A bridge is a structure that is used to get from one side of an obstacle (such as a river or lake) to the other side. Bridges provide a passageway for the different modes of transportation to cross over obstructions that are blocking the path to the desired destination. The first bridges were actually created by nature, such as a fallen tree, but nowadays there are several different types of bridges. They fall into six categories: beam, arch, cantilever, suspension, cable-stayed, and truss.

Beam

The beam bridge is the most basic type of bridge. It is comprised of a simple beam that lays horizontal between the two endpoints and is supported by piers on either end. When an object is crossing the bridge, its weight is being put on the piers. The top part of the bridge goes through a process called compression (meaning that it shrinks), while the bottom part of the bridge is being put under tension (it expands). One problem with beam bridges is the length issue. This is because beam bridges are supported by steel trusses, which caused the compression and tension to become almost obsolete, resulting in the bridge becoming too heavy to support.

Arch

This type of bridge has been around for centuries, often being made of stone or brick. They are now reinforced with steel or concrete to make them not only stronger, but also so that they’ll be longer with lower spans. Instead of the weight being pushed down directly on the bridge, the weight is transferred along the curve of the bridge to the abutments. The abutments support the bridge, prevent them from spreading out, and carry the weight of the load. When the weight is sent to the abutments, it creates a resistance against the ground and the resistance carries from stone to stone, which supports the weight.

Cantilever

A cantilever bridge is one that is firmly supported on one end, similar to a diving board or a tree. This type of bridge depends upon an equilibrium that is balanced by tension from weight being put on the structure and also compression on the bottom side. They are used in the construction of building beam, truss, and cable-stayed bridges. When being built, cantilever arms are first rigidly set, then are extended and connect in the middle with a center beam or truss ridge.

Suspension

These are the longest and typically most expensive eye-catching bridges. They are held together by two compression poles built into piers that are deep in the ground of a waterway or canyon. From these poles hang two large tension cables that are on both sides of the bridge. These cables are built into bedrock or concrete anchor blocks to provide anchorage (which carries most of the weight) and they drape over saddles on top of towers. The towers allow for the cables to be stretched for long distances.

Cable-Stayed

These are similar to suspension bridges, except they don’t require anchorages or two towers. They only need one tower, and the cables run from the roadway to the top of the tower. The single tower deals with the compression forces and the cables can run in different patterns. This type of bridge is a popular substitute for suspension bridges because they are significantly less expensive to build

Truss

It is a type of cantilever bridge, except it has interconnected beams in a triangular pattern either below or above the roadway. Through the trusses (interconnected beams), creates a very rigid structure that also transfers the weight further and more evenly than a single beam.