Masonry arches

Masonry arches

1. 1. BRICK ARCH Arches offer architectural view and enhance aesthetic beauty of buildings. They are used to cover openings of door and windows and transfer the above loads to the side of walls Brick arches are ornamental ways of bridging openings which are comprised of small units bonded together around a curve or series of curves. Arches need no additional reinforcements as brick lintels do because of wedge shaped units as load increases, the unit in the arch becomes tighter DIFFERENT COMPONENTS OF ARCH ABUTMENT OR PIER – it belongs to the portion of wall or pier upon which the arch is supported ARCH RING – it is a series of stones or bricks which contain a curve same as that of arch INTRADOS OR SOFFIT – it stands for the under-surface of an arch EXTRADOS – it belongs to the external surface of an arch or the exterior curve of the arch ring VOUSSOIRS OR ARCH BLOCK – it stands for the wedge-shaped units to develop the arch SPRINGING STONE OR SPRINGER – it is the initial voussoirs at springing level on both sides of arch SPRINGING LINE – fictious line that connects two springing lines CROWN – stands for the uppermost point of the extrados, or top part of arch KEY STONE – uppermost central wedge shaped block of an arch HAUNCH – part of the arch that is located centrally among the key and skew backs CENTER OF ARCH – the geometrical point based on which the arcs forming intrados of arch, extrados of arch and arch rings are described is the center or striking point SPAN OF ARCH – clear horizontal distance between the supports or abutments or piers is termed as span of arch RISE OF ARCH – clear vertical distance between the highest point on the intrados and the springing line is called as rise MASONRY ARCHES CLASSIFICATION Brick arches are mainly classified into three groups according to their construction and structure PLAIN BRICK ARCH AXED BRICK ARCH GAUGED BRICK ARCH

2. 1.1 PLAIN BRICK ARCH Plain Arches are those in which the bricks are not cut, or rubbed, so as to form voussoirs accurately radiating to a center. The joints are therefore wider at the "extrados" than they are at the "intrados." Such arches are used for ordinary brickwork in tunnels, and concealed work generally. In such arches, the joints are made wedge-shaped to obtain the arch curve with more thickness at the extrados and less thickness at intrados. 1.2 AXED BRICK ARCH In Axed brick arch, the brick axe is used to cut the bricks info wedge-shape. Due to cutting the bricks to the shape of a wedge, the thickness of the joints is similar to the radial line, which is not seen in rough brick arches. Since bricks are cut to wedge-shapes and not finally dressed, the appearance of this arch is not good-looking or pleasant. NEATLY CUT AND FINISHED VISUALLY UNAPPELAING AT TIMES 1.3 GAUGED BRICK ARCHES The word gauge is used in the sense of measurement, as gauged bricks are those that have been so accurately prepared to a wedge shape that they can be put together to form an arch with very thin joints between them. This does not improve the strength of the brick arch and is done entirely for reasons of appearance. Hard burned clay facing bricks cannot be cut to the accurate wedge shape required for this work because the bricks are too coarse grained, and bricks which are to be gauged are specially chosen. One type of brick used for gauged brickwork is called a rubber brick because its composition is such that it can be rubbed down to an accurate shape on a flat stone. PRECISELY CUT RUBBER BRICKS RUBBER BRICKS

3. 2. STONE ARCH Depending upon workmanship, stone arches are of two types: Rubble arches, and Ashlar arches 2.1 RUBBLE ARCH Rubble masonry arch is comparatively weak and is used for comparatively inferior work. These arches are made of rubble stones which are hammer dressed, roughly to shape and size of voussoirs of the arch and fixed in cement mortar. Rubble arches are used upto spans of 1 m. They are also used as relieving arches, over wooden lintels. Upto a depth of 37.5 cm, these arches are constructed in one ring. For greater depths (thickness), rubble stones are laid in two rings in alternate course of headers and stretchers. 2.2 ASHLAR ARCH In this type, the stones are cut to proper shape of voussoirs, and are fully dressed, set in lime or cement joints with proper bed joints. Up to depth of 60 cm, the voussoirs are made of full thickness of the arch. For determining the wedged shapes of voussoirs, it is preferable to set out the arch on a level platform, marking on it the key-stone and voussoirs along with radial mortar joints. Ashlar stone can also be used to make flat arches, in which the joints are either joggled or rebated. RUBBLE ARCH ASHLAR ARCH RUBBLE STONES RUBBLE STONES 3. RELIEVING ARCH A discharging arch or relieving arch is an arch built over a lintel or architrave to take off the superincumbent weight. This arch is constructed either on a flat arch or on a wooden lintel to provide greater strength. The ends of9 the relieving arch should be carried sufficiently into the abutments. The relieving arch makes it possible to replace the decayed lintel later, without disturbing the stability of the structure. HISTORY The Romans frequently employed the discharging arch, and inside the portico of the Pantheon the architraves have such arches over them. In the Golden Gateway of the palace of Diocletian at Split the discharging arches, semicircular in form, were adopted as architectural features and decorated with moldings. The same is found in the synagogues in Palestine of the 2nd century; and later, in Byzantine architecture, these moulded archivolts above an architrave constitute one of the characteristics of the style. In the early Christian churches in Rome, where a colonnade divided off the nave and aisles, discharging arches are turned in the frieze just above the architraves. RELIEVING ARCHES RELIEVING ARCHES BUILT ON ARCHITRAVE IN THE PANTHEON