screws in light gage steel framing

huangyhg

screws in light gage steel framing
the nominal screw shear strengths for both aisi and nz code are very close to each other. but in aisi the resistance factor is 0.5, in nz code it is 0.9. the governing vertical load combination is same in both of these codes : 1.2dl+1.6ll. what is the reason for this difference? one of the codes should be either too conservative or unconservative isn't it?
nz : new zealand code
maybe the bearing strength on the usual gages make in appilcation that the screw shear strength don't control, so except in the rare case the thin screws could control, the designs would continue being the same. o r in other words, given the bearing strengths, it is unnecessary to state the shear strength at the attainable values. but this is only conjecture.