|Dr. N. Subramanian
Joined: 21 Feb 2008
Location: Gaithersburg, MD, U.S.A.
|Posted: Tue Aug 24, 2010 3:20 pm Post subject: Pantheon Dome
. Vital Statistics:
Location: Rome, Italy
Completion Date: 128 A.D
Diameter: 142 feet
Materials: Concrete, brick
The Pantheon Dome, completed in 128 A.D., was one of the most impressive engineering accomplishments of its time -- indeed, for all time. Although Romans had been building small domed bathhouses and temples for centuries, no other dome would match the Pantheon Dome's 143-foot diameter for another 15 centuries. Unrecognized, the design of this ancient concrete building reveals unparalleled features not encountered in modern design standards. Recent studies reveal several major cracks in the dome, but it still functions unimpaired. This condition will surely excite the curiosity of our structural engineers. The building was built entirely without steel reinforcing rods to resist tensile cracking, so necessary in concrete members, and for this concrete dome with a long span to last centuries is incredible. Today, no engineer would dare build this structure without steel rods! Modern codes of engineering practice would not permit such mischief. No investor with knowledge of concrete design would provide the funding.
When Roman Emperor Hadrian decided to build a monument to reflect the power of his empire, he built a dome -- but not just any dome. Hadrian constructed a building out of bricks and concrete with a dome that was bigger and more extraordinary than anything anyone had ever seen before. The enormous building, called the Pantheon, was built as a temple to all the Roman gods almost 2,000 years ago. It still exists today, almost entirely in its original form.
The Pantheon is remarkable for its size, its construction, and its design. The enormous dome stretches 142 feet in diameter; that's the same as the distance from the Statue of Liberty's sandals to her torch! Given the dome's size and weight, Hadrian's engineers had to find ways to lighten the heavy structure. They scooped out 140 waffle-like depressions, called coffers, in five rows around the dome's base to eliminate some masonry and reduce the dome's weight. They also carved an opening, called an oculus, at the top of the dome, which reduced some mass and created a daily light show for which the Pantheon is famous.
The result was an impossibly huge dome, one that would remain the world's largest for 1,300 years.
The engineering technology required to solve the technical problems which the construction of the dome posed, was more advanced than anything which had been used before. The execution of the project and the speed of its erection surely indicate that the Pantheon was explicitly planned out in advance. The building materials were graded from the foundation up according to strength and weight, and in the dome, many successive grades of concrete were used, ending with the lightest pumice aggregate. The pozzolana mortar throughout was of the highest quality available.
The dome of the Pantheon was a very impressive marvel of technology and imagination which had not been surpassed until recent times, and even then only with the help of metal reinforcement.Thomas Jefferson was influenced by its design when he built Monticello. It's influence can be seen in almost every American State Capitol building. The Pantheon was a major breakthrough in the architectural use of space, and this can be proved by tracing its influence through the centuries.
Here's how this dome stacks up against some of the biggest domes in the world.
(diameter, in feet)
- Pantheon is a Greek word meaning "to honor all Gods."
- The oculus, or "eye" of the dome, is 27 feet wide -- five teenagers could stretch across the hole!
- At its base, the dome is 23 feet thick, but only two feet thick at the rim of the oculus.
- David Moore,The Roman Pantheon: The Triumph of Concrete,1999
- William L. MacDonald,The Pantheon: Design, Meaning, and Progeny, Second Edition ,Harvard University Press, 2002, 160pp
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