Safety assessment of the South oculus, Canterbury catedral (UK)

Abstract

The South Oculus at Canterbury Cathedral is a wrought iron space frame consisting of two layers (Ferramenta and Grille) connected by tie bars (Pins). It is in very good condition despite its almost 850 years of history. The in situ survey of the Cathedral confirmed that the Ferramenta and the external grille are in general in relative good condition with the exception of some local failures. On the contrary, the pins are the most deteriorated part of the structure. Ambient vibration tests were carried out and the modal response of the structure was identified. In order to assess the safety of the oculus with respect to wind load, a model of the structure was built with the finite element software DIANA and calibrated using the results of the experimental campaign. The non-linear analysis of the existing structure resulted in a safety factor of about ten for the wind load. In addition, parametric studies have highlighted the importance of the external grille for the structure and have provided information of the consequences of further deterioration in terms of the load bearing capacity of the Oculus.