Pier

Pier (older forms per or Pere, from Med. Lat. pera; the word is of obscure origin, and the connexion with Fr. Pierre, Lat. Petra, stone, is doubtful; equivalents are Fr. piedroit, pilier, trumeau; Ital. pi/a; Ger. Pfeiler), the term given in architecture to a vertical support in masonry or brickwork, usually rectangular on plan, which carries an arch or superstructure. The term is also sometimes given to the great circular columns which in some English cathedrals and churches carry the nave arches. In early Christian churches, when antique columns, such as abounded in Rome, were not procurable, square piers took the place of columns and sometimes alternated with them. The introduction of vaulting, however, in the 11th century, necessitated a support of much greater dimensions than those which had been deemed sufficient when the roof was of timber only, and led to the development of the compound or clustered pier. To give extra support to the subordinate arches of the nave arcade, semicircular shafts or pilasters were added, carried up to the transverse and diagonal ribs of the main vault. In Romanesque work the pier was generally square on plan with semicircular shafts attached, the angles of the pier being worked with smaller shafts. As the rings or orders of the nave arches increased in number, additional shafts were added to carry them, and the pilaster facing the nave had central and side shafts rising to carry the transverse and diagonal ribs of the vault; this development of the compound pier obtains throughout Europe in all vaulted structures. In the Early English period the piers become loftier and lighter, and in most important buildings a series of clustered columns, frequently of marble, are placed side by side, sometimes set at intervals round a circular centre, and sometimes almost touching each other. These shafts are often wholly detached from the central pier, though grouped round it, in which case they are almost always of Purbeck or Bethersden marbles. In Decorated work the shafts on plan are very often placed round a square set angle-wise, or a lozenge, the long way down the nave; the centre or core itself is often worked into hollows or other mouldings, to show between the shafts, and to form part of the composition. In this and the latter part of the previous style there is generally a fillet on the outer part of the shaft, forming what has been called a "keel moulding" (q.v.). They are also often tied together by bands, formed of rings of stone and sometimes of metal. About this period, too, these intermediate mouldings run up into and form part of the arch moulds, there being no impost. This arrangement became much more frequent in the Perpendicular period; in fact it was almost universal, the commonest section being a lozenge set with the long side from the nave to the aisle, and not towards the other arches, as in the Decorated period, with four shafts at the angles, between which were shallow mouldings, one of which was in general a wide hollow, sometimes with wave moulds. The small columns at the jambs of doors and windows, and in arcades, and also those attached to piers or standing detached, are generally called "shafts" (q.v.).

  


The term pier is sometimes applied to the solid parts of a wall between windows or voids, and also to the isolated masses of brickwork or masonry to which gates are hung. (R. P. S.) Piers of Bridges. - The piers of bridges and viaducts on land are constructed of masonry or brickwork and occasionally, in the case of high piers, of open braced ironwork, as exemplified by the old Crumlin viaduct in Wales and the Pecos viaduct in Texas. These piers, besides being proportioned in cross-section to the weight they have to support, are widened out at their base, so as to distribute the load over a sufficient area for it to be borne by the stratum on which it rests without risk of settlement. Special provisions have to 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. In soft ground, bearing piles driven down to a firm stratum, and surmounted by a planked floor or a layer of concrete, provide a convenient foundation for a pier; and in places where timber is abundant, wooden cribs filled with rubble stone or concrete have been used in the United States for raising the foundations for piers out of water. For river piers, where a firm, watertight stratum is found at a moderate depth below the river-bed, the site is often enclosed within a coffer-dam or a plate iron caisson carried down into the stratum and raised out of water; and then, after the water has been pumped out and the surface layers removed, the pier is readily built within the enclosure in the open air. When, however, a river-bed consists of silt, sand or other soft materials extending down to a considerable depth, brickwork wells are gradually sunk to a firm stratum by removing the material within them with grabs, and on them the piers are built out of water; or bottomless caissons are carried down by excavating their interiors under compressed air, and the piers are built on top of them within a plate-iron enclosure, a system adopted for the piers of the Brooklyn, St Louis, Forth and other large bridges, and essential for forming foundations on sloping rock, such as was encountered in places under the Firth of Forth.

The methods indicated above as employed for the foundations of the piers of bridges under favourable conditions belong equally to the foundations of other structures (see Foundations); but there are some methods which, by combining bridge piers and their foundations in a single structure, appertain entirely to piers. Thus iron screw piles, sunk by turning into Scale 5 0 10 20 Feet Fig. i. - Pier with Disk Piles.

the soft bed of a river till they reach a firm stratum or one sufficiently consolidated by the superincumbent layers to enable it to support the wide blades of the screws with the weight imposed on them, were formerly often arranged in converging clusters joined together at the top, so as to serve as the piers of bridges having several comparatively small spans, and intended for carrying lightly constructed railways across rivers in India and elsewhere. Hollow, cast-iron, cylindrical piles also, with a broad circular disk at the bottom to increase their bearing surface, have been used for piers founded in sandy or silty strata bolted together with a specially strong bottom ring, sometimes made of wrought iron and having a cutting edge, have been often employed for the construction of the river piers of bridges, being gradually carried down to a watertight stratum by excavating inside, and subsequently filled up solid with concrete and brickwork; the piers of the Charing Cross and Cannon Street bridges across the Thames are notable instances of the adoption of this method, which is well illustrated by the piers of the bridges across the River Chittravati in ' India (fig. 2). Sometimes, instead of two or more independent cylinders being sunk, the whole site of a pier is enclosed within a wrought-iron caisson, usually divided into sections r --- by vertical partitions, which is sunk and filled up solid in the same way as cylinders, a system adopted, for instance, for the piers of the bridge across the Hawkesbury River in New South Wales.

## P r omenade Piers

The term pier is often applied to works sheltering harbours, such as the Tynemouth piers, which are strictly breakwaters. Landing stages also, whether solid or open, have for a long time been called piers, as the Admiralty Pier and the Prince of Wales's Pier at Dover; but the open promenade piers which form a common feature at seaside resorts are the type of pier best known to the general public. These piers are supported upon open pilework of timber or iron, and consequently expose little surface to waves in storms and do not interfere with the drift of shingle or sand along the coast (fig. 3). 1 Timber piles are best suited for withstanding the shocks of vessels at landing stages, at which places they are generally used; but since they are subject to the attacks of the teredo, and expose a considerable surface to the waves, iron piles are generally adopted for the main portion of these piers. The pioneer of these piers was the old chain pier at Brighton, which was erected in 1822-1823. It was founded upon oak piles, was 1136 ft. long, and had a timber landing-stage at the end. I t consisted of four spans suspended from chains on the model of the Menai Suspension Bridge, then in course of construction, and was destroyed by a gale in December 1896. A wider and more modern type of pier was erected at the west end of Brighton in 1865-1866, ,;??11?1??-?Iil?lll??al ?II l ';?

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900 c r  FIG. 3. - Promenade Pier.

of considerable thickness; they are sunk to the requisite depth by lowering a pipe down the inside of the pile to the bottom and emitting a powerful jet of water which, stirring up the soft material and scouring it away from under the disk, causes the pile to descend. This system was first adopted for the piers of a railway viaduct crossing the wide, sandy Kent and Leven estuaries opening into Morecambe Bay (fig. I). Cast-iron cylinders, consisting of a series of rings formed of segments all and subsequently extended; whilst a new pier was completed in 1900 near the site of the old chain pier, 1 boo ft. long. The Southport pier, erected in1859-1860and afterwards prolonged, furnishes an example of an iron pier supported on disk piles sunk in sand as described above (fig. I); whilst the much more commonly used iron screw piles, adopted as early as 1847 for an open landing-pier on the Irish coast at Courtown, which was exposed to a great littoral drift of sand, are shown as the mode of support for the pier 1 The Engineer (1888), i. 380, 381 and 384.

Sand  Rock.

FIG. 2. - Cylindrical Piers for River Bridges.

at St Leonards (fig. 3). The length given to these promenade piers depends mainly on the slope of the foreshore, which determines the distance from the shore at which a sufficient depth is reached for steamers of moderate draught to come alongside the end of the pier. Thus, whereas a length of 900 ft. has sufficed for the St Leonards pier on a somewhat steep, shingly beach, the pier at Ryde, constituting the principal landing-place for the Isle of Wight passengers, has had to be carried out about half a mile across a flat alluvial foreshore to reach water deep enough for the access of the steamboats crossing the Solent. The vast sands, moreover. at the outlet of the Ribble estuary, stretching two or three miles in front of Southport at low water of spring tides, have necessitated the construction of a pier 4395 ft. long merely to get out to an old flood-tide channel, which is now completely severed by the sands at low water from all connexion with the river.

(L. F. V. - H.)