Pressure resistant square panel

摘要

A pressure resistant square panel made of steel or cast iron comprises flanges extending along peripheral edges of a pressure receiving surface of the panel, a bottom portion along bottom edges of the flanges of the pressure receiving surface, flat portions inside the bottom portion and higher therethan, and reinforcing ribs substantially X-shaped as viewed in a plan view and extending along diagonals of the panel and progressively increasing their heights from corners to a center of the panel.