Do you know about bonded and unbonded prestressed steel strands?

Prestressed concrete steel strands are divided into bonded and unbonded types according to the bonding state. There are obvious differences between the two in structure, construction and application scenarios. The following is detailed introduction:

1. Bonded Prestressed Steel Strand

In the bonded prestressed system, the steel strands are embedded in corrugated pipes or channels. The corrugated pipes are usually made of metal or plastic and need to be fixed according to the designed position. After pouring concrete, the strands are inserted into the bundles, and then tensioned and grouting are performed. The steel strands are bonded to the concrete as a whole, so that the steel strands, grouting materials and surrounding concrete components are bonded. The steel strands transmit prestress by bonding force.

Advantages:

- Stronger Load Distribution: The bond between the strands, grout and concrete makes the stress distribution of the whole structure more uniform.

- Durability: The grout can protect the strands and make the bonding system more corrosion-resistant.

- Crack Control: The bond force cooperates with the concrete stress to make the crack distribution more fine, and the formation and expansion of cracks can be better controlled, thereby improving the overall integrity of the concrete.

Application Scenarios:

Commonly used in large-span structures, bridges, high-rise buildings and other projects with high requirements for integrity and rigidity, such as continuous beam bridges, multi-story frame structures, etc.

2. Unbonded Prestressed Steel Strand

In the unbonded prestressed system, each strand is coated with special anti-corrosion lubricating grease and wrapped in a high-density polyethylene (DHPE) plastic sheath. After pouring concrete, it is directly tensioned without grouting. The strand is allowed to move slightly in the sheath and is not directly bonded to the concrete. After tensioning, the prestress is transmitted through the anchor.

Advantages:

- Easier Installation: Unbonded strands are quicker and simpler to install because no grouting is required.

- Flexibility: Unbonded systems offer great flexibility because the strands can move independently within the concrete.

- Easier Repair: The strands can be replaced or repaired individually without disrupting surrounding structures.

Application Scenarios:

Applicable to structures that require high construction speed and flexible pipeline layout in the later stage, such as floor slabs, roofs, simply supported beams, etc., especially common in prefabricated buildings, such as residential buildings, floor slabs and parking lots.

3. Main Differences:

- Construction Process: The bonded type requires grouting, which has more processes; the unbonded type omits the grouting step and is simpler to construct.

- Corrosion Resistance: The anti-corrosion sheath of the unbonded type can protect the steel strand, and its durability is relatively better, but the anchor quality requirements are higher.

- Stress Transfer Method: The bonded type transmits stress through the entire length of the bond, and the stress distribution is uniform; the unbonded type relies on the anchors at both ends, and there is a stress concentration phenomenon.

- Applicable Span: The bonded type is more suitable for structures with a span of ≥15m (such as bridges), and the unbonded type is more suitable for floors and roofs with a span of ≤12m.

- Maintenance Cost: The bonded type needs to break the concrete for later maintenance, which is costly; the unbonded type can directly replace a single steel strand, and the maintenance cost is low.

If you have demand for these two types of prestressed steel strands, you can contact us directly. We are the source factory, have quality inspection reports, and have guaranteed production. We have also established in-depth cooperation with many domestic and foreign customers. If you need to know the specific specifications and quotations, please contact us. You can also leave your needs and contact information, and we will provide you with customized solutions!