The First Modern Suspension Bridges

A bridge is a structure that is used to cross an obstacle such as a river, a channel, a valley or a highway. The simplest kind of bridge is a tree trunk that has fallen across a stream or a set of twisted ropes and bamboo poles suspended (hanging) over a river. The latter is an example of early suspension bridges. Such bridges are still used in remote areas of many parts of the world like Asia, Africa and South America.

The modern, strong, sophisticated suspension bridges are the result of the work of a German-born engineer called John Roebling. He was the first to formulate the mathematics of these impressive structures and manufacture the steel cables that replaced the ropes of the early hanging bridges. He designed the first modern suspension

The deck is the part of the bridge on which pedestrians and vehicles travel. It is a concrete and steel framework. It lies across an obstacle, a river for example, and rests on huge concrete blocks called abutments or anchorages on the opposite banks of the river. The piers are the concrete structures between the abutments. A suspension bridge must have at least one or two piers. These are the foundations of the tall towers on which the weight of the roadway and the vehicles is suspended or held up. This is made possible by the main steel cables which extend from the abutments on one side over the top of the towers to the opposite abutments. The ends of the cables are tightly entrenched in the abutments. The shorter vertical cables called suspenders attach the deck of the bridge to the main cables. Thus, although the roadway appears to be resting on the abutments and piers, it is actually suspended on the towers by means of the

The two main forces are compression and tension. Compression is the force that pushes down on the deck. It comes from gravity, the weight of the bridge and the weight of the traffic that passes along it. Whereas compression is a pushing force, tension is a pulling force. The cables receive the tension force and transmit it to the towers and the abutments in which they are firmly embedded. This force is finally dissipated, spread out thinly, to the ground.

There are many other forces to consider in suspension bridge design. These include resonance (vibration or shaking) and torsion (a rotational or twisting force) caused by speeding traffic and strong windy conditions. The choice of construction materials is equally important. Only people can cross an obstacle on rope and bamboo suspension bridges. Early suspension bridges were not practical for moving heavy loads and traffic because of the weak materials. Iron is rigid, not resilient enough, and the more flexible steel has long replaced