Hi! Question regarding to welding for Built up Member 1

[Guigu]

Hi everyone,

I’d like to get your opinions on continuous weld versus stitch weld for a built-up member. I’m currently designing a steel hatch (which is significantly smaller than steel girders) based on AASHTO LRFD. The AASHTO LRFD BDS isn’t clear on whether stitch welding is permitted in this context. The member is a simple span, and the weld will be under compression stress, so I assume fatigue cracking won’t be an issue due to the compression-compression cycle. Do you know if there’s any specification or requirement in the code that mandates continuous welds for flexural members?
Thank you guys!

 

[centondollar]

First off, there will not be compression in the weld. Web to flange welds transmit shear. Point loads causing in-plane normal stresses are the exception, but I assume that is not the main load on this structure.

Is the red line a top flange? If so, size the weld with beam theory to resist the shear flow from direct shear (V*S/I in each direction) and shear from torsion (torsion moment/enclosed area), or use the upper bound of capacity (web plastic shear resistance) to determine maximum demand on the weld.

You need weld resistance per unit length to exceed demand on the weld, meaning that stitch welds (with minimum lengths and sizes mandated by code) might suffice. On the other hand, simple span beams have no redundancy, so I'd avoid stitch welding in this case, even if allowed by the code you design to.

 

[Guigu]

"@Centondollar,

Thank you for your reply. I apologize for the confusion—what I meant was that the member is under compression stress. I’m wondering if the weld is still subject to a fatigue limit check under these conditions. This is cut cross-section view of the member, and there are several of these spaced uniformly on both sides."