Bridges

Bridges have been around since time immemorial. It goes without saying that the inventor of the world’s first bridge is unknown. It could have been as simple as a log dropped across a stream. But over time, the inventive human being built bridges to span obstacles such as rivers and ravines, avoiding arduous treks and making an easy way to get to the other side. Bridges fall into a variety of categories depending upon the engineering method used in construction. These include:
Arch bridges: as the name implies, an arch bridge is supported by one or several arches. Many ancient stone bridges of this type still exist today. Bascule bridges: lesser known but still in operation, often spanning rivers and can be raised like a drawbridge to allow boats to pass. Beam or girder bridges: the simplest form of bridge, with horizontal beams or slabs resting on supports at each end. Cantilever bridges: with beams or trusses that are either only supported at one end and cantilevered out to meet a similar section or only supported in the centre and cantilevered out in opposite directions. Truss bridges: made of a lattice of wood, concrete or these days usually steel, carrying a road, railway, pipeline etc. Suspension bridges: effectively held up by cables suspended from towers built on cofferdams with their foundations embedded in, for example, the shores of a lake or river, often with intermediate towers in the river or lake bed.