# Fillet weld strength calculation

I have 2 plates that are fillet welded to each other. How can I determinate the max force the weld can take before it cracks?

The plates are only welded on one side because the other side is not reachable.

I added a image to clarify. • Where is the force applied? is it parallel with the weld or is there an angle involved? ie where are the attachment points? – Solar Mike Jul 30 '18 at 11:55
• It is parallel with the weld. The black plate is being pulled down. – Mech_Engineer Jul 30 '18 at 12:00
• I'm clarifying how much you already know... Do you know how to calculate the strength of a weld in general? Is the load direction what is causing issues? – hazzey Jul 30 '18 at 12:49
• I would like to know how to calculate the strength of a weld, but in this case I need to know how much weight I can attach to a existing structure. The load direction is not the issue, this issue is that I can't calculate it :D – Mech_Engineer Jul 30 '18 at 12:52
• It depends on the weld technique, filler metal, weld conditions ( preheat, etc.) . and base metal. – blacksmith37 Aug 30 '18 at 16:46

Depending on the type of electrode and the properties of the base material, we get a wide range of possible answers.

Typical electrodes tensile strength is ranging between 60 -70- 80- 90 ksi. They ultimately fail at shear which we call f_w at ultimate level.

And we consider factor of safety of 75% let's assume a= width of the weld and L =length of the weld.

$$φ Rn = 0.75 f_w \times 0.707\times a \times L$$

So to simplify, you plug in 3mm=1/6 inch and 11mm = 15/32 inch length of the weld in the formula and input the f_w from the electrode's spec sheet.

At the same time you need to check the base material shear strength and factor of safety which is usually 0.60.

For fillet weld only axial tensile/compressive load is possible. Due to this load shear will produce on weld joint. We know that shear stress is equal to (applied load/minimum cross-section area). Minimum cross section is 0.707XSXL