7-Strand Low-Relaxation Prestressed Steel Strand: A High-Performance Solution for Modern Infrastructure
Engineered for durability, precision, and long-term structural integrity, 7-strand low-relaxation prestressed steel strand is a critical component in advanced construction systems worldwide. This specialized high-tensile steel product consists of seven individual wires—six outer wires spirally twisted around one central wire—to form a compact, hexagonal geometry that ensures optimal load distribution and mechanical stability. Its unique stress-relaxation behavior, defined by minimal loss under sustained tension (≤2.5% after 1000 hours at 70% of nominal strength), makes it ideal for applications where consistent prestress maintenance over decades is essential.
Manufactured to meet international standards such as ASTM A416 and EN 10138, this strand offers tensile strengths ranging from 1720 MPa to 2230 MPa, with yield strengths exceeding 1500 MPa and elongation at break greater than 3.5%. Available in diameters between 12.7 mm and 17.8 mm—with 15.2 mm being the most commonly used—the material provides flexibility across various engineering needs. The combination of high breaking force (~260 kN per 15.2 mm strand) and ductility allows it to withstand dynamic loads without brittle failure, making it particularly valuable in seismic zones or heavy-load environments.
Key advantages include exceptional stress retention over time, reducing the need for repeated tensioning and lowering lifecycle costs; ease of handling due to coil-based transportation; compatibility with standardized anchoring systems like M15 clip anchors; and enhanced corrosion resistance when coated with galvanized zinc-aluminum alloy layers—an important feature for marine, coastal, and humid climates. These properties position the strand as a preferred choice for projects demanding both performance and longevity.
Applications span multiple sectors including bridge construction (e.g., box girders in urban viaducts, cable-stayed bridges, and suspension bridge main cables), high-rise buildings (unbonded slabs in transfer floors), geotechnical engineering (deep excavation anchorages and slope stabilization), and infrastructure resilience (tunnel linings, dam reinforcement, nuclear containment structures). Real-world implementations such as Hangzhou Bay Cross-Sea Bridge and Shenzhen Ping An Financial Center demonstrate how these strands reduce concrete volume by up to 30%, improve crack resistance, and enhance overall structural efficiency.
Users consistently highlight its reliability in extreme conditions—from offshore wind foundations to pressure vessels in nuclear facilities—where even minor relaxation can compromise safety. Engineers appreciate the ability to control initial tension effectively through super-tensioning techniques (typically 80% of ultimate strength), which compensates for early relaxation effects while ensuring long-term performance consistency.
When selecting the appropriate strand, engineers must consider load requirements, environmental exposure, and anchorage compatibility. For example, larger diameters (17.8 mm) suit ultra-heavy-duty scenarios like highway overpasses or industrial crane beams, while smaller sizes (12.7 mm) may be sufficient for residential precast elements. Anti-corrosion treatments are strongly recommended in aggressive environments, especially near saltwater or chemical exposure areas.
Frequently asked questions often revolve around installation best practices, such as proper tensioning sequences, the importance of surface preparation before anchoring, and how temperature variations affect prestress values. While some confusion exists regarding the difference between bonded and unbonded tendons, modern low-relaxation strands perform reliably in both configurations, offering versatility for design teams seeking optimized solutions.
As global infrastructure continues to evolve toward smarter, safer, and more sustainable models, 7-strand low-relaxation prestressed steel strand remains a cornerstone technology—proving indispensable in projects where structural integrity, minimal maintenance, and future-proof performance define success.
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