Maximum Spacing of Intermittent fillet welds

By mjwilbur Date 11-25-2008 18:54

AWS D1.1 2004 2.11.2-1 states that the maximum longitudinal spacing of intermittent fillet welds shall not exceed 24 times the thinner plate joined. It is not clear as to whether this is the maximum center to center or is it the un-welded length between the welds. As an example, a 1/4" fillet weld spaced 3"@12 would have a 12" center to center spacing and with a length of un-welded steel of 9" within the 12". If the thinner plate was 7/16" then 24t= 10.5". The 1/4" 3@12 would be OK if the requirement is un-welded length but it would not be OK if it is center to center.

I would believe the code is concerned about the un-welded length between the welds not the center to center spacing.

By 803056

Date 11-25-2008 21:29

I take the "spacing" to be the center to center distance between the weld increments (segments).

My interpretation of the commentary is that the requirement is to ensure the welds act as one and they are close enough that paint will seal the joint to ensure moisture doesn't get in between the joined members (my interpretation). It isn't a "strength" issue.

Best regards - Al

By swnorris (****)

Date 11-25-2008 21:46

I've read the commentary and I agree with you Al. What I don't understand is this...

Example:

A W12 x 35 beam with a continuous 1/4" lintel plate intermittent fillet welded to the bottom flange versus the same beam with a 1/2" lintel plate intermittent fillet welded to the bottom flange.

The maximum spacing for the 1/4" plate would be 6" and the maximum spacing for the 1/2" plate would be 12".

The "spacing of intermittent weld connecting a plate component to other components shall not exceed 24 times the thickness of the thinner plate nor exceed 12" rule would apply, per 2.11.2.1 but, that doesn't change the "sealing" issue in the commentary. Both joints are still doing the same thing. It seems odd that the welds on the lighter plate would be closer together than the welds on the heavier plate. I guess that the lighter plate would be more prone to bowing, therefore needing the welds closer together to ensure a tighter fit. As I wrote this, I think I may have answered my own question.

By 803056

Date 11-25-2008 21:55

I believe you did. :)

Buckling is inversely proportional to the thickness of the member (plate). A 1/2 inch plate is twice the thickness of the 1/4 inch plate, but the 1/2 inch plate would experience 1/4 the buckling of the 1/4 inch plate for the same conditions. That being the case, the welds have to be spaced closer on the 1/4 inch plate than they do for the 1/2 inch plate to prevent buckling which would result in a space (gap) between the 1/4 inch plate and the other member (a beam perhaps).

Best regards - Al

By swsweld (****)

Date 11-26-2008 04:43 Edited 11-27-2008 13:04

Totally irrelevant to the intermittent spacing issue but following the same principle you put hangers more frequent on small diameter pipes and spaced further apart on large diameter pipes. Something like 3/4" steel pipe gets a hanger every 7' and a 12" steel pipe gets a hanger every 23'.

By 803056

Date 11-29-2008 14:08 Edited 11-29-2008 17:04

I think the hanger spacing is more related to the dead weight of the pipe and its contents. The smaller diameter pipe has a small moment of inertia and sags more than a larger diameter pipe. The objective is to eliminate any low spots where fluids could collect and free draining would be impossible. The concerns could include freezing, condensation causing "slugs" of condensate to pass through the system and damage equipment down stream.

Sagging, buckling, hangy down things, yep I see where you are going.

Best regards - Al

P.S. - I hope everyone had an enjoyable Thanksgiving!