Welded connection capacity.

[ronjon322]

Hi all.

I need help understanding forces in a welded connection. I am welding the end of a W14x61 strut perpendicular to the flange of another W14x61 waler at the end to form a corner. This is a rectangular temporary retaining frame for an excavated pit so all joints are in compression and 4 corners the same. Corners are NOT mitered.

My question is this: At this particular joint I have shear forces and moment forces. How do I add or combine these forces to determine if my weld has sufficient capacity. I am field welding all around the beam with a 1/4" fillet weld, 70EXX and regualr ASTM A992, grade 50 steel. Using basic LRFD, 5.5 kips/in of 1/4" fillet weld I come up with approx 360 kips of joint capactity. Shear force=63k and Moment=192k-ft.

Does it look like I have enough weld capacity? I appreciate it.

Ronnie

 

[Duwe6]

It might be in LRFD, but in ASD there is a simple formula to figure filletweld strength [assumes 70-series weld metal]

928# * [Length - inches] * [fillet size - 1/16's] = strength

So your gussets in a W14 become 928 * 7" [gusset width] * 4 [ weld size is 4/16"] = 26 kips [at 7", per side]
So the 14"(-) side of the gusset, welded both sides, is good for 104 kips. Thus, "Looks Good to Me"

But get a welding inspector to make certain that the welds are properly 'faired in', meaning run hot enough that the toe angle is significantly greater than 90°. Look in AWS D1.1 for examples of acceptable and unacceptable weld profiles. If you look at that set of detail dwgs in D1.1 for at least 20 seconds, you will know what I'm talking about, and what to look for. If the weld beads look like a pack of hotdogs, fire the welder and have that mess ground out, or air-arced off.

The reason for the inspx is the same as checking for proper cope radii - sharp corners are stress risers, and cause otherwise acceptable connections to fail.

 

[ronjon322]

Thanks Duwe6. I think I figured it out with a little Google help. I didn't know how to calculate the joint for both shear and moment.

 

[racookpe1978]

In general, it is best not to "Design by Google and the Grace of God" though.

 

[dhengr]

Ronjon322:
Some refinements to your detail.... I would extend the waler beam approx. .5" to the left, beyond the left side of the strut, so that fillet welds can be applied, both sides, btwn. the flg. of the strut and the flg. of the waler. This will improve your moment connection btwn. the strut and the waler flgs. I would inset the .75" stiff. pls. by the same amount. You want straight, clean lines of force transfer from the strut flgs. to the stiff. pls. The 192ft.kip moment might be reacted by flg. forces in the strut, approx. 192/(14/12) = 165kips of flg force. Some details show a 45̊ diagonal kicker in the corner, btwn. the waler and the strut, to help manage the corner moment. Clip the corners on the stiff. pls. so they don’t have to be fit to the web/flg. radius on the waler beam.

 

[ronjon322]

Thanks dhengr. That's the same numbers that came up with. I found an AISC LFRD moment connection guide online to help refresh my memory.

 

[sybie99]

I have received the following feedback from the welder, also see attached sketch:

Re the 20mm plate for which I received the drawing the following day after we had completed the job. I used my own expertise and experience and punched 18mm holes in the four corners and plug welded it with a 10mm fillet weld on the other side
Step 1 – grind mill scale around the area to be welded. Grind mill scale on Y16 bar, set amperage at 280 and weld all the way around the Y16 bar. Please refer to the rough sketch sent

 

[sybie99]

Apologies my reply was under the wrong thread, not sure how to remove it?