In the present work a methodology for the derivation of fragility curves for various types of industrial spherical pressure vessels is developed on the basis of static nonlinear (pushover) analysis. Damage states are defined considering only damage developed at the supporting structure and they are quantified using the displacement of the vessel as the damage parameter. The probability density function is idealised as lognormal.

The methodology is applied to two pressure vessels categories, designed without and with braces in their column support system and from the derived pushover curves it is found that the failure of the vessel is caused by the local buckling of critical column sections. Then, the effect of braces on the vessel response is investigated, concluding that bracing increases significantly the stiffness and strength of the overall system, while the stiffeners placed at their connections to columns increase significantly their ultimate ductility. Additionally, the effect of the column section classification on the response of spherical pressure vessels is also investigated.

Finally, representative fragility curves for each pressure vessel category are derived and it is found that braces reduce the fragility of the pressure vessel and provide a significant safety margin against high levels of damage, becoming more effective at progressively higher damage states.