PRESTRESSED CONCRETE STRUCTURES ASSISTANT PROFESSOR(Sr.Gr) BY P.Magudeaswaran ASSISTANT PROFESSOR(Sr.Gr)

EARLIEST EXAMPLES The concept of pre stressing was invented years ago when metal brands were wound around wooden pieces to form barrels. The metal brands were tighten under tensile stress which creates compression between the staves allowing them to resist internal liquid pressure.

INTRODUCTION – THEORY AND BEHAVIOUR UNIT-I INTRODUCTION – THEORY AND BEHAVIOUR What is Prestressed Concrete? Internal stresses of a suitable magnitude and distribution are introduced in steel wires or tendons so that the stresses resulting from external loads are counteracted to a desired degree.

NEED FOR HIGH STRENGTH STEEL AND CONCRETE High loss create the steel in prestressed concrete (1200 to 2000 N/mm2 ),so use high strength steel. High strength concrete is necessary in prestressed concrete,as the material offers high resistance in tension,shear,bond and bearing. It gives small loss of pre stress. It gives less shrinkage ,crack and higher modulus of elasticity. Reduction of cross-sectional dimensions of prestressed concrete structural elements are low compare to Rcc.

TERMINOLOGY TENDON A stretched element used in a concrete member of structure to impart prestress to the concrete. [Example] - high-tensile steel wires, bars cables or strands are used as tendons. ANCHORAGE A device generally used to enable the tendon to impart and maintain prestress in the concrete. The commonly used anchorages are the Freyssinet,Magnel Blaton, Roebling and BBRV systems.

PRE-TENSIONING A method of prestressing concrete in which the tendons are tensioned before the concrete is placed.In this method, the prestress is imparted to concrete by bond between steel and concrete. POST -TENSIONING A method of prestressing concrete by tensioning the tendons against hardened concrete. In this method ,the prestress is imparted to concrete by bearing. BONDED PRESTRESSED CONCRETE Concrete in which the prestress is imparted to concrete through bond between the tendons and surrounding concrete.Pre-tensioned members belong to this group.

NON-BONDED PRESTRESSED CONCRETE A method of construction in which the tendons are not bonded to the surrounding concrete. The tendons may be placed in ducts formed in the concrete members or they may be placed outside the concrete section. CIRCULAR PRESTRESSING When the prestressed members are curved, in the direction of prestressing, the prestressing is called circular prestressing. For example, circumferential prestressing of tanks, silos, pipes and similar structures.

UNIAXIAL,BIAXIAL AND TRIAXIAL PRESTRESSING Uniaxial prestressing When the prestressing tendons are parallel to one axis, it is called Uniaxial Prestressing. For example, longitudinal prestressing of beams. Biaxial Prestressing When there are prestressing tendons parallel to two axes, it is called Biaxial Prestressing.For example, biaxial prestressing of slabs. Triaxial Prestressing When the prestressing tendons are parallel to more than two axes, it is called Multiaxial Prestressing. For example, prestressing of domes

ADVANTAGES Take full advantages of high strength concrete and high strength steel Need less materials Smaller and lighter structure No cracks Better corrosion resistance Good for water tanks and nuclear plant Very effective for deflection control Better shear resistance

APPLICATIONS OF PRESTRESSED CONCRETE Bridges slabs in buildings Water Tanks Concrete pile Thin shell structures Off-shore platform Nuclear power plant