×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Built-Up Section - T + HSS with stitch welding on edge

Built-Up Section - T + HSS with stitch welding on edge

Built-Up Section - T + HSS with stitch welding on edge

(OP)
I'm in process of designing a frame - and I'm curious about the length and spacing of welding (stitch weld, on edges) that will be required. The material is actually 316L stainless steel, but apart from that, I'm using standard structural shapes. In short, it's an L shape resting on top of an HSS rectangular member.

The orientation is such:

L
|_|

Note that the HSS has a top, I just couldn't figure out how to draw it using text.

This will be subjected to a distributed load.

The size of the L is 3 x 3 x 1/4" T
The size of the HSS is 4 x 3 x 3/16" T

I'm not the strongest in mechanics, because it's been many years since school and furthermore, my professor was not very good to begin with. However, I seem to have calculated out the moment of inertia of the combined section, though Solidworks shows something slightly different.

I'm getting the following properties:
Atotal = 3.84 sq.in.
Centroid-System = C(1.253, 3.066) from the bottom left corner
Ixx-1 of L = I-initial + Ad^2 = 1.24 + (1.44 * 1.776^2) = 5.782 in^4
Ixx-2 of HSS = I-initial + Ad^2 = 5.24 + (2.4 * 1.066^2) = 7.967 in^4
Ixx-total = 5.782 + 7.967 = 13.749 in^4

Solidworks actually reports the Ixx-total as being 14.5, but I never quite understood that program 100%. I know that it likes to re-orient the axes, which is probably accounting for the different in values (assuming mine are correct).

Now the next part is how to actually calculate the resultant stresses in the weld, as they try to slide past each other during bending.

Do I use the shear flow equation? Or do I want to look at the moment at that point above the neutral axis, which is at 4" from the bottom left corner, or basically 0.934 above the centroid.

Any help would be greatly appreciated.

RE: Built-Up Section - T + HSS with stitch welding on edge

For what it's worth, my results are similar to yours (A=3.82 in^2, Ix = 13.52in^4, centroid @ 1.248",3.053"). Not sure what Solidworks is up to.

If the member is only significantly acting in bending, the required connection strength is simply from shear flow. However, depending on what else is going on, specifically with your connections, there may be additional stresses trying to cross the weld plane.

RE: Built-Up Section - T + HSS with stitch welding on edge

(OP)
Looks like my calculations are showing about 465 lbs/in.

That's using q = VQ / I where:
V = 5000lbs / 2 = 2500 lbs
I = 13.749 in4
Q = y' * A'

y' is 4.842 (CG angle) - 3.066 (CG entire section) = 1.776 in
A' is 1.44 (area angle)

Does that sound about right?

If so, then the strength of the weld would need to be determined, which is just the cross section of the weld * the allowable stress. At that point, I could just get the equivalent required length of weld and then space out accordingly, correct?

RE: Built-Up Section - T + HSS with stitch welding on edge

If that angle leg extends to the sides of the HSS, then you have to provide a flare-bevel groove PJP weld on each side. Additionally, the strength of the flare-bevel groove weld is a function of the radius of the HSS at the corner (among process, etc.) and there isn't much control over the strength/inch of this weld, and you normally would never try to specify an effective throat (weld area) for this type of weld. You would just select the joint designation from AISC Table 8-2, either 5/8 or 5/4 times the thickness of the HSS wall thickness.

Some background: https://www.aisc.org/WorkArea/showcontent.aspx?id=...

That said, 465 lbs/in. of demand is peanuts.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Built-Up Section - T + HSS with stitch welding on edge

MacGruber makes a good point. If the angle doesn't have to be set flush with the sides of the HSS you can move the angle over so the toe hangs past the edge of the HSS...then you can get a proper fillet on the heel of the angle and proper flare bevel under the toe.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources