The document discusses different methods of post-tensioning concrete structures. It describes the Freyssinet system as the first introduced method using steel wires grouped into cables with a helical spring. The Magnel Blaton system stresses wires two at a time using sandwich plates and wedges. The Gifford Udall system uses single wires stressed independently with double-acting jacks and tube or plate anchorages. The Lee McCall system prestresses steel bars using threaded bars tightened with nuts against bearing plates.

1. Charlie Gupta
B.Arch VIII Sem
Methods of Post
Tensioning

2. What is Post Tensioning?
• Post-tensioning is a method of producing prestressed concrete, masonry and other
structural elements.
• When the steel is tensioned after concrete placement the process is called
posttensioning.
• When a concrete or masonry element is prestressed, it means that the steel is being
tensioned and the concrete or masonry is being compressed. Compression is a force
that squeezes or crushes and tension is a force that pulls something apart.
• Post-tensioning is a form of prestressing. Prestressing simply means that the steel is
stressed (pulled or tensioned) before the concrete has to support the service loads.

5. Freyssinet System
• Freyssinet system was
introduced by the French
Engineer Freyssinet and it was
the first method to be
introduced.
• High strength steel wires of
5mm or 7mm diameter,
numbering 8 or 12 or 16 or 24
are grouped into a cable with a
helical spring inside.
• Spring keeps proper spacing
for the wire. Cable is inserted in
the duct.
• Anchorage device consists of a
concrete cylinder with a
concentric conical hole and
corrugations on its surface, and
a conical plug carrying grooves
on its surface.

6. Magnel Blaton system
• In Freyssinet system several
wires are stretched at a time. In
Magnel Blaton system, two
wires are stretched at a time
• In this system, the anchorage
device consists of sandwich
plate having grooves to hold
the wires and wedges which
are also grooved.
• Each plate carries eight wires.
Between the two ends the
spacing of the wires is
maintained by spacers.
• Wires of 5mm or 7mm are
adopted. Cables consists of
wires in multiples of 8 wires.

7. Gifford Udall System
• This system originated in Great
Britain, is widely used in India.
• This is a single wire system.
Each wire is stressed
independently using a double
acting jack.
• Any number of wires can be
grouped together to form a
cable in this system. There are
two types of anchorage device
in this system.
a) Tube anchorages
b) Plate anchorages

8. Lee McCall System:
• This method is used to
prestress steel bars.
• The diameter of the bar is
between 12 and 28mm. bars
provided with threads at the
ends are inserted in the
performed ducts.
• After stretching the bars to the
required length, they are
tightened using nuts against
bearing plates provided at the
end sections of the member.
• This system has the advantage
over others that stressing can
be done by stages as it is
possible to tighten the nut at
any stage.