Ordinary steel strand for pre-stressed concrete is the bonded steel strand for pre-stressed concrete. Because there is no isolation plastic sleeve on its surface, it is bonded to concrete when it is used for pre-tensioned pre-stressing members and bonded to the slurry of the compression slurry when it is used for post-tensioned pre-stressing members.

Before the engineering structure member is subjected to external load, in terms of the reinforcement in the tensioned module, precompressive stress is applied to improve the stiffness of the member, so as to delay the appearance of cracks, and increase the durability of the member. In the case of mechanical structures, the implication is to pre-stress them, with the benefit of increasing the rigidity of the structure itself and reducing vibration and elastic deformation, which significantly improves the elastic strength of the tensioned modules and makes the original resistance stronger.

Before the structure is subjected to external loads, the compressive stress is applied in advance to the tensile zone under external loads to improve the performance of the structure in use, which is called the pre-stressed structure. For example, the wooden barrel, before filling the water in the barrel, tighten the barrel wall with iron or bamboo hoops, so it produces a circular compressive stress to the barrel wall, and if the compressive stress applied more than the tensile stress caused by water pressure, the barrel will not crack and leak. Pre-stressing on the round pool is like adding a hoop on the barrel. Similarly, the load in the bending member before the load is added to the member to apply pre-stress, which will produce a deformation of the opposite of the deformation generated by the load, before the member is deformed due to the force along the direction, it must first to offset the deformation of the opposite of the load, so can it continue to make the member deformed along the direction of the load. In this way, the pre-stressing is like an additional protection for the member.