PRE-STRESSED CONCRETE, MATERIALS

In This Article We Covers,

  1. What Is Pre Stress Concrete
  2. Principle Of Pre Stress Concrete
  3. Materials Required For Pre Stress Concrete
  4. Advantages Of Pre Stress Concrete
  5. Limitations Of Pre Stress Concrete

WHAT IS PRE-STRESS CONCRETE

  • Concrete is very strong in compression but very weak in tension, therefore concrete is reinforced with steel bars in such direction where tensile resistance has to be offered called reinforced concrete members.
  • In, RCC the member due to low tensile resistance of concrete, a large quantity of steel reinforced is provided so that  the entire tensile resistance is taken as offered by reinforcement.
  • But there are limitations of RCC
  • Under superimposed load, the concrete present in tension zone of a RCC member develops cracks not being able to conform to the stain taking place in steel.
  • The cross section of member designed by using diagonal tensile stresses.
  • In case of long beams, beam size have got be large to carry shear.
  • In absence of loads, the RCC members develop cracks due shrinkage and hardening.
  • To overcome these limitations a very important aspect born in mind is the PRE-STRESSED CONCRETE MEMBER
  • A pre-stressed concrete member of concrete in which internal stresses are introduced in a planned manner so that stresses resulting form the superimposed load are resist up to desired limits.    

PRINCIPLE OF PRE-STRESSING

  • The basic principle of pre-stressing is to produce sufficient compressive stresses in all those parts of concrete where tensile stresses would occurs due to external loading.[dead load & live load]
  • If the induced compressive stresses are grater in magnitude than the tensile stresses developed due to external loading then the concrete is capable to carry the external load.
  • Hence size of pre-stressed concrete member required is very small and thus there will be considerable saving in volume of concrete required.

MATERIALS

  • To design any structure it is necessary to have knowledge of the physical properties of materials. The pre-stressed concrete required knowledge of steel as well as concrete .
  • PSC required both high tensile steel and high strength concrete.

HIGH STRENGTH CONCRETE :-

  • High strength concrete is having low shrinkage and creep value,
  • It has high modulus of elasticity leading  to smaller elastic strain.
  • High impermeability & more ductility.
  • High strength concrete permits higher bond between steel and concrete.
  • To sustain the high stresses at anchorage regions.
  • To have higher stiffness for reduced deflection.

HIGH STRENGTH STEEL :-

  • large pre-stressing force can be developed on small steel area there force, high tensile strength wires, strands and tendons used in pre-stressing members.
  • When concrete shorten due compressive stress, creep And shrinkage, large amount pre-stress is lost.
  • If high tensile bars used for pre-stressing, permitting a large initial pre-stress, the loss of pre-stress will be a small % of total initial pre-stress.
  • High tensile steel give high bond strength to avoid slippage

ADVANTAGES OF PRE-STRESS CONCRETE

  • Reduction of steel corrosion.
  • Increase in durability in aggressive environment.
  • Full section utilized.
  • Higher moment of inertia.
  • Less deformation.
  • Increase in shear weight.
  • Rapid construction.
  • Reduced maintenance.
  • Reduction of formwork.

LIMITATIONS OF PRE-STRESS CONCRETE

  • The use of high strength material which is costly.
  • Additional cost in auxiliary equipment’s.
  • This technology required skilled labour.
  • There is need for quality control and inspection.

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