" WELD : 3.71 x 6 = 22.2 k (THIS GIVES ME POUNDS AND I HAVE ksi ABOVE)
I KNOW IM DOING SOMETHING WRONG BUT DONT KNOW WHAT IT IS
PLS HELP

THANKS

 

[IsaacStructural]

RAINMAN3, in short, I'd do whichever is most conservative. I would normally ignore the area of the tube in bearing because I assume that the tube may not have a perfect fit up, in which case, all force will go through the welds, and none through direct bearing of the tube. This is a conservative approach, but not erroneous, because unless care is taken to fit the members carefully, you can't be sure which parts of the tube will actually be in bearing, for example, the tension side of the tube might be the side that is actually in contact with the base metal, while the compression side is offset from the base by some tiny gap, in which case the bearing would do you no good, since this can't transfer tension.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[jtseng123]

This is a simple question. Don't make it too complicate.
1. check the stress at the tube as a cantilever. This is freshman course at college.
2. check the stress at weld. The NA is still at 1/2 of the suuare fillet weld, the same as the tube. Get the linear section modulus, and calcualte the weld stress at throat area. As for allowable, it depneds. I use 10,000 psi for common structural steel, someone use 9,600 psi. Or use E*Sa, where E is the weld efficiency, Sa is the code allowable stress. The value of E depends on the type of weld ( groove weld, fillet wled) and type of stress( throat area or leg area).
3. you do not combine the weld thickness and tube thickness. Draw the force flow line, it flow from tube, then to weld. So it is wrong to use combined thickness.

 

[gtaw]

Fillet welds usually fail in shear regardless of the applied stress. AISC and AWS D1.1 uses the formula:

load = tensile strength of filler metal x .3 not to exceed 0.4 x allowable yield strength of the base metal. The lowest value is the limiting constraint.

Best regards - Al