My joint can detail report has shown that zero allowable punching shear for certain LCOMB. Would appreciate if someone can enlighten me on why there is a zero allowable punching shear stress shown on certain LCOMB. Thanks.
The 200.0 UC (and 0 allowable stress) represents a failure of the chord. Note that the chord stress for those load cases is ~345MPa (50ksi) which means that the chord is most likely overstressed.
Here is the note that is printed in the joint can listing file:
+200 - EXCESSIVE CHORD STRESS RESULTED IN A NEGATIVE ALLOWABLE