STRUCTURAL DESIGN FOR ARCHITECTURE

Structural Design for Architecture

Fig. 5.11 The

Pantheon, Rome, 2nd

century CE. This was

the largest domed

structure of Roman

antiquity. The coffer-

ing of the inner face

of the dome and

voiding of the walls

suggest that the

'architects'/'engineers'

responsible for this

building had a good

intuitive or empirical

understanding of the

structural behaviour

involved. They used

these features to

excellent architectural

effect. [Copyright:

RIBA Photo Library]

154

behaves as a series of arches, arranged around

a central axis, which exert a significant

horizontal thrust on the supporting structure.

The effect is lessened if the profile of the dome

is pointed rather than hemispherical. Cracking,

and the resultant horizontal thrusts, can be

minimised if material capable of resisting the

tensile hoop stresses is incorporated into the

dome structure. Iron chains have been used for

this purpose.

The earliest of the great domes of the

Western architectural tradition was that of the

Pantheon in Rome, constructed in the second

century CE (Fig. 5.11). This is 43 m in diameter

and was made of Roman concrete. The internal

profile was hemispherical and the dome was

supported on a cylindrical drum of concrete

faced internally in marble and externally in

brickwork. Meridional cracks developed in this

dome, in the manner described above, but the

resultant outward thrusts were absorbed by the

very thick walls of the supporting drum. The

supporting system of voided walls was of a

similar configuration to that of the systems

which were used to support vaulted halls,

which suggests that the Roman architects were

well aware that the drum would be subjected

to bending as a result of outward thrusts from

the dome.

The dome of the Hagia Sophia in Istanbul

(6th century CE) (Fig. 5.12) has a slightly

smaller span than that of the Pantheon (31 m)

but the design is considerably more audacious.

This dome is much thinner than that of the

Pantheon and it is supported on four piers, to

which the weight is transferred by four arches

and pendentives (in a square arrangement on

plan) rather than a cylindrical drum of

masonry. The piers are heavily buttressed by

the surrounding parts of the building but

nevertheless show signs that outward

movement occurred due to the lateral thrusts

produced by the dome and its supporting

arches. The configuration of the structure

suggests that the architects were aware of the

crack pattern which had developed in the