If it's not in a handbook, then you need some FEA approach to confirm that this is OK.

That being said, you could also do the following conservative calcs:

First check for a shear failure around, say, the head of the bolt by using
( t x circumference x 0.58 x Fy ). This is the value in force units that represents shear yielding around the fastener.  This rarely governs.

What WILL probably govern, will be the out of plane bending stress, so at very worst, assume a bending moment of the fastener load x tube flange width / 4 (PL/4 - simple support). Then calculate S using, for effective width, the assumption of 45 degree dispersion of load at the hole, so an effective section is a rectangle measuring (t x flange width).  Whatever local stress (normal stress) you obtain must be combined with any stress arising from local bending.

Cheers,
tg

Trainguy,

Thanks for your response. I had also thought of performing similar calcs to those you mentioned above.

Since I posted my original message I've contacted someone at the steel tube institute. Apparently there are no actual specifications dealing specifically with this topic. The nearest thing is AISC's "hollow steel structural sections" specification. They also referred me to a publication by Timoshenko named "Holes in Plates" which deals with similar failure types, but in steel plates rather than HSS. Just FYI.

Thanks again.