When the side plates have uniform or multi-diameter holes, ligament efficiency calculations are performed according to Section 13-6. In the case of uniform diameter holes, the ligament efficiency factors em and eb for membrane and bending stresses, respectively, are considered to be the same. In the case of multi-diameter holes (see Figure M), the neutral axis of the ligament may no longer be at mid-thickness of the plate; in this case, for bending loads, the stress is higher at one of the plate surfaces than at the other surface.
If the calculated values of em and eb are lower than the entered midpoint joint efficiencies, the calculated stress values are divided by these calculated ligament efficiencies. It is important to note that if the stresses have been adjusted by the ligament efficiencies, then the calculations for the allowable stresses will assume an E value of 1.0. This avoids incorrectly increasing the stress values while decreasing the allowables at the same time.