ABSTRACT
A suspension bridge is a fundamentally simple structure, with a "serial type" of static behaviour in carrying loads. In simple terms, the loads are applied to the deck, carried to the main cable through the hangers and subsequently brought to ground mainly through the towers for the vertical component and through the anchor blocks for the horizontal one. (Figure 6.1)
When subject to live loads for example, as in any redundant system, a sus pension bridge undergoes an interaction in which forces are carried through the structure depending on the relative stiffness of the different elements involved.The primary interaction is that between the deck, whose stiffness is mainly related to flexure, and the main cables, whose stiffness is instead mainly geometric and in turn dependent upon the present tensile load. Since the tensile force for suspension bridges is mainly connected to weight, such geometric cable stiffness is often referred to as "gravity stiffness''
The change in relative stiffness between the deck (in bending) and the main cable (due to tension and geometry) with span is the main parameter domi nating the behaviour of suspension bridges for many aspects. For example, with a constant tensile load, the cable stiffness decreases as span length increases, while for constant cross-section the deck stiffness also decreases, but in proportion to a higher power of the span.
