Many great buildings which were built centuries ago can still be seen in Greece and Italy, France and England. All of these buildings were construction solutions to difficult construction problems. These great buildings were not the result of scientific knowledge. They were constructed on the basis of experience, often as the result of trial and error. They have survived because of the great strength that was built into them - strength greater than necessary in most cases.
Today, however, the engineer has the advantage not only of empirical information, but also of scientific information that allows him to make careful design. When a modern engineer plans a structure, he considers the total weight of all its component materials. This is known as the dead load, which is the weight of the structure itself. He has also to consider the live load, the weight of all the people, cars, furniture, machines, etc. that the structure is to support when it is in use. In structures such as bridges that are to support fast traffic, he has to consider the impact, the force at which the live load will be exerted on the structure. He must also determine the safety factor, that is, an additional capacity to make the structure stronger than the combination of the three other factors.
The modern engineer should also understand the different stresses to which the materials in a structure are subject. They include the opposite forces of compression and tension. In compression the material is pushed together; in tension the material is pulled apart or stretched, like a rubber band. In the figure below, the top surface is bent inwards, and the material in it is in compression. The bottom surface is bent outward, and the material in it is in tension.
In addition to tension and compression, another force which is called shear should be considered. Shear is the tendency of a material to crack and break along the lines of stress. The shear may occur in a vertical plane, but it may also run along the horizontal axis of the beam, the neutral plane, where there is neither tension nor compression.
Altogether, three forces can act on a structure: vertical - those that act up or down; horizontal - those that act in horizontal plane; and those that act upon it with a turning motion. Forces that act at an angle are a combination of horizontal and vertical forces. Since the buildings that are designed by engineers are to be stationary or stable, these forces must be balanced. The vertical forces, for example, ought to be equal to each other. If a beam supports a load above, the beam itself has to have sufficient strength to counterbalance that weight. The horizontal forces must also equal each other so that there is not too much thrust either to the right or to the left. And forces that may pull the structure around must be equal to the forces that pull in the opposite direction.
Notes:
altogether adv. ,
empirical information n.
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furniture n.
machine n. , ,
push (~ together) v. .
scientific adj.
stationary adj. ,
survive v.
today adv. ,
trial and error ()
turning motion
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1. Where can great buildings, which were built centuries ago, be seen?
2. How were these buildings constructed?
3. Why did they survive?
4. What are the advantages a modern engineer has?
5. What does a modern engineer take into account to plan a structure?
6. What stresses must a modern engineer understand?
7. What are the forces that can act on a structure?
8. How must the forces be balanced?
, . .
| additional angle because of component construct dead load exert necessary only plane run solution strong surface counterbalance vertical | B , | above axis bottom combination crack etc. inwards line live load opposite right so that stable still sufficient thrust | B () - |
1.5
A, B . , .
A
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B
| fin precast pasta precious | specular final circumstance fibre | fine continuous major special | occupy typical casting aerate | mayor paste costing cure |
A
CEMENT AND CONCRETE
The basis of modern production of elements in concrete is cement powder, one of the most versatile binders. About 950 million tonnes of cement powder is produced each year around the world.
Concretes can vary greatly in their composition but those in general use are: high strength concrete, normal weight concrete, lightweight concrete, aerated concrete, and fibre reinforced concrete. Mostly, Portland cement is used but other cements are used in special circumstances. Concrete may be unreinforced, reinforced with steel or fibres or prestressed. Another important distinction is by method of production between cast-in-place concrete, which is poured into its final position on site, and precast concrete, which is poured and cured in a factory and must then be transported to site. Concrete elements can also be precast on site and lifted into their final position by crane. Methods are available for continuous casting of concrete, both vertically and horizontally.
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The basic components of concrete are coarse and fine aggregate, cement powder and water; admixtures are sometimes added in too. Most often the fine aggregate is a sand. The quantities of aggregates, cements or admixtures which are used may vary in particular circumstances. A typical concrete is a two-phase material with 60-75% of coarse and fine aggregate, which is the filler material and 25-40% of cement paste, which is the binder. This paste is hardened and formed from the reaction of water and cement powder. Voids of free water and air occupy between one and ten per cent of the volume of the mix and have a major influence on the strength and other properties of the mix.
Notes:
coarse adj.
fibre reinforced concrete
phase n. , ,
powder n.
reaction n.
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1. What is one of the most versatile binders?
2. What kinds of concrete are there?
3. How can concrete be made stronger?
4. What is cast-in-place concrete?
5. What kind of concrete is poured and cured in a factory?
6. Where can precast concrete be made?
7. How can concrete elements be lifted into their final position?
8. What are the basic components of concrete?
9. What is fine aggregate?
10. What makes the concrete paste harden?
11. What does a typical concrete consist of?
12. What influences the strength of the mix?
1. )
:
influence, circumstance, fibre, production, site, mix, precast concrete, void, tonne, distinction, aerated concrete, filler, casting, admixture,
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continuous, cast-in-place, fine, major, particular, final,
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about, bothand, mostly,
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form, harden, cure, occupy, add, prestress, reinforce, precast
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2. :
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4. . .
| column advantage carbon condition gravity available each a little reason safety | long further quantity for strain due to twist load allowable obtain | , |
5. . , . . , 1-5.
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construct (1), add (2), crack (2), cast (2), mix (2) strong (2), fail (1)
1. , , . , , .
1. The two most important building materials appeared in the 19th century.
2. The Greeks sometimes used iron rods to strengthen the building.
3. He designs buildings.
4. New designs are the result of new materials and building methods.
5. The plan shows what materials a builder must use.
6. They plan the building process.
7. Concrete is very versatile.
8. Builders had to concrete the holes.
9. He described new concrete blocks.
10. Each building functions for a long time.
11. This material has several functions.
12. Heat flows to a cooler area.
13. The flow continues until outside and inside temperatures are equal.
14. He has to know the subject of design procedures.
15. If concrete is subjected to tensile stresses, it must be reinforced with steel.
2. : + - er / or =
to produce producer
to heat heater
to calculate calculator
to build - builder
to read reader
to construct constructor
to invent inventor
to lose loser
to operate operator
to bind binder
to use user
to design designer
3. :
+ - ly =
natural - naturally
short - shortly
wide - widely
serious - seriously
usual - usually
constant - constantly
great - greatly
bad badly
general generally
easy easily
4. , .
1. The plans explain briefly what materials must be used.
2. Steel, basically an alloy of iron and a small amount of carbon.
3. A sample of rubber becomes substantially shorter and a little wider.
4. Usually failure unit stress is determined experimentally.
5. The material is used inefficiently.
6. Shearing unit stress acts unequally.
5. , .
1. About 950 million tones of cement powder are produced each year.
2. Different cements are used in special circumstances.
3. In order to get the necessary properties special admixtures are sometimes added to concrete.
4. An advantage of concrete is the ease with which its properties can be changed.
5. Concrete may be unreinforced, reinforced with steel or prestressed.
6. Concrete was poured into its final position on site,
6. :
21.02.1974; 987; 3256; 839,200; 3,482,408; 795; 437;12,457; 73,042; 02.08.1982.
B
PORTLAND CEMENT CONCRETE
Concrete has many characteristics that make it a construction material which is used most widely. Concrete is easily available, it can take the shape of the form which it is placed in, and its properties can be easily changed.
Basically, concreteis 60-80 percent aggregates (sand, stone), which are filler ingredients, and 20-40 percent "paste" (water, Portland cement), which make the binder ingredient. These materials are combined or mixed, and cured to produce the hardened concrete.
The strength of the concrete depends on the strength of the aggregate-paste bond. The entire mass of the concrete is placed in a plastic state and almost immediately begins to develop strength (harden), a process which, under necessary conditions, may continue for years. Because concrete is at the beginning in a plastic state, it can be used in all kinds of construction, no matter what their size or shape are. But concrete in a plastic condition must be placed within forms, and these forms cannot be removed until the concrete has hardened.
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In types of work where concrete is subjected to counteract compressive stresses, it is a very good building material. However, if the concrete is subjected to tensile stresses, it must be reinforced with steel, as concrete is weak in tension.
Notes:
beginning n.
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1. Why is concrete most widely used?
2. What is it made of?
3. What does the strength of concrete depend on?
4. Where is concrete placed?
5. When must it be reinforced with steel?
1. . .
2. , - er. .
3. , - ly. .
4. : , , .
1. ) :
form, mass, characteristics, percent, binder, state, shape, tension, bond, drawback,
:
easy, weak, entire, plastic, available, immediately,
:
almost, within, no matter what, however, most, as,
:
combine, place, remove, change, cure, subject.
b) , . , .
2. .
| A | B tensile stress its certain kind require shock compressive stress | A , | B low until instead harden take necessary beam |
3. :
basic - basically
produce - production
1.6
A, B . , .
A
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B
| admixture grade durability sulphate | ingratitude control apply provide | chemical private during great | permeability central shrinkage alter | apple ingredient ratio admission |
A
CONCRETE MIX
The type of concrete mix and the properties of the hardened concrete may be altered. In order to do that the proportions of the ingredients may be varied, the type of cement and aggregates may be altered and admixtures may be used. The aggregates must be strong and durable materials in order to take the loads that are applied and ought not to react chemically with the cement paste. Aggregates help to reduce the volume changes in the concrete due to shrinkage or temperature changes. Aggregates can be selected in order to provide a concrete with properties such as low weight, low shrinkage, high thermal insulation, good fire resistance.
Various kinds of cement are available, for example, those which harden rapidly or those which resist chemical attack, such as sulphates in the soil. Blended cements are also available which give low heat output during the curing period of concrete. The blended cements consist of mixtures of Portland cement and admixtures which are carefully graded. These may replace up to about 70% of the Portland cement which would have been required.
The mix proportions of the concrete, and admixtures, will generally control the strength, permeability, frost resistance and resistance to chemical attack. The strength of the hardened concrete depends greatly on the water to cement ratio. A typical value of this ratio should be about 0.5 by weight. An increase in the value of this ratio would produce a concrete with more voids and result in lower compressive strength. A large number of properties, such as tensile strength, durability, chemical resistance and density are connected with the compressive strength of concrete.
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Notes:
attack n. ,
blended cement
frost resistance
output n.
react v.
replace v.
sulphate n.
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1. How can the properties of concrete be altered?
2. What kind of material must aggregates be?
3. How do aggregates influence the volume changes in the concrete?
4. How can aggregates be selected?
5. What kinds of cement are there?
6. What do the blended cements consist of?
7. What is the amount of admixtures in the blended cements?
8. What will the mix proportions of the concrete control?
9. What does the strength of the hardened concrete depend on?
10. What properties are connected with the compressive strength of concrete?
1. )
:
shrinkage, increase, ratio, curing, thermal insulation, permeability, soil,
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generally, durable, rapid,
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during, up to,
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control, apply, grade, provide, alter, help.
) ? . , ed.
) ? ? ?
2. :
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3. , , ? .
4. . .
| along drawback costs vary directly between too up to inside provide | , | even certain state lift general way various durable apply separate | , |
5. :
durable - strong
small - fine
void - hole
surface - plane
1. .
1. The properties of the hardened concrete will be altered if the proportions of the ingredients are changed.
2. Steel wouldnt have become available in large quantities if the Bessemer process hadnt been invented ().
3. If the owner wanted this builder to do the building work he would give him the contract.
4. If the beams support a plaster ceiling they fail at a unit stress that causes plaster cracking.
5. I would have told her about the examination if I had seen her yesterday.
6. If a force remains constant the cross section unit stress will change when the cross section changes.
7. If the cost of this building material were lower we would choose it.
8. If I had seen my friend on Monday, I would have asked his advice ().
9. We shall have to wait for him if he doesnt come in time.
10. Concrete wouldnt crack if it were reinforced.
2. . .
1. It would be better to reduce temperature changes.
2. For this purpose concrete would be easier to produce at the factory.
3. We could have used some admixtures but we didnt know the results of the test.
4. Smaller size would increase deformation.
5. An increase in the value of this ratio would produce a concrete with more voids.
3. .
1/10; 0.46; 2.54; 684.75; 3/5; 0.5; 2.5; 3.63; 8½; 7/8; 35.04; 28.8; ¼; 65.5; 0.91; ¾;
4. , .
1. Sometimes concrete should be used reinforced with steel.
2. Concrete that is precast at a factory has to be transported to the site.
3. The builders were not able to precast concrete on site because of bad weather () conditions.
4. The quantities of aggregates, cements or admixtures were to be varied according to the design.
5. A typical hardened and compacted concrete is a two-phase material with aggregate, which should be an inert filler material.
6. Concrete ought to be placed in a plastic state in a form.
7. Because concrete is at the beginning in a plastic state, builders are able to use it in all kinds of construction.
8. If concrete is to counteract tensile stresses, it has to be reinforced with steel.
5. , there + be.
1. There are different kinds of concrete reinforcement.
2. There will be precast walls in this building.
3. There were temperature changes which caused cracking.
4. There mustnt be weak aggregates in a concrete mix.
5. There are natural and artificial building materials.
6. There should not be too much thrust either to the right or to the left.
B
