If the bridge is built on difficult ground, as in the case of the Humber bridge, the anchorage can present a fearsome problem. The deck of a suspension bridge is usually suspended by vertical hangers, though, some bridges, following the example of the Severn bridge, use inclined ones to increase stability. But the structure is essentially flexible, and great effort must be made to withstand the effects of traffic and wind. If, for example, there is a daily flow of traffic across a bridge to a large city on one side, the live load can be asymmetrical, with more traffic on one side in the morning, and more traffic on the other side in the evening. This produces a periodic torsion, and the bridge needs to be strong enough to resist the possible effects of fatigue.
Great attention needs to be paid to aerodynamic stability in suspension bridges.
The effects of wind are much better understood than they used to e, and the advent of the streamlined deck, used first in the Severn bridge, have reduced the cost of suspension bridges. The box-section of the Severn bridge contributes not only to aerodynamic stability, but to torsional stiffness. This and the inclined hangers owe much to the ingenuity and imagination of Fritz Leonhardt. The greater inherent rigidity of the triangulated cable-stayed bridges, compared with the suspension type, makes life easier for their designers and builders. On the other hand, if a cable-stayed bridge is built by the cantilever method, it is very vulnerable when the structure is very long but has not yet been joined together.