IS 1785 (Part 1) : 2000plain hard-drawn steel wire for prestressed concrete, Part 1: Cold-drawn stress-relieved wire

IS 1785 Part 1:2000 is the specification for plain hard-drawn steel wire for prestressed concrete — cold-drawn stress-relieved wire. It is a single-wire prestressing tendon form (used in pre-tensioned precast — railway sleepers, poles, hollow-core, small precast — and in some wire-tendon systems), distinct from multi-wire strand.

It sits in the prestressing stack:

• IS 1343 — prestressed concrete design · IS 1785 Part 2 — *as-drawn* wire (the non-stress-relieved companion)
• IS 6003 — indented PSC wire · IS 14268 — 7-ply strand · IS 10790 Part 1 — sampling

Hard-drawn prestressing wire comes in two conditions, and IS 1785 Part 1 covers the stress-relieved one — which matters:

• Cold-drawn then stress-relieved — the stress-relief heat treatment improves relaxation behaviour, ductility and the stress-strain characteristics, giving the predictable, lower-relaxation performance prestressed design needs
• As-drawn wire (Part 2) is *not* stress-relieved — higher relaxation, different behaviour; the two parts are not interchangeable, and the design (IS 1343) assumes a specific condition
• Controlled breaking load, proof stress, elongation, relaxation — the design relies on all

The engineering point: the wire condition (Part 1 stress-relieved vs Part 2 as-drawn) is a structural selection, not a procurement detail — using as-drawn where stress-relieved was designed gives higher relaxation loss and a different stress-strain response than the IS 1343 calculation assumed. Single-wire tendons are also acutely notch- and corrosion-sensitive at their working stress.

Scenario: prestressing wire for pre-tensioned precast (sleepers/poles/hollow-core) designed to IS 1343.

Step 1 — design basis: the IS 1343 loss/strength calc assumes a specific wire condition and relaxation — typically stress-relieved (IS 1785 Part 1).

Step 2 — specify Part 1 (stress-relieved): correct diameter/grade, breaking load, proof stress, elongation, relaxation class — *not* Part 2 as-drawn.

Step 3 — verify by test: sample per IS 10790 Part 1; mechanical tests — not coil-tag acceptance.

Step 4 — handle: protect from nicks/corrosion; control bond surface for pre-tensioning transfer.

Step 5 — accept per IS 1343.

Stress-relieved wire to the design's assumed condition delivers predictable, low-relaxation prestress; substituting as-drawn wire changes relaxation and stress-strain behaviour the design did not allow for.

1. Substituting Part 2 (as-drawn) for Part 1 (stress-relieved). Different relaxation and stress-strain behaviour — not interchangeable; the design assumes one.

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

3. Nicks/corrosion. Acutely notch- and corrosion-sensitive at working stress — surface damage causes premature failure.

4. Ignoring relaxation in loss calc. A defined IS 1343 input — wrong condition/class → wrong effective prestress.

5. Bond-surface neglect (pre-tensioning). Transfer relies on the wire surface — contamination/incorrect surface impairs transfer.

• IS 1343 — prestressed concrete design · IS 1785 Part 2 — as-drawn PSC wire (non-interchangeable companion)
• IS 6003 — indented PSC wire · IS 14268 — 7-ply strand · IS 6006 — stress-relieved strand
• IS 10790 Part 1 — sampling of prestressing steel · IS 1608 Part 1 — tensile test · IS 456 — concrete

IS 1785 Part 1 is reaffirmed and is the stress-relieved plain hard-drawn PSC wire — the structurally well-behaved single-wire tendon for pre-tensioned precast. The defining practitioner point is the Part 1 vs Part 2 condition distinction: stress-relieving improves relaxation, ductility and the stress-strain curve, so Part 1 (stress-relieved) and Part 2 (as-drawn) are not interchangeable, and the IS 1343 design assumes a specific condition — substituting the wrong one changes prestress loss and behaviour invisibly. As with all prestressing steel: never accept on coil tags (sample/test per IS 10790 Part 1), and protect it absolutely from nicks and corrosion, to which it is acutely sensitive at its working stress. Specify the condition the design assumed, verify it, and handle it as the high-stress critical material it is.