Steel strand tensile elongation value: steel strand prestress tensioning construction design and control tension, refers to the tension before the completion of the cable tension in the anchor clamp. Therefore, when steel strand tensioning elongation of theoretical calculation, should to the distance between the steel wire at both ends of the anchorage points as the calculated length of steel strand, but in prestressed tension steel strand to control tensile force is at the jack tool anchor control, so control and calculation, general with the distance between the steel wire at both ends of the anchorage points, plus steel wire in tensioning jack working length, as the calculated length of prestressing steel strand tensioning theoretical elongation. The prestressed cable tension, the exposed part of the steel strand, most of them are wrapped in Anchorage and Jack, steel strand stretching elongation cannot in the steel strand, the direct measurement, so it can only be used to measure a pull jack piston stroke, calculation of steel strand tensile elongation, but should also be shrinking minus strand a Laquan process of anchor plug.