Английский язык для студентов строительных специальностей
UNIT 11.BUILDING THE WALLS 249
Masonry is commonly used for the walls of buildings, retaining walls and monuments. Brick and concrete block are the most common types of masonry in use in industrialized nations and may be either weight-bearing or a veneer. Concrete blocks, especially those with hollow cores, offer various possibilities in masonry construction. They generally provide great compressive strength and are best suited to structures with light transverse loading when the cores remain unfilled. Filling some or all of.the cores with concrete or concrete with steel reinforcement (typically rebar) offers much greater tensile and lateral strength to structures.
The use of materials such as brick and stone can increase the thermal mass of a building, giving increased comfort in the heat of summer and the cold of winter, and can be ideal for passive solar applications. Brick will not require painting and so can provide a structure with reduced life-cycle costs, although sealing appropriately will reduce potential spalling due to frost damage. Non-decorative concrete block generally is painted or stuccoed if exposed. The appearance, especially when well crafted, can impart an impression of solidity and permanence. Masonry is heat resistant and thus provides fire protection. Masonry walls are more resistant to projectiles, such as debris from hurricanes or tornadoes than walls of wood or other softer, less dense materials. Extreme weather causes degradation of masonry wall surfaces due to frost damage. This type of damage is common with certain types of brick, though rare with concrete block. If non-concrete (clay-based) brick is to be used, care should be taken to select bricks suitable for the climate in question. Masonry tends to be heavy and must be built upon a strong foundation (usually reinforced concrete) to avoid settling and cracking. If expansive soils (such as
adobe clay) are present, this foundation needs to be quite elaborate and the services of a qualified structural engineer may be required, particularly in earthquake prone regions.
Masonry boasts an impressive compressive strength (vertical loads) but is much lower in tensile strength (twisting or stretching) unless reinforced. The tensile strength of masonry walls can be strengthened by thickening the wall, or by building masonry piers (vertical columns or ribs) at intervals. Where practical, steel reinforcements can be added.
The strength of a masonry wall is not entirely dependent on the bond between the building material and the mortar; the friction between the interlocking blocks of masonry is strong enough to provide a great deal of strength on its own. The blocks sometimes have grooves or other surface features added to enhance this interlocking, and some dry set masonry structures forego mortar altogether.
Solid masonry without steel reinforcement tends to have very limited applications in modern wall construction. While such walls can be quite economical and suitable in some applications, susceptibility to earthquakes and collapse is a major issue. Solid unreinforced masonry walls tend to be low and thick as a consequence.
Solid brickwork is made of two or more layers of bricks with the units ranning horizontally (called stretcher bricks) bound together with bricks ranning transverse to the wall (called header bricks). Each row of bricks is known as a course. The pattern of headers and stretchers employed gives rise to different bonds such as the common bond (with every sixth course composed of headers), the English bond, and the Flemish bond (with alternating stretcher and header bricks present on every course). There are no significant utilitarian differences between most bonds, but the appearance of the finished wall is affected. Vertically staggered bonds tend to be somewhat stronger and less prone to major cracking than a non-staggered bond.
250 Английский язык для студентов строительных специальностей
UNIT 11.BUILDING THE WALLS
20. Identify the topic of each paragraph of Text 11B.
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