The two most renowned suspension bridges in the United States are undoubtedly San Francisco's Golden Gate and New York City's Brooklyn bridges. A suspension bridge's essential components are its towers, cables, decking, and anchorages. The three main types of suspension bridges are single-span truss bridges, double-span truss bridges, and cable-stayed bridges.
Single-span truss bridges have one main supporting truss that carries the load. These bridges are the simplest to build and maintain and are found everywhere from small town streets to large interstate highways. They are typically only 40 feet (12 m) or less in width.
Double-span truss bridges have two main supporting trusses that carry the load. These bridges are more complex to build and maintain than single-span truss bridges but can be wider. They are commonly used for long spans over large bodies of water or across valleys.
Cable-stayed bridges use vertical stay cables attached to the tops of the towers instead of horizontal truss members. This removes the need for any kind of flooring or decking and allows the bridge to be fully open to traffic during construction and maintenance. Cable-stayed bridges are commonly used for high-speed rail lines or major city streets because they are easy to see through when driving under it at speed.
Suspension bridges may still be found deep in the bush as well as in most major towns nowadays. The location of these elements determines how it can be best used to support a road or rail traffic.
In general terms, suspension bridges can be divided into three main types: single-span (or single-tower), double-span, and multiple-span (or multi-tower). A single-span suspension bridge consists of a single central tower supporting both the roadway and the railway track. These are by far the most common type of suspension bridge today. They can be either open or closed structures. An open single-span bridge is one where the central tower is exposed to view; this is the case of the Golden Gate Bridge in San Francisco and the Point Defiance Bypass Bridge in Tacoma, Washington. A closed single-span bridge has no central tower standing above the cross-members of the framework. Instead, the underside of the deck is supported by vertical cables attached to the sides of the tower on which it rests. These bridges are found mainly in rural areas where they provide visual appeal and help prevent flooding.
A double-span suspension bridge has a pair of identical towers spaced apart by a central section called a "motorway" or "bridge".
A typical suspension bridge is a continuous girder hung by suspension cables that run through the main towers through a specific structure known as a saddle and finish in large anchorages. Tension in the cables and compression in the towers are the primary forces in a suspension bridge. The shape of the supporting piers and the depth to which they are driven into the ground determine how much tension can be applied to the cables.
The main components of a suspension bridge are its towers, girders, and cables. All three must be strong enough to support the weight of the people and vehicles crossing them. The size of the bridge's towers determines how far apart their top edges can be placed without causing them to overbalance. The distance between the tops of two adjacent towers on a single-lane bridge is called its clear height. A multilane bridge has more than two lanes, so it can have taller towers. Its maximum clearance from one tower to another is called its navigable width.
Girder bridges consist of long, horizontal trusses connecting vertical posts set into the ground at each end. The trusses form a grid pattern with individual strands of wire running through holes in the posts. The ends of these wires are then tied together to create a continuous cable across the bridge. Girder bridges are the most common type of suspension bridge and use multiple layers of wire to provide greater strength and stability.
Suspension bridges are so named because the highway is suspended by cables from two towering towers. The two towers bear the majority of the weight. They then direct the compression pressures from the wires into the earth. Suspenders are smaller cables seen on suspension bridges. They help to prevent the bridge from swaying in the wind.
The main types of support for a suspension bridge are anchor rods, which go down into the ground or water, and trusses. Trusses are made up of equal lengths of steel connected with girders. They provide much greater strength than anchor rods alone do. However, anchor rods can be used in combination with trusses if necessary. For example, an anchor rod could be used as one of the main supports and then another rod farther away would be used in conjunction with the first one to extend the distance that it reaches into the ground or water.
Anchor rods are usually made of stainless steel but they can also be made of concrete. Concrete anchor rods are more common for large bridges because they can hold more weight before they break. Waterproof paper or plastic coating can be used to cover the outside of an anchor rod to make it less visible. This is especially important for bridges that cross rivers or streams where the anchor rods will be extending into the water.
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