I chose to report on the pantheon because I’ve seen pictures and I am also very fascinated by all the Roman monuments. I looked all around the internet and libraries. The Pantheon was very hard to find information about. It was very challenging but I found enough information to complete this report.
This famous building stands in the business district of Romemuch as it was built some 18 centuries ago. Amazingly, it has withstood the ravages of both the elements and war permitting a firsthand view of a unique product constructed by Roman hands. Now, it is exposed to acid rain and fumes from passing automobiles and overshadowed by buildings of inferior taste; but, with trust in the future, the Pantheon will survive.
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. Additional constraints when attempting to build a structure as large as the Pantheon will be discussed later, but briefly they include the use of inadequate hand tools and unsafe lifting devices. I believe we can learn from this activity. Workers can build from a plan and can successfully use their proven practices only if construction quality controls are maintained.
History tells us that the Pantheon is a Greek word meaning to honor all Gods (particularly the Olympian divinities). It is ironic that our building has existed throughout many wars while being dedicated to all Gods; one can readily perceive this to be a temple for our one God. And, the Church has claimed this holy structure as a resting place for its most famous Popes, so we continue to
honor its magnificent divinity.
The first incarnation of this ancient temple was built by Agrippa, the son-in-law of the Roman Emperor Augustus, about 27 B.C. Today, above the entrance carved in stone are the words M. AGRIPPA L. F. COS. TERTIUM FECIT which is translated,
Marcus Agrippa, son of Lucius, in his third consulate, made it. Indeed, it is worth mentioning that Agrippa’s engineering talents
were used in building the famous Pont de Gard aqueduct in France.
As with many cities, tragedy in the form of large fires such as those of 60, 64, 79, 100 and 110 A.D. seemed to strike Rome.
Originally, many Roman buildings contained travertine (limestone rock) which easily cracked in fires. The first Pantheon was
severely damaged and required replacement except for some parts of the lower porch section and foundation.
The Pantheon was rebuilt by the Emperor Hadrian during the period 118 to 128 A.D. (a time given by Ward-Perkins).2 But the
Ward-Perkins’s period is disputed by, Lugli who said the building was started sometime after 123 A.D. and was finished by
Emperor Pius about 140 A.D.3 However, most of the bricks were made and placed in the Pantheon in 123 A.D., a date that the
maker stamped on his bricks. This was discovered in 1892 by the French archaeologist, George Chedanne. It appears the
construction of the rotunda walls took a period of 4 to 5 years, and the dome required a like period because of its height and the
meager tools the Romans used. This long construction period was fortunate as it gave this pozzolan concrete ample time to cure
and gain strength.
Was the second temple like the first? Yes, the fundamental principle of the old Roman religion required that the temples be rebuilt without changes in original form. Tradition required that the main entrance face north, and thus the whole building was oriented on the north-south axis of the building.
A description of its structural features is separated into the configuration, foundation ring, circular walls, and dome to more clearly define various components. How these pieces are unique in view of today’s design requirements will be discussed shortly.
The Pantheon is one of the great spiritual buildings of the world. It was built as a Roman temple and later consecrated as a Catholic Church. Its monumental porch originally faced a rectangular colonnaded temple courtyard and now enfronts the smaller Piazza della Rotonda. Through great bronze doors, one enters one great circular room. The interior volume is a cylinder above which rises the hemispherical dome. Opposite the door is a recessed semicircular apse, and on each side re three additional recesses, alternately rectangular and semicircular, separated from the space under the dome by paired monolithic columns. The only natural light enters through an unglazed oculus at the center of
the dome and through the bronze doors to the portico. As the sun moves, striking patterns of light illuminate the walls and floors of porphyry, granite and yellow marbles.
Inside the Pantheon
The building design is one of a large round shape very much like a large barrel with a dome covering the top. There is a light-well in the center of the dome. Layers of beautiful thin brickwork cover the outside, round walls. Small access holes appear occasionally in the wall which were used during construction to frame interior voids. The main entrance is thoroughly impressive:
double bronze doors 21 feet high (6.4 meters), a lasting and fitting contribution from their metal smiths. These doors are protected
by a high, broad porch, made with 16 well arranged granite columns supporting a gable styled roof. The beams in the roof
structure of the porch are wooden. They were substituted for bronze members stripped-out by those in later years needing metal
for their canons. Professional Roman surveyors located the inlaid marble floor to conform with a convex contour which drained
away the rain from the oculus for these hundreds of years.
In the following descriptions, some general dimensions are given to indicate the magnitude of this undertaking by the Romans. The rotunda has a rather awesome inner diameter of 142.4 feet (43.4 m), made mostly of concrete. Comparatively speaking, this distance represents about one half the length of our football field. And from the floor to the top of the opening in the dome is the same distance. As a matter of fact, we could think of the design of this building as one that could contain a theoretical ball some 143 feet in diameter. The design is not entirely unusual because there are other Roman buildings which have a similar configuration, but the size is unusual. Other buildings such as the Temple of Mercury (71 feet/21.5 m diameter) at Baiae and Domitian Nympheaum at Albano (51 feet/15.6 m diameter) have domes of this type. The Pantheon still has the longest span constructed before the 19th Century.
To provide details on this complex configuration, the following figures show the building with its two-ring foundation, voids in the walls, and the step-ring and coffer arrangement in the dome.
The Pantheon was built on marshy, unstable earth which gave a serious supporting problem to its builders. The Jutland Archaeological Society described in detail various aspects of the ring foundation; they found it rested on a bed of bluish colored river clay.8 This condition invited disaster, and in the final construction phase, the foundation cracked at the two ends of the North-South axis.
If one section of a building settles slightly faster and lower than an adjacent section, very large bending stresses are initiated at a point between these two sections which can crack the concrete. And uneven settling was the problem given to the builders. The present-day engineering solution to this type of foundation problem is to drive piles through the clay to bedrock so the building will be firmly supported all the way around. The Roman builders chose a different approach. They built a second ring to hold the first ring from cracking further and to give the clay more area to support the structure. It worked because
the building has lasted over 1800 years.
In addition to keeping the crack from extending, the builders placed buttress walls on the south side opposite the massive porch.
This acted as a clampng device; and although the structural projection appears to be an additional room, it only serves the purpose of being part of the clamp.
These rings are made of pozzolan concrete consisting of travertine pieces in layers held together by a mortar of lime and pozzolan. This will be discussed later in this work. Interestingly enough, the Jutland Society’s investigation showed the foundation material had become rock hard,11 a case we might expect when we study the chemistry of pozzolanic reaction under these conditions.
How It Stands up
The challenge of determining stresses within various sections of the Pantheon has always excited both architects and engineers who are interested in the building. Technical design people recognized that the long 143 foot span of the ancient dome could have critical stress concentrations leading to a catastrophic failure of the structure, but this has not happened.
Nothing in life seems perfect, and this is the case with the Pantheon. The dome and walls have cracked. Concrete cracks under excessive tensile stress as viewed in a hoop condition. A. Terenzio, an Italian superintendent of monuments, documented cracking in the walls and dome duringhis inspection of the Pantheon in 1930.
Terenzio identifies fractures `reaching from the base of the rotunda to the summit of the dome’ that he thought were brought about by differential settlement from uneven loading of the wall, particularly near the entrance of the rotunda in the principal niche. Rather than finding vertical differential settlement, we have observed only traces of lateral opening across the cracks corresponding to the effect of hoop tension.
Terenzio believed cracking occurred shortly after construction because of dated brick repairs.
The Mark and Hutchinson study showed that meridional cracking in the dome was in the lower half extending up to about 57 degrees from the horizontal on the spring line. An earlier stress analysis of this dome by Cowan theoretically placed this point at 37 degrees 36′.
This is the point where hoop stresses in the dome change from tension to compression presenting a point of weakness within the unreinforced concrete dome. This theoretical point is in reasonable agreement with the actual end of meridional cracking. The Mark and Hutchinson study located the cracks as occurring generally at the openings within the upper cylindrical wall which increased local tensile hoop stresses. In addition to dome, Terenzio mentioned that cracks in the walls extended upward from 24.6 feet (7.5 m) above the floor.
The cracking pattern of the concrete in the Pantheon provides an unique stress configuration acting in the dome and walls. Mark and Hutchinson describe this picture as one in which the major internal forces in the cracked dome are only in the meridional direction, and this region serves as a series of arches which bears a common compression keystone in the form of the uncracked upper dome. The cracked walls serve as a series of independent piers to support these arches.
Perhaps as insurance against som future dislocation, should we add a steel band around a step-ring? Although the building has survived centuries, this valuable, cracked landmark of Roman history should be protected against future earthquakes at a small cost.
As you can tell the Pantheon was a great structure created by the Romans. I believe it has played a great role in Greek history. Even though this building is unpopular to many people, but this report proves that it is one of the greatest and most historical man made creation.
Encarta 95 Encyclopedia
H. W. Cowan, The Master Builders. John Wiley and Son, New York, 1977
Http://www.broyan/sor/index.pa-pr/Pantheon.html- Programmer: Jack M. Loudel