Masonry

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Masonry - The art or trade of building in stone, universally practiced since ancient times.

Masonry may be divided into two broad categories called rubble and ashlar. 

Rubble is composed of irregular and coarsely jointed quarried or field stone. 

Ashlar is made up of carefully worked stones set with fine, close joints. 

Either kind of masonry may be laid with mortar; when laid without mortar, it is called dry masonry.

Bricks: Blocks of clay or other ceramic used for construction and decorative facing. Bricks may be dried in the sun but are more usually baked in a kiln. They cost relatively little, resist dampness and heat, and can last longer than stone. The color varies according to the clay used and in proportions according to architectural tradition. Some bricks are made of special fireclays for use in fireplaces or ovens. Others may be made of glass or they may be textured or glazed. Bricks may be arranged in various patterns, called bonds, according to the way the long sides (stretchers) or short sides (headers) are placed.

Tile: Thin slab of glazed or unglazed fired clay used structurally or decoratively on floors, walls, and roofs; sometimes, by extension, thin slabs of glass, plastic, stone, asphalt, or acoustically absorbent material such as asbestos, as well as hollow ceramic blocks used structurally (as in drains or partitions).

Tiles are usually formed by pressing moist clay into a mold; modern floor tiles are often machine pressed from fine-grained clay. Tiles can also be slip cast, or formed by pouring slip (liquid clay) into a porous mold and allowing it to stiffen. Glaze and metal oxide-painted designs may be added before the tile is fired. Depending on the clay and the firing temperature, fired tiles range from porous earthenware to hard, highly vitrified porcelain. 

Roofs: The three common systems for tile roofs are an under-layer of concave tiles covered at the joints by an over-layer of convex tiles; overlapping S-shaped tiles; and flat, shingle-like tiles (sometimes of stone).

Floors: The most common modern ceramic floor tiles are small, highly vitrified, machine-pressed tiles in various colors.

Builders who were hired for the construction of a structure ordinarily carry out their work under the observation of an Architect and or an Engineer, who acts as agent of the owner. City Inspectors review the work for general compliance with the local building code. The immediate responsibility of the contractor, Architect, and Engineer ends when the local authorities approve the building for occupancy and the owner accepts the building. However, the contractor, Architect, and Engineer are legally responsible for any deficiencies in the construction or design for a period of several years after acceptance, the time depending on the terms of the contract and local laws. 

Elements of a Building 

The major elements of a building include the following:

1. The foundation, which supports the building and provides stability:

2. The structure, which supports all the imposed loads and transmits them to the foundation;

3. The exterior walls, which may or may not be part of the primary supporting structure;

4. The interior partitions, which also may or may not be part of the primary structure;

5. The environmental-control systems, including ventilating, fire-pits, and lighting

6. The vertical transportation systems, such as dumbwaiters, service shafts, ramps and stairways;

7. The power, water supply, and waste disposal systems.

Building Loads

The loads imposed on a building are classified as either "dead" or "live." Dead loads include the weight of the building itself and all major items of fixed equipment. Dead loads always act directly downward, act constantly, and are additive from the top of the building down. Live loads include wind pressure, seismic forces, vibrations caused by machinery, movable furniture, stored goods and equipment, occupants, and forces caused by temperature changes. Live loads are temporary and can produce pulsing, vibratory, or impact stresses. In general, the design of a building must accommodate all possible dead and live loads to prevent the building from settling or collapsing and to prevent any permanent distortion, excessive motion, discomfort to occupants, or rupture at any point.

Foundations 

The structural design of a building depends greatly on the nature of the soil and underlying geologic conditions and modification by man of either of these factors.

Ground Conditions 

If a building is to be constructed in an area that has a history of earthquake activity, the earth must be investigated to a considerable depth. Faults in the crust of the earth beneath the soil must obviously be avoided. Some soils may liquefy when subjected to the shock waves of a quake and become like quicksand. In such cases, either construction must be avoided altogether or the foundation must be made deep enough to reach solid material below the potentially unstable soil. Certain clay soils have been found to expand 23 cm (9 in) or more if subjected to long cycles of drying or wetting, thus producing powerful forces that can shear foundations and lift lightweight buildings. Some soils with high organic content may, over time, compress under the building load to a fraction of their original volume, causing the structure to settle. Other soils tend to slide under loads.

Soils that have been modified in some way often perform differently, especially when other soil has been added to or mixed with existing soil, or when the soil has been made wetter or drier than normal, or when cement or chemicals such as lime have been added. Sometimes the soil under a proposed building varies so greatly over the entire site that a building simply cannot be constructed safely or economically.

Soil and geologic analyses are necessary, therefore, to determine whether a proposed building can be supported adequately and what would be the most effective and economical method of support.

If there is sound bedrock a short distance below the surface of the construction site, the area over which the building loads are distributed can be quite small because of the strength of the rock. As progressively weaker rock and soils are encountered, however, the area over which the loads are distributed must be increased.

The most economical foundation is the reinforced-concrete spread footing, which is used for buildings in areas where the subsurface conditions present no unusual difficulties. The foundation consists of concrete slabs located under each structural column and a continuous slab under load-bearing walls.

Mat foundations are typically used when the building loads are so extensive and the soil so weak that individual footings would cover more than half the building area. A mat is a flat concrete slab, heavily reinforced with steel, which carries the downward loads of the individual columns or walls. The mat load per unit area that is transmitted to the underlying soil is small in magnitude and is distributed over the entire area. For large mats supporting heavy buildings, the loads are distributed more evenly by using supplementary foundations and cross walls, which stiffen the mat.

Piles are used primarily in areas where near-surface soil conditions are poor. They are made of timber, concrete, or steel and are located in clusters. The piles are driven down to strong soil or rock at a predetermined depth, and each cluster is then covered by a cap of reinforced concrete. A pile may support its load either at the lower end or by skin friction along its entire length. The number of piles in each cluster is determined by the structural load and the average load-carrying capacity of each pile in the cluster. A timber pile is simply the trunk of a tree stripped of its branches and is thus limited in height. A concrete pile, on the other hand, may be of any reasonable length and may extend below groundwater level as well. For extremely heavy or tall buildings, steel piles, known as H-piles because of their shape, are used. H-piles are driven through to bedrock, often as far as 30 m (100 ft) below the surface. H-piles can be driven to great depths more easily than piles made of wood or concrete; although they are more expensive, the cost is usually justified for large buildings, which represent a substantial financial investment.

Caisson foundations are used when soil of adequate bearing strength is found below surface layers of weak materials such as fill or peat. A caisson foundation consists of concrete columns constructed in cylindrical shafts excavated under the proposed structural column locations. The caisson foundations carry the building loads at their lower ends, which are often bell-shaped.