Building with Earth: Design and Technology of a Sustainable Architecture

wrapped together with galvanised steel
wire at 50 cm intervals. The arch was verti-
cally positioned and fixed to steel bars that
stick out of the plinth. This connection must
be capable of absorbing tensile forces dur-
ing an earthquake. Above the adobe vault, a
membrane of PVC-coated polyester fabric
was fixed and tightened to the plinth. This
has two functions: first,
it provides shelter against rain and wind;
second, it pre-tensions the arch, thereby
increasing its stability against tremors
during earthquakes.
Such tremors may deform the vault to a
certain extent, causing adobe joints to open,
but the vault will not collapse, since it is
held up by the tensile pre-stressed mem-
brane at the top and the compressive pre-
stressed bamboo arch underneath. The
stability of this structure, then, depends
mainly on its ductility. However, it must be

taken into account that if the pre-tension

of the membrane is high, the optimal sec-

tion of the vault is more like an ellipse and

not a reversed catenary.

For earthquake regions in Argentina and

Iran, the author developed a similar pre-

tensioned system for mud brick vaults. Illus-

tration 15.46shows a design for an orphan-

age building in Bam, Iran, where vaults are

constructed with thicknesses of 25 cm.

They are pre-tensioned by steel strips,

which are tightened to the reinforced con-

crete ring beam at the bottom of the vault.

Equal pre-tension forces in all parts are

ensured by using a calibrated torque

wrench. The optimal section of the vault

is derived by a computer programme. It

guarantees that the resultant forces from

the dead load of the structure and the

pre-tension forces run along the middle

of the vault cross-section.

146 Earthquake-resistant building

15.44 15.45

15.42

15.43

15.46