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Text 9: ROMAN CONCRETE
During the Roman Empire, Roman concrete was made from quicklime, pozzolana, and an aggregate of pumice. Concrete, as the Romans knew it, was in effect a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains which trouble the builders of similar structures in stone or brick.Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.
The widespread use of concrete in many Roman structures has ensured that many survive to the present day. The Baths of Caracalla in Rome are just one example of the longevity of concrete, which allowed the Romans to build this and similar structures across the Roman Empire. Many Roman aqueducts and Roman bridges have masonry cladding to a concrete core, a technique they used in structures such as the Pantheon, the dome of which is concrete.
The secret of concrete was lost for 13 centuries until 1756, when the British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. Portland cement was first used in concrete in the early 1840s.
Text 10: FROM THE HISTORY OF BRICKMAKING
Bricks were first used for building in the Middle East. More than 6,000 years ago the Sumerian people living in the valley of the Tigris and Euphrates rivers discovered that the muddy clay deposited by the two rivers was ideal for building. The clay was mixed with water and straw and pressed into rectangular moulds. The bricks were then turned out of the moulds and left to dry in the sun. Sun-dried bricks such as these, known as abode after the clay from which they are made, are still used for building in warm, dry regions throughout Africa and South America. Adobe is cheap and can last for centuries.
The next development in the history of brickmaking came around 4,000 years ago when the brick kiln was invented in the valley of the Tigris and Euphrates. Brickmakers found that if bricks were fired after they had been dried in the sun, they were harder and better able to withstand damp. The earliest type of kiln was a beehive-shaped mound of dried bricks with arches at the bottom in which the fires could be lit. Later kilns were permanent buildings in which the bricks were slowly heated up and allowed to cool over a period of four days.
From the Middle East, the ancient craft of brickmaking spread westward to Egypt and the Mediterranean and eastward to India and China. Roman builders brought bricks to Britain in the 1st century AD, but when the Roman Empire fell in the 5th century, the art of brickmaking was lost for some 600 years. It was revived by the Italians in the 11th century and spread quickly throughout northern Europe. By the mid-17th century brick-built walls were replacing the old timber frameworks in buildings.
Text 11: THE ELASTIC THEORY OF STRUCTURES
A significant achievement of the first industrial age was the emergence of building science, particularly the elastic theory of structures. With it, mathematical models could be used to predict structural performance with considerable accuracy, provided there was adequate quality control of the materials used. Although some elements of the elastic theory, such as the Swiss mathematician Leonhard Euler's theory of column buckling (1757), were worked out earlier, the real development began with the English scientist Thomas Young's modern definition of the modulus of elasticity in 1807. Louis Navier published the elastic theory of beams in 1826, and three methods of analyzing forces in trusses were devised by Squire Whipple, A. Ritter, and James Clerk Maxwell between 1847 and 1864. The concept of a statically determinate structure — that is, a structure whose forces could be determined from Newton's laws of motion alone — was set forth by Otto Mohr in 1874, after having been used intuitively for perhaps 40 years. Most 19th-century structures were purposely designed and fabricated with pin joints to be statically determinate; it was not until the 20th century that statically indeterminate structures became readily solvable. The elastic theory formed the basis of structural analysis until World War II, when bomb-damaged buildings were observed to behave in unpredicted ways and the underlying assumptions of the theory were found to require modification.
Text 12: NANOTECHNOLODY'S FOR REAL IN THE BUILDING INDUSTRY
Nanotechnology is sometimes seen as all hype, with little real-world application. But nanomaterials are already all around us. Take the buildings that we live and work in, for instance. You will find nanotechnology used to create stronger steel, self-cleaning glass, solar-collecting fabrics, and even smog-eating concrete. And not only are these nanomaterials present in our buildings, they are making them better places to live and work.
Self-cleaning glass has a nanoparticle coating dirt can't stick to, eliminating the need for expensive and dangerous manual window washing on tall buildings. Solar-collecting fabric is the first of a new wave of building components that convert solar radiation into electricity. That means no more applying unattractive solar panels to the roof, but instead integrating energy production into building facades. Nanocomposite steel is more corrosion resistant than conventional steel, and can reduce installation costs by up to 50%. And the quantity required to make a building may be up to 40% less than conventional steel. Smog-eating concrete is produced by applying a nanolayer of titanium dioxide to concrete, which triggers a catalytic reaction that destroys many pollutants in contact with the surface. At the very least, these materials reduce building maintenance costs, leaving more money for other improvements, and they can help clean up the environment. They can reduce energy costs as well. And for every nanomaterial available today, there are approximately seventy more in research and development, meaning that building construction and architecture are in for some big changes thanks to small technology.
. Text 13: A HORIZONTAL SUPPORT
A beam is a structural component mainly working in bending through the agency of vertical forces and that transmits to the bearing points the loads that are applied to it. A beam is a lengthened and horizontal support made of metal, wood, reinforced or prestressed concrete and whose section has been studied for a good bending strength. Beams are mainly subjected to bending moments and shearing forces. Simple beams are made up of only one piece, of a section calculated to withstand the strains that aim at making them bending. When the strains become too strong, reinforced beams or compound beams are then used. Beams rest:
Text 14: ROOF
The roof of a building often reflects the climate of the place in which the building is located since it protects the people in it from rain and sun. In dry countries the roof is flat and can be used as an outdoor room when the sun is not too hot. Where it often rains the roof usually slopes so that the wet can run off it, and where there are snowfalls, the roof slopes steeply so that the snow will slide off and not build up into a thick layer. A roof that slopes is called a pitched roof. After a time people found it inconvenient to live in a house with sloping sides, so they built upright walls and laid big beams called tie-beams across the top at regular distances from each other. Then they put up the triangular frameworks resting on the tie-beams. These triangles of beams are called trusses. A ridge-piece, purlins, and rafters were used to complete the skeleton of the roof.
In the Middle Ages the wooden frame of the roof was not hidden by a ceiling on the inside and was often richly decorated. To increase the effect of height and space the hammer-beam roof was designed. This had no tie-beams, but instead there were short beams sticking out from both walls, and to these beams other timbers called struts were fixed to support the main rafters.
The waterproof covering of a pitched roof is usually of tiles, slates, or shingles. Tiles are thin slabs of baked clay, generally red or brown in colour. Strips of wood called battens are fixed to the outside of the rafters, usually over sheets of weatherproof roofing -felt which help to keep out draughts and wind-blown snow. The tiles, shingles, or slates are then hung on by projecting pieces called nibs, or nailed or clipped to the battens in regular horizontal rows or courses. Flat roofs usually consist of boards covered with overlapping sheets of roofing felt coated with bitumen. When a roof has to cover a large space, steel trusses are used instead of wood. Large flat roofs may be made of reinforced concrete with a waterproof covering.
Text 15: STRUCTURAL BUILDING ENGINEERING
Structural building engineering includes all structural engineering related to the design of buildings. It is the branch of structural engineering that is close to architecture. Structural building engineering is primarily driven by the creative manipulation of materials and forms and the underlying mathematical and scientific ideas to achieve an end which fulfills its functional requirements and is structurally safe when subjected to all the loads it could reasonably be expected to experience. This is subtly different from architectural design, which is driven by the creative manipulation of materials and forms, mass, space, texture and light to achieve an end which is aesthetic, functional and often artistic.
The structural design for a building must ensure that the building is able to stand up safely, able to function without deflections or movements which may cause fatigue of structural elements, cracking or failure of fixtures, fittings or partitions, or discomfort for occupants. It must account for movements and forces due to temperature, creep, cracking and imposed loads. It must also ensure that the design is practically buildable within acceptable manufacturing tolerances of the materials. It must allow the architecture to work, and the building services to fit within the building and function (air conditioning, ventilation, electrics, etc). The structural design of a modem building can be extremely complex, and often requires a large team to complete.
Text 16: STRUCTURAL ENGINEER
Structural engineers analyse, design, plan, and research structural components and structural systems to achieve design goals and ensure the safety and comfort of users or occupants. Their work takes account of safety, technical, economic and environmental concerns, but they may also consider aesthetic and social factors.
Typical structures designed by a structural engineer include buildings, towers and bridges. Other structures such as oil rigs, space satellites, aircraft and ships may also be designed by a structural engineer. Most structural engineers are employed in the construction industry, however there are also structural engineers in the aerospace, automobile and shipbuilding industries. In the construction industry, they work closely with architects, civil engineers, mechanical engineers, electrical engineers, surveyors, and construction managers.
Structural engineers ensure that buildings and bridges are built to be strong enough and stable enough to resist all appropriate structural loads in order to prevent or reduce loss of life or injury. They also design structures to be stiff enough to not deflect or vibrate beyond acceptable limits. Fatigue maybe an important consideration for bridges and for aircraft design, or for other structures which experience a large number of stress cycles over their lifetime. Consideration is also given to durability of materials against possible deterioration which may impair performance over the design lifetime.
Text 17: SURVEYING AS A CAREER
The basic principles of surveying have changed little over the ages, but the tools used by surveyors have evolved tremendously. Engineering, especially civil engineering, depends heavily on surveyors.
Whenever there are roads, railways, reservoir, dams, retaining walls, bridges or residential areas to be built, surveyors are involved. They establish the boundaries of legal descriptions and the boundaries of various lines of political divisions. They also provide advice and data for geographical information systems, computer databases that contain data on land features and boundaries.
Surveyors must have a thorough knowledge of algebra, basic calculus, geometry, and trigonometry. They must also know the laws that deal with surveys, property, and contracts. In addition, they must be able to use delicate instruments with accuracy and precision. In the United States, surveyors and civil engineers use units of feet wherein a survey foot is broken down into lOths and lOOths.
In most states of the U.S., surveying is recognized as a distinct profession apart from engineering. Licensing requirements vary by state, however these requirements generally all have a component of education, experience and examinations. In the past, experience gained through an apprenticeship, together with passing a series of state-administered examinations, was required to attain licensure. Nowadays, most states insist upon basic qualification of a degree in surveying in addition to experience and examination requirements.
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