IS 1343 limits the concrete compressive/tensile stresses at transfer (initial prestress, low concrete strength) and at service (after losses, full load), and classifies prestressed members into Type 1 (no tensile stress allowed), Type 2 (tension permitted but no cracking) and Type 3 (cracking permitted with controlled crack width). The member type drives the whole serviceability design — it is chosen first.
Key Requirements
•Check stresses at BOTH stages: at transfer (high prestress, immature concrete) and at service (after all losses, full load)
•Type 1 — no tensile stress (e.g. liquid-retaining, fully-prestressed); Type 2 — tension allowed, no cracking; Type 3 — cracked, crack width limited
•Tendon stress at jacking and after losses limited to a fraction of the characteristic tensile strength
•Transfer-stage concrete strength must be reached before stressing (verify cubes, IS 516)
•Member type fixed early — it governs allowable tension, durability and the serviceability checks
Reference Tables
Prestressed member types (IS 1343)
Type
Tension at service
Typical use
Type 1
No tensile stress
Liquid-retaining, fully-prestressed critical members
Type 2
Tension allowed, NO cracking
Most building/bridge prestressed members
Type 3
Cracking allowed, crack width limited
Partial prestressing, where some cracking is acceptable
Confirm stress limits and crack-width values against the current BIS edition and the exposure condition.
Practical Notes
✓Stresses are most critical at transfer, not service — immature concrete under near-maximum prestress; many problems are transfer-stage, not in-service.
✓Choose the member type from the exposure/serviceability need first — it dictates allowable tension and the rest of the design.
Common Mistakes
⚠Checking only the service stage and missing the critical transfer-stage stresses.
⚠Stressing before the concrete reaches the specified transfer strength.
⚠Designing to Type 3 (cracked) where the exposure/durability needs Type 1/2.