Buckling of Shallow Dished Ends under External Pressure—a Caveat

The application of BS 5500 to the design of some shallow steel torispheres subjected to external pressure can result in safety factors which are lower than the expected 1.5. Some examples in which this occurs with elastic, perfectly plastic steels having yield points in the range 150 N/mm ² < σ _yp < 400 N/mm ² are given in the present note. Results are also given which show how the collapse pressures increase when linear strain hardening is included in the analysis.

For shallow aluminium torispheres, the Code rules seem safe but, since elastic buckling of the imperfect spherical cap may often be the controlling failure mode, the designs can be rather inefficient in the use of material.

Experiments on externally pressurized shallow torispheres having relatively low yield points are desirable in order to develop satisfactory buckling design rules for both the knuckle and the spherical cap regions of these dished ends.