Pre stressed steel strands are stranded steel cables composed of 2, 3, 7, or 19 high-strength steel wires, which have undergone stress relief treatment (stabilization treatment) and are suitable for prestressed concrete or similar purposes. The main characteristics of prestressed steel strands are high strength and good relaxation performance, and they are also relatively straight when unfolded. The common tensile strength grades are 1860 megapascals, as well as strength grades such as 1720, 1770, 1960, 2000, and 2100 megapascals. This type of steel also has a high yield strength. Today, the manufacturer of prestressed steel strand equipment will talk to you about its classification and specifications.
classification
According to the number of steel wires in a steel strand, it is divided into 2 wire steel strand, 3 wire steel strand, 7 wire steel strand, and 19 wire steel strand.
According to surface morphology, it can be divided into smooth steel strands, scored steel strands, die drawn steel strands (compact), epoxy resin coated steel strands, etc.
It can also be classified according to diameter, strength level, or standard.
specifications
In the instructions and checklist, we often see that there are 15-7 Φ 5. 12-7 Φ 5. 9-7 Φ Pre stressing steel strands of grade 5 specifications. By 15-7 Φ For example, 5 represents a single steel wire with a diameter of 5.0mm, and 7 Φ 5 represents 7 such steel wires forming a steel strand, while 15 represents each bundle of steel strands consisting of 15 wires Φ The overall meaning of 5 steel strands is "a bundle of steel strands composed of 7 steel wires with a diameter of 5mm (each bundle has a total diameter of approximately 15.24mm, with a size deviation of+0.40-0.20; each steel wire has a diameter of approximately 5.0mm).". The general cross-sectional area is calculated as 140mm ^ 2, and the theoretical fracture value is 140 * 1860=260.4kN. According to the standard of 60% -65% prestress, it can withstand a tensile force of 156.24-169.26kN.
material
High carbon steel wire rods are used, which are cold drawn into steel wires after surface treatment. Then, a certain number of steel wires are twisted into strands according to the steel strand structure, and then stabilized through stress relief treatment. To extend durability, steel wires can have metallic or non-metallic coatings or coatings, such as zinc plating, epoxy resin coating, etc. To increase the adhesion with concrete, there may be scratches on the surface. The pre-stressed steel strand pulled by the mold undergoes a mold compression process after being twisted, making the structure more compact and the surface more suitable for anchor gripping. The production of unbonded steel strand uses ordinary prestressed steel strand, coated with anti-corrosion grease or paraffin, and then wrapped with high-density polyethylene (HDPE).
application
In most post tensioned and pre tensioned prestressed engineering projects, smooth steel strands are the most widely used prestressed steel. Molded steel strands are mainly used for lifting engineering, as well as for nuclear power and other projects. Galvanized steel strands are commonly used in bridge tie rods, cables, and external prestressing projects. The use of epoxy resin coated steel strands is similar to that of galvanized prestressed steel strands.
Various countries have standards for prestressed steel strands, such as the Chinese standard GB/T 5224, the American standard ASTM A416, the British standard BS 5896, the Japanese standard JIS G3536, the Australian and New Zealand standard AS/NZS 4672, and the Brazilian standard NBR-7483. If you want to know more related content, you can consult with prestressed steel strand equipment manufacturers.