Page 34 - Design of Reinforced Masonry Structures

INTRODUCTION 1.3

which have survived intact for 900 years; the structure of the Taj Mahal, India; and the 1200
miles of sewers which the Victorians built under the city of London.
The earliest evidence of masonry construction is the arches found in the excavations at Ur
in the Middle East. These ruins have been dated at 4000 B.C. Arch structures dating to 3000 B.C.
have been found in Egypt [1.5]. The oldest surviving stone masonry structure is said to be an arch
bridge over Meles River at Smyrna, Turkey [1.6]. The advanced civilizations in Mesopotamia
and Egypt used stone masonry for building arches and vaults. Sumerians, living in the Tigris-
Euphrates Valley in Mesopotamia, are known to have used bricks and stones as early as 4000 B.C.
Their permanent building material was brick, at first only sun-baked; burned bricks were rare
because of lack of fuel. Stone was used sparingly because it had to be imported by way of water
from Persia or else carried by humans down from the eastern hills [1.7]. The pyramid of Khufu
in Egypt, built about 2700 B.C., is still one of the largest single stone masonry structures built by
*
humans even though its original height of 147 m (482 ft) is now reduced to 137 m [1.8]. Romans
of the pre-Christian period were master builders of the earlier civilizations; they built monumen-
tal buildings, bridges, and aqueducts, and used solid squared-stone masonry exhaustively. The
earliest specimen of a stone arch, a voussoir arch, still extant in Rome, is over a drain in front of
the Temple of Saturn, built between the sixth and the fourth centuries B.C. The Romans preferred
use of stones over the sun-dried bricks, apparently for reasons of durability. Augustus boasted that
he “found Rome in brick and left it of marble.” Although baked bricks were also used by Romans
for building arches, it was in stone that they made their most significant contribution. The descrip-
tion of the building skills of early Romans can be found in the writings of Marcus Vitruvius
Pollio, the famous mason and architect who lived in the first century B.C. [1.9] and whose Ten
Books on Architecture [1.10] comprise the earliest building manual to survive from the earliest
times (all earlier works have been lost). The Great Wall of China built more than 600 years ago
†
is made from stones and bricks [1.11]. A historical description of masonry construction and the
many magnificent ancient stone buildings can be found in the literature [1.8, 1.12]; a brief sum-
mary can be found in Ref. [1.3]. An interesting and pictorial description of the historical develop-
ment of brick construction through ages can be found in Ref. [1.13] which cites 171 references
on the subject matter. One of the best introductions to history of brick construction all over the
world is a collection of essays in Ref. [1.14].

1.4 EVOLUTION OF REINFORCED MASONRY

In unreinforced masonry structures, the lateral stability is provided by gravity. Because
masonry is weak in tension, no tension can be allowed to develop at the base of the struc-
ture. This requires unreinforced masonry structures to be sufficiently massive (meaning
large base width) that the resultant of all forces acting on the structure does not fall outside
the middle third of the base. This requirement imposes an economic limit on the height of
the masonry structures that can be built. Furthermore, slender structures proved incapable

of withstanding lateral loads due to earthquakes as demonstrated by damage during seismic
events in many countries throughout the world, such as India, China, Iran, Mexico, the
former U.S.S.R., and Turkey, to name a few. Extensive damage and collapse of masonry
structures during earthquakes continue to demonstrate the need for a better engineered
construction. Reinforced masonry provided the required answer, and thus began the

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The height of this pyramid was not surpassed by any Gothic cathedral, except the Beauvias cathedral in the north
of France whose tower collapsed in the year 1284, 12 years after its completion. The spire of Ulm Cathedral, built in
the nineteenth century, is slightly taller (159 m). The first multistory structure to exceed it in height was the Singer
Building in New York (206 m or 675 ft) erected in 1907 [1.8].
†
The Great Wall of China is reported to have first appeared in the seventh century B.C. and was strengthened or
expanded in the succeeding 2300 years virtually by every dynasty in China [1.11].