SCAFFOLDING. A temporary wooden structure, by means of which the workmen employed in erecting the framework of a building are enabled to place the various materials in their definitive positions. Scaffoldings are either supported wholly, or in part, by the buildings to which they are attached ; or they are made totally independent of those buildings, with points of support upon the ground. Sometimes the machinery for hoisting the building materials is placed upon the independent scaffoldings ; at others, it is placed on the walls, or at the foot of the structure, or again, the materials may be carried up inclined roads formed in the scaffolding.
When scaffoldings are supported by the buildings they are designed to serve, they are usually formed by inserting cross-bearers in the walls (if the Flatter should be of a con siderable thickness, and at some distance apart), which cross bearers project beyond the faces of the wall for a sufficient dis tance to allow the construction of a gang way for the workmen, and the extremities are strengthened by means of inclined struts. These cross-bearers are placed about 5 feet apart, horizontally; and in rows, vertically, about 6 feet apart ; and upon them boards of 11 or 14 inches in thickness are laid. Holes are left in the walls to receive the bearers, or putlogs, as they are called, and the feet of the struts are clipped by vertical ties, which clip also the putlogs, and thus form a complete frame acting on both sides of tho wall ; the whole of this framing is removed on the com pletion of the work, and the putlog-holes are filled in. When the walls aro close together, the putlogs bear upon them without any struts, but the scaffolding in such cases rarely goes beyond the external face of the wall, so that the workmen are obliged to lay the materials "overhand." Chimney shafts are built in this manner, without framed scaffolding ; many of the keeps of medieval castles were built by means of framed projecting trusses; and in Violist le Due's Dictionnairo RaisonntS do l'Arehitecture Franeaise; some curious illustrations of the manner in which the medieval architects combined in the same scaffolding the functions of a working stage, and of an inclined road, will be found.
The ordinary scaffoldings used in the south of England, which are partially independent of the buildings, are composed of poles fixed iu the ground at distances of about 9 feet from centre to centre ; these poles are called the standards, and they are tied together by horizontal poles, or ledgers, at distances of about 6 feet vertically, as well as by raking braces, Upon the ledgers putlogs are laid at distances of about 4 or 5 feet, and with clear bearings, between the wall and the outer ledger, of from 3 feet 6 inches to 5 feet. The boards are laid upon the putlogs. Both the putlogs and boards are left loose, in order to allow materials to be hoisted without difficulty ; but the standards, ledgers, and braces are firmly bound together by cords and wedges ; nails or screws being, it is to be observed, rarely used in tho construe tion of scaffolding. It is7customary to strengthen some portions of the
scaffolds thus formed, in order to provide for the reception of the hoisting machinery when stonework is used in conjunction with bricks; but of late years the scaffoldings of buildings in which stone is largely employed have been executed with framed baulk timber and constitute structures of great solidity. Detailed accounts of scaffolds of this description are to be found in the Transactions of the Institu tion of Civil Engineers,' in the 'Builder,' in the 'Nouvelles Annales de Construction,' in the 'Annales des Pouts et Chanssdes; &c., in Rondelet's Art de Batir; Kraft's' l'Art de la Charpente; Perronnet's 'Nouvelle Architecture Hydraulique,' Fontana's Templum Vatica num; rte. Descriptions of scaffoldings which have been made to serve at the same time as centres, or supports for parts of the work of the permanent structure, are to be found in those works. In Foster's • Bauzeitung ' for 1854 there is a very good account of the suspended scaffolding used in the reconstruction of the Pont Neuf, to which it is desirable to call attention. See also Emy's Traitd de la Charpenterie.' The scaffoldings which are erected independently of the buildings, throughout, are in point of fact timber structures of a very elaborate description, and they have to resist not only the various actions pro duced by the movements of the materials and of the workmen, but also those produced by the wind, acting as the latter frequently does with a great leverage. It becomes essential, under these circum stances, to frame and brace the whole system with extreme care; and, should the scaffolding have to remain a long time in place, precautions must be taken to guard against any decay of the wood. This, of course, would be the most likely to commence in the portions of the scaffolding built into the ground, or in those directly exposed to the action of the rain ; the scarf or tenon joints also are very likely in these structures, which always have a degree of flexibility, to give access to the atmospheric moisture, and thus to rot. It is only in buildings of the greatest importance, or of a very peculiar nature, that scaffoldings entirely independent of the walls are used ; for their construction really requires the erection of a timber frame on each side of the wall, and is consequently a very costly operation. The scaffolds used for raising the obelisks of Luxor, and in the Piazza in front of St. Peter's at Rome, are amongst the most remarkable works of this kind yet executed. See Fontana and Emy.