Self-anchored suspension bridges

Abstract

Since 1870, only about 25 highway bridges have been executed as a self-anchored suspension bridge. The rise of the cable stayed bridge since 1955 made this suspension type an obsolete alternative for a long period of time. The largest existing main span for a self-anchored suspension bridge is 300 metres and dates from 1999. Main difficulties for this bridge type to reach spans over 300 metres can be blamed on erection problems and the buckling stability of the girder. Erecting the deck structure prior to the main cable makes this bridge technically and economically less attractive than for instance the cable stayed bridge. A dimensional inventory has shown that the deck slenderness is limited to about ? = 1/95 and the sag ratio varies between 1/5-1/8. The deck slenderness is related to the required bending stiffness to have sufficient resistance against buckling. Also the relatively high sag ratios, compared to conventional suspension bridges, are mainly chosen to reduce the normal force in the deck that is imposed by the main cable. A parameter study into the structural behaviour has revealed that the most important bridge parameters are the bending stiffness EIdeck of the deck and the axial stiffness EAmain cable of the main cable. A well chosen ratio between the EIdeck and EAmain cable influences the maximum bending moments and the deflections in the girder. In the pre-design process of a suspension bridge type it is favourable to consider: -A slender stiffening girder, to reduce the maximum bending moment in the girder -A stiff main cable, to increase the global stiffness of the bridge and to reduce the maximum bending moment in the girder -A high sag to span ratio, to reduce the normal force in the deck and the maximum bending moment in the deck.