39
CONSTRUCTION WORLD
NOVEMBER
2016
This reduction allows for the construction of a slanting front face which
creates both functional strength for the pylon as well as being aesthet-
ically pleasing. Additionally, for the stability of the structure, the pylon
base required 20 x 1,2 m piles to be cast each more than 20 m deep to
make contact with bedrock below.
The pylon also requires five cross beams to assist in torsion control
to brace the two legs. These are spaced about 4 m apart and begin at
35 m from the base of the pylon. Once completed the pylon legs will
support the heavyweight 27-strand cables measuring up to 88 m long,
as well as the weight of the structure, traffic and other calculated
exterior forces. Following the final tensioning and completion of the
concrete work, the final step in the construction of the bridge will be
the addition of a bitumen running course to provide a smooth surface
for the Rea Vaya buses, as well as a ‘bolt-on’ structural steel pedestrian
walkway.
Dependable partnership
Van Rensburg’s summation is, “For a job of this size and complexity
we prefer to deal with a professional and dependable partner. Form-
Scaff helped us overcome some of the challenges associated with
working on a project which requires dynamic design solutions in
very limited time spans.
“A good example is the cable formwork tubes that are cast into
the pylon which needed to be lined-up perfectly with the ties at the
bottom. This is not an easy task considering the tubes have to be held
in place for multiple lifts as the concrete pouring progresses. In the end
however we worked on solutions and in collaboration with Form-Scaff
were able to overcome these potential pitfalls,” says Van Rensburg.
“Another challenge was the balancing and anchoring of the bridge
considering it has an 88 m reach on the Sandton side – and just a
33 m reach on the other. To overcome this, Hatch, the design engineers,
called for the construction of a much thicker, solid deck on the short
side of the bridge to help counterbalance the weight deficit. The piers
also needed to be anchored from the deck level into bedrock on the
short side to provide additional stability.
Overcoming challenges
“Likewise, the solution for the cable formwork tube alignment issue
has also been solved and involves slotting the formwork to allow them
to be lifted after each pour without interfering with the cable tubes.
“Although these were technically challenging, they are just
some of the many complex issues that you get on a live site. In my
experience the kind of technical support you surround yourself with
ultimately determines the manner and success of the solutions created
to address them.
“Having worked with Form-Scaff on a number of similarly
complex projects in the past we are 100% confident in their overall
ability to deliver according to the specifications of the project.
On this particular site the expertise and technical support provided
by them has been pivotal to the success of the project overall,”
concludes Van Rensburg.