《专业英语》课件Unit-6.pptx

1、TextConcrete and reinforced concrete are used as building materials in every country.In many including the Unite State and Canada,reinforced concrete is a dominant structural material in engineered construction.The universal nature of reinforced concrete construction stems from the wide availability

2、 of reinforcing bars and the constituents of concrete,gravel,sand,and cement,the relatively simple skills required in concrete construction,and the economy of reinforced concrete compared to other forms of construction.Concrete and reinforced concrete are used in bridge,buildings of all sorts,underg

3、round structures,water tanks,television towers,offshore oil exploration and production structures,dams,and even in ships.As we know,concrete has comparatively low tensile and bending strength compared to its high compressive strength,and concrete is easy to crack even under a very low stress.For str

4、uctural applications it is normal practice to incorporate steel bars to resist any tensile forces.Steel reinforcement is used in the concrete,can overcome the deficiencies in the tensile and bending strengths of concrete.Concrete can be poured,pumped,or even sprayed into all kinds of shapes.And wher

5、eas steel has great tensile strength,concrete has great strength under compression.Thus,the two substances complement each other.TextCompared with concrete,the enormous advantage of steel is its tensile strength;that is,it does not lose its strength when it is under a calculated degree of tension,a

6、force which,as we have seen,tends to pull apart many materials1.The useful strength of ordinary reinforcing steels in tension as well as compression,i.e.the yield strength,is about 15 times the compressive strength of common structural concrete,and well over 100 times its tensile strength.The steel

7、is the vital part of the structure,since concrete is deficient in tensile strength.It is possible to build a structure frame from steel without concrete,but not from concrete without steel.On the other hand,steel is a high-cost material compared with concrete.Although steel occupies only a small par

8、t of the volume of reinforced concrete(on the average about 2 percent),it is a major part of the cost.As a very rough guide,the cost of the formwork,the cost of the concrete and the cost of the steel are approximately the same,i.e.one third of the total.It follows that the two materials are best use

9、d in combination if the concrete is made to resist the compressive stresses and the compressive force,longitudinal steel reinforcing bars are located close to the tension face to resist the tension force,and usually additional steel bars are so disposed that they resist the inclined tension stresses

10、 that are caused by the shear force in the beams.2 TextHowever,reinforcement is also used for resisting compressive forces primarily where it is desired to reduce the cross-sectional dimensions of compression members,as in the lower-floor columns of multistory buildings.Even if no such necessity exi

11、st,a minimum amount of reinforcement is placed in all compression members to safeguard them against the effects of small accidental bending moments that might crack and even fail an unreinforced member3.They also complement each other in another way:they have almost the same rate of contraction and

12、expansion.They therefore can work together in situations where both compression and tension are factors.Steel rods are embedded in concrete to make reinforced concrete in concrete beams or structures where tension will develop.The proper adhesion between the steel and the concrete is of the greatest

13、 importance,and bars should be of a sufficiently small diameter to offer an adequate area of contact with the concrete;note that the smaller the diameter of the bars,the greater their surface area for any given percentage of reinforcement.The practical limit is reached when the bars become so numero

14、us that they obstruct the proper placing of concrete.TextConcrete and steel form such a strong bondthe force that unites themthat no relative movements of the steel bars and the surrounding concrete occur.This bond is provided by the relatively large chemical adhesion which develops at the steel-con

15、crete interface,by the natural roughness of the mill scale of hot-rolled reinforcing bars,and by the closely spaced rib-shaped surface deformations with which reinforcing bars are furnished in order to provide a high degree of interlocking of the two materials4.Still another advantage is that the st

16、eel is therefore completely surrounded by the concrete and the steel does not rust in concrete.Acid corrodes steel,whereas concrete has an alkaline chemical reaction,the opposite of acid.In order to minimize corrosion of reinforcement and consequent spalling of concrete under severe exposure conditi

17、ons such as in bridge decks subjects to deicing chemicals,galvanized or epoxy-coated rebar may be specified5.Although the structure is made in one piece,the reinforcing bars are not.The component pieces of a rigid structural steel frame are joined together by welding of other means,and the same coul

18、d be done to the bars in a concrete structure to produce a rigid frame of reinforcement.This would,however,be a considerable and unnecessary expense.TextWe are therefore dealing with individual reinforcing bars which generally do not exceed 12 m(39 ft)in length because longer bars are difficult to t

19、ransport.These bars are joined by bonding them to the concrete.The steel stress is thus transmitted to the concrete by bond or anchorage,and it is then transmitted to another bar by the same means.It is thus necessary to provide adequate space for the reinforcement to development the stress by trans

20、mission from the concrete.The adoption of structural steel and reinforced concrete caused major changes in traditional construction practices.In the earlier steel of concrete frame building,the curtain walls were generally made of masonry,they had the solid look of bearing walls.Today,however,curtai

21、n walls are often made of lightweight materials such as glass,aluminum,of plastic,in carious combinations.It was no longer necessary to use thick walls of stone or brick for multistory buildings,and it became much simpler to build fire-resistant floors.Both these changes served to reduce the cost of

22、 construction.It also became possible to erect buildings with greater heights and longer spans.New Words and Phrasescrack v.开裂；n.裂缝，裂纹pour v.浇注，倾倒pump v.抽吸，泵送spray v.喷涂complement n.补充，补充物reinforcing steel=Reinforcing bar 钢筋longitudinal a.长度的，纵向的，轴向的shear force 剪力multistory building 多层建筑rate of contr

23、action 收缩率rate of expansion 膨胀率embed v.放入，埋入，嵌入reinforced concrete 钢筋混凝土adhesion n.附着力，黏合（力）bond n.结合力，黏结力；v.握裹，黏结interface n.界面，接触面，交界面mill n.制造厂，粉碎机hot-rolled reinforcing bar 热轧钢筋New Words and Phrasesrib-shaped surface 肋形表面interlock n.连动，联结，结合；相互关系alkaline a.碱性的；n.碱性corrosion n.腐蚀，侵蚀spalling n.剥落，

24、层裂galvanized a.镀锌的epoxy-coated 环氧涂层的rigid a.刚性的frame n.框架anchorage n.锚固；锚具curtain wall 幕墙bearing wall 承重墙Notes1.Compared with concrete,the enormous advantage of steel is its tensile strength;that is,it does not lose its strength when it is under a calculated degree of tension,a force which,as we hav

25、e seen,tends to pull apart many materials.与混凝土相比，钢筋的最大优点是抗拉强度；也就是说，它在一定的拉力作用下，钢的强度不损失，正如我们看到的，这个拉力能够使得许多材料被拉开。2.It follows that the two materials are best used in combination if the concrete is made to resist the compressive stresses and the compressive force,longitudinal steel reinforcing bars are

26、located close to the tension face to resist the tension force,and usually additional steel bars are so disposed that they resist the inclined tension stresses that are caused by the shear force in the beams.如果混凝土被用来抵抗压应力和压力，纵向钢筋被放在受拉力一侧用来抵抗拉力，其他的附加钢筋用来抵抗由剪力引起的斜向拉应力，这样两种材料组合使用最佳，如钢筋混凝土梁。3.Even if no

27、such necessity exist,a minimum amount of reinforcement is placed in all compression members to safeguard them against the effects of small accidental bending moments that might crack and even fail an unreinforced member.即使没有这种必要，少量钢筋被用在所有的受压构件中可以保证它们免受小的附加弯矩的影响，这个弯矩能使得构件开裂甚至可能使得无筋构件破坏。Notes4.This bo

28、nd is provided by the relatively large chemical adhesion which develops at the steel-concrete interface,by the natural roughness of the mill scale of hot-rolled reinforcing bars,and by the closely spaced rib-shaped surface deformations with which reinforcing bars are furnished in order to provide a

29、high degree of interlocking of the two materials.这种黏合力是由产生在钢筋混凝土表面的相对较大的化学附着力、热乳钢筋工厂的原始粗糙度以及带肋钢筋表面的间隔较小的变形所提供的，这种带肋钢筋主要是为了使两种材料有很高的联结。5.In order to minimize corrosion of reinforcement and consequent spalling of concrete under severe exposure conditions such as in bridge decks subjects to deicing che

30、micals,galvanized or epoxy-coated rebar may be specified.在严重的暴露环境下，例如易遭受除冰盐的桥面，为了减小钢筋的腐蚀和随之而来的混凝土剥落，一些镀锌或环氧涂层钢筋被指定使用。Exercises（Translate the following Chinese into English,or English into Chinese）1.As a result,cracks develop whenever loads,or restrained shrinkage or temperature changes,give rise to

31、tensile stresses in excess of the tensile strength of the concrete.2.This is particularly true if dense,air-entrained concrete has been used for surfaces exposed to the atmosphere,and if care has been taken in the design to provide adequate drainage off and away from the structure.3.On the other han

32、d,concrete undergoes drying shrinkage,which,if restrained,may cause deflections or cracking.Furthermore,deflections will tend to increase with time,possibly doubling,due to creep of the concrete under sustained loads.4.Consequently,tensile and shear reinforcement in the tensile regions of sections h

33、as to be provided to compensate for the weak tension regions in the reinforced concrete element（Steel bar is the main role under tensile stress in the tensile regions）.5.Ultimate failure leading to collapse can be caused by crushing of the concrete,when compressive stresses exceed its strength;by yi

34、elding or failure of the rebar,when bending or shear stresses exceed the strength of the reinforcement;or by bond failure between the concrete and the rebar.Exercises（Translate the following Chinese into English,or English into Chinese）6.典型的混凝土混合料具有高的抗压缩应力，然而，任何明显的张力（例如，由于弯曲）会打破微观刚性晶格，导致混凝土的开裂和分离。7.材料的极限强度是通过破坏（断裂）发生位置的应力来测定的。8.在道路上使用除冰的盐-用来降低水的冰点，可能是导致钢筋混凝土或预应力混凝土桥面，路面，停车场过早失效的主要原因之一。9.钢筋是用来加强混凝土额外的抗拉张力，没有加强的话，很多混凝土建筑将不复存在。10.钢筋混凝土可以浇注成各种形状，如梁、柱、板和拱，因而适用于建筑物的具体形状。