Building with earth - Gernot MINKE (1)

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wrapped together with galvanised steel
wire at 50 cm intervals. The arch was vertically
positioned and fixed to steel bars that
stick out of the plinth. This connection must
be capable of absorbing tensile forces during
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 membrane
at the top and the compressive prestressed
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 section
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 pretensioned
system for mud brick vaults. Illustration
15.46 shows a design for an orphanage
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 concrete
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.
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Earthquake-resistant building
15.46