Dome construction
Construction of a concrete dome is unique compared to
conventional methods of concrete construction, but allows
for rapid construction and superior strength and durability.
Most concrete construction involves wood, steel or even
earth formwork to place concrete or shotcrete within or
against. The method for building domes however involves
inflating a heavy-duty industrial fabric which serves as
a formwork; an ‘air form’, as the industry refers to it.
Domtec’s DomeSkin™ air forms are each custom designed
to fit the volumetric capacities of the product to be stored,
while also fitting into height and width restrictions of
each site. The type of reclaim system is also taken into
consideration as often times a smaller dia. footprint is
desired to decrease the floor area, length of reclaim tunnels
and equipment size and cost. This results in SiloDomes™
consisting of a hemispherical shape and a cylindrical base
section, all prefabricated into the air form itself. Such was
the case for both domes in New Zealand. Each SiloDome™
had to be built within a limited available footprint area,
which also resulted in decreasing the cost of the reclaim
system. Although the cylindrical part of the dome is more
expensive to build than a hemisphere, the money saved by
decreasing the floor size and reclaim equipment is typically
greater than the cost to build a cylindrical portion of a
dome.
The DomeSkin™ is built using wide rolls of industrial
fabric that are custom designed, cut and ‘heat welded’
together using specialty equipment to fabricate a giant
balloon that will be inflated and used as a single-side form
to shoot concrete (‘shotcrete’) against.
The DomeSkin™ has a dual purpose. Not only does
is serve as the air form during construction, ultimately it
also performs as the finished exterior roof membrane. The
construction takes place on the inside of the DomeSkin
TM
,
so the dome is literally built from the outside in: roof,
insulation, and finally the structure. All rebar and heavy
equipment to be used in the project such as cranes and
forklifts must be placed under the air form before it is
inflated because once inflated, the formmust remain under
pressure for the duration of construction. The construction
equipment only leaves the interior once the dome is
complete. This meant a 35 t mobile crane, a telehandler
and all 480 MT of rebar had to be strategically positioned
within the pile cap and under the air form prior to it being
inflated.
After inflation two inches of polyurethane foam are
sprayed to the interior of the dome. The foam provides
greater rigidity to the DomeSkin
TM
and provides a surface
to which an initial ‘pre mat’ of rebar can be attached, and
provides a surface which shotcrete better adheres to. Once
the foam is sprayed the time-intensive job of hanging rebar
to the dome and embedding that rebar in shotcrete to the
engineered thickness takes place.
In February 2015 construction began on the Timaru
dome, a 36 m dia., 31.5 m tall dome. First, the custom
fabricated DomeSkin™ air form was carefully attached
and bolted down to the foundation and then inflated.
The dome was built following Domtec’s quality control
