Bridge-Friction Losses

When stressed, tendons inside the ducting experiences friction losses.

Two parameters are important for the calculation of friction losses: friction coefficient at the tendon profile angle change and wobble coefficient over the tendon length.

Wobble coefficient is the measure of unintentional local misalignment of ducting that leads to the contact between tendon and duct surfaces. Thus, wobble coefficient is taken as zero for external tendons since ducting is not provided. For the portion passing through deviator and diaphragm, the wobble is ignored due to very short length of contact.

Friction loss depends on the tendon profile. Such loss is significant for curved tendon profile, draped profile with large angle changes and long tendon.

The maximum economic length of internal tendon is about 120m before the effect of friction is too huge and affects the efficiency of tendon. For external tendon however, insignificant loss is expected even if its length is very long.