The important general characteristics of hardened normal weight concrete and concrete structures, which are made with Portland cement, compared to other building materials and structures are as follows:
Concrete has a high compressive strength, so that it is particularly suitable for use in walls and columns.
If it is not in the form of prestressed concrete, concrete has a low strength to weight ratio which results in general choice of steel or timber beams when there are long spans, and light loads which are applied.
In building, the weight of concrete can provide good sound insulation, for example in floors.
Concrete has good fire resistance. This property often gives it an important advantage over steel. The fire resistance can be made a little lower by aggregates that contain silica.
There is no damage to reinforced concrete at temperatures which are lower than 300C (580F) and a limestone aggregate can withstand temperatures up to about 800C (1,500F) without great damage.
Unreinforced concrete is able to withstand amounts of tension, up to approximately 1/10 of its compressive strength. This property is of great importance as it allows concrete to withstand some shear stress without cracking.
Notes:
silica n.
1. How many important general characteristics of hardened concrete structures are there?
2. What are they?
3. How can fire resistance of concrete be influenced?
4. What temperatures can limestone aggregate withstand?
5. How high are the amounts of tension that unreinforced concrete is able to withstand?
1. . .
2. . .
1. ) :
sound, insulation, timber, floor, wall, choice, span, choice, importance, damage,
:
light, a little, particularly, other, suitable, approximately,
:
as follows, as, without, so that, for example, by, some, compared to,
:
contain, apply, provide, give, withstand, allow.
b) , . , .
2. .
| A | B strength shear stress reinforced concrete structural concrete cracking fire resistance amount | A | B tension load importance limestone withstand often advantage |
3. :
|
|
|
durable - durability
important - importance
1.7
A, B . , .
A
[hjH'mIdItÁ]; ['fPlqV]; ['mPdqrIt]; ['selsIqs]; [I'nISql]; ['fxrqnhaIt]; ['rIGId]; [Ll'DqV]; ['pWmqnqnt]; ['eqrIq]; [q'veIlqbql]; [sIg'nIfIkqntlI]; ['jHZVqlI]; [Ik'strJmlI]
B
| humidity cellulose permanent extremely | humanity area moderate avoidable | rigid available era significantly | follow although Celsius fellow | initial regard usually Fahrenheit |
A
CONCRETE
PART I
A property that is particularly connected with concrete is shrinkage, which is the permanent, contraction of concrete. It is caused by loss of water from the cement paste after hardening. The rate of shrinkage is rapid in the period which immediately follows the set of the concrete but becomes much slower with time. Because of the low tensile strength of concrete, shrinkage when it is limited leads to cracking.
Cast-in-place reinforced concrete as a method of construction is able to be applied to non-standard areas and shapes. It forms heavy, rigid, fireproof construction with relative ease.
Because all the necessary materials are easily available, construction work in cast-in-place concrete may start almost immediately, which sometimes gives faster completion times than if shop fabricated elements are used, such as those in steel or precast concrete.
About 50% of the cost of cast-in-place construction is that of the formwork. Hence, standard dimensions, that enable constant re-use of formwork, will significantly reduce the cost of cast-in-place concrete work.
In order to obtain good strength and durability, concrete must be allowed to cure, in conditions of temperature and humidity that are reasonably controlled after the initial set of the concrete. In general, moderate temperatures, between 20 C and 40 C (68F and 86F), and moist or wet conditions are the best. The total curing period is extremely long. However, curing is often considered to be over after the concrete has gained a reasonable strength, although curing and strength are not related. A minimum curing period is usually at least seven days.
Notes:
completion n. ,
contraction n.
moist adj.
.
1. What property is associated with concrete?
2. What is shrinkage caused by?
3. What is the rate of shrinkage?
4. Why does shrinkage lead to cracking?
5. What is the advantage of cast-in-place reinforced concrete?
6. Why is the use of cast-in-place concrete sometimes better than the use of shop fabricated elements?
7. What is the cost of formwork?
8. Why is it useful to re-use the formwork?
9. What should be done to obtain good properties of concrete?
10. What conditions are these?
11. What is the total curing period?
12. What is a minimum curing period?
1. )
:
formwork, re-use, set, humidity,
|
|
|
:
fireproof, heavy, initial, extremely, wet, reasonable, moderate, shop fabricated, relative, significantly, rigid, permanent, reasonably,
:
at least, hence, in general,
:
be over, enable, relate (~ to), lead, follow, gain.
) ? .
) ? ? ?
2. :
; ; ; ; (); ; , ; (); ; ; ; , ; , ; ;
; ; , ; ; ; (); ; , ; ; , ;
; ; , ; ; , ; ; ; ; ; ;
, ; -; ; ; ; , ; ; ; ; ; ;
3. , . .
4. . .
| damage approximately shrinkage loss cracking cost span suitable dimension about | almost connect enable reduce contain floor importance as follows condition timber |
5. :
| precast concrete loss minimum rapid | standard heavy start fast | reduce after best long |
1. . .
1. They are massive structures with stone walls that withstand the thrust of their great weight.
2. Because of non-standard areas and shapes on the site the material the builders used was cast-in-place reinforced concrete.
3. If the beam is too long, or if it has to support too much weight, it is subjected to shear.
4. One of the reasons these structures have survived () is because of the great strength that was built into them.
5. In Rome, for example, most of the people lived in great blocks that were often ten storeys () high.
6. When a modern engineer plans a structure, he considers the total weight of all its component materials.
7. An engineer must consider the live load the structure will support when it is in use.
8. These properties of materials are based on the values which are given by standard tests.
9. The shrinkage we observed () has stopped.
10. The modern engineer must also understand the different stresses which the materials in a structure are subject to.
2. , . .
| absorption action addition combination compression conduction | construction deformation direction formation insulation location | production solution transportation development placement reinforcement |
3. that .
1. A property that is connected with concrete is shrinkage.
|
|
|
2. About 50% of the cost of cast-in-place construction is that of the formwork.
3. Engineers know that standard dimensions will enable to re-use the formwork.
4. Three forces can act on a structure: those that act up or down; those that act in horizontal plane; and those that act upon it with a turning motion.
5. Sound is absorbed by spaces in the material that contain air.
6. An important mechanical property of building materials is that of strength.
7. Steel and cement appeared in the nineteenth century and people had been producing steel up to that time by a process that limited its use.
8. We must determine the safety factor, that is, an additional capacity to make the structure stronger.
4. , .
1. A metal bar breaks when it is pulled with a force of 200.000 lb.
2. Nothing is designed to be stressed to the point where it is ready to fail.
3. This is the area that resists displacement.
4. Shear unit stresses will act on the cross-sectional area.
5. The unit stress at the location of the highest unit stress is considered.
6. The cross sections were changed in size by forces.
7. The actual unit stress changes when the cross section is changed.
8. Unit stress is computed on the basis of the area as it is before any force is applied.
5. . , .
1. It forms heavy, rigid, fireproof construction with relative ease.
2. Construction work in cast-in-place concrete may start almost immediately.
3. In order to construct a building, engineers must determine several important factors.
4. Wind increases loads a structure is subjected to.
5. The increase of these forces may cause deformation.
6. Concrete gains strength with time.
7. The gain of strength of these concrete units was achieved by the use of new admixtures.
8. It will reduce the cost of concrete work.
9. Engineers have to know how much this or that building material costs.
10. Standard dimensions enable constant re-use of formwork.
11. It is possible to re-use the formwork in castin-place construction.
B
Concrete is subject to dimensional changes due to temperature variations, initial shrinkage and moisture movements among others. Concrete has low tensile strength and the dimensional changes may cause cracking of the concrete. Measures which prevent cracking are necessary in the design of concrete structures but may not always be completely successful.
An elastic material under load is subject to a deformation which causes an elastic strain. Some materials, including concrete, continue to change although there is no increase in load. This deformation causes a further strain, the creep strain, which for concrete, over time, is usually greater than the elastic strain; the creep strain always increases with time and finally reaches a limit. Creep is higher at higher temperatures and is about double at 70C (158F) that at 20C (68F). The effects of shrinkage can be reduced if construction joints are provided.
Concrete has a relatively high value of elastic modulus. For example, a concrete column of common proportions has only elastic deflections under load. Concrete may also be useful as a tie when it is required to limit the extension; the tie would normally be prestressed. Long term loads cause further slow deformations by creep and this effectively reduces the value of the elastic modulus of the concrete.
Notes:
elastic strain
measure n.
|
|
|
.
1. What causes dimensional changes of concrete?
2. What does a deformation cause in an elastic material?
3. What does elastic strain result in?
4. How does creep depend on temperature?
5. How can the effects of shrinkage be reduced?
6. Does concrete have a high or low value of elastic modulus?
7. When may concrete be useful as a tie?
8. What reduces the value of the elastic modulus of the concrete?
1. . .
2. , - ion, - ment. ?
1. ) :
joint, variation, limit, deflection, elastic modulus, extension, tie,
:
long, term, completely, over time, successful, dimensional, double, common, elastic,
:
among, always, also, due to, only,
:
prestress, prevent, reach, continue, require.
b) , . , .
2. .
| A | B several double project drawing safety support reason | A | B allowable still bottom inwards basis tie component |
3. :
reason - reasonable - reasonably
vary - various - variation
1.8
A, B . , .
A
[q'prPksImIt]; [dI'strOI]; ['kwIklI]; [geIn]; [In'SVq]; [rI'kwaIq]; [sq'fISqnt]; ["hPrI'zPntl]; ['vWtIkql]; [sI'ment]; ['sWfIs]; ['fWDq]; [tWm]; ['ADq]
B
| feather sufficient gain team | ensure destroy suffice require | order vertical virtual horizontal | approximate unsure cement other | surface term quickly further |
A
CONCRETE
PART II
Concrete cannot be placed during very cold weather because freezing water will destroy a concrete which has set partly. An approximate limit is that no wet concrete, after it is placed in its final position, should be at a temperature less than 5C or 40F. Even then insulation of the concrete will be necessary and the curing period, which is required to gain strength, will be long. In hot weather the problem during placement is to prevent a premature set and, after placement, in order to ensure a proper cure. The concrete must not dry out too fast because this may cause cracking.
One of the principal disadvantages of the use of cast-in-place concrete is the time that is required before the removal of the formwork. This period of time is necessary so as to allow the concrete to gain sufficient strength before it has to support itself; therefore the period before the removal of formwork must be longer for horizontal elements, such as beams and slabs, than for vertical elements, such as columns. Because of the cost of the formwork and in order to allow as rapid re-use as possible, cements which gain strength quickly are preferred by contractors. However, these cements produce such heat after they set that they may cause thermal cracking. In addition, the high temperature at which curing takes place leads to losses in the long term properties of the concrete. Slag cements and other low heat cements are better from this point of view. The formwork to beams and slabs is usually removed after a reasonable period of time but the props remain for a further period.
Typical minimum periods before removal of formwork for concrete with a surface temperature of 16C (60F) are from 9 hours to 15 days.
Notes:
freezing water
premature adj.
prop n.
slag n.
.
1. Why cant concrete be placed during very cold weather?
2. What is the minimum temperature allowable for wet concrete?
3. What is the problem during placement of concrete in hot whether?
|
|
|
4. Why must concrete not dry out too fast?
5. What are the principal disadvantages of using cast-in-place concrete?
6. Why cant formwork be quickly removed?
7. How does it influence the choice of cements?
8. What are the disadvantages of the cements which gain strength quickly?
9. What cements are better from this point of view?
10. What are typical minimum periods before removal of formwork?
1. )
:
contractor, disadvantage, placement, slab, point of view,
:
partly, proper, principal, as as ,
:
dry, destroy, prefer, ensure, set.
) ? . , ed.
) ? ? ?
2. :
; ; ; ; ; ; ; (2); ; ; ; ; ; ; (, ); ; ; ;
; ; , ; ; ; ; ; ; ; ; ; ; ;
; ; ; , ; (2); ; ; ; ; ; ; , ; ; ;
; ; ; ; ; ; -; ; ; ; ; ; , (2); ; ; .
3. , , , , 48()? .
4. . .
| deflection joint creep among double strain elastic modulus tie variation moisture | value withstand extension common shear results in dimensional prevent reach limit |
5. :
| harden ensure variation common | start permanent lead in general | hence gain be over contain |
1. , a s as .
1. The re-use of formwork should be as rapid as possible.
2. These measures can be not as successful as we considered.
3. Cast-in-place concrete is as strong as precast concrete.
4. After the initial set temperature and humidity conditions of the concrete are controlled as carefully as reasonable.
5. Resistance to rain and moisture is as an important property of building materials as their strength.
6. Scientific knowledge is as significant in construction as experience.
2. , al, -able. , ive, .
3. , have.
1. Curing is often considered to be over after the concrete has gained a reasonable strength.
2. Concrete has low tensile strength.
3. Concrete has to be reinforced with steel.
4. Concrete has many characteristics that make it a constructional material.
5. These may replace up to about 70% of the Portland cement which would have been required.
6. The builders had to use cast-in-place concrete because of the conditions of the site.
4. . .
1. Concrete cannot be placed during very cold weather because freezing water will destroy a concrete.
2. The curing period, which is required to gain strength, will be long.
3. Builders must know that the formwork is usually removed after a reasonable period of time.
4. Because of the cost of the formwork cements, which gain strength quickly, are preferred by contractors.
5. If it is not in the form of prestressed concrete, concrete has a low strength.
6. The tensile stresses concrete is subjected to require that it must be reinforced with steel.
5. , .
1. If cracks appear under small overload, they usually will close when the load is removed.
2. If the pressure is enough, none of the beams will fall out.
3. If this concept were applied to a concrete beam in practice, steel tendons would be tensioned and placed along the centroidal axis of the beam.
4. If the tendons were given a small tension, they could lose nearly all the prestress in a few months.
5. If a beam supports a load above, the beam itself must have sufficient strength to counterbalance that weight.
6. If they change some details, they will be able to improve the design.
7. You would get good results if you applied this method of calculation.
6. , . .
| application calculation composition consideration corrosion division | fabrication limitation occupation opposition relation repetition | selection separation transmission measurement movement requirement |
B
PRECAST CONCRETE
A concrete structure may be constructed by casting the concrete in place on the site, by building it of elements cast in some other place or by a combination of the two. Concrete cast in other than its final place is called precast.
In contrast to cast-in-place concrete construction in which columns, beams, girders and slabs are cast and connected together by successive pours, precast concrete requires connections to tie the structure together. These connections can be a major construction problem.
Form costs are much less with precast concrete because the forms do not have to be supported. They may be set on the ground in a convenient position. In addition, a thin wall is difficult to concrete if it must be cast vertically because the concrete has to be placed in the narrow opening at the top of the form. Such a wall is easily precast on the ground.
Precast units can be standardized. Repeated use of forms and mass production techniques make the cost of construction lower. Furthermore, high quality can be maintained because of the control that can be kept on production under factory conditions. However, there is always the possibility that transportation, handling, and building up costs for the precast units will be high.
Notes:
contrast (in ~ to) (-)
handling n. , ( -)
possibility n. ,
.
1. How may a concrete structure be constructed?
2. What do we call precast concrete?
3. What are the advantages of precast concrete?
4. Why does the use of precast concrete reduce costs?
5. How can the use of precast concrete increase costs?
1. , al, ive. .
2. , - ion. ? .
1. ) :
quality, control, transportation, mass production technique, connection, ground, girder, top, place,
:
successive, furthermore, thin, convenient, other than,
:
standardise, cast, maintain, tie, keep.
b) , . , .
2. .
| A | B select unit masonry form rust eliminate site | A | B wall thick other major however next depend |
3. :
control (n.) - control (v.)
set (n.) - set (v.)
tie (n.) tie (v.)
C
PRESTRESSED CONCRETE
Prestressed concrete is concrete with stresses applied to it before use so as to counteract stresses that will be produced by loads. Prestress is most effective with concrete, which is weak in tension, when the stresses which are applied are compressive. In order to produce compressive prestress a concrete member can be placed between two abutments, with jacks between its ends and the abutments, and pressure is applied with the jacks. The most common way is to stretch steel bars or wires, that are called tendons, and to anchor them to the concrete; when they try to gain their initial length, the concrete resists and is prestressed. The tendons may be stretched with jacks or by electrical heating.
Prestressed concrete is particularly useful for beams. It permits the use of steel at stresses several times larger than those permitted for reinforcing bars. Furthermore, it permits economical use of high-strength concrete, for when an engineer designs a member with reinforced concrete, he considers that all concrete below the neutral axis is in tension and cracked, and therefore ineffective, whereas the full cross section of a prestressed concrete beam is effective in bending.
A particularly desirable characteristic of prestressed concrete is that as long as the material is maintained in compression it cannot crack. If cracks appear under overload, they usually will close when the load is removed. Sometimes concrete is prestressed mostly in order to prevent cracking.
Basic principles. When you take a pile of books and apply pressure to the end pair not one of the books will fall out if the pressure is enough. The effect of compressive prestresses is much the same.
But if this concept were applied to a concrete beam in practice, steel tendons would be tensioned and placed along the centroidal axis of the beam. The prestress that would be achieved would result in a uniform compression at every section. Loads would produce both tensile and compressive stresses at the middle of the span. The prestress would combine with these. As the result the compression would be increased and the tension avoided. The whole concrete section would be resisting bending effectively, and there would be no cracks.
In practice, however, tendons are rarely placed along the centroidal axis. A smaller prestressing force is required, and therefore less steel for the tendons, if the steel is placed below the centroidal axis of the beam. With the eccentric prestress, stresses at each section of the unloaded beam may vary from tension at the top to compression at the bottom. When loads are applied to the beam, they produce both tensile and compressive stresses at the middle of the span. At the top of the beam they cause compressive stresses, which are reduced by the tensile prestress there. In other sections the tensile stresses produced by the loads are counteracted by the compressive prestress.
Notes:
centroidal axis
concept n. ,
eccentric prestress
overload n.
pile n. .
tendon n.
unloaded adj.
.
1. What is prestressed concrete?
2. How is concrete prestressed?
3. What is tendon?
4. Why is prestressed concrete particularly useful for beams?
5. How does the use of prestressed concrete influence cracking?
6. What would be the result if steel tendons were tensioned and placed along the centroidal axis of the beam?
7. Why are tendons rarely placed along the centroidal axis?
8. What is the influence of loads on a beam with the eccentric prestress?
, . .
| reinforcing bar apply top pair both and bending jack anchor achieve avoid uniform permit counteract pressure the same whereas | B | section wire abutment as long as place length heating bottom economical desirable prestress stretch rarely end tension middle | B , |
1.9
A, B . , .
A
["xlq'mInIqm]; [Ik'stent]; [kWv]; [streIt]; ["Instq'bIlItI]; ['IndqstrI]; [TWd]; ['kwPntItI]; [kqm'baIn]; ['Genqrql]; ["kxrIktq'rIstIk]; [dI'zaIn]; ['aIn]; ['brItl]
B
| design iron aluminium generous | straight combine thread general | brittle instability extend extent | quantify curve industry carve | street third characteristic quantity |
A
METAL
Construction materials are used in large quantities and it is therefore important that the materials which are used are cheap. Although bulk costs of metal are higher than those of most other building materials, the costs of iron and steel, and aluminium to a much lesser extent, are still reasonable when they are compared to those of other metals and these metals have found wide application in building.
Structural carbon steel is the most important class of steel for the construction industry. These steels are cheap and convenient to use; the class includes steels which have not more than 0.25 % carbon. There are several grades of structural carbon steel available. Those grades which have higher carbon contents are stronger. However steels which have higher carbon contents are, in general, more brittle at low temperatures and more difficult to weld.
The important general characteristics of structural carbon steels and steel structures are as follows:
Steel has a high ratio of strength to weight that is combined with a low ratio of cost to strength, which accounts for the wide use of steel as roof beams.
Steel for construction purposes is produced in the form of straight or curved rolled sections of various cross-sectional shapes, or flat plate.
Although the use of high strength steel will often produce a lighter structure for the same design strength than one in a weaker material, the structure may suffer from excessive deflection or instability.
Steel loses strength and stiffness at high temperatures. At 480C (900F) steel keeps about two-thirds of its original stiffness and strength. However the loss of stiffness is rapid above this temperature.
Notes:
bulk costs 蠠
carbon steel
class n. , ,
.
1. Why is it important that the materials are cheap?
2. Which metals have found wide application in building?
3. What kind of steel is the best for construction?
4. What are the advantages of these steels?
5. Which steels does this class include?
6. How does the strength of steel depend on its carbon contents?
7. What are the disadvantages of steels with higher carbon contents?
8. Why is steel widely used for roof beams?
9. What can the use of high strength steel result in?
10. How does the strength and stiffness of steel depend on temperature?
1. )
:
contents, industry, stiffness, aluminium, rolled section, instability, extent, grade, plate,
:
brittle, straight, cheap, flat,
:
curve, account (for), weld, suffer, find.
) ? .
) ? ? ?
2. :
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
; ; ; (); ; ;
; ; ; ; ; ; ; ; ; ; ; ;
, ; , ; ; , ; ; ; ; ; , ; , ; ; .
3. , : , . .
4. . .
| anchor jack kind bending heating every section tension knowledge whole | reinforcing bar gravel constant abutment pressure then middle prestress enough wire |
5. , 1-9. , . . , ?
stable, long, heat, economy, bend, transport, standard, place.
1. , .
1. The experiments () showed that high quality of a steel joint resulted both from the strength of steel and from its ductility ().
2. The experiments show that high quality of a steel joint results both from the strength of steel and from its ductility.
3. They promised () that the precast concrete units would be brought to the site tomorrow.
4. They promise that the precast concrete units will be brought to the site tomorrow.
5. The lecturer () said that many great buildings had been constructed on the basis of experience.
6. The lecturer says that many great buildings were constructed on the basis of experience.
7. The tests showed creep was about double at 70C that at 20C.
8. The tests shows creep is about double at 70C that at 20C.
9. We were told that at 480C (900F) steel kept about two-thirds of its original stiffness and strength.
10. We are told that at 480C (900F) steel keeps about two-thirds of its original stiffness and strength.
2. , one.
1. A multi-storey building has a number of floors which are erected one above the other.
2. Structural carbon steel is the one most important for the construction industry.
3. One must know the qualities of building materials.
4. One of the simplest types of construction is the solid concrete slab.
5. The floor beams transmit the loads in one direction only.
6. In contrast to cast-in-place concrete construction precast one requires connections to tie the structure together.
7. When you take a pile of books and apply pressure to the end pair not one of the books will fall out if the pressure is enough.
8. These beams are too long, we need shorter ones.
3. . -ant/-ent.
sufficient strength, different properties, permanent stress, fire resistant, important characteristics, significantly advantage, convenient conditions.
4.
+ - ness =
useful - usefulness
serious - seriousness
weak - weakness
dark () darkness
hard () hardness
brittle brittleness
stiff () stiffness
5. . .
1. Structural carbon steel is the most important class of steel for the construction industry.
2. However steels with higher carbon contents are more brittle at low temperatures and more difficult to weld.
3. Although the use of high strength steel will often produce a lighter structure for the same design strength than one in a weaker material, the structure may suffer from excessive deflection or instability.
4. In such cases it may be necessary to use a larger amount of material of a lower quality or a different material, such as wood.
5. High strength connections are much easier made between steel components than between timber and precast concrete ones.
6. The most common way is to stretch steel bars or wires, that are called tendons
B
High strength connections are much easier made between steel components than between timber and precast concrete ones. Connections in steel can be made by welding or bolting. They are a significant proportion of the total cost of a steel structure. Normal jointing methods allow dimensional errors in production or construction of the steelwork. A cheaper and easier connection may be made if the joint is not required to be a fixed one. The experiments showed that high quality of a steel joint resulted both from the strength of steel and from its ductility.
Most jointing methods are improved by use of a material which has such a combination of strength and 'plasticity' and this accounts for the use of steel for connections in wood and precast concrete and, often, for the initial choice of a steel structure.
Convenient connection methods and a high strength to weight ratio make steelwork suitable for prefabrication and fast erection on site. However the size of prefabricated components is limited by the means of transport to site and sometimes the capacity of cranes on site.
Steel is dimensionally stable although it is subject to temperature movements. In general a typical single storey building of simple shape with steel columns would require a movement joint at about 50m (160ft) intervals.
Notes:
ductility n. ,
jointing n.
prefabrication n. /
temperature movement
.
1. How can connections in steel be made?
2. What do normal jointing methods allow?
3. What does high quality of a steel joint result from?
4. What do these qualities of a steel joint account for?
5. What is the use of prefabricated components limited by?
6. What do steel structures require?
7. Why do they require it?
1. ) :
erection, means, transport, steelwork, welding, error, interval, movement joint, storey, plasticity,
:
simple, fixed,
:
result from, improve, bolt, prefabricate.
b) , . , .
2. .
| A | B connection stable between joint quality convenient require subject to | A | B single account for choice site crane dimensional timber significant |
3. :
plastic (adj.) - plasticity
weld - welding
loss - lose
1.10
A, B . , .
A
['lxmIneItId]; [steIG]; [rI'laIqbql]; [skrH]; ['seljVlq]; [jH'nJk]; [glH]; [Ik'spleIn]; ["mxnjV'fxkCq]; [weIt]; ['mPdjVlqs]; ["nevqDq'les]; ['laI]; [greIn]
B
| weighed manufacture screw cellular | nonetheless modulus glue nevertheless | grain laminated lie manufacturer | lay stage reliable unique | glee explain models weight |
A
WOOD
Many of the qualities that make wood a unique building material result from the structure of wood. It has a cellular structure which looks like a number of tubes that lie in the direction of the grain. They have approximately square cross-sections and are weakly glued one to the other. This can explain why wood is weak across the grain, and why its compressive strength is only about ⅓ of its tensile strength. Wood is the most popular construction material all over the world if we speak about the amount which is used and the number of suitable applications. Commercial woods are divided into softwoods such as pines and firs and hardwoods such as oak and ash. However the development of some reliable wood glues has brought in a range of manufactured products which are based on wood such as glued laminated timber, plywoods, etc.
The qualities of wood depend on its moisture content. Moisture content affects the weight, strength, durability and size of wood. For example, dry wood has about twice the strength and stiffness of green wood.
Wood has low strength under long term loads and at high temperatures but it has good resistance to short term loads and high strength at low temperatures.
Wood has good stiffness, which means that it has a relatively high value of elastic modulus. Nevertheless, deflection is often the critical factor in the design of timber beams. Under long term loads, the further deformations due to creep may cause sagging, if it is not taken into account at the design stage.
Wood is a very good material to cut and work and, because of its structure, it is able to accept nails. Common methods of fixing are with nails, screws, bolts, metal plates, etc.
Notes:
ash n.
cellular adj.
commercial wood
grain n.
green wood
oak n.
pine n.
plywood n.
sagging n.
.
1. What is the structure of wood?
2. How does the structure of wood influence its strength?
3. Why is wood considered the most popular construction material?
4. What kinds of commercial woods are there?
5. What are the examples of these kinds of commercial woods?
6. What new wood products have been developed?
7. Why is it important for wood to be dry?
8. When does wood have low strength?
9. When does it have good resistance?
10. What does stiffness mean?
11. What is the critical factor in the design of timber beams?
12. What may cause sagging?
13. Why is wood a very good material to work?
14. What are common methods of wood fixing?
1. )
:
bolt, screw, stage, softwood, range, development, tube, nail, hardwood, a number of,
:
short term, critical, reliable, dry, laminated, popular, unique,
:
across, nevertheless,
:
accept, cut, fix, glue, lie, mean, bring, affect, speak, work.
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2. :
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4. . .
| creep angle strong axis right live load solution thrust exert component | whereas as long as avoid uniform ground girder cast convenient furthermore maintain |
5. :
| cheap find disadvantage partly | quick bottom close v. rarely | result from cut dry hardwood |
1. , .
1. Structural members of any length and cross section and with any required curve can be made.
2. No cracks appeared under overload.
3. Anything less strong would not be good for that purpose.
4. Each piece has some characteristic that seriously reduces strength.
5. They used no laminated timber in this structure.
6. Nothing could be done to avoid cracking.
7. Because concrete is at the beginning in a plastic state, it can be used in construction of any size or shape.
8. The builders bound the layers together with mortar or some other binder.
9. In hot weather something should be done to prevent a premature set of concrete.
10. No wet concrete, after it is placed in its final position, should be at a temperature less than 5C or 40F.
2. , one.
1. They have square cross-sections and are glued one to the other.
2. The pieces are glued one over the other.
3. No one lamination ( ) is as long as the member.
4. Connections were made between steel components and between timber and precast concrete ones.
5. One should be careful when working with glued laminated timber.
6. Loads will produce tensile stresses and compressive ones.
3. :
50m (160ft); 1/3 of its tensile strength; 31.01.1845; 24ft (7,2m); 12in ´ 12in; 60-80 %; 20C; 150 kg/m2; 90 cm; 3.5m; 100 ´ 300 mm; 7/8 of its length; 4.5ft x 6.24ft; 03.10.1998; 32 lb; 145F.
4. :
Cellular structure, square cross-section, metal plate, section dimensions, timber construction, connection methods, temperature movements, joint movement problem, construction industry, precast concrete component, carbon contents, design strength, production technique, transportation costs.
5. , .
| special particular wide usual constant | great large near equal extreme | initial reasonable significant complete economical |
B
GLUED LAMINATED TIMBER
Construction with sawn wood is limited by the size, shape, and characteristics of available trees. Lumber longer than 24 ft (7.2 m) or with a cross section dimension greater than 12 in. x 12 in. is difficult to obtain in large quantities. When lumber of these sizes is sawed, each piece much more often has some characteristic that seriously reduces strength or lowers the quality of its appearance than it is with pieces. Heavy timber construction and long spans are not feasible with sawn lumber. Sawn lumber cannot be bent into curves except in cross sections and is generally used straight.
However, structural members of any length and cross section and with any required curve can be made if pieces are glued together. The pieces, which are of standard lumber cross section, are glued one over the other, wide face to wide face, as laminations. No one lamination is as long as the member. They are glued end to end to reach the full length. A structural member made this way is called a glued-laminated member. The supporting members for heavy timber construction are glued-laminated timbers.
Lumber of 2 in. thickness is generally used for laminations. These laminations can be used straight in columns or beams and can be bent to form arches.
Notes:
end to end
glued-laminated member
glued-laminated timber
lamination n.
lumber n.
saw v.
sawn wood
tree n. ,
.
1. What are the limitations for construction with sawn wood?
2. Why is large size lumber not good for construction?
3. What is not feasible with sawn lumber?
4. How can structural members of any length and cross section be made of lumber?
5. How are lumber pieces glued to reach the full length?
6. What can laminations be used for?
1. :
except (prep.), lower (v.), thickness (n.), curve (n.), feasible(adj.), face (n.).
, . , .
2. .
| A | B some available straight shape arch size span reduce dimension quality | A | B beam wide glue cross section column quantity bend piece appearance obtain |
3. :
form n. - form v. - formwork
long - length
1.11
A, B . , .
A
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B
| mechanical both science reinforcement | bind toothless toughness corrosion | band variation molecule compost | corrugation molecular quarter suitable | matrix since mattress composite |
A
PLASTIC
The construction industry uses over a quarter of all the plastics that are produced. However of the large number of plastics available, only a small number are suitable for use in the major elements of a building. The principal distinction among plastics is between the thermosetting and thermoplastic materials. Both types may be reinforced by fibres and in the case of thermosetting plastics this is almost always necessary in order to obtain good mechanical properties. Plastics are widely used because of their high strength to weight ratio, their ease of forming and their resistance to corrosion.
The most popular thermosetting plastic in use in the construction industry, due to its cost, strength, relative hardness and toughness, is fibreglass reinforced polyester, GRP, a composite which has a polyester resin matrix and glass fibre reinforcement. In a reinforced plastic the matrix binds the fibres together and protects them from damage; the fibres are much stronger than the surrounding matrix material. Fillers such as glass, mica and sand can also be incorporated so as to improve properties.
The properties of
