St Peter’s Dome

History of The Dome Michelangelo’s final great work. Construction work began in 1506 under Pope Julius II. Michelangelo died before seeing its completion on February 18th, The dome itself was completed in 1590, although further cosmetic changes would continue until 1626.

Interior View of Dome

Dome Design The tallest dome in the world. Rises m from ground, with an internal diameter of 41.47m. Built with of two shells of brick, the outer having 16 stone ribs, and is raised from the piers on a drum. Contains 16 pairs of Corinthian columns, each 15 metres high, connected by an arch. Dome is an ovoid shape, exerting less outward thrust than a hemispherical dome. Fig.1 Michelangelo's plan

Failure of Dome This design, however, was found structurally lacking. Early in the 18th Century, significant cracks began propogating up the side In 1748 an engineer called Polemi, was commissioned to rectify the problem.

Solution He discovered that the cracking was due to outward thrust of the dome being too great for the buttressing. Four iron rings were installed at the base of the dome to cope with this outward thrust.

Conclusion The Reason for the failure was caused my the complexity of the structure. Designers underestimated the forces on the dome. At the time there weren’t ways of analyzing elaborate structures such as this. Trial and Error was the main method of analysis. If such a project was undertaken today there it would be much simpler to analyse and construct