The Difference Between Unbonded and Bonded Steel Strand

unbonded prestressed steel strand
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Prestressed concrete steel strands are used in a wide range of applications. It has relatively high texture strength and good plasticity, but it has a great contribution to supporting buildings, like subways, bridges, dams, nuclear power plants, and housing construction. Steel strands can also be divided into bonded steel strands and unbonded steel strands.

Definition of Bonded and Unbonded Steel Strand

The unbonded steel strand is coated with a layer of grease and a plastic sheath on the steel strand (which can be called bare wire). In engineering construction, because of the grease and sheath on the surface of the unbonded steel strands in the concrete, the steel strands are isolated from the concrete, can be loosened freely, and remain unbonded with the concrete, so it is called unbonded steel. stranded wire.

There are also galvanized unbonded steel strands used for reinforcement projects, that is, galvanized steel strands are coated with grease and plastic sheaths to double guarantee the anti-corrosion effect.

Bonded steel strands do not have this layer of protection.

Application Difference of Bonded and Unbonded Steel Strand

Bonded steel strands are mainly used for civil construction projects with large static loads, large-span factory buildings, or high-rise buildings. The advantage is that the construction speed is fast, the thickness of the beam and slab is reduced, and the structural performance and economic effect are increased.

Bridge construction and large-span garage prestressed construction are designed with bonded steel strands because of the large dynamic load. Because the construction grout is directly bonded to the concrete, it produces a strong grip. It is not as difficult to anchor both ends as in the construction of unbonded steel strands, which enhances the safety factor.

The difference from the bonded steel strand is that the prestress does not bond with the surrounding concrete. Unbonded steel strands are mainly used in post-tensioning prestressing systems. During its working period, the prestress and the surrounding concrete slide longitudinally relative to each other. The prestress is completely transferred to the concrete by the anchorage.