PROJECTS 36
Precast concrete accounts for the major portion of the building materials used in the construction of a shopping mall directly above a 390m section of the KwaZulu-Natal South Coast railway line at Isipingo Station. Built for Prasa and spanning 20 520m² over two floors (excluding the ramps and existing building), the new building is being erected on either side of and integrated with the existing Isipingo station building, which – in turn – is being modernised and upgraded. The new building comprises two floors, the first to be used for retail space and the level above for parking. The precast portion of the mall structure, designed by specialist precast concrete contractor Bedrock Group, is being built using precast columns, beams
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and hollow-core slabs, as well as precast
of various sizes, cast over pile caps,
parapet walling for the upper floor.
propped with braces and adjusted into a vertical position with shims. After
Unimpeded traffic
additional reinforcing was installed,
A major proviso for the construction of
concrete was poured around the base of
the mall was that the line remain open to
the columns. The braces were removed
normal rail traffic during construction. In-
after 14 days once the concrete had
situ construction, which involves shutter-
cured sufficiently.
ing and propping, would obviously not have worked and therefore precast concrete
Heavy beams
proved the only viable building option.
Of the 211 beams used on this project,
All 141 columns were produced on
132 measured 3-9m and were cast at
site and were cast with corbels for beam
Bedrock’s production yard in Westmead.
support. However, a variation order was
Up to 15m long, the remaining 79 beams
issued after the first 121 units had been
were cast on site.
cast, changing the building from a three-
T he beams were placed between
to a two-storey structure. This meant
(Above): A beam supports hollow-core slabs prior to the casting of the structural topping.
the columns to support the 10m pre-
the existing columns had to be shortened
(Below): A partially completed section of the mall.
stressed hollow-core slabs, which were
from 22m to 17m. Depending on the width of the flooring, the columns were placed in rows of either two, three or four abreast. Cast with starter bars flanking a column foot of 340mm x 600mm x 1 400mm, they were lowered onto structural blindings
(Top): A beam is about to be lifted by the 460-tonne mobile crane prior to placement between the western abutment and the central pier. (Above): Concrete pouring of the pavement. (Left): The central diaphragm’s reinforcing prior to the pouring of concrete. The Y40s can be seen protruding from the ends of the beams in a knitting formation. (Right): The completed bridge.
(Above): The bottom end of some columns showing the base foot flanked by starter bars.
PRECAST | ISSUE ONE | 2020
