Pantheon
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. 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 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. 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 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. 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 Http://www.broyan/sor/index.pa-pr/Pantheon.html- Programmer:
Jack M. Loudel