How prestressed concrete works

 

What happens when any beam carries a load? It bends and its center sags lower than its ends. Thus the bottom fibers are stretched while the top fibers are compressed. Since concrete resists compression well, the designer puts enough of it in the top to absorb all the compression safely. On the other hand, since the concrete has very little tensile strength – but steel has a lot – he inserts steel bars to take care of tensile stresses.

The trouble is that concrete shrinks as it hardens. The reinforcing bars, however, do not shorten much and consequently offer resistance to the concrete shrinkage, actually putting the bars in compression. When the concrete is loaded, the load causes considerable tension in the reinforcement. Since this reinforcement started out with a slight compression, and then in turn is subjected to considerable tension, it is obvious that its change in lengths is of such magnitude that the concrete cannot usually follow; it cracks.

In prestressing, concrete’s virtue of high compressive strength is used to compensate for its lack of tensile strength through a very different concept in the use of reinforcing steel.

Steel wires are strung through a concrete beam, for example, are stretched and then anchored at the ends of the beam when the concrete is hard, to put a “squeeze” on the beam. The wires either are strung through a hole in the beam provided by a mold, and are tensioned against the end of the beam (we shall call this process post-tensioning), or else they are stretched first and held by some anchorage, after which the concrete is poured around them. When the concrete is hard, the wires are cut and the ends of the wires return to their original shape outside the beam – because the stress is relieved there – and act as wedges to help hold the wires bonded to the concrete in tension.

In prestressing, the concrete in the beam is squeezed so that it is always in compression, and any tensile stresses that might appear due to loading, and cause cracks, are automatically canceled out. The application of the stresses before the beam is loaded is the basis for the name “prestressed concrete”.

The advantages of prestressed concrete are:

a) it is economical of materials due to the use of higher steel and concrete stresses;

b) it eliminates cracks because the concrete is always in compression;

c) it permits less depth of beam as related to the span, and hence gives more headroom (this is especially important with bridges and airplane hangars);

d) beams do not have to be cast at the site in one form, but may be cast in small sections or blocks at the factory with reinforcing wires threaded through them. When the wires are stressed, the small units are brought together like one large beam;

e) it develops remarkable resistance to shear stresses. In one case its resistance to this shearing action was 800 psi.

The items which contribute most to the higher cost of making prestressed concrete in comparison with regular reinforced concrete are the special form-work and devices required to anchor the prestressing steel on the ends of the beam, and the cost of the actual prestressing operation in the field.

VOCABULARY NOTES

beam балка, брус, перекладина

to bend изгибать, сгибать

to sag провисать; прогибаться

to stretch растягиваться; простираться

to compress сжимать

tensile stress растягивающее напряжение

tension напряжение; растяжение; натяжение

magnitude величина, размер; значение (цифровое )

virtue сила действия

to string подвешивать провода

to anchor закреплять

squeeze сжатие; сдавливание

to pour отливать; заливать (бет. смесь)

to relieve выпускать (газ); понижать (давление)

formwork опалубка

shear срезание, срез

EXERCISES

I. Read the text, translate it into Russian.

II. Discuss the advantages of prestressed concrete.

PRESTRESSED BEAMS, ARCH BEAMS, SLABS

AND SHELLS

 

The prestressing of these structural systems may be achieved in two ways:

a) Pretensioning of the reinforcing before the concrete is hardened.

The steel is tensioned against exterior anchors and embedded in fresh concrete. When, after certain, curing process, the concrete is sufficiently hardened to carry the stretching forces, the steel is released from the prestressing bed, thus inducing compressive stresses in the concrete as a result of the bond between the embedded steel and concrete.

b) Pretensioning of the reinforcing after the concrete is hardened.

The prestressing wires or cables are pulled through ducts or grooves left for them in the concrete member or are surrounded by a sheath of thin sheet metal before the concrete is placed, in order to prevent bond prior to pretensioning.

When the concrete is hardened sufficiently, the wires or cables are tensioned by jacks acting against the ends of the concrete member. During the pretensioning the wires or cables are held in predetermined positions by means of special spacers. After the prestressing load is applied to the cables or wires, they are grouted in under high pressure for protection against corrosion and to establish bond.

Economic consideration. The economy of various structures for a given span and live load depends primarily on the dead load of the structure, the total coast of materials used, the man-hours required for construction, and the cost of maintenance.

VOCABULARY NOTES

hard жесткий, твердый

to harden затвердевать

to embed вставлять; внедрять; монтировать

curing (concrete) выдерживание (бетона)

bond связь; соединение; сцепление

duct канал (для арматуры)

groove желобок; паз

jack домкрат

spacer распорка

grout раствор

 

EXERCISES

I. Answer the following questions:

1. What different groups of prestressed structures do you know?

2. What is the main difference between them?

3. How is the prestressing of the beams, arch beams slabs and shells achieved?

4. What are the main economic considerations of prestressing?

II. Make a brief summary of the text.

BUILDING INDUSTRY

Building is the process of constructing buildings as distinct form of the art of science of designing buildings, which is architecture.

The building industry has developed from the process of using natural materials for building simple shelters in early times to the complex industrial process of modern times. Many of the materials used today are made in factories and are often partly put together before they even reach the building site.

Large Modern Buildings. When we look at the buildings around us we may put them into two groups: large commercial, industrial, of institutional buildings, and the smaller, residential buildings in which many people live.

The large buildings of the first kind may be “high rise” buildings, which in extreme cases can be described as “skyscrapers”. There are special techniques used in building skyscrapers. Other large buildings such as factories, warehouses, schools, and hospitals also have to be built of materials that will bear heavy weights. Often it is desirable to produce spaces inside without posts or supporting walls. Arches, called trusses, are used to span the area to be left open. These may be made of wood, metal, or reinforced concrete. Concrete is a material used frequently in modern buildings, especially this kind of large commercial building. Another way to span a large space is to use a dome, which may be made of plastic or glass, as well as concrete or metal.

VOCABULARY NOTES

building materials строительные материалы

natural materials природные материалы

commercial buildings торговые здания

industrial buildings промышленные здания

residential buildings жилые здания

high-rise buildings высотные здания

skyscraper небоскрёб

to bear (bore, born) выдерживать нагрузку

post стойка

supporting walls несущие стены

arch арка

truss ферма

span пролёт

dome купол

plastic пластмасса

 

EXERCISES

I. Read the text “Large Modern Buildings” and answer the following questions:

1. What is a building?

2. What was the beginning of building industry?

3. What are the main two groups of large modern buildings?

4. What are the specific features in constructing “high-rise” buildings?

II. Make up the summary of the text.

BUILDING HOUSES

 

The ordinary houses which many of us live in appear to be comparatively small and simple, and you might not realize how many different people have been employed to build them.

The outer “shell” of the house may be made of brick, wood, or stone, but that may not be what is actually holding the building up.

In order to understand how a house is built we must start at the beginning.

When a building contractor is asked to put up a building, he must first look at the site, choose the people who are going to work for him, and plan a schedule of work so that he knows which people should be on the site at the right time.

Some of the people needed to build a house are bricklayers, plasterers, carpenters, plumbers, electricians, painters, and roofers, as well as all the laborers who help them. When you have so many people working together in a small space you must not have they getting in each other’s way and they must not be waiting about on the site with no work to do because someone else has not finished his job on time.

Foundations. The first thing to do is to level the ground and make the foundations. These are usually made of concrete which is poured into trenches dug in the ground. They have to be strong enough to hold up the building, and so it is important to prevent them from cracking or shifting. While the foundations are being built, the main drains must be laid to connect up the public sewers.

A timber-framed building has concrete foundation walls on top of a “footing” of concrete, and then timber “sills” which are anchored to the concrete while it is still wet. In brick-built houses the layers of bricks start on top of the concrete foundations. The first layers or courses of bricks must be built very carefully, for the whole house will rest on them.

It is important to prevent dampness coming up from the ground into the house, and so all houses have to have a damp-proof layer built into them. In brick- built houses this is a layer of waterproof material put into the brickwork when it reaches about 15 centimeters (6 inches) high, in timber-framed houses the waterproof material must go in the layer of concrete, and in all houses it must be incorporated into the floor when it is being laid. The floor of the house will be made of a layer of rubble, gravel, or stones, covered with concrete.

Building the walls. Once the foundations and floor are complete, the main part of the house can be built up. In timber-framed houses the main supporting joists are sometimes made of steel or reinforced concrete. Heavy timbers must be used for supporting the roof and stairs and for door and window frames; for the rest of the structure lighter timber is used. In brick-built houses the walls are built up in double layers and the wooden framework for doors and windows, as well as the wooden joists for the floors, are incorporated as work goes on. As the house rises it is necessary to provide scaffolding and platforms for the workers to stand on. This is made of steel tubing with planks laid across, ladders to go up and down, and hoists to lift up the building materials.

Roofing. The roof of the house may be flat or sloping. Rafters of wood are laid across, which are then covered with slates or tiles. In some places they are called shingles. They may be made of any material that is waterproof, including clay, concrete, metal, and asbestos. They are laid so that they overlap and let the water run off.

A timber-framed house must be covered with timber, bricks, or some other covering to finish the walls. There will also probably be an insulating layer of, for instance, fiberglass, to keep the house warm and dry. This will be put in between the living space and the roof to prevent heat escaping upwards. Brick-built houses have insulation put in the cavity between the walls and below the roof.

Finishing the inside. When the outer shell is complete, work can begin inside of the house. The walls are usually lined with plaster. Later it will be painted or papered for decoration; wet plaster must be given a few weeks to dry out before that can be done. Plastering must be carefully timed to fit in with the work of the plumbers and electricians.

Plumbers lay pipes for the water supply, heating system (including gas pipes where they are needed), and drainage. They also have to fix the drainage pipes on the outside of the house, which will join up to the drains and sewers, and put in the bathroom and kitchen fittings to which the pipes are connected. Most of these pipes have to be hidden from view in the finished house and so some of them will be fixed so that they are behind the plaster after it has been applied, and some will be under the floorboards. Similarly, the electric wires and fittings will mostly be embedded in plaster or laid under the floors. Sometimes the wires are encased in plastic tubes which are laid around the edge of the floors and window frames. The plumber and electrician also work together in installing such things as central-heating boilers.

At the same time, carpenters will be working inside the house finishing the wooden floors, staircases, window frames and doors, as well as fitting cupboards. Last of all, the painters and decorators come in to paint the house inside and out.

 

VOCABULARY NOTES

site строительная площадка

bricklayer каменщик

plasterer штукатур

carpenter плотник

plamber водопроводчик

electrician электрик

painter маляр

roofer кровельщик

labourer рабочий

cracking растрескивание

shifting сдвиг, смещение

to anchor скреплять, фиксировать

damp-proof layer влагостойкий слой

joist брус, балка

heavy timber твердые породы дерева

light timber мягкие породы дерева

scaffolding леса, возведение лесов

hoist подъемное устройство

flat roof плоская крыша

sloping roof покатая крыша

rafter стропило, балка, бревно

slate шифер, шиферная плитка

tile черепица, кафель

shingle кровельная дранка, тонкая доска

cavity пустота (внутри чего-либо)

fitting установка, сборка, монтаж

EXERCISES

I. Read the text “Building Houses” and translate it. Pay attention to the usage of the terms.

II. Read the list of main building professions and explain what each of them does in building the house:

bricklayer

plasterer

carpenter

plumber

electrician

painter

roofer

III. Read and translate the following compound words and combinations of words. Use them in your own sentences.

Brick-built house; timber-framed building; damp-proof layer; waterproof material; brickwork; wooden framework; central-heating boiler.

IV. Retell the text according to the following plan:

1. The beginning of house construction.

2. Foundation construction.

3. Building the walls.

4. Roofing.

5. Finishing the inside.

 

 

FOUNDATIONS

 

A building has two main parts, the substructure (the part below ground) and the superstructure (the part above ground). The substructure is usually called the foundation and includes the basement walls even though these may extend above the ground.

Both the substructure and superstructure help to support the load (weight) of the building. Thedead load of a building is the total weight of all its parts. The live load is the weight of the furniture, equipment, stored material, and occupants of a building. In some regions, the wind loadof a building is important if the structure is to withstand storms. The snow load may also be an important factor. In some areas, buildings have to be constructed to withstand earthquake shocks.

The purpose of foundation is to carry the load of structure and spread it over a greater area, evenly and without undue settlement, to the ground beneath. They carry both dead and live loads. There are three main types of foundations: (1) spread, (2) pier, and (3) pile.

Spread foundations are long slabs of reinforced concrete that extend beyond the outer edges of the building. Such foundations are not as firm as those based on solid rock. The footing areas in contact with the soil must be of sufficient size to spread the load safely over the soil and to avoid excessive or uneven settlement. Any such settlement would cause walls to crack or doors to bind.

Pier foundations are heavy columns of concrete that go down through the loose topsoil to a bed of firm rock. This bed may also be sand, gravel, or firm clay. If the bed consists of firm clay, the pier is usually enlarged at the base, to increase the bearing area.

Pile foundations are long, slender columns of steel, concrete, or wood. Machines called pile drivers hammer them down as deep as 60 meters to a layer of solid soil or rock. Workers can tell when the columns reach their proper depth by the number of blows. The pile driver needs to drive the columns a few centimeters deeper. These columns transmit the building load to the supporting soil.

The importance of pile foundations in building and industrial construction as well as in civil engineering has increased considerably over recent years. The piles transmit the loads of the structure to deep-lying, load bearing strata of the subsoil. Today’s modern, large structures force the civil engineer to develop advanced methods and techniques in order to make sure that the ever increasing and highly concentrated loads are safely transferred to the subsoil without causing settlements.

The significance of pile foundations is reflected in the large number of pile systems currently available on the market. Depending on the method of production, piles can be divided into two main types: cast in-situ concrete piles and prefabricated piles.

Cast in-situ piles are mostly bored piles while precast piles or prefabricated piles are driven.

Beams, girders, and columns support a building much like bones support the body. They form the skeleton of the superstructure and bear the weight of the walls and each floor of the building. Beams and girders run horizontally. Girders are usually larger than beams. Closely spaced beams are called joists, especially in wooden buildings. Purlins are small beams that brace ratters or girders and help provide the structure to support roofs. Beams above window and door openings are called lintels. Slabs are beams whose width is greater than their depth.

Columns are heavy vertical supports that carry the load of beams and girders. Trusses consist of many wood or steel supports that are connected in triangular patterns. They provide the strength and rigidity to span large distances with relatively small amounts of material. Arches are curved supports that usually extend over openings.

 

VOCABULARY NOTES

live load переменная нагрузка

dead load постоянная нагрузка

spread foundation уширенный фундамент

pier foundation столбчатый фундамент

pile foundation свайный фундамент

girder балка; ферма; прогон

joist балка; брус

purling обрешетина; прогон

lintel перемычка

truss ферма

arch арка

EXERCISES

I. Read the text and translate it.

II. Put up questions to the following sentences:

1. Foundations carry both the dead and live loads.

2. Spread foundations are long slabs of reinforced concrete between the outer edges of the building.

3. Pier foundations go down through the topsoil to a bed of firm rock.

4. Pile foundations transmit the load to the supporting soil.

III. Answer the questions to the second part of the text:

1. What is the main function of beam, girder and columns?

2. What is the difference between beam and girder?

3. What is joist? purlin? lintels?

IV. Make up the summary of the text.

BRICKMAKING

Brick is formed in three ways: the soft-mud, stiff-clay, and pressed brick processes. In the soft-mud process, clay is mixed with water to form a stiff paste which is then thrown by hand or forced by machine into wooden or metal box-like molds the size of a brick. Sand or water is sprinkled on the inside of the molds to keep the clay from sticking. The sand or water also gives the brick a pleasant finish. Such bricks are called “sand-struck” or “water-struck” bricks. The soft, wet bricks are removed from the molds for drying. The molds are used again.

In the stiff-clay process, the ground clay is mixed with water in a long trough containing a revolving shaft with blades. The blades mix the clay with water as they revolve and at the same time push it forward into an extrusion machine. This forces it through a rectangular opening in the same way as toothpaste is squeezed from a tube. It comes out, or is extruded, in a long bar the length and width of a brick. A moving belt carries the clay bar to a cutter, which is a metal frame with a number of wires stretched across it. The wires are spaced 65 millimeters (2 inches) — the height of a brick — apart. The wires are brought down on the bar to cut it into bricks, which are then dried. Bricks formed in this way are known as extruded wire-cut bricks.

In the pressed brick system, the clay is semidry, and is pressed by heavy machine into metal molds under such high pressure that the clay particles hold together. Because pressed brick has very little water, it needs little drying.

After being formed, both the soft-mud and the stiff-clay bricks are loaded on to carts on rails and pushed into driers, and then into kilns to be fired. The driers are long rooms or sheds through which hot air is forced by large fans. Water must be removed from the bricks before firing, as a wet brick warp when fired. Drying takes two to three days and then the bricks are ready for firing.

Until the 17^th century a lot of brick-making was carried out in brick-fields near where the bricks were to be used. The clay was dug from the field and molded there. It was then fired in a “clamp”, which a temporary kiln was built of fuel and bricks. The inside of this stack consisted of unfired bricks and fuel, usually small coals, while the outside was made of fired bricks. The clamp was then set alight and allowed to burn itself out. This took several weeks.

In permanent brickyards, an early type of kiln was used. This was a separate building which, after the unfired bricks stacked inside it, was closed and the fires lit. The kiln gradually warmed up until the necessary heat was reached, and after about two days the fire was allowed to die down and the kiln became cool enough for the bricks to be carried out.

The problem with both the clamps and the early kilns was that they did not give evenly fired bricks. This meant that the bricks were very variable in quality. Some bricks would have to be re-fired and the cracked ones would be thrown away. They were also uneconomical with fuel.

Nowadays kilns usually allow a continuous process. There are many different types, the most modern of which is the tunnel kiln. This kiln is 90 meters (300 feet) or more in length. The fire burns all the time in a zone about half way through the tunnel. The dried bricks are drawn slowly through the fire on carts, taking two or three days to travel the whole length of the tunnel. This speeds up production, is easily controllable, and economical with fuel.

Materials. Clay is the material most often associated with bricks, but since the late 19^th century other materials have been used. For example, calcium silicate bricks, sometimes known as sand-lime bricks, are made by pressing a mixture of moist sand and lime into brick shape by machine. The bricks are then steamed under high pressure in an autoclave (a sort of giant pressure cooker). This process produces bricks of an attractive light sandy color which can be textured and pigmented in a variety of ways.

Pigments and texturing can also add interest to concrete bricks which are naturally light gray in color. These are made from a mixture of crushed rock and Portland cement mixed together and moistened. The cement sets and hardens to bind the particles of rock together.

Shape. Not all bricks are completely solid. Some have “frogs” in them. A frog is a recess in the brick named after the frog in horse’s hoof. They make it easier to press and fire the bricks and also reduce the weight. Lighter bricks are easier to handle and cheaper to transport. Nowadays many machine-made bricks have holes in them for similar reasons. These are called perforated bricks. “Specials”, as the name suggests, are bricks made for a specific purpose. They are usually shaped to fit angles and curves or to produce a decorative effect. There are various commonly made ones such as “angled”, “radial”, and “bull-nosed”.

Color. The color of clay bricks depends on several factors. The type of clay used, chemicals in the clay, the supply of oxygen while the bricks are being fired, and the temperature the bricks reach during firing. The colors range from dark purple to light yellow. The red color of ordinary brick is due to the iron found in most clay. A large amount of iron gives a bright-red color; reducing the supply of oxygen may give dark-blue. By adding manganese to the clay a brown color is produced. Clay combined with lime produces yellow bricks. Facing bricks, to be used in the outer walls of buildings, can be given a rough or textured surface, or they may be glazed to add to their attractiveness.

Sand-lime bricks are naturally white, off-white, or pink, depending on the sand used to make them. By adding pigments, any colors from pale pastels to dark tones can be produced.

Blocks are essentially oversize bricks — commonly about the size of six bricks. They may be made of clay or concrete. Clay blocks are usually hollow; concrete blocks may be solid or hollow. The advantage of blocks over bricks is that building can be carried out faster with them.

 

VOCABULARY NOTES

soft-mud мягкий раствор

stiff-clay жесткая глина

pressed brick прессованный кирпич

mold форма

to sprinkle разбрызгивать; посыпать

trough желоб

wire-cut-brick проволочный кирпич

kiln печь

sand-lime brick песчано-известковый кирпич

perforated brick дырчатый кирпич

EXERCISES

I. Read and translate the following text. Annotate it in Russian.

II. Speak on the three-ways of forming bricks.

III. Speak about the materials, used for brick-making; different shapes of bricks; possible colors of bricks.

IV. Make up sentences from the following words:

1. Brick-making – sand – water – are – widely – for – used

2. Heavy machine – is pressed – under – clay – in – pressure – high

3. Before – from the bricks – water – firing – removed – must be

4. Must be – bricks – carefully – in the wall – arranged – to produce – good – strength – appearance – high – and

V. Determine the part of speech and the grammatical form of the following words. Translate them into Russian:

1. Construct; construction; constructional feature; construction site reconstruction; a reconstructed building.

2. Conclude; conclusion; conclusive; inclusively.

3. Require; requirement; required.

4. Undertake; undertaker; undertaking; undertook.

 

 

BRICKLAYING

When a wall is built of bricks, the bricks are set in mortar. Mortar usually consists of a mixture of sand and either lime or Portland cement or, more often, a mixture of the two. Enough water is used in mixing the mortar to produce a paste in which the bricks can be firmly bedded. The bricks must be carefully arranged or “bonded” as it is called, in the wall in order to produce a structure of good strength and appearance, the pattern of the brickwork depending on the bond which is used. The “pointing”, or finishing, of mortar joints is also given careful attention since it affects the appearance and the weather resistance of the wall.

Each layer of bricks is called a “course” and the bricklayer has to be very skillful to keep the courses exactly level and the thickness of mortar between each course of bricks the same throughout the length and depth of the wall. The corners of the walls must be absolutely upright or “plumb”.

Nowadays the outer walls of buildings often consist of an outer and inner wall with a space of about 5 centimeters (2 inches) between them, the two layers being held together at intervals by small metal ties. These cavity walls, as they are called, help moisture evaporate better than solid walls. A layer of insulating material is often put in the space between the walls to prevent heat escaping from the building. This is known as “cavity wall insulation”.

When bricks are built in curves, as in arches or curved walls, the bricklayer has to shape the bricks in order to fit them together. Sometimes quite soft bricks called “rubbers” are used; these can be rubbed on a hard stone in order to shape them so accurately that they can be built with thin mortar joints. Work of this type is known as “gauged brickwork” and demands great skill.

VOCABULARY NOTES

cavity впадина; полость

coarse of brick ряд кирпича

gauged brick лекальный кирпич

 

EXERCISES

I. Read the following text and retell it keeping close to the text.

PARTITION WALLING

Partitions, as they are normally called, are internal walls usually built of the same materials as other types of walling previously described. When they are used simply as dividing walls and have only their own weight to carry, they are termed “non-load bearing” partitions. When, however, they are required to support the weight of the structure above, they are termed “load bearing” partitions.

“Non-load bearing” partitions are often built of light-weight materials, such as thin light-weight precast concrete blocks, hollow clay blocks and timber studding covered with either plasterboard, fiberboard, match-boarding, plywood, chipboard, resin bonded block-board or other form of cladding. The construction of a stud partition is used in a typical timber framed house. Where sound insulation is of the utmost importance, as in ordinary houses, even “non-load bearing” partitions should be built of bricks or dense precast blocks. Partitions of light-weight precast concrete blocks and hollow clay blocks have fire-resisting qualities and contribute to thermal insulation and are, therefore widely used.

Stud partitions, although commonly used in former years, are not so common nowadays, due to mainly to their low resistance against fire. On the other hand, they contribute quite a great deal to thermal insulation. Special partitions, for use in toilets etc., are often made of pressed steel, plastics, asbestos cement, tiles or glass. These are normally prefabricated and erected in sections and can be easily removed or re-arranged.

Piers are a particular form of walling, which is either completely isolated from the other walling or is attached there to. These are often constructed in brickwork, although they also occur in stonework and concrete block-work. Attached piers are intended to strengthen the walling, usually at those points where a load is being directly supported. Isolated piers, acting as columns, usually support the weight of a floor or beam between the walls of the main structure.

 

EXERCISES

I. Read the following text and note the interesting facts.

II. Find the Russian equivalents for the following words:

non-load, load-bearing, light-weight precast concrete, plaster board, fiberboard, match-boarding, plywood, chipboard, resin bonded block-board, dense precast block, hollow clay block, pressed steel, asbestos cement, tile, glass.

III. Answer the questions:

1. What is a partition?

2. What is the difference between “non-load bearing” and “load bearing” partitions?

3. What building materials are used for partitions?

4. What building materials are used for thermal insulation in stud partitions?

5. What is a pier?

6. What types of piers are mentioned in the text? Characterize them.

IV. Give a brief summary of the text.

THE NEW LOOK IN BUILDINGS

Buildings have taken on a new look in the past decade. Metal and thin-wall back-up with more glass have completely changed the facades of the new buildings. The construction is more expensive than brick, and the large glass areas increase air conditioning costs. But people like the new look.

Until recently masonry was the principal material for the exteriors of buildings. Individual stones or bricks have been laid one on top of another to express the aesthetic conceptions of architects since prehistoric times. In recent years there has been some use of metal for window and door frames.

Before 1946 metal facades were used only to a very limited degree. In that year the Aluminum Company of America started a big research program to develop practical methods for the use of aluminum as a building facade material.

The three basic requirements for a metal-glass façade are:

a) light-weight,

b) ease-of-erection,

c) weather-tightness.

In 1948 most cities required a spandrel wall having a 4-hr. fire rating. An 8-in. brick wall would satisfy this requirement, but brick weighs 120 lb. per cu. ft. Since light-weight construction was important, a back-up wall 4 in. thick (either precast or poured) made of diacrete and cement was developed, weighing 20 lb. per sq. ft. compared to 80 lb. for an 8 in. brick wall. Light-weight construction, in many instances, brought savings in the structural frame as well as in building costs.

Ease of erection is important. In most cases, façades made of metal can and should be erected from the inside of the building, thus avoiding outside scaffolding. This item can create large savings in both time and money. Weather conditions become of little importance, and a minimum of time is lost. This contrasts with earlier operations which were practically brought to a stop by adverse weather conditions. Since metal frames are light, they can be handled easily by a few men without resort to expensive equipment.

Weather tightness is essential. Joints should be treated to shed water, and their number kept to a minimum. Generally they are located at expansion joints, at mullions, and at ceiling and floor levels. Today panels are mostly one story high and extended the full width between vertical mullions. Weather-tightness is generally attained by use of neoprene gaskets or calking compounds.

There should be no maintenance cost as far as metal-glass façade is concerned except window cleaning, which deserves consideration. Two methods are commonly used:

1) use of reversible in-swinging windows,

2) use of outside window-washing scaffolding, running up and down the facade, in which case mullions are designed to provide guides for the scaffolding and the glass in all windows can be fixed.

Close cooperation among the architect, engineer and contractor during the design is essential to achieve greatest economy. Materials, methods and budgets can be worked out for acceptable treatment of the facade. The architect, being an artist as well, will envisage certain shadow lines for his facade treatment and will justly insist that these be maintained. However, there are many ways to put the pieces together and still achieve the desired architectural features. Methods of assembly greatly influence cost.

Increased research by manufacturers is developing improved methods of shop handling and field erection that create savings in labor costs. Today there are many manufacturers in the business, and competition is healthful. The large selection available in design and color tends to create a greater desire for curtain-wall construction.

VOCABULARY NOTES

frame корпус; каркас

facade фасад; внешний вид

to erect сооружать; воздвигать

tightness плотность; герметичность

spandrel wall стенка подоконная

back - up wall опорная стена

scaffolding леса; возведение лесов

to handle управлять; оперировать

to shed распространять; проливать

mullion средний брусок оконной рамы

to attain достигать

gasket (техн.) прокладка

calking уплотнение

(in) swinging window (не)распашное окно

curtain wall подвесная стена

EXERCISES

I. Read the text; translate into Russian; speak about the advantages of light-weight construction.

II. Answer the following questions:

1. How does the weather affect the erection of a building and the building itself?

2. What can create large savings in both time and money?

III. Form sentences with the following words and put questions to these sentences.

1) research – started – has been – year – this – a – program big.

2) this new building – of – may affect – weather conditions – the erection.

3) window cleaning – only – are – there – two methods – of.

4) large aluminum panels – the – wants – architect – to use.

IV. Explain the meanings of the following words and use them in the sentences of your own:

architect, treatment, assembly, business, frame, facade, precast, light-weight construction.

V. Get ready to retell the text.

 

 

HIGH-RISE BUILDING

 

High-rise building, also called “high-rise”, a multistory building tall enough to require the use of a system of mechanical vertical transportation such as elevators. The skyscraper is a very tall high-rise building.

The first high-rise buildings were constructed in the United States in the 1880s. They arose in urban areas where increased land prices and great population densities created a demand for buildings that rose vertically rather than spread horizontally, thus occupying less precious land area. High-rise buildings were made practicable by the use of steel structural frames and glass exterior sheathing. By the mid-20^th century, such buildings had become a standard feature of the architectural landscape in most countries in the world.

The foundations of high-rise buildings must sometimes support very heavy gravity loads, and they usually consist of concrete piers, piles, or caissons that are sunk into the ground. Beds of solid rock are the most desirable base, but ways have been found to distribute loads evenly even on relatively soft ground. The most important factor in the design of high-rise buildings, however, is the building’s need to withstand the lateral forces imposed by winds and potential earthquakes. Most high-rises have frames made of steel or steel and concrete. Their frames are constructed of columns (vertical-support members) and beams (horizontal-support members). Cross-bracing or shear walls may be used to provide a structural frame with greater lateral rigidity in order to withstand wind stresses. Even more stable frames use closely spaced columns at the building’s perimeter, or they use the bundled-tube system, in which a number of framing tubes are bundled together to form exceptionally rigid columns.

High-rise buildings are enclosed by curtain walls, these are non-load-bearing sheets of glass, masonry, stone, or metal those are affixed to the building’s frame through a series of vertical and horizontal members called mullions and muntins.

The principal means of vertical transport in high-rise is the elevator. It is moved by an electric motor that raises or lowers the cab in vertical shaft by means of wire ropes. Each elevator cab is also engaged by vertical guide tracks and has a flexible electric cable connected to it that provides power for lighting, door operation, and signal transmission.

Because of their height and their large occupant populations, high-rises require the careful provision of life-safety systems. Fire prevention standards should be strict, and provisions for adequate means of egress in case of fire, power failure, or other accident should be provided. Although originally designed for commercial purposes, many high-rises are now planned for multiple uses. The combination of office, residential retail, and hotel space is common.

VOCABULARY NOTES

dense плотный

density плотность

structural frame строительный каркас

sheathing обшивка

gravity load гравитационная нагрузка

pier устой; столб

pile свая

caisson кессон

cross - bracing крестовая связь

lateral боковой; поперечный

rigid жесткий; устойчивый

rigidity жесткость; устойчивость

to bundle связывать

curtain wall навесная стена

mullion средник

muntin горбылек (оконного переплета)

egress выход

retail розничная торговля

EXERCISES

I. Read the text and answer the following questions:

1. What is a high-rise building?

2. When were the first skyscrapers constructed?

3. What kind of foundation can be used in high-rise buildings?

4. What kind of walls was used in construction of high-rises?

II. Speak on high rise buildings making use of the following words and word combinations:

first high-rise building

urban areas

frame

column

beam

curtain walls

elevator

life-safety systems

III. Put questions to the following sentences:

1. The first skyscraper was built in American city Chicago.

2. Steel was the main structural material for framework.

3. The walls were hung to the skeleton as curtains.

4. The principle means of vertical transport in skyscraper is the elevator.

5. The first high-rise building was designed for commercial purposes.

IV. Retell the text using questions and answers of ex. III.

GLASS-WALLED SKYSCAPER

Delicate and transparent a narrow shaft of glass 24 stories high pierces the NEW YORK CITY, mirror like exterior incongruously reflecting its massive opaque skyscraper neighbors.

Its broad, two-story high base keeps surrounding buildings at a respectable distance. This glass tower was designed to be seen by the man in the street as well as to capture daylight for interior illumination.

It is the new headquarters office LEVER BUILDING in New York.

The building, which is completely air conditioned, contains 21 office floors, plus three floors for mechanical equipment on top.

A garage in the basement accommodates 50 automobiles. Cross building area is 289,600 sq. ft. net office area 131,000 sq. ft.

Street level is occupied by an auditorium seating 200, a demonstration kitchen, service areas in the rear, including provision for off-street, loading and a glass-enclosed lobby, with stainless steel trim.

Though there are entrances from the three bordering streets, the lobby is set back on all three sides, leaving space for an arcade and garden. Building columns outside the lobby thus are exposed to view from the street. Hence, the structure appears to be standing on stilts.

The second floor covers the entire lot, except for an open well directly over the garden. Purpose of the well is to admit daylight into the interior of the building base.

EXERCISES

I. Read the text and translate it.

II. Discuss the most interesting facts.