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Information on Types of Bridges

Bridges have been in use all over the world and throughout history, employing varying designs and load capacities to move traffic over water, chasms and other impassible terrain. As needs and engineering possibilities have evolved, so have bridge designs, bringing a number of practical designs into use. Older bridge types, such as arch and beam bridges, are still used today alongside newer lift and cable-stayed designs, demonstrating the engineering prowess of ancient bridge builders.

  1. Arch Bridges

    • In arch bridges, the weights of both the bridge and the traffic traveling over it are displaced to the ground on either side of the bridge by arches beneath them. The arch on each end is built into the ground at the base of the bridge; the curves of the arches rise up, coming to a peak at the center of the bridge and supporting the structure. If the ground below supports it, multiple arches can be used to extend the length of the bridge. Arch bridges are among the oldest bridge designs and were widely used in ancient Rome.

    Lift and Swing Bridges

    • In waterways where tall boats need to pass, lift bridges allow water traffic while accommodating pedestrian and vehicle traffic across the waterway from above. In its default state, the lift bridge provides a path for land traffic to cross over a waterway. When a boat needs to pass beneath it, the bridge is closed to land traffic; then, a mechanical system is activated to raise the bridge high above its resting spot and allow the boat to pass beneath. In waterways with solid land at the center, swing bridges may be built. Swing bridges allow water and land traffic as well, but they pivot 90 degrees horizontally rather than being lifted into the air.

    Suspension and Cable-Stayed Bridges

    • In suspension bridges, flexible chains or ropes stretch from the tops of sturdy towers to the deck of the bridge below, allowing the bridge's weight to be supported from the towers. In common designs, one tower rises on either side of the bridge and the curve of the hanging chains creates an image similar to an upside-down arch; if the ground beneath the bridge allows for it, more towers can be added to increase the length of the bridge. A variation on the suspension bridge design, called a cable-stayed bridge, employs cables attached to the tops of tall pillars or beams to support the bridge. In cable-stayed bridges, the beams can be angled to direct the brunt of the bridge's weight over a desired area.

    Beam Bridges

    • A beam bridge has no external support structure; it is essentially a flat surface that relies on the land at either end as the sole means of support. Modern designs in beam bridges employ specially designed beams to support the weight of the bridge and its traffic.

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