If not done earlier for aesthetic reasons, it is structurally and economically
advantageous to vary the bridge depth in the longitudinal direction beginning
with span lengths of about 60 m onwards. For span lengths over 150m this
cannot be avoided. According to [ 18] , the depth, ds, over the piers should
vary so that it is about 3 times as large as at mid-span, dF. The depth of
the box girder should vary in the longitudinal direction between the piers and
mid- span in such a way that the forces in the tensile and compressive chords
increase linearly and therefore the shear forces in the webs remain roughly
constant throughout the span. Suitable ratios are: