Where the prestress is transferred — the anchorage in post-tensioning, the bond length in pre-tensioning — the concrete sees intense, locally concentrated forces. IS 1343 requires end-zone (anchorage-zone) reinforcement to resist the bursting and spalling tensile stresses, and an adequate transmission (transfer) length in pre-tensioned members. The end zone is where prestressed members most commonly distress.
Key Requirements
•Post-tension: design anchorage-zone reinforcement for bursting + spalling tensile forces behind the anchorage
•Pre-tension: provide adequate transmission (transfer) length for the prestress to develop by bond (indented wire IS 6003 shortens it)
•Concentrated anchorage force → local bearing + transverse tension — confine and reinforce the end block
•Detail end-zone links/spirals per the anchorage system and IS 1343
•The transfer-strength concrete must be in place before the end zone sees the force (IS 516 cubes)
Practical Notes
✓End-zone bursting cracking is one of the most common prestressed-member defects — it is a detailing problem (under-reinforced anchorage zone), not a global-design one.
✓Pre-tensioned end cracking usually means insufficient transmission length / poor bond — indented wire (IS 6003) or revised detailing helps.
Common Mistakes
⚠Under-reinforcing the anchorage zone for bursting/spalling forces.
⚠Insufficient transmission length in pre-tensioned members (end cracking).