Why dished or spherical end-plates give a higher strength?

Dished or spherical end-plates provide higher strength due to their geometric shape, which allows for uniform distribution of stress across the surface. This curvature helps to minimize stress concentrations that can occur in flat plates, particularly at the edges. Additionally, the shape enhances resistance to external pressures and loads, making them more effective in handling internal and external forces compared to flat end-plates. Overall, the design contributes to a more efficient structural integrity and durability.