The 1997 UBC, section 2218.E6.3 has shear capacities for screws in sheet
metal -- which I take to include self-drilling self-tapping screws like TEKS
and TRAXX. The AISI Specification for the Design of Cold-Formed Steel
Structural Members available from AISI, 1101 17th Street, NW Washington, DC
20036, also has formulas for screw connections in sheet metal (it may also be
available from ICBO since it is a UBC reference document).