A suspension bridge has two towers, one at either end of the structure. These towers play an integral role in the stability of the bridge by supporting the massive cables that hold the entire bridge in the air. While these towers can range from highly ornate to utilitarian and plain, the twin tower structure must be incorporated for a bridge to be categorized as a suspension bridge.
With the weight of the bridge resting on cables which in turn rest on the towers, suspension bridge towers must have a solid foundation. According to the City University of New York archives, the Verrazano-Narrows Bridge in New York has foundations sunk to a depth of 105 feet below mean high water. The depth of the foundation depends on the depth of weight-bearing soil.
Suspension bridge anchors are placed into the shoreline material at both ends of the bridge. Depending upon the design, anchors can be constructed from rock or concrete. The cables are attached into the anchors to maintain tension on the bridge. While the cable remains tightly bunched over most of the structure, they are usually separated into strands before being attached to the anchors in order to distribute the tension load.
Perhaps the most central design element to a suspension bridge are the cables. These incredibly strong steel strands are affixed to one anchor then threaded over the towers and attached to the anchor on the other side. The primary weight-bearing cables don't actually attach to the roadway: smaller, connected suspension cables are used for that. The main cables must be both strong and flexible to withstand natural pressure; otherwise, the bridge is susceptible to winds, as was seen in the Tacoma Narrows Bridge collapse of 1940.
The final primary component of a suspension bridge is the deck, or the roadway upon which cars drive and pedestrians walk. The deck is built from massive pieces of steel-reinforced concrete hoisted into the air and laid into place upon the bridge. Deck pieces are connected with bolts and rivets, then suspension cables connect each section of deck to the main cables.