Steel Construction Vol 40 No 1 - Architecturally Exposed Steel | Page 20

SAISC PROJECTS
Furthermore, the floor level of the lower
retail level is up to 3m below the
founding levels of the highway piers and
columns. This meant the construction
had to be isolated while building around
these existing piers and columns.
A lateral support system was designed to
protect the bridge piers, to ensure that
the safety of motorists was not
jeopardised. A roofing system was also
developed to cater for storm water
flooding from the highway in these areas.
Although not so widely used on modern
retail developments nowadays, the use of
corrugated steel sheeting conformed and
aided in capturing the heritage nature of
the potato sheds by maintaining the
original look and feel of the structure.
The roof structure comprises of 13m long
double-pitched steel trusses covering a
total of 4 600m². The reinstated old railway
pedestrian bridge was adapted to serve as a
fire escape for the adjacent Market Theatre.
The development feasibility demanded
several levels of underground basement
parking, which placed the potato sheds
structures at risk. The heritage authorities
approved the application to dismantle the
sheds in order to construct the basement
– provided they were restored and reassembled in their precise location
afterwards.
The structures were carefully surveyed on
site through a complex auditing process
that saw each element numbered, labelled
and documented, so that it could be
identified and re-installed in its correct
location later. Following the dismantling
process, the structures were transported
to a workshop facility for storage and
restoration.

An initial desk-top structural analysis
revealed that most of the steel truss
lacing members exceeded the slenderness
requirements stated in SANS10162. The
increase in live load and dead load from
added required services and materials
would also contribute to the structure’s
load tolerance requirements. To
strengthen the steel structures, a
stiffening procedure was implemented,
which entailed the strategic positioning
of flat bars welded onto the existing steel
elements. These flat bars improved the
structural properties of the elements
without impairing the heritage nature and
aesthetics of the steel trusses.

Pretoria Porsch

With the potato sheds being repositioned
onto a reinforced concrete floor at a new
level, a number of the existing steel
columns had to be extended to offset the
previous sloped geometry of the structure.
To draw a distinction between old and new
the joining connections were kept visible.
The potato sheds were originally designed
as a shade structure and was not weather
proof.
New down pipes were fitted strategically
into the expressed structure of the old
sheds trusses and steel column system.
Lightweight stiffened steel framed drywalls
and glass shop-fronts were used for the
vertical facades along the perimeter of the
potato sheds. The facades were designed
in such a manner to maximise the visual
impact of the overhead potato shed trusses
while ensuring a safe and weather-tight
structure for its occupants.

The facade support structure
is made out of hot rolled
vertical members bracketed
off the exposed steel circular
columns and cold rolled girts
of matching depth were used
to allow flush faces internally
and externally which were
clad with aluminium panels.

This heritage-inspired project will make
Newtown Junction a go-to destination for
the people of Johannesburg as well as
visitors to the city.

PROJECT TEAM
Client:
OT Venter Investments
Architect:
Empowered Spaces Architecture
Structural Engineer:
LS & A Consulting Engineers
Quantity Surveyor:
BTKM Quantity Surveyors
Main Contractor:
Probest Projects
Steelwork Contractor:
Central Welding Works
Detailing Company:
Segmiller Engineering services
Painters:
DRAM Industrial Painting Contractors
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Steel Construction Vol. 40 No. 1 2016