1. Basic Concepts
15.24 galvanized
Prestressed Steel strand is a commonly used core component in prestressed concrete structures. Its nominal diameter is 15.24mm (about 0.6 inches). It is made of multiple high-strength steel wires twisted together, and the outer layer is hot-dip galvanized to enhance corrosion resistance. This specification is one of the most widely used types of steel strands in civil engineering, especially suitable for large-span, high-load structural scenes.
2. Structure and material properties
Structural composition
The typical structure is 7-wire twisting: 1 steel wire in the center and 6 steel wires on the periphery are wound in the left (or right) direction, with a twist pitch of 12-16 times the diameter to form a stable spiral structure.
The cross-sectional area of a steel strand with a nominal diameter of 15.24mm is about 140mm², and the specific parameters must comply with domestic and international standards such as GB/T 5224 and ASTM A416.
Material and process
Steel wire material: 82B high carbon steel (carbon content about 0.8%), cold drawing strengthening and low temperature tempering treatment, tensile strength is usually 1860MPa, elongation ≥3.5%.
Galvanizing process: hot-dip galvanizing (Hot-Dip Galvanizing), zinc layer thickness ≥85μm (according to ISO 1461 standard), can form electrochemical protection in humid, salt spray and other environments, delaying steel corrosion.
3. Main performance indicators
Item Typical parameters Standard requirements
Nominal diameter 15.24mm Allowable deviation ±0.2mm
Cross-sectional area 139-140mm² ——
Tensile strength ≥1860MPa GB/T 5224 stipulates ≥1860MPa
Breaking tensile force ≥260kN (1860MPa grade) ——
Zinc layer weight ≥300g/m² (double-sided) ASTM A416 requires ≥183g/m²
Stress relaxation rate 1000 hours relaxation rate ≤2.5% (initial stress 70% nominal strength) GB/T 5224 requires ≤3.5%
Elastic modulus (1.95-2.05)×10⁵MPa ——
4. Key links in production process
Steel wire preparation: High carbon steel billet is hot rolled → cold drawn (multiple passes) → tempered (to eliminate internal stress) to form a diameter of about 5mm
Twisting: 7 steel wires are twisted at a specific angle on the stranding machine to ensure a tight structure and avoid looseness.
Galvanizing: The steel strand is immersed in molten zinc at 450-480℃ to form a composite structure of Fe-Zn alloy layer and pure zinc layer. The thickness uniformity needs to be verified by copper sulfate test (≥6 times without red rust).
Relaxation optimization: The finished product is treated with constant temperature tensioning (such as 100℃×24 hours) to reduce the stress relaxation under long-term load.
15.24 Practical application of galvanized prestressed steel strand
I. Construction engineering field
Large bridge construction
Prestressed concrete beam: used for the main beam of cross-river bridges and highway bridges (such as T beams and box beams), which offsets the tensile stress generated by the load by tensioning the steel strand to reduce cracks.
Cable-stayed bridges and suspension bridges: as the core material of the cable or hanger (such as PE sheath + galvanized layer for double corrosion protection), it bears the bridge deck load.
High-rise buildings and large-span structures
Unbonded prestressed floor slabs: In large-span buildings such as commercial complexes and gymnasiums, the cross-sectional dimensions of beams and columns are reduced to improve space utilization.
Roofs and trusses: Prestressed steel trusses such as airport terminals and convention centers achieve large-span column-free spaces through steel strand tensioning.
Foundation engineering
Pile foundations and anchor cables: Prestressed pipe piles (PHC piles) in pile foundations of high-rise buildings, and anchor cables in deep foundation pit support (such as multi-strand anchor cables composed of 15.24mm diameter steel strands).
2. Water conservancy and energy engineering
Water conservancy hubs
Dam reinforcement: Arrange steel strands in the concrete dam body to improve impermeability and crack resistance, such as prestressed anchoring of the dam body of a reservoir dam.
Sluices and ship locks: Prestressed components of the gate panel bear water pressure loads.
Energy engineering
Nuclear power plant containment: Steel strands are used in prestressed concrete containment to resist internal pressure and external impact.
Wind power foundation: The annular prestressed steel strands of the offshore wind power tower foundation withstand strong wind loads and wave impacts.
3. Transportation and municipal engineering
Railway engineering
Ballastless track slab: In the prestressed concrete slab of the high-speed railway ballastless track, the steel strands are used to control the cracks in the slab body and ensure the smoothness of the track.
Railway bridges: For example, the simply supported beams and continuous beams of the passenger-dedicated bridge use 15.24mm steel strands as prestressed tendons.
Municipal facilities
Integrated pipe gallery: Prestressed construction of the top slab of the large-span pipe gallery reduces the amount of concrete and improves seismic performance.
Sewage treatment pool: Circumferential prestressing of the circular pool (such as wrapping the pool wall with steel strands) to prevent cracking caused by water pressure.
4. Special engineering scenarios
Marine engineering
Offshore platform foundation: The prestressed steel strands of the oil platform and the abutment of the cross-sea bridge need to be equipped with double-layer anti-corrosion (galvanized + epoxy coating) to resist seawater erosion.
Breakwater: Prestressed tendons in concrete breakwater components enhance the ability to resist wave impact.
Mines and slope management
Deep foundation pit support: Anchor cable support in mine shaft excavation (such as anchor cable groups composed of multiple bundles of 15.24mm steel strands) stabilizes the slope soil.
Tailings dam reinforcement: Fix the dam body with prestressed anchor cables to prevent landslides.
Application advantages and technical points
1. Core advantages
High bearing capacity and economy: The breaking tensile force is more than 260kN, which is suitable for large load scenarios and can reduce the amount of concrete by 30%-50% compared with ordinary steel bars.
Strong durability: The service life of the galvanized layer in a neutral environment can reach more than 50 years, and it can be used in a highly corrosive environment (such as coastal areas) with a PE sheath.
Construction flexibility: It can be cut into any length according to design requirements, and precise tensioning can be achieved through anchors (such as clip-type anchors), with high construction efficiency.
2. Precautions
Anti-corrosion details
When storing, it needs to be suspended to prevent moisture and avoid contact between the zinc layer and acidic substances; it should be covered with canvas during transportation to prevent mechanical damage.
After tensioning, the exposed part of the anchor needs to be sealed with concrete or coated with anti-corrosion grease to prevent rust.
Construction specifications
The tensioning control stress must be 60%-75% of the nominal strength, and over-tensioning is strictly prohibited; the double control method (stress control + elongation verification) is adopted, and the error is ≤±6%.
When multiple steel strands are tensioned at the same time, it is necessary to ensure uniform force to avoid eccentric tension and breakage.
Environmental adaptability
In industrial pollution areas and salt spray environments, it is recommended to use "galvanizing + epoxy coating" composite anti-corrosion; in freeze-thaw areas, the low-temperature toughness of the steel strand needs to be verified.
Summary
15.24 Galvanized prestressed steel strands have become an indispensable core material in modern civil engineering due to their high strength, corrosion resistance and ease of construction, especially in large-span, high-load and harsh environment projects. It plays a key role. Its applications cover bridges, buildings, water conservancy, energy and other fields, and have promoted technological breakthroughs in complex projects such as super-high-rise buildings, cross-sea and cross-river projects. In actual applications, it is necessary to strictly control material standards, anti-corrosion processes and tensioning construction in combination with project requirements to ensure structural safety and long-term durability.15.24MM
Galvanized PC Steel Strand
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