Saving Michelangelo's Dome, by Wayne Kalayjian
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Saving Michelangelo's Dome: How Three Mathematicians and a Pope Sparked an Architectural Revolution
byWayne Kalayjian (Goodreads Author)
This book is a history focused primarily on the restoration of the dome of St. Peter’s Basilica that occurred in the 1750s. The scope of history begins in ancient Rome with the first construction on the site and continues through the dome’s construction in 1588-90, the restoration 160 years later, and then the book’s history continues on to describe the subsequent development of the modern practice of engineering.
The title’s reference to Michelangelo and the subtitle’s reference to “Architectural Revolution” are both a bit hyperbolic. It’s true that Michelangelo made a design, but he died years before the dome’s construction and the final design deviated from his design. A more appropriate subtitle—in my opinion—would have been, “The First Use of Analytical Mathematics in Design of Repairs to a Major Structure.” Or perhaps an alternative subtitle could have been, “The Birth of Structural Engineering.”
The main point made by the book is that this was the first time mathematics was used to estimate forces created and resisted within a structure, and then using these forces—combined with knowledge of the strength of materials based on testing—calculated the needed size of new structural members. Prior to this time structural decisions were based on intuition and experience.
Cracks developed in the dome after its construction and by 150 years later they were of sufficient size to be alarming, The dome’s circumference had increased by 18 inches as reported in this book. Using my own calculations this means that the radius increase—and the average outward movement at its edges—would have been a little under three inches over a diameter of 137 feet. The inherent strength of the elliptical dome shape prevented total collapse, but this amount of movement in a dome constructed of mortar and rock that depends on remaining in compression in order to not collapse is flirting with disaster—finite analysis performed in 2019 using modern analysis methods showed that structural failure was imminent if outward movement had continued. The installed structural repair consisted of multiple iron chains installed around the base of the dome and its supporting drum cylinder that were then wedged into a state of tension (steel cables were obviously not available at the time).
Ironically the results and recommendations of the mathematicians was not acknowledged as the basis for the design of the repairs chosen for construction. Instead construction was based upon the recommendation of a respected architect who recommended improvements that just happened to be close to what the mathematicians had recommended. No rational explanation was given for his design so one has to conclude that his design was based on intuition or perhaps there was some unacknowledged influence from the recommendation of the mathematicians. This architect insisted that the dome was in no imminent danger of collapse but that the repairs should be made to prevent future increase in crack sizes for cosmetic reasons.
Near the end of the book there is a quick history given of the history of the development of the engineering profession. First the enlightenment’s development of advanced physics was used to design military works, thus the first engineers were known as military engineers.
The title’s reference to Michelangelo and the subtitle’s reference to “Architectural Revolution” are both a bit hyperbolic. It’s true that Michelangelo made a design, but he died years before the dome’s construction and the final design deviated from his design. A more appropriate subtitle—in my opinion—would have been, “The First Use of Analytical Mathematics in Design of Repairs to a Major Structure.” Or perhaps an alternative subtitle could have been, “The Birth of Structural Engineering.”
The main point made by the book is that this was the first time mathematics was used to estimate forces created and resisted within a structure, and then using these forces—combined with knowledge of the strength of materials based on testing—calculated the needed size of new structural members. Prior to this time structural decisions were based on intuition and experience.
Cracks developed in the dome after its construction and by 150 years later they were of sufficient size to be alarming, The dome’s circumference had increased by 18 inches as reported in this book. Using my own calculations this means that the radius increase—and the average outward movement at its edges—would have been a little under three inches over a diameter of 137 feet. The inherent strength of the elliptical dome shape prevented total collapse, but this amount of movement in a dome constructed of mortar and rock that depends on remaining in compression in order to not collapse is flirting with disaster—finite analysis performed in 2019 using modern analysis methods showed that structural failure was imminent if outward movement had continued. The installed structural repair consisted of multiple iron chains installed around the base of the dome and its supporting drum cylinder that were then wedged into a state of tension (steel cables were obviously not available at the time).
Ironically the results and recommendations of the mathematicians was not acknowledged as the basis for the design of the repairs chosen for construction. Instead construction was based upon the recommendation of a respected architect who recommended improvements that just happened to be close to what the mathematicians had recommended. No rational explanation was given for his design so one has to conclude that his design was based on intuition or perhaps there was some unacknowledged influence from the recommendation of the mathematicians. This architect insisted that the dome was in no imminent danger of collapse but that the repairs should be made to prevent future increase in crack sizes for cosmetic reasons.
Near the end of the book there is a quick history given of the history of the development of the engineering profession. First the enlightenment’s development of advanced physics was used to design military works, thus the first engineers were known as military engineers.
More than any others, these ingenieurs were the best trained and best equipped to build, for example, more reliable systems of fresh water, along with better sanitation and improved transportation networks to meet these looming public needs. They created a new profession known as the civil engineer (génie civil), to differentiate these kinds of large-scale municipal projects, dedicated to the public’s well-being, from those of a more traditional military officer (génie militaire).I included the above reference to civil engineering because that was my profession prior to my retirement.
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