Stitch Weld - Length Calculation

[skeletron]

For continuous welds, I am in the learned habit of calculating the required length based on strength and then adding a nominal amount of weld to account for start/stop and potential poor quality at the beginning of the weld. For a 1/4" weld I take this as:

start + stop = 2 x weld leg size
nominal amount to account for poor quality at beginning of the weld = 1" minimum
total extra = 1.5" for 1/4" weld

I would round to the nearest 1" after adding this number, within reason.

When working with stitch welds, I find myself uncertain whether this additional 1.5" is necessary. This uncertainty mainly originates from a 3" stitch only being about 50% effective in my habitual system.

Can anyone clarify whether adding a nominal amount of weld (as suggested above) applies to stitch welds? Or, is the total stitch length equal to an equivalent total continuous length (e.g. 3 x 3" stitches == 9" continuous weld)?

 

[Tomfh]

Seems a bit excessive to add that much fat to every stitch…

 

[DrZoidberWoop]

........
start + stop = 2 x weld leg size
nominal amount to account for poor quality at beginning of the weld = 1" minimum
total extra = 1.5" for 1/4" weld
.........

I'd say adding additional length equivalent to the sum of the weld start & stop would be more than sufficient, but not necessary. Imposing another 1" on top of that is too conservative and in some cases might be less efficient (i.e. more time consuming w/ only a little weld material saved) than letting the welder go at the joint w/ a continuous single-pass weld.

Also, a reputable fabricator shouldn't have that much slop in their welding. They're in the business of using as little wire/stick as possible to reduce fab costs. Welders who deliver work w/ welds outside a 1" length tolerance wouldn't last long here.

 

[cliff234]

I never thought about adding any additional weld length at start/stops on intermittent welds. If adding additional weld length was necessary, I am certain AWS would have addressed it in the welding code. (That is an extremely comprehensive document!)

 

[Lomarandil]

I'm another in the camp of "it comes out in the wash". Obviously keep stitch lengths reasonable (I tend to use 6x or 8x leg size rather than the 4x minimum), but I don't otherwise add any extra length beyond what I need to get the utilization into my target range.

 

[skeletron]

This is a field weld scenario, but thank you for confirming my initial suspicions.

 

[RattlinBog]

For field stitch welds, I'm typically more concerned with the pitch than the weld length. AISC 360 J3.5 gives requirements for max fastener spacing for painted/unpainted steel and steel subject to corrosion. Section E6 gives even more stringent connection spacing requirements for built-up compression members.

I've seen a fair amount of issues with pack rust developing in old built-up members and connections with stitch welds or bolts that were spaced too far apart.

Stitch welds help limit distortion, so maybe adding excess weld length beyond strength needs could cause some unintended consequences.