Engineering and Construction

Cable-stayed bridges virtually behave as continuous beams with elastic supports at the cable anchorage points. Cable lengths are adjusted during construction so that the effect of cable extension under dead load conditions is cancelled out. Provided that high tensile material is used for the cables then non-linear effects due to self- weight can be shown to be negligible.

For initial design the deck may be proportioned as a continuous beam, as shown in Fig. 4.16, to which are added:

(a) deck deflections at the cable positions due to extension.
(b) axial forces due to horizontal component of the cable forces.

Where a single plane of cables is used then an initial design check must be made to ensure that sufficient torsional rigidity is provided (using single or twin box girders) to control transverse tilt of the deck at mid-span when traffic loading occupies one carriageway.

Fig. 4.16 Cable-stayed bridges, initial analysis. (a) Anchored side spans (harp shown); (b) harp; (c) fan