Compress and WRC 537 - square / rectangular attachment

[tngu]

Hello Everyone;

As I understand it WRC 537 applies to attachments that are circular / square / or rectangular in shape.

When modelling a vertical vessel with I-beams oriented with flanges in compress reports the following assumption:

"Note: continuous welding is assumed for all support leg fillet welds.
The following leg attachment weld analysis assumes the fillet weld is present on three sides (leg top closure plate is used)."

My question is if there is only three side attachment how does compress apply the rules of WRC 537 which treats square or rectangular attachments?

Thanks in advance