Question

The loss of prestress due to elastic shortening of concrete is least in:

• A. One wire pretensioned beam
• B. One wire post - tensioned beam
• C. Multiple wire pretensioned beam with sequential cutting of wires
• D. Multiple wire post-tensioned beam subjected to sequential prestressing.

Answer 1

The correct option is B One wire post - tensioned beam

Elastic shortening loss

(i) Pre tensioned members:- When the tendons are cut & the prestressing force is transferred to the member, the concrete undergoes immediate shortening due to the prestress. The tendon also shortens by the same amount which leads to the loss of prestress.

(ii) Post tensioned member :- If there is only one tendon there is no loss because the applied prestress is recorded after the elastic shortening of the member.

In case of multiple wire post tensioned member usually tendon are not stretched simultaneously. Moreover the first tendon that is stretched is shortened by the subsequent stretching of all the other tendons, & the last tendon is not shortened by any subsequent stretching. Therefore in multiple wire beam loss of prestress is more.