REQUIREMENTS ON TENDONS FOR EXTRADOSED BRIDGES

Extradosed bridges are getting more popular in all countries. After a successful start in Japan also in Europe a lot of projects are realized. For extradosed bridges the tendon layout is similar to cable stayed bridges, but due to the increased stiffness of the superstructure and the flat inclination of the tendon the actions on the tendons (especially fatigue loads) are much lower. Special care has to be taken on the properties of the tendons used. Due to the environmental exposure especially for the corrosion protection and leak tightness identical requirements are essential for both bridge types. On basis of theoretical considerations it was verified that a stay cable tested according to fib-bulletin 30 also fulfills the requirements for extradosed tendons. As usually the fatigue resistance for external tendons is only shown for a stress range of Delta sigma=80 MPa, fatigue tests with higher stress range have to be performed on external tendons to guarantee the usage in extradosed bridges. In the article the requirements regarding static and fatigue behaviour, the transfer of load differences to the pylon at the saddle, the exchangeability of tendons and durability aspects are discussed.