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, 1564.
• 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 136.57 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