Limit States — Deflection, Crack Width & Durability
IS 1343 is limit-state: ultimate-limit-state flexure and shear capacity, and serviceability-limit-state deflection and cracking. Prestressed deflection includes the upward camber from prestress and long-term creep — net deflection can reverse over time. Crack width is limited per the member type (Type 1/2/3) and the exposure, with durability cover protecting the highly stress-sensitive tendon from corrosion.
Key Requirements
•Ultimate limit state: flexural and shear capacity with partial safety factors
•Serviceability: deflection including prestress camber and long-term creep (net deflection can reverse with time)
•Crack width limited per member Type (1/2/3) and exposure (Type 1 = none)
•Durability cover sized for the exposure — tendon corrosion is catastrophic (notch-sensitive at working stress)
•Grouting of bonded post-tensioned ducts (IS 8543) is the tendon's corrosion protection — not optional
Practical Notes
✓Prestressed deflection is two-sided: initial upward camber, then long-term creep can swing it down — check the net at the relevant time, not just initial.
✓Tendon durability is existential: a corroding high-stress tendon fails suddenly — cover + full grouting (IS 8543) are non-negotiable, not finishing items.
Common Mistakes
⚠Checking initial camber but not long-term (creep) net deflection.
⚠Crack-width limit not matched to the member type/exposure.
⚠Treating tendon cover/grouting as secondary (it is the corrosion defence).