Do the assumptions made between unbonded tendon systems and the “Effective Force” method apply for bonded tendons as well?
The effective force assumption for post-tensioned tendons has been the primary method of design in North America for many years. Both ACI and PTI have been discouraging its use in favor of using the “Variable Force” method, but the practice is still common. The method applies to both bonded and unbonded systems. The application of the method is tied to a maximum tendon length for stressing. For unbonded tendons the practice is to limit the length to 38m (125 ft). For bonded tendons, this length is shorter. The practice is to select 33 to 35m (100 -115 ft) as maximum length. The shorter length for bonded tendons is due to a greater friction loss, which impacts the in-service performance for cracking and deflection. This, however, is compensated in part in greater increase in stress of bonded tendons at ultimate limit state.