Weld Problem 1

[purplemonkey]

Hey guys,

I am trying to determine weld throat for a certain loading case (see attached file). This is my first time working on weld strengths so I am not sure if my answers are valid.

Given the dimensions, a safety factor of 4.5, and electrode tensile strength of 70 ksi, I am getting some unreasonably low throat sizes for the fillet welds.

I am getting .012 in for the throat size of the weld? What am I missing here.

The load type I am assuming is pure tensile.

 

[SnTMan]

Well, without doing the arithmetic, I'd say that what you have calculated for a throat size is about right. To get the leg size divide by 0.7, make it the next higher 1/16.

You've got what looks to be 34 linear inches of weld. Not so many lb/in.

How much confidence do you have in that last 5 thousandths of a lb?

Regards,

Mike

 

[metengr]

Sizing of fillet welds is based on the following approach using the 4.5 SF for the load applied;

Using information from AWS publications;

Allowable stress = 0.3 x UTS of the fillet weld x (1.0 + .5 sin^1.5 theta)

theta = angle of loading to the fillet weld in degrees


so stress = 0.3 x 70 x (1.0 + .5 x 1 (90 degrees)) = 31.5

Now the fillet weld size = Applied Load/[(31.5)x 2 welds x length of weld x .707]

 

[connectegr]

With a quick look: 5 kips/(17" x 2 welds x 0.928 kips/in) = .1585 / 16 fillet welds. Less that 1/16 fillet weld required. Probably require 3/16 due to material thickness. An increase is also allowed for fillet welds in tension, but I don't think you will need it. Note that this assumes the flange is adequately thick to evenly distribute the load over the entire length of weld.

Note: 0.928 kips/ in is for ASD, 1.392 kips/in for LRFD.

http://www.FerrellEngineering.com

 

[purplemonkey]

Thanks for the responses! Please forgive my ignorance but I have a couple of questions:

1) @ metengr: the stress given is as follows:

0.3 x 70 x (1.0+.5x1(90deg))

What is the the 0.3 factor?

2) @ connectegr: what is ASD and LRDF?

 

[connectegr]

ASD Allowable Stress Design - service loads

LRFD Load & Resistance Factor Design - ultimate strength loading

These methods of structural analysis, and require that the weld strengths are proportionate to the method used.

I would expect the loads you are showing to be service loads. And the weld size I showed above is the leg size, not the throat size. Fillet welds are noted by leg size.

http://www.FerrellEngineering.com

 

[metengr]

The 0.3 is for shear strength.

 

[SnTMan]

Well maybe not 0.012, I thought it said 0.12.

My apologies.

 

[gtaw]

Assuming you are welding low carbon steel or high sterngth low alloy steel you could consider referring to AWS D1.1 for allowable stresses for structural applications.

If you were to use D1.1 as the basis of design, the minimum fillet size would have to comply with table 5.4 to ensure sufficient heat input to ensure good ductility in the weld.

Best regards - Al