Bridges and Tunnels

Bridges and Tunnels

Sequoia YES

​Arch Bridge

An arch bridge works by conveying the downward pressure of gravity inward to the center of the structure — toward a central stone called the keystone — rather than straight down. This principle is called compression, and it enables the arch below to support the surface, or deck, above it. ​

​Beam Bridge

​In beam bridges, the force of compression pushes the load inward onto piers at the middle of the bridge. Simultaneously, the pulling or stretching force of tension pulls the load outward toward the abutments at both ends of the bridge.

​Cantilever Bridges

​Cantilever bridges are often supported with trusses. A bridge truss takes the load off the deck and transfers it to the supporting piers and abutments, helping the cantilevers withstand tension in the upper supports and compression in the lower ones.

Suspension Bridges​

​Suspension bridges are just what their name sounds like: They’re stabilized with vertical pillars or pylons connected by suspension cables. Attached to these main cables are smaller, vertical suspenders that hold up the bridge deck using tension, the main force that sustains suspension bridges.

Cable-Stayed Bridge​

​A cable-stayed bridge is a variation on the suspension bridge that connects the crossbeam or bridge deck directly to pillars or towers. There’s no main cable, just a large number of vertical suspenders affixed to the top of the tower. These suspenders use tension to help keep the bridge deck stable and in place.

Tied-Arch Bridge​

A tied-arch bridge combines features of an arch bridge and a suspension bridge. It uses horizontal thrust from both sides to support an arched structure, as in a regular arch bridge. But instead of an arch supporting the structure from below, the arch rises above the road, and vertical ties descend to increase support of the decking.​

​Truss Bridges

​A truss bridge distributes its load across a series of small sections fitted together. Formed by structural beams for smaller bridges or box girders for larger ones, bridge trusses are typically bound together by welded or riveted joints in a series of triangles.