The opportunity to carry out a structural diagnosis of the Fort of Socoa made it possible to study the mechanical behaviour of an annular vault under seismic loading.

Far from modern engineering structures, this military construction raises fundamental questions.

• What modelling strategy should be used in an engineering context?
• How can the stereotomy and complex shapes of such a structure be approached?
• How should the seismic issue be considered within a regulatory framework sometimes ill-adapted to historic structures?
• What are the expected failure modes, and how do they compare to those of classical masonry structures?
• Which indicators and stability criteria should be retained? 

To answer these questions, we propose a comprehensive methodology combining parametric geometric generation and structural analysis using the discrete element method.

This study reveals a unique collapse mechanism, hybrid between that of a dome and that of an arch. Above all, it once again demonstrates the ability of masonry to reach a new equilibrium state despite the presence of cracking, confirming the resilience of stone structures. This study thus offers a pathway for the structural justification of complex masonry works subjected to seismic actions.