Plastic buckling of axially compressed thick unstiffened steel cones

• Collapse load of axially compressed thick cones depend on the modeling of material.
• For axially compressed thick cones, design codes underestimates the collapse load.
• For cones with r2/t<75, elastic perfect plastic material model is not sufficient.

The paper examines the effect of material modeling behavior on the elastic–plastic buckling of relatively thick unstiffened steel cones subjected to axial compression. Cones are assumed to be made from mild steel with radius-to-thickness ratio, (r2/t) of 34.3 and cone angle of 26.56°. Three material models were considered: (i) elastic-perfectly plastic, (ii) engineering stress–strain and (iii) true stress true strain. The accuracy of numerical predictions as compared to experimental results was seen to be strongly dependent on the material modeling strategy. Plastic mechanism design approach previously proposed for cones under axial compression was modified to widen the range of its applicability by catering for the effect of excessive plastic deformation. The proposed model utilizes the concept of true stress true strain nature of constitutive equation in determining the squash load. Predictions of collapse load given by the modified constitutive model were compared with initial plastic mechanism design approach and available design codes (API, ECCS, and ASME code case 2286-2) for published experimental data on axially compressed unstiffened steel cones in the elastic–plastic range. Results indicate that the proposed model gives much better predictions of load carrying capacity than both the initial design approach and the available design codes.