Once a precast prestressed concrete structural member is put in place, how does anybody know that it retains all of the properties it was designed to retain?
Now there is a way to eliminate some of this guesswork, at least to the extent of knowing how much tension is lost in prestressing elements over time. Korean inventor Jae Man Park has come up with an "Apparatus for Retensing Pre-Stress Structure." Park's invention reveals to an inspector or engineer the existing amount of tension in prestressing strands. The device has a built-in pressure meter that gives a constant reading of the stressing tension. Periodic readings are recorded on a table on the side of the tensioning device.
The device itself includes the means for tightening the strands, and the meter will inform the technician of when the correct level of tensioning is reached without the need for any guesswork or mathematical interpolation. Tensioning is accomplished by a built-in hydraulic jack tensioner.