The Civil Engineering Contractor June 2019 | Page 23

AJ King, site manager for Shotcrete Africa SCP and supervisor Alphious Mahlabela.
the structure while improving its
appearance. The structure rises up
towards the building entrance and
narrows down to a diminishing
point – indicating the way to the
door almost like a target. That was
the biggest challenge from a design
point of view. Once I had decided
on that design, I had to look at what
I could take away – one usually
has heavy buttresses on an arch,
but we were able to do away with
this due to the capabilities of the
concrete and the expertise of the
engineers we were working with,”
says Breytenbach.
“We wanted to open up the
western side of the structure and
have sufficient natural light, and
we were lucky in that protection
from the elements was afforded
by the existing building. We used
polycarbonate as a roofing material,
because it doesn’t transfer a lot of
heat, clad over ribs tucking into the
structure on the sides which turned
three-dimensionally.”
As you approach the building the
portico opens up in a well-lit manner,
closing in as the entrance is neared,
tilting up slightly. Two large pillars
and the gutters act as the keystone
to the structure. There are long
spans of unsupported cantilevered
concrete between the pillars, “and
that’s a homage to the material we’re
working with and what it is capable
of,” explains Breytenbach.
www.civilsonline.co.za
Scope of work
“I believe this is one of the only
structures where every element of
rebar has its own bar-mark – every
single piece is individual, because
everything is either diminishing or
increasing in size and the whole
structure is moving in three
directions. It’s not like a normal
column.” The steel design was done
by engineers SCIP (Francois Deysel
and Jacques le Roux).
Peri was responsible for the
formwork, lay out and assembly. Each
was cut by laser into 200mm sections
so that Peri could get the stop ends
correct, because each one turns. “We
didn’t want to place the covering
material on top but below in order
to create a draught through it. It was
impossible to cast it as a sleeve in situ,
and that is where Shotcrete came in
when we looked at how to practically
build it,” says Breytenbach.
With sufficient admixtures such
as Penetron added to the concrete, a
slump of just 55 to 65 was achieved.
The columns are 800mm deep and
2.4m wide, and a whole column
could be erected in a single day
without shuttering at the back. “It is
quite amazing,” enthuses Breytenbach.
With lateral support, the result was
that the structure did not have a
weight of concrete pushing down.
From Peri, Callie Middel
(estimator), Shane Treherne (sales
engineer) and Jacques van der Walt
ON SITE
Architect Pieter Breytenbach, of Deter
Architects & Designers.
were responsible for the project.
Middel explains that Peri was
responsible for the design work for
the formwork and shoring, which was
done by Jacques van der Walt, senior
formwork designer at Peri.
“All formwork elements for the
soffits were pre-fabricated by Peri
off-site to be delivered for assembly
on site. This was however not possible
in the case of the formwork and many
items were attended to by AJ King
(site manager for Shotcrete Africa
SCP) on site. This project was unique
to say the least as well as challenging
in terms of formwork, reinforcing and
the shotcrete operation. The solution
to constructing the canopy had to
be found in a close collaboration of
the trades involved, architect Pieter
Breytenbach and his team, the team
at Peri, the rebar team and the team
at Shotcrete,” says Middel.
“The structure is asymmetric
so section and formwork design
work had to be done in 3D taking
existing structures into account.
From a formwork point of view,
this project was highly unusual and
many contractors took the decision
not to get involved. The placement
of concrete is only possible by the
wet-shotcrete method,” says Middel.
Shotcrete Africa SCP, with assistance
from Peri, installed all the formwork.
The construction method started
with the installation of a designed
network of props and scaffolding to
CEC June 2019 | 21