Fatigue of suspender anchorages under axial and bending loads of suspension bridges

Abstract

Fatigue-induced damage is the primary failure mode observed in cables used in cable-supported bridges, such as suspenders in suspension bridges, stay cables in cable-stayed bridges, and hangers in arch bridges. Typically, cable failures occur at their anchorages in a combination of axial and bending fatigue. A computational framework to estimate axial and bending fatigue load spectrums caused by girder buffeting and train load is presented for suspenders of suspension bridges. The threaded rods of upper suspender anchorages were then accordingly evaluated. The results show that under girder buffeting of 15 m/s mean wind speed, short suspenders at the mid-span experience a maximum axial stress range of up to 35.00 MPa and a maximum rotation angle range of approximately 0.90°. Under train loads, the suspenders exhibit a maximum axial stress range of 26.88 MPa and a maximum rotation angle range of 1.42°. Threaded rods used in all suspenders generally do not experience damage under the axial fatigue load spectrum, but short suspenders in mid-span may experience significant cumulative damages under the bending fatigue load spectrum due to girder buffeting and train load. Girder buffeting tends to cause about 3 to 5 times more damage than train load. The predicted life for a failed suspender is generally consistent with actual observations (2.6 versus 2.0 years). Therefore, it is strongly recommended that the bending fatigue of short suspender anchorages due to girder buffeting should be carefully investigated in fatigue design, in addition to the bending fatigue of train load excitation.