I. PRE-STRESSED CONCRETE
WHAT IS PRE-STRESSED CONCRETE?
Pre-stressed concrete is a form of concrete where initial
compression is given in the concrete before applying the
external load so that stress from external loads is counteracted
in the desired way during the service period. This initial
compression is introduced by high-strength steel wire or
alloys (called ‘tendons’) located in the concrete section.
How does Prestressed concrete Work?
In the real life, high tensile strength steel wires are inserted
into the beam section and they are stretched and anchored,
then released. Now the steel tendon wants to gain its original
length and tensile stresses are transformed into compressive
stress in the concrete. Now after loading there are two kinds
of forces on the beam,
Internal prestressing force
External forces (Dead load, Live load, etc.)
WHEN WAS PRE-STRESSED CONCRETE
INTRODUCED?
In 1929, Eugène Freyssinet (1879-1962) was a skilled
craftsman and a prolific bridge builder, who invented
prestressed concrete.
WHO PATENTED PRE-STESSED CONCRETE?
Eugène Freyssinet
• French engineer considered the father of prestressed.
• His initial recommendations for practical use of pre-
stressing in 1933: (1)Use metals with very high
elastic limits (2)Submit them to very strong initial
tensions (3)Use stiff concrete.
• Designed and build: Luzancy Bridge (across Marne
River, France)-1946; Le Veurdre Bridge (across
Allier River, France)-1910-1911
Gustav Magnel
• Belgian professor who brought pre-stressed concrete
to the English- speaking world
• Spent WW2 exploring Freyssinet’s ideas and
carrying out some research on pre-stressed concrete.
• Magnel had unique ability to communicate in
English to teach
• He was known as an excellent teacher. His goal in
teaching was simplify complex problems.
• Designed/build: Walnut Lane Memorial Bridge in
Philadelphia, Pennsylvania (1976)
ULRICH FINSTERWALDER
• German engineer who developed the double
cantilever idea of pre-stressing construction.
• Progressed idea that pre-stressed concrete can be a
safe, economical, and elegant solution to almost any
major structural problem.
• Designed: Bendorf Bridge over the Rhine River,
Germany (1962)
ADVANTAGES
• by using high tensile steel improve the efficiency of
the materials
• works for a span greater than 35m.
• Prestressing enhance shear strength and fatigue
resistance of concrete
• Dense concrete is provided by prestressing systems
thus improving the durability
• Best choice for the construction of sleek and slender
structures.
• Prestressing helps to reduce the dead load of the
concrete structure
• Prestressed concrete remains uncracked even at
service load conditions which proves the structural
efficiency
• Composite construction by using the prestressed
concrete unit and cast-in-unit derives the economic
structure.
DISADVANTAGES
• Higher material costs
• Prestressing is an added cost
• Formwork is more complex than for RC (flanged
sections, thin webs) – thus, precast not as ductile as
RC
COMPARING TO THE CONVENTIONAL
REINFORCED CONCRETE
In conventional reinforced concrete, the high tensile strength
of steel is combined with concrete's great compressive
strength to form a structural material that is strong in both
compression and tension.
Prestressing removes several design limitations conventional
concrete places on span and load and permits the building of
roofs, floors, bridges, and walls with longer unsupported
spans. This allows architects and engineers to design and
build lighter and shallower concrete structures without
sacrificing strength.
APPLICATIONS OF PRESTRESSED CONCRETE
1. FOUNDATION:
Prestressed Concrete Piles —the prestressed concrete pile is
an ideal choice for deep foundations with heavy loading on
weak soil. At present, prestressed concrete piles are being
used as sheet piles, fender piles and soldier piles. It also used
for carrying vertical loads with different soil strengths and
found to be durable in varied environments ranging from sub-
arctic to the desert.
