IS 6006 : 1983uncoated stress-relieved strand for prestressed concrete

IS 6006:1983 is the specification for uncoated stress-relieved strand for prestressed concrete — multi-wire prestressing strand (the broader stress-relieved strand family that the low-relaxation 7-ply IS 14268 refined). It is a tendon-material spec for pre-tensioned/post-tensioned PSC.

It sits in the prestressing stack:

• IS 1343 — prestressed concrete design · IS 8543 — bonded post-tensioning construction
• IS 14268 — *low-relaxation* 7-ply strand (the modern preferred form) · IS 1785 Part 1 — PSC wire · IS 10790 Part 1 — sampling

Like all prestressing tendons, IS 6006 strand is controlled on the properties the IS 1343 design depends on:

• Specified breaking load, 0.2% proof stress, elongation/ductility and stress-strain behaviour — the design uses all of these
• Stress-relieved condition for force/dimensional stability
• Relaxation class — this is the key selection point: modern PSC overwhelmingly specifies low-relaxation strand (IS 14268) because it loses far less prestress over time; ordinary stress-relieved (normal-relaxation) strand has higher relaxation loss that *must* be matched to the IS 1343 loss assumption

The engineering point: the relaxation class must match the design loss calculation. The recurring, serious error is treating 'stress-relieved strand' as interchangeable with 'low-relaxation strand' — if the design (IS 1343) assumed low-relaxation losses and normal-relaxation strand is supplied, the long-term effective prestress is below design. For new work the low-relaxation IS 14268 strand is the standard choice; this spec must be read against the design's relaxation assumption.

Scenario: prestressing strand for a PSC member designed to IS 1343.

Step 1 — read the design loss basis: what relaxation class did the IS 1343 loss calculation assume? (Modern design → low-relaxation, IS 14268.)

Step 2 — specify the matching strand: strand whose relaxation class matches that assumption — do not substitute normal-relaxation for low-relaxation.

Step 3 — verify by test: sample per IS 10790 Part 1; breaking load, proof stress, elongation (relaxation as required) — not coil-tag acceptance.

Step 4 — protect & stress: corrosion/nick protection; stress and grout per IS 8543 with elongation reconciliation.

Step 5 — accept per IS 1343/IS 8543.

The non-negotiable: the supplied strand's relaxation class must equal the design's — anything else under-prestresses the structure.

1. Treating stress-relieved as equivalent to low-relaxation. Different relaxation losses — if the design assumed low-relaxation (IS 14268), normal-relaxation strand under-prestresses it.

2. Coil-tag acceptance. Prestressing steel must be sampled/tested per IS 10790 Part 1.

3. Nicked/corroded strand. Notch- and corrosion-sensitive at working stress — surface damage causes premature failure.

4. Relaxation class absent from the loss calc. Wrong class → wrong effective prestress.

5. Specifying an outdated form for new work. Modern PSC standard is low-relaxation IS 14268; read this spec against the design assumption.

• IS 14268 — low-relaxation 7-ply strand (modern preferred) · IS 1343 — PSC design
• IS 8543 — bonded post-tensioning construction · IS 1785 Part 1 — plain hard-drawn PSC wire · IS 6003 — indented PSC wire
• IS 10790 Part 1 — sampling of prestressing steel · IS 1608 Part 1 — tensile test · IS 456 — concrete

IS 6006 is reaffirmed and is the broader stress-relieved-strand spec that the low-relaxation 7-ply IS 14268 strand refined and largely superseded for modern PSC. The decisive practitioner point is identical: a prestressed structure depends on the prestress it retains, relaxation is the strand-property part of long-term loss, and the supplied strand's relaxation class must match the IS 1343 design assumption. The classic, costly error is treating 'stress-relieved strand' as interchangeable with 'low-relaxation strand' — supply the wrong class and the structure is quietly under-prestressed. As with all prestressing steel: never accept on coil tags (sample/test per IS 10790 Part 1), protect it absolutely from nicks and corrosion, and for new work default to low-relaxation IS 14268 read against the design's loss basis.