IS Specifications for prestressed concrete

edited by Editorial Team | ,

The code of practice for prestressed concrete is IS:1343-1980. In this post some of the very important specifications which one should keep in mind before going for design of prestressed concrete is discussed.

Minimum cover to prestressed steel

  • Pre-tensioned members – 20 mm
  • Post-tensioned members – 30 mm or dia of cable whichever is bigger.
  • For an aggressive environment, the above values should be inc. by 10 mm.

Spacing of cables or bars

  • In the case of single wires for pretension system
    • < 3 times dia. of wire
    • < 1.5 times the max. size of aggregate
  • In the case of cables or large bars
    • < 40 mm
    • < max. size of cable or bar
    • < 5 mm plus the max. size of aggregate

Breaking of wires

  • During tensioning it should not exceed 2.5 % of total wires.
  • After tensioning it should not be condoned without special investigations.

Grouting

  • Cement paste should be used for grouting with a water-cement ratio of 0.5.
  • For large ducts, cement mortar with fine sand passing 150 micro m, IS sieve can be used.
  • Compressive strength of 100 mm cubes of the grout shall not be less than 17 MPa at 7 days.
  • The grouting pressure should not be less than 0.7 MPs.

Minimum reinforcement

  • Longitudinal reinforcement – 0.2 % Ag for mild steel and 0.15 % Ag for HYSD steel.
  • Members with dynamic loadings – 0.3 % Ag not greater than 0.2 % Ag.
  • Without dynamic loadings – Not greater than 0.1 % Ag.

Side face reinforcement

When the depth of the web exceeds 500 mm, longitudinal reinforcement 0.1 % area of the web should be provided and distributed equally on each face of the web with spacing not exceed 200 mm.

Deflection

Total deflections should not exceed span/250.

  • Deflections after erection of partitions not exceed span / 350 or 20 mm.
  • If finishes are present , the upward deflection should not exceed span/300.

Check this post to know more about prestress concrete.

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