How Does a Beam Bridge Work?

Beam bridges disperse the weight of traffic and the weight of the beam itself by utilizing strong pillars for supports on each end. Adding additional supports along the length of the beam increases the strength of the bridge. The material used for the beam and for the supports can also be modified, with steel-and-concrete-beam bridges able to handle heavier loads than wooden-beam bridges.

Beam bridges are acted upon by the two opposing forces of compression and tension. Compression is the action of weight pushing down on the top of the bridge, encouraging it to buckle. Tension works on the bottom side of the bridge, working to pull each end apart and create snapping.

Though beam bridges can be modified to handle additional stress, there are limits to the distances they can span. Trusses can be placed either above or below the beam to spread out the stress of the load. Deck trusses are placed underneath the beam, while through trusses are built on top of the beam. Arches have a much greater capacity than trusses to spread out the tension experienced by bridges. They are often used to span very long distances, though they can be more difficult to construct.