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Apier, inarchitecture, is an upright support for a structure orsuperstructure such as anarch orbridge. Sections of structural walls between openings (bays) can function as piers. External or free-standing walls may have piers at the ends or on corners.
The simplestcross section of the pier issquare, orrectangular, but other shapes are also common. Inmedieval architecture, massivecircular supports called drum piers,cruciform (cross-shaped) piers, andcompound piers are common architectural elements.
Columns are a similar upright support, but stand on a round base; in many contexts columns may also be called piers. In buildings with a sequence ofbays between piers, each opening (window or door) between two piers is considered a single bay.
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Single-spanbridges haveabutments at each end that support the weight of the bridge and serve as retaining walls to resist lateral movement of the earthenfill of the bridge approach.[1] Multi-span bridges require piers to support the ends of spans between these abutments. In cold climates, the upstream edge of a pier may include astarkwater to prevent accumulation of broken ice during peak snowmelt flows. The starkwater has a sharpened upstream edge sometimes called acutwater. The cutwater edge may be of concrete or masonry, but is often capped with a steel angle to resist abrasion and focus force at a single point to fracture floating pieces of ice striking the pier. In cold climates, the starling is typically sloped at an angle of about 45° so current pushing against the ice tends to lift the downstream edge of the ice translating horizontal force of the current to vertical force against a thinner cross-section of ice until unsupported weight of ice fractures the piece of ice allowing it to pass on either side of the pier.[2]
In theArc de Triomphe, Paris (illustration, right) the central arch and side arches are raised on four massiveplanar piers[clarification needed].
Donato Bramante's original plan forSt Peter's Basilica in Rome has richly articulated piers. Four piers support the weight of thedome at the central crossing. These piers were found to be too small to support the weight and were changed later byMichelangelo to account for the massive weight of the dome.[3]
The piers of the fourapses that project from each outer wall are also strong, to withstand the outward thrust of the half-domes upon them. Manyniches articulate the wall-spaces of the piers.[3]
