Structural assessment of the Guastavino Masonry Dome of the Cathedral of Saint John the Divine

Abstract

Historic masonry structures have survived many centuries so far, yet there is a need to better understand their history and structural safety. This thesis applies structural analysis techniques to assess the Guastavino masonry dome of the Cathedral of Saint John the Divine. This dome is incredibly thin with a L/t ratio of 200. Thus, it is important to assess this dome and its supporting arches, and confirm they are within adequate safety limits. This thesis gives an overview of the basic principles of masonry structural analysis methods, including equilibrium and elastic methods. Equilibrium methods are well suited to assess masonry structures as their stability is typically a matter of geometry and equilibrium rather than material strength. Using membrane theory and graphical analysis equilibrium methods, a complete analysis of the masonry dome and its supporting arches under symmetric and non-symmetric loading was performed. The arches supporting the dome carry the orthogonal thrust coming from the dome to the main piers. This thesis presents a strategy on how to evaluate the flow of forces for such a system, based on the fundamental principles of equilibrium methods. The analysis demonstrates the safety of the dome of the cathedral under gravitational loading and determines that the steel reinforcing in the dome is unnecessary for the safety of the dome.