Loads
This analysis will consider only the dead and live loads acting on the cables, and will neglect wind forces. In general, the wind forces acting on the bridge are complex, and although they are critical for the actual design and analysis of a suspension bridge, they are not necessary to understand the basic behavior and will be neglected here for simplicity. (Horizontal braces are built into the deck to resist the horizontal effects of wind, but vertical stiffening was not necessary since the weight of the deck itself was enough to overcome the vertical effect of wind.)
Both the dead and live loads are assumed to be uniformly distributed along the span. The dead load is composed of the weight of the cables, both the large ones and the smaller suspenders, but mainly the weight of the road deck. An estimated uniform dead load of qd,m = 39 k/ft is assigned to the main span between the supports, and a value of qd,s = 40 k/ft is used for the side spans.
Over the length of the bridge there is a total dead load of:
The analysis will deal with the uniform load rather than a total point load because the distribution of the load is critical to the shape of the cables. The live load, which includes both traffic and snow loads, will be estimated as ql = 8 k/ft all along the bridge. This value does not represent the heaviest load to which the bridge might be subjected. The maximum load is unreasonable to use in design, because in all probability, the bridge will never be filled with tractor-trailer trucks bumper to bumper in all eight lanes.
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