The Arch Bridge Arch bridge construction began in the time of the Romans and are one of the oldest types of bridges and have great natural strength. Instead of pushing straight down, the weight of an arch bridge is carried outward along the curve of the arch to the abutments at each end. These abutments keep the the arch in perfect tension by preventing it from spreading out.
This is the Pont du Gard aqueduct built by the Romans over 2000 years ago near Nîmes, France. Its recent fame has been enhanced by its use in comercial advertising. Built completely of precisely cut and stacked stones. Mortar is used only in its top tier; the rest of the stone structure stays together by the sheer force of its own weight. The Pont du Gard aqueduct
Restrictions When should you use an Arch Bridge? Use in places where you need a very open structure over a large span.
Beam Bridge Beam bridges come in many different forms. The most basic beam bridge consists of a horizontal beam that is supported at each end by piers. The weight of the beam pushes straight down on the piers.
This is the world's longest continuous span beam bridge bridge. The Lake Ponchartrain Causeway is almost 24 miles long and consists of two, two- lane sections that run parallel to one another. The southbound portion was completed in 1956 and is made up of 2243 separate spans.The northbound portion was completed in 1969 and is pieced together from 1500 longer spans. Lake Ponchartrain Causeway, LA
Restrictions Beam Bridges are not well suited for locations that require unobstructed clearance below. While you can have a series of continuous spans a single span can rarely span greater than 250 feet
Suspension Bridge Suspension bridges are light weight and strong spanning distances from 2,000 to 7,000 feet While they are some of the most architecturally pleasing they can also be the most expensive to build. A suspension bridges name, comes from the roadway suspended from cables, extending from one end of the bridge to the other. These cables are free moving and rest on top of towers. They are secured at each end by anchorages which absorb much of the tension in the cables.
At the time it opened for traffic in 1940, the Tacoma Narrows Bridge was the third longest suspension bridge in the world. It was promptly nicknamed "Galloping Gertie," due to its behavior in wind. Not only did the deck sway sideways, but vertical undulations also appeared in quite moderate winds. Tacoma Narrows Bridge Drivers of cars reported that vehicles ahead of them would completely disappear and reappear from view several times as they crossed the bridge. Attempts were made to stabilize the structure with cables and hydraulic buffers, but they were unsuccessful. On November 7, 1940, only four months after it opened, the Tacoma Narrows Bridge collapsed in a wind of 42 mph – even though the structure was designed to withstand winds of up to 120 mph. Click on image to view video
Restrictions. Can span the longer distances from than most other bridges. Spanning 2,000 to 7,000 feet. Because of the expense of the cable and getting it into place, these tend to be the most expensive to build.
Cable Stays Cable-stayed bridges may look similar to suspensions bridges – both have roadways that hang from cables and both have towers. The difference lies in how the cables are connected to the towers. In suspension bridges, the cables ride freely across the towers, transmitting the load to the anchorages at either end. In cable-stayed bridges, the cables are attached to the towers, which alone bear the load.
Built in 1988, the Sunshine Skyway is one of the first cable-stayed bridges to attach cables to the center of its roadway as opposed to the outer edges. A 1981 accident in which a tanker hit a support and knocked out 1261 feet of the old Skyway bridge killing 36, inspired the construction of a protection system on this new bridge. Sunshine Skyway Bridge
Restrictions For medium length spans (those between 500 and 2,800 feet). They require less cable than traditional suspension bridges. They can be constructed out of identical pre-cast concrete sections, and are faster to build than suspension bridges. They are some of the most architecturally pleasing bridges.
Special thanks to the Nova Online Super Bridges site http://www.pbs.org/wgbh/nova/bridge/build.html for much of this information.