Based on discussion of attached plate and analysis of beam elements calculation results, a experience formula is deduced for the calculation of a beam elements inertial moment.

This paper believes that the calculating formula of moment of inertia for bow-shaped test piece in GB/T 13096. 2-91 is wrong because of printing error.

According to bending stiffness formula of the flat plate, the idea of equivalent inertia moment is proposed, which constitutes a new second main stiffness formula for corrugated plate.