12.7mm unbonded PC Strand

12.7 A brief introduction to unbonded Prestressed Steel strands

I. Basic concepts

12.7 Unbonded prestressed steel strands are a special type of steel used in prestressed concrete structures. Their "unbonded" characteristics mean that the steel strands are not directly bonded to the concrete, but isolated by a protective layer wrapped around the outside of the steel strands. This design allows the steel strands to slide freely when subjected to force, thereby reducing friction losses and improving the durability and construction convenience of the structure.

II. Structural composition and specifications

Structural composition

Steel strand body: usually made of 7 high-strength steel wires, with a diameter of about 12.7mm, and a standard tensile strength of 1860MPa (high-strength steel).

Protective layer: The outer layer is wrapped with a high-density polyethylene (HDPE) sheath, and the interior is filled with anti-corrosion lubricating grease, which plays a role in waterproofing, corrosion prevention and friction reduction.

Main Specifications

Item Value

Diameter 12.7mm

Area of ​​the whole strand About 114.0mm²

Standard value of tensile strength 1860MPa

Relaxation rate ≤2.5% (1000 hours)

III. Core advantages

Convenient construction: No need to reserve channels and grouting, it can be laid directly in the template, simplifying the construction process and shortening the construction period.

Strong durability: HDPE sheath and grease layer form double protection, effectively isolate external corrosive media (such as water, chloride ions), and extend the service life of the structure.

Stable force performance: In the unbonded state, the stress distribution of the strand is more uniform, the friction loss is small, and long-distance tensioning can be achieved.

Adapt to complex components: It is easy to arrange in curved or variable-section components to meet the needs of diversified architectural design.

IV. Application scenarios

Construction engineering: Suitable for large-span floor slabs, bridges, parking lots, transfer layers of high-rise buildings, etc., such as large-span shopping malls and gymnasium roof structures.

Municipal engineering: can be used for structures that require crack resistance and anti-seepage, such as sewage treatment tanks and liquid storage tanks.

Special structures: such as nuclear power plant containment, pressure vessels and other projects with extremely high durability requirements.

V. Construction points

Laying requirements: Position according to the design drawings, the spacing between fixed points should not be too large (usually ≤600mm) to avoid damage to the sheath.

Tensioning process: Use two-end or one-end tensioning, the tensioning sequence must meet the design requirements, and control the tensioning force accuracy (error ≤±5%).

End treatment: After tensioning, cut off the excess steel strands and seal them with anchor concrete or special anchor protective cover to prevent the sheath from cracking and the steel strands from rusting.

VI. Industry standards and specifications

Common domestic standards: "Steel Strand for Prestressed Concrete" (GB/T 5224), "Technical Code for Unbonded Prestressed Concrete Structures" (JGJ 92).

International reference standards: ASTM A416 (USA), EN 10138 (Europe), etc.

VII. Comparison with bonded steel strands

Type Bonding method Construction complexity Durability Application scenarios

Unbonded Sheath isolation Low High (corrosion resistance) Large span, complex components

Bonded Cement grouting bonding High Medium (need to ensure grouting quality) Bridges, prefabricated components

VIII. Precautions

Avoid direct sunlight and contact with sharp objects during storage to prevent sheath aging or damage.

If the sheath is found to be damaged during construction, it must be repaired with waterproof tape in time to avoid grease leakage and water infiltration.

 

With the above characteristics, 12.7 unbonded prestressed steel strands have become one of the commonly used materials for large-span prestressed structures in modern buildings with their high efficiency and durability.12.7mm Unbonded PC Strand

Chunpeng Group is a leading and professional manufacturer of prestressed concrete (PC) steel materials, with over 30 years of industry experience.

We are committed to delivering high-quality products and innovative solutions for infrastructure and construction projects worldwide.

Our Core Products are pc steel strand (Ultra High Tensile Strength PC Strand, Normal Tensile Strength PC Strand), Unbonded PC Strand , Galvanized PC Steel Strand, Weather-Resistant & Anti-Corrosion PC Strand, and PC Steel Wire. 

In addition to our PC strand products, we also supply Prestressed Anchorage Systems and Photovoltaic Mounting Systems.