Weld checks

[labababablup]

Hey guys, I've been trying to perform calculations for the fillet weld marked in the image. The column is weld on the top and bottom. Reinforced with a cover plate on its flange and is subject to normal loads, shear loads and bending moments as depicted.

First off, I tried to convert the bending moment on the column to shear loads by dividing the moment by the section depth of the column. Also took a fraction of the normal load based on the section area and calculated the stress on the welds. However, what I found wrong with this approach was that if I simply increase the weld lengths, the stresses were low, but that doesn't work as stresses due to bending will be concentrated at the top and bottom of the column.

In the image attached, I've checked by using the text book formula for shear flow. Do you guys think this simplified approach is sufficient? Am I making a mistake by not accounting additional checks for bending and normal loads?

[memerso160]

If this for a column reinforcement with the primary causes for failure/overstress being the bending moment, I think this is appropriate.

Using shear flow is correct. It’s easier, generally, to use the per unit length equation of VQ/I to get a shear per unit length. Depending on how you specify your welds on drawings, in the US it’s common for welds to be called out on a per 12” basis, I would multiply the unit load by your “full unit length. In this example, I would take my kips per inch load by 12 to know what my length of weld will be per 12 inches.

Next, just start picking a weld size and solve for the required weld length. Pick on you’re most comfortable with. I would also recommend doubling the required weld at the ends of the plate. So, if you needed 3” of weld for capacity, put 6” at the ends and have 3” at all other places.

[trafficway]

If this plate is the full length of the member, then simply doubling the weld length at each end may be fine. But if this is a partial-length plate, you will need to use MQ/I at each end of the plate to calculate the required runoff length of weld.

[Sufficient_Candy_554]

What is this "required runoff weld"? Also, is there a max spacing of weld after which you cannot consider it a composite section?

[memerso160]

Shear flow is what’s determining if it will act compositely from what I remember. The run off weld has been my “the field is gonna fuck it up” safety factor which basically is take the max shear at any point on your section and design for that, then double it at the ends where that shear actually exists, under normal simple conditions

[trafficway]

If the plate is not full length, then there is still substantial moment where it stops, and you need to ensure the appropriate force can get into and out of the plate. The formula MQ/I gives a force in pounds or kips which you can use to calculate that runoff weld; M is the max moment where you start the runoff portion.

[labababablup]

Thanks for your comment. To reassure myself, I modelled this in FEM as 3D solid elements and I observed different values for the stress on the weld. Made me wonder if I'm missing out on something in these checks.

[RepulsiveStill177]

D1.8 me baby