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Structural Concrete Frames 385
Wires wedged
into anchor ring
Slotted head of jack
Ram forces
anchor cone in
Piston
Concrete anchor cone
Concrete anchor
cylinder cast into
beam
Spiral reinforcement
Hole for
grout
Groove
for wire
Figure 6.33 Freyssinet system.
The freyssinet system
A duct is formed along the length of the concrete beam as it is cast. The duct is formed by
casting concrete around an inflatable tube which is withdrawn when the concrete has
hardened. At each end of the beam, a high tension, concrete anchor cylinder is cast into
the beam. The purpose of the anchor cylinder is to provide a firm base for the head of the
jack used to tension wires. A 7 mm diameter cable of high-tensile wires arranged around
a core of fine-coiled wire is threaded through the duct. The wires are held at one end
between the cast in concrete anchor cylinder and a loose concrete anchor cone that is
hammered in tightly to secure the wires. A hydraulically operated ram is anchored to the
stressing wires, and the ram of the jack is positioned to bear on a loose ring that bears on
the concrete anchor cone around the wires. A piston on the ram applies stress to the wires,
which are anchored by the ram, forcing the anchor cone into the anchor cylinder as illustrated
in Figure 6.33. The stressing wires are released from the jack and the protruding
ends of wire cut off. A grout of cement and water is forced under pressure into the cable
duct to protect the wires from corrosion (Photograph 6.8a and b).
The Gifford–Udall–CCL system
A duct is formed along the length of a concrete beam around an inflatable former which
is withdrawn when the concrete has hardened. Steel thrust rings are fixed to the ends of
the beam, through which the stressing wires are threaded the length of the beam. The