PIER. In architecture (q.v.) it usually denotes a vertical support in masonry, brickwork or concrete which carries an arch or superstructure. In this sense it is applied both to those por tions of a structure which are visible above ground and to isolated or detached supports underground described as foundation piers. The term is sometimes applied to the solid parts of a wall between windows or voids, and also to the isolated masses of brickwork, masonry or concrete to which gates are hung.
Bridge Piers.—In the construction of bridges (q.v.) and via ducts, pier denotes the solid structure upon which the bridge superstructure (including arches) is supported. Occasionally in the case of high piers supporting viaducts and bridge superstruc tures the upper portions are constructed of open-braced iron- or steel-work.
Foundation piers for bridges are formed of solid masonry, brickwork or concrete and, sometimes, reinforced-concrete is em ployed for the purpose. In places where timber is abundant, as in some parts of the United States and Canada, wooden cribs filled with rubble stone or concrete have been used for raising the foundations of piers out of water.
Special provisions must be made for the foundations of piers where the ground is soft for some depth, or loose water-bearing strata are encountered, and especially where the piers of large bridges crossing rivers have to be constructed under water. Among the means employed in these situations are steel and iron cylin ders, wells, caissons, bearing piles or some form of coffer-dam within which the foundations may be constructed. (See CAISSON, FOUNDATIONS, COFFER-DAM.) Piles are sometimes employed to provide both the foundations and the piers carrying a structure of viaduct character. Thus screw piles, having wide bearing-blades of cast-iron in the form of a screw-thread turned about a central shaft or column of cast iron or steel, are sometimes sunk through soft strata till they reach a firm bed, or one sufficiently consolidated by the superin cumbent layers to enable it to support the weight imposed on the broad blades. Hollow, cast iron, cylindrical piles with a broad cir
cular disc at the bottom to increase their bearing surface, have also been used for piers founded in sandy or silty strata of con siderable thickness. They are sunk by hydraulic jetting, i.e., the scouring away of the soft material from under the disc by means of a jet of water emitted under high pressure from a pipe lowered within the pile. Water jets are also employed to facilitate the sinking of screw and other forms of piles. (See FOUNDATIONS.) Harbour Piers.—The term pier is often applied to works sheltering harbours such as the Tynemouth piers which are strictly breakwaters (q.v.). Landing stages also, whether solid or open, have for a long time been called piers, as the Admiralty pier and the Prince of Wales' pier at Dover, the former essen tially a breakwater with provision for berthing vessels and land ing passengers on its sheltered side. The jetties (q.v.) thrown out from the shore to protect the entrance to a river harbour are also sometimes described as piers. In North America the term is commonly employed for a wharf structure that projects into a river, fairway or harbour.