Building with Earth: Design and Technology of a Sustainable Architecture

145 Earthquake-resistant building

Vaults

An important rule for the design of plinth

and foundation is that the resulting force at

the bottom of the vault must pass through

the inner third of the surface of the founda-

tion. This means that eccentricity should be

less than^1 / 6. The foundation must have a

reinforced concrete or steel beam, which

can also withstand the additional horizontal

forces created by an earthquake.

Illustration 15. 37shows a section of a build-

ing which was built in an earthquake-prone

area in Bolivia. Its plinth has structurally dan-

gerous proportions, as the resultant force

from the vault creates a bending moment in

the plinth and does not stay within the inner

third of the wall, as necessary. This structure

will readily collapse when hit by an earth-

quake.

The cross-section of a vault is very important

for stability. For vaults that carry only their

own dead loads, an inverted catenary is the

optimal section, as no bending moments

will occur within the vault. Pointed vaults, as

shown in 15.39, or ”flat“ vaults as shown in

15.40, typical for Iranian architecture, col-

lapse very easily when hit by seismic shocks,

whereas the vault in 15. 41withstood the

heavy earthquake in Bam, Iran, in December

2003. Only the front part fell off.

The best solution for the facades of vaults is

to build them to be light and flexible, either

of mats covered with earth plaster, or of

timber planks.

Illustration 15.38shows a design by the

author for an earthquake-resistant low-cost

housing project in the region of Gujarat,

India.

In 2001, a proposal by the author for stabil-

ising adobe vaults with bamboo arches,

which guarantee a certain degree of ductili-

ty, was realised in a test structure built in

2001 at the University of Kassel, Germany

(15.42to 15.45). It was built using special

U-shaped adobes that rest on an arch, itself

built of three layers of split bamboo. The

bamboo sections were soaked in water for

three days in order to render them flexible.

Then they were bent over sticks, which

were pushed into the ground along a cate-

nary curve (15.43). To maintain the shape of

the arch, the three bamboo sections were

15. 37

15.38

15.39

15.40

15. 41