YBT 152-1999 High-Strength Low-Relaxation Prestressed Hot-Dip Galvanized Steel Strand

Standard Overview

YB/T 152-1999 High-strength low-relaxation hot-dip galvanized steel strand for prestressing is a metallurgical industry standard of the People's Republic of China. It was approved on 1999-08-19 by the former National Metallurgical Industry Bureau and implemented on 2000-01-01. The standard is a non-equivalent adoption of the strand part of French standard NF A35-035:1993. It specifies the geometrical dimensions, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certificate of high-strength low-relaxation galvanized prestressing strand.

Scope

The standard applies to low-relaxation prestressing strand composed of seven hot-dip galvanized round wires, with nominal diameters of 12.5 mm and 15.7 mm and strength grades of 1770 MPa or 1860 MPa, used in bridge cables, lifting and fixing tension members, and prestressed structures that are not in direct contact with concrete mortar.

Key Technical Requirements

Definitions

• Seven-wire strand: a strand of seven wires in which six outer wires are tightly helically stranded around one centre wire.
• Hot-dip galvanized: each wire forming the strand passes through a zinc bath.
• Stabilizing: the strand is heated under tension at a certain temperature to reduce creep of the structure and achieve low stress relaxation.

Manufacturing

• Wires are hot-dip galvanized before stranding; the strand must undergo continuous stabilizing treatment after stranding.
• The lay ratio is 12–16 times the nominal strand diameter; the finished strand must not unravel after cutting.
• Free-lay straightness: camber per metre not greater than 25 mm.

Mechanical Properties

• Maximum load, yield load and elongation comply with the strength-grade tables for 12.5/12.9 mm and 15.2/15.7 mm strand.
• 1000 h relaxation loss at an initial load of 70% of the nominal breaking load: ≤ 2.5%.
• Elastic modulus is taken as (195 ± 10) GPa unless otherwise specified by the manufacturer (not a delivery condition).

Process Performance

• Skew tensile test: coefficient ≤ 28% for general applications; ≤ 20% for strand used as cables.
• Fatigue test: general strand shall not fracture after 2 million cycles; strand for cables shall not fracture after 2 million cycles at the specified pulsating stress amplitude.

Zinc Coating

• Zinc coating weight: 190–350 g/m² (other values by agreement).
• Adhesion: after 6 turns in the wrapping test, the zinc layer must not flake.
• Uniformity: no bright deposit or orange-red copper adhesion after two 60 s immersions in copper sulphate solution.
• Surface: continuous zinc layer, no local dezincification or exposed steel; minor scratches that do not affect quality are allowed.

Inspection and Packaging

• Batch acceptance: each batch ≤ 100 t of the same grade, specification and process.
• Sampling: dimensions and surface per coil; tensile test 10% of batch (min. 3 coils); relaxation one sample per 200 t; skew tensile test once per 1000 t; fatigue test one sample per 100 t.
• Packaging: coil on a mandrel of not less than 610 mm diameter (unless otherwise agreed), secured with at least 6 straps, with rust-proof paper and polypropylene moisture-proof outer packaging.

Original Document

The full original standard document (Chinese) is available for download:

Download YB/T 152-1999 (PDF)