The Panthanon Essay, Research Paper

The Pantheon

Introduction 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 exc!

ite 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 existe!

d 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 replace!

ment 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 origina!

l 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. Body 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 t!

he 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 substi!

tuted 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. Foundation 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 s!

howed 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 ope!

nings 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. Conclusion 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. Bibliography Encarta 95 Encyclopedia H.

W. Cowan, The Master Builders. John Wiley and Son, New York, 1977