HSS truss welded connections

[Hunt007]

For welded connections, I've always gone with the theory of the max weld thickness (leg length, not throat thickness) is the thickness of the base metal.

I've come across some info in the CISC - Design Guide for HSS Connections that says the IIW (International Institute for Welding) recommends fillet wells that have a throat thickness of 1.07 times the member wall thickness. It says this weld size will develop the full capacity of the member.

I can't find the equivalent recommendation in the AISC HSS Connections manual.

I have an HSS with a thickness of 6mm, and according to the IIW, I can use a 10mm fillet weld all around, which to me seems excessive.

Just wondering if anyone has come across this IIW recommendation, and how they justify using such a large weld when typically welds aren't larger than the base metal.

 

[ishvaaag]

I have this same afternoon seen that allowance at the Packer and Henderson 1992 guide of CISC that I didn't remember, and has surprised me since here throats were (Spain, by the EA-95 code) chosen so that sizes were always less than the thickness, for fillet welds. Anyway it is well sanctioned (for the referred 350 MPA=Fy steels) it seems since also Eurocode takes such approach. If you have

Design Guide for Hollow Structural Section Connections
J.A. Packer
J.E. Henderson
CISC 1992

go to p.220.

It seems they use a brute force approach to near develop the section at the connection (it is said a TRHOAT 1.46 times the thickness would be needed to develop it); you can design for the lesser extant forces if you account for actual weld effectivenesses according to formulations in tables; and for fatigue where such engrossment wouldn't be convenient it is suggested it might still be a proper allowance.

What amounts to divergent allowance in the practice for these connections from common fillet welds ... likely the bigger rigidity of the weld parts is compensated by the flexibility allowed by the tubes there. And to attain enough force at the connection at the reduced reliability caused by the increased HAZ they choose just go as big. Looks a compromise decision to allow for the existence of HSS trusses.