The strength of a bridge depends on a variety of factors, such as span, intended purpose and materials used. For centuries, bridges have been used effectively to close a gap between two areas. Today, bridges are used more often as a way of creating shorter commutes in congested areas, crossing waterways, railways and existing roads. It takes manpower, good physics and smart architecture to accomplish the task of designing and building a strong bridge.
A beam bridge, simply explained, is piers on each end holding up a horizontal beam. Those piers anchor into the ground to keep the bridge in place. The closer the piers exist to each other, the stronger this type of bridge becomes and the more weight it can support. If the piers sit too far apart, the beam will not have adequate support, and the bridge could fail and collapse. For this reason, this type of bridge doesn't span more than 250 feet. Originally made out of wood, beam bridges are now made out of concrete, asphalt and steel.
Arch bridges get strength through their form, as well as the strength of the materials used. The weight of the traffic pushes the bridge weight outward, toward the abutments, rather than downward at the top center of the bridge. Every part of the bridge becomes compressed and stressed. Because of this, building bridges with materials that can sustain their strength under pressure, such as steel, stone and concrete, makes the arch bridge even stronger. Commonly, these bridges do not span more than 200 to 800 feet.
The suspension bridge maintains supreme strength even when spanning out 2000 to 7000 feet, making it ideal for crossing over large bodies of water. Each end of the bridge anchors into strong piers, and the bridge suspends from steel rope, eyebars or other materials. Although expensive to build and possibly even a challenge for some architects, suspension bridges subsist as possibly one of the most versatile bridge types because of their strength and capability of spanning out thousands of feet. Most have a system beneath the design to keep the bridge from any movement or distortion.
The cantilever bridge is a modified version of the beam bridge. However, like a diving board, one end of the beam anchors to the ground. The other end anchors near the center of the span. To support the beam going across, the steel tubes at the bottom squeeze under compression while the steel limbs at the top pull. The cantilever bridge can endure great amounts of weight and can reach spans of up to 1800 feet.