![]() ![]() It was the world's first iron bridge, 140 foot single arch and is a semicircle. The Darby Bridge was built from 1777-1779 near Coalbrookdale, London. ![]() Arch bridges can span up to 1800 feet.įind pictures of two arch bridges. In 1809, Perronet transformed and perfected the stone arch by finding that pier that are 1/5 of the arch are ideal for safety and that forces thrust downward and horizontally all the way to the abutments. Arch bridges have evolved with the changing of fashion and materials (from stone to concrete and steel). The Romans often built multi arch bridges and cofferdams to cross rivers for its armies. The arch is built curving in from the ends, supported by scaffolding called falsework until the keystone is in place. The forces are spread around the arch to the legs that are kept from spreading out (buttressed) by the abutments. These "voissoirs" are wedge-shaped and gradually take the curve of the arch. The traditional shape is made from a series of blocks cut to fit together perfectly. The arch is most successful when its two legs can be set on either bank. Nearly all their bridges used the arch design because it could support more weight than a flat bridge. The Romans took arch bridges to grander designs. Longer girder bridges up to 700 ft have steel deck.Īrch bridges were built 6000 years ago. Straight steel beams, girders, lying on abutments, support concrete slab decks. Most American bridges are girder designs. If the truss is shaped into an arch, even longer bridges are possible. It is commonly used for railroad bridges because it can span great distances and carry heavy loads. Truss bridges get their strength from the rigidity of the triangle. If the linear structural elements are arranged in a lattice, such as a triangular pattern, you get a truss bridge and each member shares only a portion of the weight on any part of the structure. The piers balance the downward forces by pushing up. It has to withstand compression (pushing down of the weight of the bridge, the load and gravity) on top and tension (stretching) on the bottom. The beam type made up of a pair of girders that rest on piers and support a deck. The first one was a tree falling over a stream. The beam bridge is the simplest and cheapest and the most common. Many bridges use a combination of designs. It is the balance between the downward forces (the weight and gravity) and the upward forces (supports) that causes a bridge to stand and carry loads. Bridge types differ in length, function and the load they can bear. There are seven main types of bridges: the beam, truss, arch, suspension, cantilever, cable-stay and drawbridge.
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