Arch Bridges
Arch bridges have a beautiful design. Early arch bridges were made of cement and stones. They proved to be very strong. Many early arch bridges are still standing today. The design allows the weight to be carried along the arch to the ends rather than being pushed straight down. Supports are added to the ends to make the bridge even stronger. These supports, called abutments, keep the ends from spreading out and cracking. This is the secret to why the design has held through the test of time.
Arch bridges are continually under compression, so they have to be designed from heavy, sturdy materials. The Romans used stones to build their arch bridges. The Pont du Gard was built some time B.C. The bridge has stone suspension and mortar on the top tier. This arch bridge is still standing today.
Technology and new materials have made it possible for arch bridges to be built that are longer and have more elegant arch’s. The designs are being made to add appeal to the structure than just to help the structure stay usable. Most arch bridges are built between 200 and 800 feet. The New River Gorge in West Virginia spans 1,700 feet.
The actual construction of an arch bridge is difficult. The structure is not stable until the two spans meet in the middle. Keeping everything safe and in place until that part is complete proves to be very difficult. A way to do this is involves building a scaffold below it to allow the spans to rest on. Another method is to use heavy cables to suspend the spans. This method is more useful if the arch is being built over a waterway.
Pre-cast concrete was used to build the Natchez Trace Bridge in Franklin, Tennessee in 1994. This pre-cast concrete is very economical to use. The bridge has proved to be a success and has influenced the building of other bridges throughout the United States.
Technology continues to bring changes to the bridge building industry. However, it is believed the arch bridge will continue to be a popular model. It is sturdy, holds up well, it is one of the cheaper types of bridges to build, and people generally enjoy the look of the arch bridge.
