土木工程英語翻譯2
The history of civil engineering
Another advance in steel construction（結(jié)構(gòu)） is the method of fastening together（連在一起） the beams. For many years the standard method was riveting. A rivet is a bolt with a head that looks like a blunt screw（圓頭螺絲釘） without threads（螺紋）. It is heated, placed in holes through the pieces of steel（鋼構(gòu)件）, and a second head is formed at the other end by hammering（錘擊）it to hold it in place（固定就位）. Riveting has now largely been replaced by welding, the joining together of pieces of ste Fundamentally, engineering is an end-product-oriented discipline that is innovative, cost-conscious and mindful of human factors. It is concerned with the creation of new entities, devices or methods of solution: a new process, a new material, an improved power source, a more efficient arrangement of tasks to accomplish a desired goal or a new structure. Engineering is also more often than not concerned with obtaining economical solutions. And, finally, human safety is always a key consideration.Engineering is concerned with the use of abstract scientific ways of thinking and of defining real world problems. The use of idealizations and development of procedures for establishing bounds within which behavior can be ascertained are part of the process.
Many problems, by their very nature, can’t be fully described—even after the fact, much less at the outset. Yet acceptable engineering solutions to these problems must be found which satisfy the defined needs. Engineering, then, frequently concerns the determination of possible solutions within a context of limited data. Intuition or judgment is a key factor in establishing possible alternative strategies, processes, or solutions. And this, too, is all a part of engineering.
Civil engineering is one of the most diverse branches of engineering. The civil engineer plans, designs, constructs, and maintains a large variety of structures and facilities for public, commercial and industrial use. These structures include residential, office, and factory buildings; highways, railways, airports, tunnels, bridges, harbors, channels, and pipelines. They also include many other facilities that are a part of the transportation systems of most countries, as well as sewage and waste disposal systems that add to our convenience and safeguard our health.The term “civil engineer” did not come into use until about 1750, when John Smeaton, the builder of famous Eddystone lighthouse near Plymouth, England, is said to have begun calling himself a “civil engineer” to distinguish himself from the military engineers of his time. However, the profession is as old as civilization.
In ancient Egypt the simplest mechanical principles and devices were used to construct many temples and pyramids that are still standing, including the great pyramid at Giza and the temple of Amon-Ra at Karnak. The great pyramid, 481 feet(146.6 meters)high, is made of 2.25 million stone blocks having an average weight of more than 1.5tons (1.4 metric tons). Great numbers of men were used in the construction of such monuments. The Egyptians also made obelisks by cutting huge blocks of stone, some weighing as much as 1000 tons (900 metric tons). Cutting tools of hard bronze were used.The Egyptians built causeways and roads for transporting stone from the quarries to the Nile. The large blocks of stone that
were erected by the Egyptians were moved by using levers, inclined planes, rollers, and sledges.The Egyptians were primarily interested in the know-how of construction; They had very little interest in why-for of use .In contrast, the Greeks made great strides in introducing theory into engineering problems during the 6th to 3rd centuries B.C. They developed an abstract knowledge of lines, angles, surfaces, and solids rather than referring to specific objects. The geometric base for Greek building construction included figures such as the square, rectangle, and triangle.
The Greek architekton was usually the designer, as well as the builder, of architectural and engineering masterpieces. He was an architect and engineer. Craftsmen, masons, and sculptors worked under his supervision. In the classical period of Greece all important buildings were built of limestone or marble; the Parthenon, for example, was built of marble.
The principal construction materials
The principal construction materials of earlier times were wood and masonry-brick, stone, or tile, and similar materials. The courses or layers（磚層）were bound together with mortar or bitumen, a tarlike substance, or some other binding agent. The Greeks and Romans sometimes used iron rods or clamps to strengthen their building. The columns of the Parthenon in Athens（雅典的帕臺農(nóng)神廟）, for example, have holes drilled（鉆孔） in them for iron bars that have now rusted away（銹蝕殆盡）. The Romans also used a natural cement called pozzolana, made from volcanic ash, that became as hard as stone under water. Both steel and cement, the two most important construction materials of modern times, were introduced（推廣） in the nineteenth century. Steel, basically an alloy of iron （鐵合金）and a small amount of carbon, had been made up to that time（到那個時候） by a laborious（繁復的） process that restricted it to such special uses as sword blades（刀刃）. After the invention of the Bessemer process （貝塞麥煉鋼法）in 1856, steel was available in large quantities at low prices. The enormous advantage of steel is its tensile strength; that is, it does not lose its strength when it is under a calculated degree (適當?shù)? of tension, a force which, as we have seen, tends to （往往）pull apart many materials. New alloys have further increased the strength of steel and eliminated some of its problems, such as fatigue, which is a tendency for it to weaken as a result of continual changes in stress（連續(xù)的應力變化）.Modern cement, called Portland cement, was invented in 1824. It is a mixture of limestone（石灰石） and clay, which is heated and then ground into a powder（磨成粉末）. It is mixed at or near the construction site （施工現(xiàn)場）with sand, aggregate (small stones, crushed rock, or gravel), and water to make concrete. Different proportions of the ingredients （配料）produce concrete with different strength and weight. Concrete is very versatile; it can be poured, pumped, or even sprayed into （噴射成）all kinds of shapes. And whereas steel has great tensile strength, concrete has great strength under compression. Thus, the two substances complement each other（互補）.They also complement each other in another way: they have almost the same rate of contraction and expansion. They therefore can work together in situations where（在…情況下） both compression and tension are factors（主要因素）. Steel rods（鋼筋） are embedded in（埋入）concrete to make reinforced concrete in concrete beams or structures where tension will develop（出現(xiàn)）. Concrete and steel also form such a strong bond - the force that unites（粘合） them - that the steel cannot
slip（滑移） with the concrete. Still（還有） another advantage is that steel does not rust in concrete. Acid（酸） corrodes steel, whereas concrete has an alkaline chemical reaction, the opposite of acid.
The adoption of structural steel and reinforced concrete caused major changes in traditional construction practices（施工作業(yè)）. 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（防火地面）. Both these changes served to（有利于） reduce the cost of construction. It also became possible to erect（建造）buildings with greater heights and longer spans.Since the weight of modern structures is carried（承受） by the steel or concrete frame, the walls do not support the building. They have become curtain walls, which keep out the weather and let in light. In the earlier steel or concrete frame building, the curtain walls were generally made of masonry; they had the solid look of bearing walls（承重墻）. Today, however, curtain walls are often made of lightweight materials such as glass, aluminum, or plastic, in various combinations.
el by melting（熔化） a steel material between them under high heat.
Prestressed concrete is an improved form of reinforcement（加強方法）. Steel rods are bent into the shapes to give them the necessary degree of tensile strength. They are then used to prestress （對..預加應力）concrete, usually by one of two different methods. The first is to leave channels in a concrete beam that correspond to（相應于） the shapes of the steel rods. When the rods are run through the channels, they are then bonded to the concrete by filling the channels with grout, a thin mortar or binding agent. In the other (and more common) method, the prestressed steel rods are placed in the lower part of a form（模板） that corresponds to the shape of the finished structure（成品結(jié)構(gòu)）, and the concrete is
poured around them. Prestressed concrete uses less steel and less concrete. Because it is so economical, it is a highly desirable（非常理想） material.Prestressed concrete has made it possible to develop（建造） buildings with unusual shapes, like some of the modern sports arenas, with large space unbroken by any obstructing supports（阻礙的支撐物）. The uses for this relatively new structural method are constantly being developed（不斷地擴大）.The current tendency is to develop（采用） lighter materials, aluminum, for example, weighs much less than steel but has many of the same properties. Aluminum beams have already been used for bridge construction and for the framework of a few buildings.
Lightweight concretes, another example, are now rapidly developing（發(fā)展） throughout the world. They are used for their thermal insulation(絕熱性). The three types are illustrated below（舉例說明如下）: (a) Concretes made with lightweight aggregates; (b) Aerated concretes (US gas concretes) foamed（起泡） by whisking（攪拌）or by some chemical process during casting; (c) No-fines concretes.
All three types are used for their insulating properties（絕熱性）, mainly in housing, where they give high（非常） comfort in cold climates and a low cost of cooling（降溫成本）in hot climates. In housing, the relative weakness of lightweight concrete walls is unimportant, but it matters（有重大關(guān)系） in roof slabs, floor slabs and beams.
In some locations, some lightweight aggregates cost little more than（幾乎等于） the best dense（致密） aggregates and a large number of （大量） floor slabs have therefore been built of lightweight aggregate concrete purely for its weight saving, with no thought of（沒考慮） its insulation value.
The lightweight aggregate reduces the floor dead load（恒載） by about 20 per cent resulting in（導致）considerable savings in the floor（樓蓋結(jié)構(gòu)） steel in every floor and the roof, as well as in the column steel and (less) in the foundations. One London contractor（承包商）prefers to use lightweight aggregate because it gives him the same weight reduction in the floor slab as the use of hollow tiles, with simpler organization and therefore higher speed and profit. The insulation value of the lightweight aggregate is only important in the roof insulation, which is greatly improved（改進）.
Structural Analysis
A structure consists of（由..組成）a series of connected parts used to support loads. Notable（顯著的） examples include buildings, bridges, towers, tanks, and dams. The process（過程）of creating any of these structures requires planning（規(guī)劃）, analysis, design, and construction（施工）. Structural analysis consists of （包括）a variety of mathematical procedures（數(shù)學程序）for determining such quantities as the member forces and various structural displacements（位移） as a structure responds to its loads. Estimating realistic loads for the structure considering（根據(jù)）its use and location is often a part of structural analysis. Only two assumptions are made regarding（關(guān)于）the materials used in the structures of this chapter. First, the material has a linear stress-strain relationship（線性的應力-應變關(guān)系）. Second, there is no difference in the material behavior when stressed in tension vis-a-vis（與..相比）compression. The frames and trusses studied are plane structural systems（平面結(jié)構(gòu)體系）. It will be assumed that there is adequate bracing perpendicular to（垂直于）the plane so that no member will fail due to an elastic instability（彈性失穩(wěn)）. The very important consideration regarding such instability will be left for the specific（具體的）design course.
All structures are assumed to undergo only small deformations as they are loaded. As a consequence（因此）we assume no change in the position or direction of a force as a result of （由于）structural deflections（變位）. Finally, since linear elastic materials and small displacement are assumed, the principle of superposition will apply in all cases. Thus the displacements or internal forces that arise from two different forces systems applied one at a time（一次一個）may be added algebraically（幾何相加）to determine the structure’s response when both system(s) are applied simultaneously.In the real sense（真正意義上）an exact analysis of a structure can never be carried out since estimates always have to be made of the loadings and the strength of the materials composing（構(gòu)成）the structure. Furthermore, points of application（作用點）for the loadings must also be estimated. It is important, therefore, that the structural engineers develop（形成）the ability to model（模擬）or idealize（使..理想化）a structure so that he or she can perform a practical force analysis of the members.
Structural members are joined together in various ways depending on the intent（意圖）of the designer. The two types of joints most often specified（規(guī)定的）are the pin connection and the fixed joint（節(jié)點）. A pin-connected joint allows some freedom for slight（輕微）rotation, whereas the fixed joint allows no relative rotation between the connected members. In reality, however, all connections exhibit（顯現(xiàn)）some stiffness toward joint rotations, owing to friction（摩擦）and material behavior. When selecting a particular model for each support
（支座）or joint, the engineer must be aware of how the assumptions will affect the actual performance（運行）of the member and whether the assumptions are reasonable for the structural design. In reality, all structural supports actually exert（產(chǎn)生）distributed surface loads（面荷載）on their contacting members. The resultants（合力） of these load distributions are often idealized as the concentrated forces（集中力）and moments, since the surface area （表面積）over which the distributed load acts is considerably smaller than the total surface area of the connecting members. The ability to reduce an actual structure to（將..簡化為）an idealized form can only be gained by experience. In engineering practice, if it becomes doubtful（不明確）as to how to model a structure or transfer the loads to the members, it is best to consider several idealized structures and loadings and then design the actual structure so that it can resist（抵抗）the loadings in all the idealized models.
Almost all truss systems are configured（裝配）so that analysis using the method of joints must begin at one end and proceed（繼續(xù)）joint by joint toward the other end. If it is necessary to evaluate the forces carried by a member located（位于）some distance from the ends, the method of joints requires the calculation of the forces in many members before the desired one is reached. The method of sections provides a means（方法）for a direct calculation in these cases. After the support reactions have been calculated the truss is cut through（切開）(analytically分析上) so that one part of the truss is completely severed from the rest. When this is done, no more than three unknown members should be cut. If possible（如果可能）the cut（切口）should pass through the member or members whose internal forces are to be found. A free-body diagram of the part of the truss on one side of（在..一邊）this section is drawn, and the internal forces are found through the equilibrium equations. Since the system of forces（力系）on the free-body diagram is a plane non-concurrent（非共點）force system, three equilibrium equations may be written and solved for the three unknowns.
Influence lines（影響線）have important application for（應用）the design of structures that resist large live loads（活荷載）. An influence line represents（代表）the variation of either the reaction, shear, moment, or deflection at a specific （特定的）point in a member as concentrated force moves over the member. Once this line is constructed（作圖）, one can tell at a glance（一眼便知）where a live load should be placed on the structure so that it creates（引起）the greatest influence at the specified point. Furthermore, the magnitude（大�。﹐f the associated （相關(guān)的）reaction, shear, moment, or deflection at the point can then be calculated from the ordinates（縱坐標）of the influence-line diagram. For these reasons（因此）, influence lines play an important part in the design of bridges, industrial crane rails（吊車軌道）, conveyors, and other structures where loads move across their span（全長）. Although the procedure（步驟）for constructing an influence line is rather basic（基本的）, one should clearly be aware of the difference between constructing an influence line and constructing a shear or moment diagram. Influence lines represent the effect of a moving load only at a specified point on a member, whereas shear and moment diagrams represent the effect of fixed loads at all points along the axis of the member.
Deflections of structures can occur from various sources（原因）, such as loads, temperature, fabrication errors, or settlement. In design, deflections must be limited in order to prevent cracking of attached（附屬的） brittle materials such as concrete or plaster (石膏) . Furthermore, a structure must not vibrate or deflect（變位）severely in order to “appear” safe
for its occupants（居住者）. More important, though（然而）, deflections at specified points in a structure must be computed if one is to analyze statically indeterminate structures. We often determine the elastic deflections of a structure using both geometrical and energy methods. Also, the methods of double integration（雙重積分）are used. The geometrical methods include the moment-area theorems（彎矩圖面積定理）and the conjugate-beam method（共軛梁法）, and the energy methods to be considered are based on virtual work（虛功）and Castigliano’s theorem（卡氏最小功定理）. Each of these methods has particular advantages or disadvantages.
Concrete and reinforced concrete are used as building materials in every country. In many, including the United States and Canada, reinforced concrete is a dominant（主要的） structural material in engineered construction（建造的建筑物）. The universal（通用的）nature of reinforced concrete construction stems from（歸因于）the wide availability of reinforcing bars（鋼筋）and the constituents（組成部分）of concrete, gravel,sand, and cement, the relatively simple skills required in concrete construction（施工）, and the economy（經(jīng)濟性）of reinforced concrete compared to other form of construction. Concrete and reinforced concrete are used in bridges, buildings of all sorts（各種各樣）, underground structures, water tanks, television towers, offshore oil exploration and production structures（近海石油開采和生產(chǎn)結(jié)構(gòu)）, dams, and even in ships.
value of Reinforced Concrete
Concrete is strong in compression but weak in tension. As a result, cracks develop（形成）whenever（每當）loads, or restrained shrinkage（收縮限制）or temperature changes, give rise to（導致）tensile stresses in excess of（超過）the tensile strength of the concrete. In the plain concrete（素混凝土）beam, the moments due to applied loads are resisted by an internal tension-compression couple（拉壓力偶）involving tension in the concrete. Such a beam fails very suddenly and completely when the first crack forms. In a reinforced concrete beam, steel bars（鋼筋）are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be developed in the bars.
Economy Frequently, the foremost（最重要的）consideration is the overall cost（總費用）of the structure. This is, of course, a function of the costs（費用函數(shù)）of the materials and the labor necessary to erect them. Frequently, however, the overall cost is affected as much or more by the overall construction time（總的`建造時間）since the contractor and owner must allocate（分配）money（資金）to carry out the construction and will not receive a return on this investment （收回投資）until the building is ready for occupancy（居�。�. As a result, financial savings（財務的節(jié)約）due to rapid construction may more than offset（足以抵消）increased material costs. Any measures designer can take to standardize the design and forming（加工）will generally pay off（使人得益）in reduced overall costs.
The choice of whether a structure should be built of concrete, steel, masonry, or timber（木材）depends on the availability（可得性）of materials and on a number of（許多）value decisions（價值判斷）.
Economy Frequently, the foremost（最重要的）consideration is the overall cost（總費用）of the structure. This is, of course, a function of the costs（費用函數(shù)）of the materials and the labor necessary to erect them. Frequently, however, the overall cost is affected as much or more by the overall construction time（總的建造時間）since the contractor and owner must allocate（分配）money（資金）to carry out the construction and will not receive
a return on this investment （收回投資）until the building is ready for occupancy（居�。�. As a result, financial savings（財務的節(jié)約）due to rapid construction may more than offset（足以抵消）increased material costs. Any measures designer can take to standardize the design and forming（加工）will generally pay off（使人得益）in reduced overall costs. In many cases the long-term economy（長期的經(jīng)濟性）of the structure may be more important than the first cost. As a result, maintenance（維護）and durability（耐久性）are important considerations.
Suitability of Material for Architectural and Structural Function A reinforced concrete system frequently allows the designer to combine the architectural and structural functions（功能）. Concrete has the advantage that it is placed in a plastic condition（塑性狀態(tài)）and is given the desired shape and texture（密度）by means of the forms and the finishing techniques（加工技術(shù)）. This allows such elements（構(gòu)件）as flat plates or other types of slabs to serve as load-bearing elements while providing the finished floor and ceiling surface（樓面和頂棚面）. Similarly, reinforced concrete walls can provide architecturally attractive surfaces in addition to having the ability to resist gravity, wind, or seismic loads. Finally, the choice of size or shape is governed（決定）by the designer and not by the availability of standard manufactured members.
Fire Resistance The structure in a building must withstand the effects of a fire and remain standing（直立）while the building is evacuated（撤空）and the fire is extinguished（熄滅）. A concrete building inherently（固有地）has a 1- to 3-hour fire rating（耐火等級）without special fireproofing （防火）or other details（說明）. Structural steel or timber（鋼結(jié)構(gòu)或木結(jié)構(gòu)） buildings must be fireproofed to attain similar fire ratings.
Rigidity The occupants of a building may be disturbed （干擾）if their building oscillates（搖動）in the wind or the floors vibrate as people walk by（走過）. Due to the greater stiffness and mass（剛度和質(zhì)量）of a concrete structure, vibrations are seldom a problem. Low Maintenance Concrete members inherently require less maintenance than do structural steel or timber members （結(jié)構(gòu)鋼構(gòu)件或結(jié)構(gòu)木構(gòu)件）. This is particularly true（尤其正確）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 （使水排出） from the structure.
Availability of Materials Sand, gravel, cement, and concrete mixing facilities（攪拌設施） are very widely available, and reinforcing steel（鋼筋）can be transported to most job sites（施工現(xiàn)場）more easily than can structural steel（結(jié)構(gòu)鋼）. As a result, reinforced concrete is frequently used in remote areas.
On the other hand, there are a number of factors that may cause one to select a material other than (..除外，不是..）reinforced concrete. These include：
Low Tensile Strength As stated（敘述）earlier, the tensile strength of concrete is much lower than its compressive strength (about 1/10), and hence concrete is subject to（易遭受）cracking. In structural uses this is overcome by using reinforcement to carry tensile forces and limit crack widths（寬度）to within acceptable values. Unless care is taken in design and construction, however, these cracks may be unsightly（難看）or may allow（使..能）penetration（滲透）of water.
Relatively Low Strength Per Unit of Weight or Volume The compressive strength of concrete is roughly 5% to 10% that of steel, while its unit density is roughly 30%
that of steel. As a result, a concrete structure requires a larger volume and a greater weight of material than does a comparable（類似的） steel structure. As a result, long-span structures（大跨結(jié)構(gòu)）are often built from steel.
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