REALISTIC REQUIREMENTS FOR UNBONDED POST-TENSIONING TENDONS

Abstract

There is a considerable difference between the physical capabilities of a prestressing tendon in a and the physical conditions which can be imposed upon that tendon when it is installed and left unbonded in a concrete structure. For example, the maximum force which can be developed in an unbonded tendon in an actual structure is about 90 percent of the rated* ultimate tendon force, yet most specifications require that the anchorages develop 100 percent of the rated strength. The maximum total elongation possible in an unbonded tendon in a structure is in the order of 1.0 percent, yet specifications require between 2 and 3 percent. Performance specifications for unbonded post-tensioning tendons have, thus, consistently been written solely on the basis of testing machine capabilities, rather than actual structural requirements. They are based on what the tendon can do, rather than on what it actually has to do. It is extremely important that the designer of unbonded posttensioned structures recognizes the difference between the capabilities