Test 2.Types of Cranes

 

Cranes exist in an enormous variety of forms. Some are classified by shape, others by the function they perform, and still others by their form of mobility. Cranes are classified according to the greatest load they can move; on this basis they vary in size from one ton to over 250 tons.

Derrick is a special type of crane in which the distance from the end of the jib to the pillar can be changed. A guy derrick consists of a pivoted pillar that is braced by guy ropes, and a jib that is attached at the base of the pillar. A tower derrick is similar to a guy derrick except that its jib is movable and may be secured at different heights on the tower, or pillar.Tower derricks are used mostly in building construction.

Pillar crane has a self-supported column, or pillar, that can be turned on its vertical axis. A horizontal or inclinable jib is attached to the pillar. The load is raised or lowered from the end of the jib.

Portable jib craneis small and is attached to the columns or walls of a building by means of simple adaptors, or brackets that are placed at the required locations. Portable jib cranes are particularly useful in various areas of shops and warehouses.

There are several types of traveling cranes.One of the most common is traveling jib crane. Its pulley system is suspended from a trolley that moves along the length of the horizontal jib. Traveling bridge cranes consist of two elevated tracks that are bridged by a girder that travels along the tracks on wheels. Gantry cranes are designed for use outdoors or where an overhead runway is not practical. Gantry cranes have a bridge that is supported at both ends by vertical columns, or legs. The legs are mounted on wheels or rollers so that the entire structure can move along rails or tracks.

Truck craneis mounted on a truck that moves on large wheels or on tractor caterpillar treads. Cranes that travel on caterpillar treads are often called crawler cranes. Truck cranes are quite versatile because they are self-propelled and can be equipped with accessory booms, or jibs, to extend to about 46 meters high. Locomotive cranes are similar to truck cranes, but are designed to travel on standard gauge tracks.

Hoisting and transporting cargo to and from ships are often done with floating cranes,which are mounted on pontoons or barges. Floating cranes are also used for water work such as driving piles and raising sunken vessels and other objects.

Materials such as earth and rocks are often lifted and transported by cable cranes.The load is carriedin buckets attached to a cable that moves between two towers.

Notes:

jib(boom)-стрела грузоподъемного крана

pillar- стойка; колонна; вертикальная станина; вертикальная опора

guy derrick-вантовый деррик

pillar crane - мачтовый кран, башенный кран

portable jib crane - переносной дерикк-кран

traveling jib crane - подвижной мачтовый кран

gantry crane - портальный кран

truck crane - автомобильный кран

locomotive crane - железнодорожный кран

floating crane - плавучий кран

cable crane -кабельный кран

 

SUPPLEMENTARY TEXTS

House

Houseis a building that provides shelter, comfort, and protection. Houses vary in size from one-roomed mud huts to many-roomed mansions. They may have only one storey (floor), or several storeys. They stand in cities, towns, and villages, and in both suburban areas and the country. Types of houses vary with the needs and wealth of the inhabitants, and with the building materials that are available. Many large buildings are divided into flats, or apartment. Each flat is a complete, self-contained home on one storey. Houses may also be divided into self-contained maisonettes, each occupying two or more storeys.

Styles of houses vary widely from country to country. And, in many countries, the style of new houses has changed with passing time. Many house styles are named after the country or period of their origin. Others are named after the architects who created them. European historical styles include Romanesque, Gothic, Renaissance, Baroque, and Rococo. Architects who founded styles used for houses include the Italian Andrea Palladio and the Adam brothers of Britain.

The factors that influence the size and design of houses include climate, social customs, building techniques and materials, fashion, and wealth. Religious beliefs also influence style. For example, houses in some countries of eastern Asia have roofs that curve upwards at the eaves. The people believe that these roofs protect them from evil spirits. Other house styles are a result of social conditions. For example, in Britain during the early 1800’s, many wealthy people and the nobility commissioned the best architects to design their homes. They built fine, graceful houses suited to a leisurely life requiring large domestic staffs. But, today, most new houses are easy to maintain and comfortable for small families.

Local styles of houses are now less common than in earlier times. House styles have become more uniform in most parts of the world, because of new building materials and methods. A factory may produce prefabricated parts for houses to be erected quickly on site, instead of being built in stages.

 

Environment

Environment has an important effect on the houses that people build. In areas of great heat or cold, houses must be built to protect people from extreme temperatures. The traditional houses of the Eskimo people of the Arctic were built of blocks of snow. These snowhouses, called igloos, provided excellent insulation against the very low temperatures outside. In the extreme heat of the deserts of the Middle East, nomadic people called Bedouins lived in large tents made of fabric woven from the hair of their camels or goats. The thick material protected the people from the sun but could be opened at the sides so that air could circulate. Since the mid-1900’s both of these traditional styles of house have been replaced by housing built of more modern materials.

In Japan, houses were traditionally made from light materials, such as paper and bamboo. These paper houses collapse harmlessly if there is a volcanic eruption or an earthquake. Then the people can quickly and cheaply rebuild them. The stilt houses of Southeast Asia are also well adapted to their environment. People build these houses on tall poles in areas where floods might wash away ordinary houses, or where insect pests might invade them.

In alpine regions, where much snow falls, houses have steeply sloping roofs. As a result, the snow falls off easily. Sloping roofs are also needed in places where heavy seasonal rains fall. But, in hot, dry countries many houses are box-like, with flat roofs. The houses remain cool in the intense heat because the shuttered windows are small and the thick walls are painted white to reflect the sunlight.

In towns and cities, land is expensive, and much housing must occupy a small area. As a result, builders may construct tall blocks of flats or long, continuous rows of terraced houses. But, in the country, more land is available and detached houses and single-storey bungalows stand in their own large gardens or grounds. The suburbs of many British cities have semi-detached houses, each of which is linked to a similar house.

 

Materials

Materials used to build houses vary from mud and grass for tribal huts to factory-made one-room units for blocks of flats. Kinds of materials may be divided into two types: traditional, and modern.

Traditional materials include snow, mud, wood, bark, twigs, creepers, grass, leaves, dried blood, and stones. They may be used as they are found. Generally they are not strong materials. As a result, houses built from them must be small. But bamboo is strong and light and it may be split and joined easily. Large jungle leaves give good protection from heavy rain. Mud seals cracks in walls and prevents draughts. A mixture of mud and animals blood dries to make a solid floor.

Traditional materials also include wood, stone, timber, slate, tile, bricks, mortar, and plaster. They include natural and manufactured materials that are fashioned with tools. All heavily wooded countries have many timber houses. These houses are warm in cold weather, because wood is a good insulator. Stone houses are common in areas where stone can be quarried locally. But stone is a bad insulator and stone walls must be thick. Slate and factory-made tiles make strong, permanent roofs.

Wood has long been a popular building material because it is usually more plentiful and cheaper than other materials. Wood can be cut and shaped to provide a variety of house styles. Wood is also popular because so many different types are available. Wood is also used for such interior features as stairways, cabinets, floors, and doors. Wood can be natural, stained, painted, or carved.

Brick is one of the oldest and most common building materials. Brick wears well and, like wood, is usually; easy to obtain. Bricks are available in a number of colours and finishes.

Concrete block and stone make strong, attractive houses. Concrete blocks are made by pouring a mixture; of cement into a mould. They make durable houses that are relatively cheap to maintain. Builders also make houses of stone that has been taken from quarries and split into usable sizes. Because stone is an expensive building material, it is usually applied in a veneer, or coating, over an inner wall of brick or concrete block.

Modern materials in today’s houses differ greatly from those of 100 or even 50 years ago. Industries have developed new materials that help architects design better, longer-lasting houses. For example, builders once used iron for gutters and pipes. The iron rusted. Today, builders can use plastic, which does not rust. Aluminum, which does not rust, and nonrotting plastic materials such as PVC can be used instead of wood or metal for window frames and doors.

Older houses usually had small windows that let in only a small amount of light. Their window frames were loosely constructed and were not always airtight. Houses today have improved, airtight window frames to conserve heat.

Building stone

Building stone is one of the world's most important construction materials. It comes from natural stone deposits in the earth and is mined through quarrying. It is used as crushed stone or as dimension stone.

Crushed stone is generally limestone or dolomite that has been crushed and graded by screens to certain size classes. It accounts for about 99 per cent of all building stone It is widely used in concrete and as a surfacing for roads.

Dimension stone is cut from large blocks and slabs into definite shapes and sizes. It is used most often for finishing and decorating all types of structures. Constructors expect good dimension stone to last more than 100 years. Dimension stone includes granite, limestone, sandstone, marble, and slate.

Granite is one of the strongest building stones. But it is difficult to cut and handle because it is so hard. It is used in the construction of many public buildings. Granite can be polished to a glossy finish and is an excellent background for carvings and lettering.

Limestone is a hard and lasting building stone that can be cut easily and shaped with saws, planes, and even lathes. These stones are sometimes placed over the rough stonework of a building to make an attractive surface. Limestone is also used to tile floors, and for sills, steps, and trimming.

Sandstone is easy to work and is used for the same purposes as limestone. Sandstone that is well-cemented with silica is a durable and weather-resistant material.

Marble is white, streaked with veins of black, gray, green, pink, red, and yellow. Builders use marble to decorate stairways, hearths, floors, and as paneling.

Slate is fine-grained rock that can be split easily into thin slabs and used for roofing shingles and flagstone flooring.

Brick

Brick is a rectangular building block made of clay, shale, or various other materials. Bricks are strong, hard and resistant to fire and damage from the weather. They cost relatively little, resist dampness and heat, and can last longer than stone. The color varies according to the clay used. 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.

Bricks are used to build such structures as houses, commercial and public buildings, fireplaces, and furnaces.

Bricks are divided into two general classes: building bricks and refractory bricks.

Different categories of building bricks are used for load-bearing walls, for structures carrying exceptional loads and where appearance is important. The highest-quality and most attractive building bricks are called face bricks. They are used in highly visible areas of structures, such as the interior or exterior walls of houses. Face bricks come in a variety of colors and surface textures. Most are made from high-grade fire clay or low-grade shale.

Refractory bricks can withstand temperatures between 2000° and 4000° F. (1093° and 2204° C), They are also highly resistant to chemical damage, physical wear and thermal changes. Refractory bricks are used in a wide variety of structures, including fireplaces and industrial furnaces.

The methods used to make bricks vary according to the raw materials used, the intended use of the bricks and other factors. However, the production of bricks generally involves four basic steps: (1) preparing the ingredients, (2) forming bricks, (3) drying bricks, and (4) firing brick.

 

Glass

Glass is one of the most important and useful materials in the world. Few manufactured substances add as much to modern living as does glass. Yet few products are made of such inexpensive raw materials as silica sand (silica, or silicon dioxide), soda ash (sodium carbonate), and limestone (calcium carbonate). These constituents need to be very pure for the glass to be clear. Glass can take many different forms. It can be spun finer than a spider web or molded into a disk. It can be stronger than steel, or more fragile than paper. Most glass is transparent. Glass can also be colored to any desired shade.

There are many kinds of glass. The float glass is made in the form of flat sheets. It is used chiefly in windows, in mirrors, room dividers. It provides the best qualities of the old plate glass with more than ten times the productivity of the plate glass process. It is also significantly more energy efficient and can be produced in a full range of thicknesses. The electro-float process led to the mass production of solar-control glass or tinted windows, which reduce solar heat gain and glare in buildings. One of the newer and most fascinating products of glass manufacture is fiber glass. It can be laminated with plastics or toughened, or a wire mesh can be sandwiched into glass sheets to provide strength or fire-resistant properties. Fiberglass insulates the walls of many homes. Foam glass, when it is cut, looks like a black honeycomb. It is filled with many tiny cells of gas. Each cell is surrounded and sealed off from the others by thin walls of glass. Foam glass is so light that it floats on water, like cork. It is widely used as a heat insulator in buildings, on steam pipes, and on chemical equipment. Foam glass can be cut into various shapes with a saw.

Glass building blocks are made from two hollow half-sections sealed together at a high temperature. Glass building blocks are good insulators because they withstand high temperatures on the inside and low, outdoor temperatures at the same time, because of the dead-air space inside thus making suitable block for building purposes. The blocks are laid like bricks.

Timber

Timber is one of the earliest construction materials and one of the few natural materials with good tensile properties. Hundreds of different species of wood are found throughout the world, and each species exhibits different physical characteristics. Only a few species are used structurally as framing members in building construction. In the United States, for instance, out of more than 600 species of wood, only 20 species are used structurally. These are generally the conifers, or softwoods, both because of their abundance and because of the ease with which their wood can be shaped. The species of timber more commonly used in the United State» for construction are Douglas fir, Southern pine, spruce, and redwood. The ultimate tensile strength of these species varies from 5,000 to 8,000 psi (350 to 560 kg/sq cm). Hardwoods are used primarily for cabinetwork and for interior finishes such as floors.

Because of the cellular nature of wood, it is stronger along the grain than across the grain Wood is particularly strong in tension and compression parallel to the grain, and it has great bending strength. These properties make it ideally suited for columns and beams in structures. Wood is not effectively used as a tensile member in a truss, however, because the tensile strength of a truss member depends upon connections between members. It is difficult to devise connections which do not depend on the shear or tearing strength along the grain although numerous metal connectors have been produced to utilize the tensile strength of timbers.

Green lumber has a natural moisture content ranging from 35 to 40%. It subsequently dries, or seasons, to a moisture content of 5 to 25%, depending on the relative humidity of the atmosphere. As a result of the shrinkage of the cells caused by this change in moisture content, wood shrinks (primarily across the grain) as it dries. This .shrinkage produces defects in lumber, such as the bow in a plank and cracks, or checks, parallel to the grain. Another natural defect that somewhat reduces the strength of wood boards is the knot, which represents the origin of a branch.

Ceramics

Ceramics are one of the three most important types of engineering materials that are primarily synthetic. The other two are metals and plastics. Ceramics include such everyday materials as brick, cement, glass, and porcelain. Most ceramics are hard and can withstand heat and chemicals. These properties give them a wide variety of uses in industry.

Manufacturers make common ceramics from such minerals as clay, feldspar, silica, and talc these minerals, called silicates form most of the earth's crust. Clay is an important silicate. But it is not used in all ceramic materials. Glass, for example, is made from sand. Most ceramic products, like their mineral ingredients, can withstand acids, gases, salts, water, and high temperatures. But not all ceramic products have the same properties. Common ceramics are good insulators - that is, they conduct electricity poorly. However, certain ceramics lose their electrical resistance and become superconductors when they are cooled. Some ceramic materials are magnetic.

The properties of ceramics make them especially suitable for certain products. Products made of ceramic materials include abrasives (materials used for grinding), construction materials, dinnerware, electrical equipment, glass products, and refractories (heat-resistant materials).

 

Cement

Cement is a fine, gray powder. It consists chiefly of calcium silicates and is used primarily in making concrete. Cement is mixed with water and materials such as sand, gravel, and crushed stone to make concrete. Cement and water form a paste that binds the other materials together as the concrete hardens. Nearly all the cement used today is portland cement which is a hydraulic cement, or one that hardens under water. Portland cement is used chiefly to make concrete. But it can also be mixed with soil and water to form soil-cement, which is used in road paving and dam construction and for lining reservoirs.

Portland cement contains about 60 per cent lime, 25 per cent silica, and 5 per cent alumina. Iron oxide and gypsum make up the rest of the materials. In the plants, the materials go through a chemical process that consists of three basic steps: (1) crushing and grinding, (2) burning, and (3) finish grinding.

 

Aluminum

Aluminum is the oldest and best known light metal. Aluminum is the most plentiful metallic element in the earth's crust and the third most common of all the elements, after oxygen and silicon. But unlike some other metals, such as gold and silver, aluminum never occurs free (uncombined) in nature. It is always chemically combined with other elements.

People had no way of separating aluminum from these elements until the 1800’s. Scientists then developed processes for separating the elements and producing aluminum. Aluminum, with its alloys, has many valuable properties that make it an exceptionally useful metal. These properties include (1) light weight, (2) strength, (3) corrosion resistance, (4) electrical conduction, (5) heat conduction, and (6) light and heat reflection.

The world uses more aluminum than any other metal except iron and steel.

Low weight and resistance to corrosion combine with its toughness to make aluminum very suitable for the bodies of vehicles and also for castings-gear-boxes, pistons, cylinder heads. It is used for making cooking utensils, ladders, refrigerators, wrapping material. The construction industry uses aluminum in such items as gutters, panels, residential roofing, tubes for electric wires and window. Its shiny surface reflects heat, and aluminum foil is used for the heat insulation of houses. Buildings with aluminum roofs reflect much of the sun's heat and so stay cooler in hot weather.

Aluminum paint protects ironwork from rust, obliterates dark paint, and reflects light. Some important aluminum alloys are magnesium and duralumin (95% aluminum + 4% copper -f 1/2% manganese + 1/2% magnesium) which is only half as dense as steel but twice as strong; unlike aluminum, it can be tempered by heat treatment; it is used for making aircraft, houses, furniture and motor pistons.

Aluminum can be shaped by almost any metalworking process. It can also be bolted, glued, riveted, soldered, welded, and otherwise joined by most methods used for other metals. Finally, aluminum can be recycled.

Iron and steel

Iron and steel are the world's cheapest and most useful metals. These hard, durable metals are used in making thousands of products, from paper clips to automobiles.

The word iron can refer to both an element and a number of alloys (mixtures) of iron and other metallic elements.

Steel is produced by refining (purifying) iron and alloying it with other metals. Iron may be thought of as a basic material of steel, and steel may be considered the refined product of iron.

The properties of any kind of iron or steel depend largely on the chemical composition of the alloy.

Cast iron is any iron alloy that contains from 2 to 4 per cent carbon and from 1 to 3 per cent silicon, because of its high carbon content, solid cast iron cannot be shaped, no matter how hot it is heated. This kind of iron is made into useful objects by pouring the liquid metal into molds and letting it harden. Cast iron's hardness, low cost, and ability to absorb shocks make it an important construction material.

Steel finds its use in corrugated sheets for roofing, for girders, frames, etc. Various shapes are employed in construction.

 

Types of construction

In bearing-wall construction, the walls transmit the load to the foundation. In skeleton construction, all loads are transmitted to the foundation by a rigidly constructed framework made up of beams, girders, and columns. This skeleton carries the roof, walls, and floors, together with their loads. Bearing-wall construction is usually most economical for buildings less than four stories high, but skeleton construction is better for taller buildings. All buildings in the skyscraper class are of skeleton construction. The 10-story Home Insurance Building in Chicago was one of the first buildings to have a skeleton construction. Completed in 1885, this building is often considered the world's first metal-framed skyscraper.

Many parts of a building have no structural function. Nonbearing walls and curtain walls carry only their own weight and serve to divide the interior of a building or to keep out the elements. Such walls are called non-bearing partitions. Other nonbearing parts include windows, doors, stairs, elevators, and other equipment.

In one method of construction, called tilt-up construction, concrete wall panels are formed at ground level. Cranes or derricks then lift them into position.