Cable-stayed bridges - Computational Analysis and Design of Bridge Structures - page 337

(a) When supports are rigid, bending moments at supports are negative

(b) When supports are vertical cables, bending moments at supports become less or even positive

(c) When support cables are slanted, bending moments become positive

Figure 11.14 (a) Continuous girder; (b) vertical cable supports; (c) slanted cable supports.

as well as demonstrating the general engineering concept and the practical/
economic benefits of building such a bridge, are covered in this section.

11.2.2 ideal state
What would be the best jacking stress of each cable in terms of increasing
the girder span capacity? This is a unique question to cable-stayed bridges
during structural analyses and design. From the girder capacities' perspec-
tive, the answer is found when the maximum bending moments due to
dead loads on the girder are the same as those of a continuous girder as
shown in Figure 11.16. Although the live load distribution does not depend
on the cable stress level and does not change once a cable-stayed bridge
is structurally determined, dead loads dominate in cable-stayed bridges.
Therefore, as long as the dead load distribution reaches a desired state, the
span capacity can be increased. This simple idea is based on the fact that