What is PC strand?

PC strand stands for "prestressed concrete strand." It is a high-strength, pre-stressed reinforcement used in the construction industry to reinforce and strengthen concrete structures.

The pre-stressing process involves applying tension to the PC strand before placing it in the concrete. This tension helps counteract the tensile forces that the concrete might experience, improving its load-bearing capacity and durability. PC strands are commonly used in the construction of bridges, highways, buildings, and other structures where high strength and durability are essential.

Steel strand is made of multiple carbon steel wires that are twisted in a spiral shape on a stranding machine and tempered at low temperature to eliminate stress. The entire steel strand has high breaking force, good flexibility and easy construction. It is currently the most widely used prestressed steel bar.

Steel strands can be divided into: smooth steel strands, galvanized steel strands, monofilament epoxy-coated steel strands, filled steel strands, unbonded steel strands (smooth, monofilament, galvanized) etc.

Smooth steel strands

Commonly smooth steel strands are made of 7 steel wires, with a diameter of 15.2mm (American standard 15.24mm) and a standard tensile strength of 1860MPa.

Diameter of 6.9mm, 9.5mm, 12.7mm and 17.8mm are also available.

Filled epoxy steel strand

The outer layer is coated with a melt-bonded epoxy coating, and the gaps between the steel wires are completely filled with a melt-bonded epoxy coating, thereby preventing corrosive media from pouring into the seven-wire steel strand through capillary force or other hydrostatic forces.

With following 2 main strengths:

Excellent mechanical properties and fatigue resistance

1. Do not damage the original structure of the steel strand base material;

2. Epoxy resin firmly bonds the 7 steel wires of the steel strand;

3. Eliminate the fretting wear and fatigue phenomenon between the wires of the steel strand;

4. There is no need to peel off the epoxy coating when anchoring, and special clips are used for direct anchoring.

Excellent anti-corrosion properties

1. The gaps between the steel wires between the steel strands are completely filled with epoxy resin to prevent corrosive media from entering the inside of the steel strands through capillary action;

2. The epoxy resin coating on the surface of the steel strand has sufficient thickness, and strict quality control ensures that there are no pinholes in the entire length of the steel strand;

3. Special epoxy resin with high strength and toughness ensures that the epoxy resin can extend synchronously with the steel strand body during tensioning, and the coating will have no pinholes or cracks after tensioning.

Sand-embedded epoxy steel strand

Sand-embedded epoxy-coated steel strand is a type of filled epoxy-coated steel strand. The surface of the epoxy coating is embedded with sand to enhance the bonding strength with concrete and cement slurry. It is mainly used In internal prestressing, geotechnical anchorage and suspension bridge anchorage projects.

Monofilament coated epoxy steel strand

Using high-voltage electrostatic spraying method, epoxy resin powder is sprayed on the steel strand, and then heated, melted, solidified, and cooled to form a dense epoxy coating film on the surface of the steel wire.

With following main strengths:

1. Eliminate the fretting wear and fatigue phenomenon between steel wires;

2. Good anti-corrosion performance;

3. PE damage can also be independently anti-corrosion.

Galvanized steel strand

The surface of the steel wire is galvanized to form cathodic protection, and then the galvanized steel wire is twisted to form a steel strand. As an active metal, zinc will consume itself in corrosive environments to protect the inner metal. Therefore, galvanized steel strand has superior anti-corrosion properties.

Unbonded steel strand

Apply anti-corrosion wax oil to the surface of the steel strand, and then wrap it with hot-extruded PE. Mainly used for unbonded prestressed tendons in post-tensioning. Can also be used for external cords in exposed or corrosive environments. According to the different inner-wrapped steel strands, it can be divided into ordinary unbonded steel strands, unbonded monofilament epoxy steel strands, and unbonded galvanized steel strands.

What is a prestressed anchor system?

The prestressed anchor system is an important part of the complete set of prestressed concrete technology. A complete anchor system usually includes: anchors, wedgs, anchor support systems, connectors, etc.

Anchor - In a post-tensioned structure or member, a permanent anchoring device used to clamp the prestressed tendons to maintain and transfer the tension of the prestressed tendons to the concrete (or steel structure).

Wedg - a temporary anchoring device used to maintain the tension of the prestressed tendons and fix it on the production platform (or equipment) during the construction of pre-tensioned components; during the construction of post-tensioned structures or components, it is used on the tensioning jack Or a temporary anchoring device (also called tool anchor) that clamps the prestressed tendons on the equipment (transfers the tensile force to the prestressed tendons).

Connector - The function of the connector is to extend the steel bar to meet the structural requirements when the steel bar length is insufficient during use.

Anchor support system:

The support system under the anchor includes anchor pads, spiral bars, etc. that match the anchors and are arranged in the anchoring concrete.

The anchor pad can evenly transfer the prestressed force to the concrete components and prevent local stress concentration in the anchorage area.

Spiral bars are mainly used to reinforce the concrete in the anchorage area and prevent concrete damage.

What is prestressed tensioning equipment?

Prestressed tensioning equipment mainly includes two categories: electric tensioning equipment and hydraulic tensioning equipment. Electric tensioning equipment is only used for pre-tensioning methods, while hydraulic tensioning equipment can be used for both pre-tensioning and post-tensioning methods. Hydraulic tensioning equipment consists of hydraulic jacks, high-pressure oil pumps and external oil pipes.

Tensioning equipment should be equipped with force measuring instruments to accurately establish prestress values. Tensioning equipment should be used and kept by dedicated personnel, and should be maintained and tested regularly.

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