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When a project calls for maximum prestressing force in a single strand, engineers and contractors often turn to 15.7mm PC strand. As one of the largest common diameters of prestressing steel strand, it is selected for applications where structural demands exceed what smaller strands like 12.7mm or 15.2mm can efficiently deliver — long-span bridges, heavy precast beams, and major infrastructure works. Because prestressed concrete performance depends heavily on the strand used, choosing the correct specification and grade is not a minor detail; it directly affects load capacity, durability, and long-term structural safety.
This guide explains what 15.7mm PC strand is, how it performs, and how to select the right product for your project.
PC strand (prestressing concrete strand) is a high-strength steel product made by twisting seven individual wires together — one straight center wire surrounded by six helically wound outer wires. This seven-wire construction gives the strand its characteristic strength, flexibility, and resistance to fatigue under repeated loading. The "15.7mm" designation refers to the strand's nominal diameter, measured across the outer wires.
Unlike conventional reinforcing steel (rebar), which is embedded passively in concrete to resist tension after cracking occurs, PC strand is actively tensioned before or after the concrete is cast. This process — prestressing — puts the strand under tension and the surrounding concrete under compression, allowing the finished structural member to carry far greater loads, span longer distances, and resist cracking more effectively than conventionally reinforced concrete of the same size. Because 15.7mm strand has a larger steel cross-section than smaller diameters, it can transfer a higher prestressing force per strand, which is why it is favored for heavy-duty or large-span structural elements.
The table below summarizes the typical specifications associated with 15.7mm PC strand. Actual figures vary depending on the applicable standard, steel grade, and manufacturer, so buyers should always confirm exact values against the relevant certification for their project.
Specification | Details |
Nominal Diameter | 15.7mm |
Structure | 7-wire strand (1 center wire + 6 outer wires) |
Typical Tensile Strength | 1770–1860 MPa, depending on specification and grade |
Surface | Plain or coated (e.g., epoxy-coated) options available |
Relaxation | Low relaxation option available |
Standards | ASTM A416 / EN 10138 / GB/T 5224 |
Application | Bridges, beams, precast concrete, infrastructure |
It's important not to treat any single breaking-load figure as universal for 15.7mm strand. The actual breaking load depends on the nominal steel area, the tensile strength grade specified, and the standard the strand is manufactured and certified against. Manufacturers such as TJ Wasungen typically offer 15.7mm PC strand across multiple grades and specifications, so buyers should request the specific datasheet or mill test certificate for the exact product being ordered.
The performance of PC strand in a structural application is determined by several interrelated mechanical properties:
Tensile strength — the stress the strand can withstand before failure, typically expressed in MPa. This is the primary strength grade classification (e.g., 1770 MPa or 1860 MPa).
Breaking load — the actual force (in kN) the strand can resist before breaking, calculated from tensile strength multiplied by the nominal steel cross-sectional area.
Nominal cross-sectional area — the effective steel area of the strand, which increases with diameter and directly affects load-carrying capacity.
Elongation — the strand's ability to stretch under load before fracture, an important indicator of ductility and safety margin.
Relaxation — the gradual loss of tension in the strand over time under sustained load; low-relaxation strand is designed to minimize this loss and is now the standard choice for most prestressed applications.
Modulus of elasticity — describes the strand's stiffness, which engineers use to calculate elongation during stressing operations and predict prestress losses.
These properties matter because prestressed concrete design depends on precise, predictable behavior of the strand under load. A strand's diameter determines its steel area, the steel area combined with the tensile grade determines its breaking load, and all of these factors together determine how much prestressing force can be applied to a given structural member. Larger diameters like 15.7mm allow designers to achieve higher prestressing forces with fewer strands, which can simplify anchorage layout in some designs — though this must always be balanced against duct sizing, anchorage compatibility, and spacing requirements.
Choosing between common PC strand diameters depends on the specific demands of the structure being built. The comparison below highlights the general differences:
Feature | 12.7mm | 15.2mm | 15.7mm |
Diameter | |||
Typical Use | Slabs, beams, precast | Bridges, beams, infrastructure | Heavy-duty prestressing |
Steel Area | Lower | Medium | Higher |
Load Capacity | Lower | Higher | Higher |
Handling | Easier | Moderate | Requires appropriate equipment |
While 15.7mm strand offers the highest load capacity of the three, the largest diameter is not automatically the correct choice for every project. Engineers should select strand size based on the specific design loads involved, compatibility with the anchorage system being used, strand spacing within ducts, and the standard specified for the project. In many cases, 12.7mm or 15.2mm strand remains the more practical and economical choice; 15.7mm is generally reserved for applications where higher prestressing force per strand provides a genuine structural or design advantage.
Prestressed bridge girders often require substantial tensioning force to span long distances while controlling deflection and cracking. 15.7mm strand's higher load capacity per strand can be advantageous in these heavy-duty girder and box-girder applications, particularly where anchorage and duct design accommodate the larger diameter.
Precast structural beams manufactured for industrial buildings, warehouses, and commercial structures frequently use higher-capacity strand to achieve longer spans with fewer supporting columns.
Precast concrete elements used in rail infrastructure are subject to repeated dynamic loading, making the fatigue resistance and strength of larger-diameter strand a relevant consideration in certain sleeper and track-support designs.
Structures requiring long, unsupported spans — such as stadium roofs, large industrial floors, or multi-span bridges — often rely on higher prestressing forces, where 15.7mm strand can help reduce the total number of strands needed.
Highways, large precast components, piles, and poles are among the broader infrastructure applications where higher-capacity PC strand is commonly specified. TJ Wasungen's PC strand product range identifies bridges, beams, slabs, sleepers, piles, and poles as typical applications across its strand offerings.
Plain 15.7mm PC Strand Plain strand has a standard, uncoated steel surface. It is well suited to controlled environments and applications relying on direct bonding between the strand and surrounding concrete, where corrosion exposure is limited and managed through proper concrete cover and detailing.
Epoxy-Coated 15.7mm PC Strand Epoxy-coated strand adds a protective layer that improves resistance to corrosion, making it a suitable option for aggressive environments such as marine structures, de-icing salt exposure, or other conditions where long-term durability is a priority. TJ Wasungen lists 15.7mm epoxy-coated PC strand as a product option specifically for heavy-duty prestressing applications where both higher load capacity and enhanced corrosion protection are required.
PC strand is manufactured and certified against several major international standards, and the applicable standard should be determined by the project's location and specification requirements — not treated as interchangeable:
ASTM A416 — the primary US standard for uncoated seven-wire strand used in prestressed concrete, defining tensile strength grades, dimensional tolerances, and relaxation classes.
EN 10138 — the European standard covering prestressing steels, including wire, strand, and bar, with its own strength classifications and testing requirements.
GB/T 5224 — the Chinese national standard for steel strand for prestressed concrete, widely used in strand manufactured for the Chinese domestic market and export.
Each standard defines its own requirements for tensile strength, dimensions, mechanical properties, relaxation behavior, and quality documentation. Buyers should specify the exact standard required by their project or destination market when ordering, and confirm that the mill test certificate provided matches that standard.
Before placing an order, buyers and procurement teams should confirm the following:
Required nominal diameter
Tensile strength grade
Whether low-relaxation strand is required
Plain or coated surface finish
Compatibility with the anchorage system specified for the project
Required breaking load per strand
Environmental conditions the strand will be exposed to
Applicable standard (ASTM A416, EN 10138, GB/T 5224, or another regional standard)
Availability of a mill test certificate
Required quantity and coil or packing specifications for transport
Reputable manufacturers verify PC strand quality through a series of standardized tests, including:
Tensile test — confirms the strand meets its rated tensile strength grade
Breaking load test — verifies actual failure load against specification
Elongation test — measures ductility and deformation capacity before failure
Relaxation test — checks tension loss over time under sustained load
Diameter and dimensional inspection — confirms the strand meets tolerance requirements
Surface inspection — checks for defects, rust, or coating consistency
Chemical and material verification — confirms the steel composition matches specification
Mill Test Certificate (MTC) — documents all test results for traceability and project compliance
Producing 15.7mm PC strand involves several controlled stages:
High-carbon steel wire preparation — selecting and preparing raw wire rod as the base material
Wire drawing — reducing wire diameter progressively to the required specification while increasing tensile strength
Stranding into seven wires — twisting one center wire with six outer wires into the finished strand geometry
Stabilization / heat treatment — a controlled thermal process that sets the strand's low-relaxation properties and mechanical performance
Surface treatment — applying coatings such as epoxy where corrosion protection is specified
Mechanical testing — verifying tensile strength, elongation, and relaxation against the applicable standard
Coil formation — winding the finished strand into coils for handling and transport
Export packaging — preparing coils for shipment with appropriate protective packing
TJ Wasungen's manufacturing process follows these core stages — wire drawing, seven-wire stranding, stabilization, and quality testing — to produce PC strand suited to demanding structural applications.
Sourcing directly from a manufacturer, rather than a reseller, offers practical advantages for contractors, engineers, and procurement teams:
Consistent specifications across production batches
Bulk production capacity for large infrastructure projects
In-house quality control and testing
Mill test certificates provided with shipments
Export-ready packaging suited to international shipment
Ability to accommodate custom requirements (grade, coating, coil size)
Technical support for specification and standard selection
Direct factory communication without intermediary delays
TJ Wasungen manufactures 15.7mm PC strand alongside other common diameters, offering both plain and epoxy-coated options across the standards commonly required for bridge, precast, and infrastructure projects.
What is 15.7mm PC strand?
It is a seven-wire, high-strength steel strand with a nominal diameter of 15.7mm, used to prestress concrete structures for greater load capacity and crack resistance.
What is 15.7mm PC strand used for?
It is commonly used in bridges, precast concrete beams, railway sleepers, large-span structures, and heavy-duty infrastructure projects that require higher prestressing force.
How strong is 15.7mm PC strand?
Typical tensile strength ranges from 1770 to 1860 MPa, depending on the specification and grade selected.
What is the breaking load of 15.7mm PC strand?
Breaking load depends on the nominal steel area and tensile grade specified, so it varies by standard and product; buyers should confirm the exact figure from the manufacturer's datasheet or mill test certificate.
What is the difference between 15.2mm and 15.7mm PC strand?
15.7mm strand has a larger diameter and steel area than 15.2mm, giving it higher load capacity, though 15.2mm remains more common for many standard bridge and beam applications.
Is 15.7mm PC strand available in low relaxation grade?
Yes, low-relaxation 15.7mm PC strand is widely available and is the standard choice for most modern prestressed concrete applications.
Can 15.7mm PC strand be epoxy coated?
Yes, epoxy-coated 15.7mm PC strand is available for applications requiring additional corrosion protection.
Which standards apply to 15.7mm PC strand?
Common standards include ASTM A416, EN 10138, and GB/T 5224, and the applicable standard should be selected based on project location and requirements.
How is 15.7mm PC strand tested?
Testing typically includes tensile strength, breaking load, elongation, relaxation, dimensional, surface, and material composition checks, documented in a mill test certificate.
How do I choose the right 15.7mm PC strand for my project?
Confirm diameter, tensile grade, relaxation class, surface finish, anchorage compatibility, required breaking load, environmental exposure, applicable standard, and certification requirements before ordering.
15.7mm PC strand is a high-capacity prestressing solution suited to demanding structural applications, from bridge girders to heavy precast infrastructure. Because its performance depends on the specific grade, standard, and surface treatment selected, buyers should always confirm specifications against project design requirements and request full mill test documentation before ordering.
Looking for 15.7mm PC strand for your next prestressed concrete project? Contact TJ Wasungen for specifications, certification, packing details, and bulk pricing.
