Weld spacing for preventing deflection in built up members

[SeanTee]

I'm trying to reduce the deflection in an already installed steel member by welding another member to the top.
If I calculate my spacing based on shear flow I find that need 1" of 1/4" fillet every 60".
I'm assuming that to created the rigid member I desire I will need to do welds more often than that, but I'm not sure how to determine that.
Any suggestions?

 

[phamENG]

AWS has limits on spacing of intermittent fillet welds. I believe it's 24x the thickness of the thinner part (center to center). There was a thread on it recently. As long as you meet that minimum and satisfy your shear flow, I'd say you'll be fine.

 

[Klitor]

The thread:

https://www.eng-tips.com/viewthread.cfm?qid=464122

 

[Agent666]

Agree with phamENG, there's just the forces to satisfy via shear flow and the members are constrained to act as one. Just be aware that you'll be locking in stresses and deflections that are already present in the existing member. So the strengthening is only good for reducing deflections under any loads that follow. This could tie example be only a proportion of the total load seen by the member.

 

[KootK]

I'm trying to reduce the deflection in an already installed steel member by welding another member to the top.

What is the nature and size of this supplemental member? Plate? WT? HSS?

What is the nature and size of the original member? WF?

How is the load delivered to the original member? Shear connections to its side(s)?

I ask these things because, if the supplemental member has a meaningful moment of inertia relative to the original member, the welds may experience a tension demand in addition to a shear demand.

In general, I agree with the other guys though: satisfying the minimums out to be be adequate with respect to creating a rigid, composite section from a shear flow perspective.

 

[SeanTee]

The original member is a C12x20.7 and I'm adding a HSS5x2.5x.25.
The load is transferred to the end of the cantilever as a shear.

Its a LL deflection (bouncy feeling deck) and still under construction so no worries about locking deflections.

I found the AISC reference as J3.5 (2012). I saw this before but it is under the bolt section so I thought I should check, because the amount of possible ways for something can fail that I haven't though of seams infinite.

Thanks all.

 

[dik]

Can you use 3/16 with 2"@18"?

Dik