Design Specification for Steel Gates of Water and Hydropower Projects stipulates that the main beam

as the principal load-bearing component of a hydraulic steel gate

shall be designed as an elastic structure; the water-stopping panel

which has a large strength margin

shall be designed as an elastoplastic structure that accounts for local plasticity. However

applying the plastic-elastic design for the converted stress strength of panels functioning as beam flanges is highly hazardous

particularly for high-head gates or pumped-storage gates. Based on this

this paper presents a new verification criterion for the equivalent stress strength of panels by separating the design functionally－a plastic design for the local bending strength of the panel performing water-retaining function

and an elastic design for the overall bending strength of the panel also serving as a beam flange. We derive a new formula for verifying panel equivalent stress by multiplying the equivalent stress from current codes by an expansion factor. This formula is validated through a comparative analysis of four safety verification formulas－elastic

plastic

equivalent stress

and the function-differentiated equivalent stress described in this paper. Results indicate the current code's verification method for this equivalent stress strength poses safety risks

while our new formula increases its value by 20% to 35%. Engineering case studies of two high-head flat gates verify the accuracy and rationality of the new formula

laying a basis for high-head gate design and code revision.