建筑結(jié)構(gòu)外文文獻(xiàn)翻譯

1、<p>　　Architecture Structure </p><p>　　We have and the architects must deal with the spatial aspect of activity, physical, and symbolic needs in such a way that overall performance integrity is assured

2、. Hence, he or she well wants to think of evolving a building environment as a total system of interacting and space forming subsystems. Is represents a complex challenge, and to meet it the architect will need a hierarc

3、hic design process that provides at least three levels of feedback thinking: schematic, preliminary, and final.</p><p>　　Such a hierarchy is necessary if he or she is to avoid being confused , at conceptual

4、stages of design thinking ,by the myriad detail issues that can distract attention from more basic considerations .In fact , we can say that an architect’s ability to distinguish the more basic form the more detailed iss

5、ues is essential to his success as a designer .</p><p>　　The object of the schematic feed back level is to generate and evaluate overall site-plan, activity-interaction, and building-configuration options .T

6、o do so the architect must be able to focus on the interaction of the basic attributes of the site context, the spatial organization, and the symbolism as determinants of physical form. This means that ,in schematic term

7、s ,the architect may first conceive and model a building design as an organizational abstraction of essential performance-space in</p><p>　　At the schematic stage, it would also be helpful if the designer co

8、uld visualize his or her options for achieving overall structural integrity and consider the constructive feasibility and economic of his or her scheme .But this will require that the architect and/or a consultant be abl

9、e to conceptualize total-system structural options in terms of elemental detail .Such overall thinking can be easily fed back to improve the space-form scheme.</p><p>　　At the preliminary level, the architec

10、t’s emphasis will shift to the elaboration of his or her more promising schematic design options .Here the architect’s structural needs will shift to approximate design of specific subsystem options. At this stage the to

11、tal structural scheme is developed to a middle level of specificity by focusing on identification and design of major subsystems to the extent that their key geometric, component, and interactive properties are establish

12、ed .Basic subsystem in</p><p>　　When the designer and the client are satisfied with the feasibility of a design proposal at the preliminary level, it means that the basic problems of overall design are solve

13、d and details are not likely to produce major change .The focus shifts again ,and the design process moves into the final level .At this stage the emphasis will be on the detailed development of all subsystem specifics .

14、 Here the role of specialists from various fields, including structural engineering, is much larger, sinc</p><p>　　To summarize: At Level I, the architect must first establish, in conceptual terms, the overa

15、ll space-form feasibility of basic schematic options. At this stage, collaboration with specialists can be helpful, but only if in the form of overall thinking. At Level II, the architect must be able to identify the maj

16、or subsystem requirements implied by the scheme and substantial their interactive feasibility by approximating key component properties .That is, the properties of major subsystems need be</p><p>　　Of course

17、 this success comes from the development of the Structural Material.</p><p>　　1.Reinforced Concrete</p><p>　　Plain concrete is formed from a hardened mixture of cement ,water ,fine aggregate, co

18、arse aggregate (crushed stone or gravel),air, and often other admixtures. The plastic mix is placed and consolidated in the formwork, then cured to facilitate the acceleration of the chemical hydration reaction lf the ce

19、ment/water mix, resulting in hardened concrete. The finished product has high compressive strength, and low resistance to tension, such that its tensile strength is approximately one tenth lf its</p><p>　　It

20、 is this deviation in the composition of a reinforces concrete section from the homogeneity of standard wood or steel sections that requires a modified approach to the basic principles of structural design. The two compo

21、nents of the heterogeneous reinforced concrete section are to be so arranged and proportioned that optimal use is made of the materials involved. This is possible because concrete can easily be given any desired shape by

22、 placing and compacting the wet mixture of the constituent</p><p>　　The techniques necessary for placing concrete depend on the type of member to be cast: that is, whether it is a column, a bean, a wall, a s

23、lab, a foundation. a mass columns, or an extension of previously placed and hardened concrete. For beams, columns, and walls, the forms should be well oiled after cleaning them, and the reinforcement should be cleared of

24、 rust and other harmful materials. In foundations, the earth should be compacted and thoroughly moistened to about 6 in. in depth to avoid ab</p><p>　　Hydration of the cement takes place in the presence of m

25、oisture at temperatures above 50°F. It is necessary to maintain such a condition in order that the chemical hydration reaction can take place. If drying is too rapid, surface cracking takes place. This would result

26、in reduction of concrete strength due to cracking as well as the failure to attain full chemical hydration.</p><p>　　It is clear that a large number of parameters have to be dealt with in proportioning a rei

27、nforced concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on. Consequently, trial and adjustment is necessary in the choice of concrete section

28、s, with assumptions based on conditions at site, availability of the constituent materials, particular demands of the owners, architectural and headroom requirements, the applicable codes, a</p><p>　　A trial

29、 section has to be chosen for each critical location in a structural system. The trial section has to be analyzed to determine if its nominal resisting strength is adequate to carry the applied factored load. Since more

30、than one trial is often necessary to arrive at the required section, the first design input step generates into a series of trial-and-adjustment analyses.</p><p>　　The trial-and –adjustment procedures for th

31、e choice of a concrete section lead to the convergence of analysis and design. Hence every design is an analysis once a trial section is chosen. The availability of handbooks, charts, and personal computers and programs

32、supports this approach as a more efficient, compact, and speedy instructional method compared with the traditional approach of treating the analysis of reinforced concrete separately from pure design.</p><p>

33、;　　2. Earthwork </p><p>　　Because earthmoving methods and costs change more quickly than those in any other branch of civil engineering, this is a field where there are real opportunities for the enthusiast.

34、 In 1935 most of the methods now in use for carrying and excavating earth with rubber-tyred equipment did not exist. Most earth was moved by narrow rail track, now relatively rare, and the main methods of excavation, wit

35、h face shovel, backacter, or dragline or grab, though they are still widely used are only a few of </p><p>　　Earthworks or earthmoving means cutting into ground where its surface is too high ( cuts ), and du

36、mping the earth in other places where the surface is too low ( fills). Toreduce earthwork costs, the volume of the fills should be equal to the volume of the cuts and wherever possible the cuts should be placednear to fi

37、lls of equal volume so as to reduce transport and double handlingof the fill. This work of earthwork design falls on the engineer who lays out the road since it is the layout of the </p><p>　　The cheapest wa

38、y of moving earth is to take it directly out of the cut and drop it as fill with the same machine. This is not always possible, but when it canbe done it is ideal, being both quick and cheap. Draglines, bulldozers and fa

39、ce shovels an do this. The largest radius is obtained with the dragline,and the largest tonnage of earth is moved by the bulldozer, though only over short distances.The disadvantages of the dragline are that it must dig

40、below itself, it cannot dig with force into c</p><p>　　Face shovels are between bulldozers and draglines, having a larger radius of action than bulldozers but less than draglines. They are anle to dig into a

41、 vertical cliff face in a way which would be dangerous tor a bulldozer operator and impossible for a dragline. Each piece of equipment should be level of their tracks and for deep digs in compact material a backacter is

42、most useful, but its dumping radius is considerably less than that of the same escavator fitted with a face shovel.</p><p>　　Rubber-tyred bowl scrapers are indispensable for fairly level digging where the di

43、stance of transport is too much tor a dragline or face shovel. They can dig the material deeply ( but only below themselves ) to a fairly flat surface, carry it hundreds of meters if need be, then drop it and level it ro

44、ughly during the dumping. For hard digging it is often found economical to keep a pusher tractor ( wheeled or tracked ) on the digging site, to push each scraper as it returns to dig. As soon as the</p><p>　

45、　Bowl scrapers are often extremely powerful machines;many makers build scrapers of 8 cubic meters struck capacity, which carry 10 m ³ heaped. The largest self-propelled scrapers are of 19 m ³ struck capacity (

46、25 m ³ heaped )and they are driven by a tractor engine of 430 horse-powers.</p><p>　　Dumpers are probably the commonest rubber-tyred transport since they can also conveniently be used for carrying concr

47、ete or other building materials. Dumpers have the earth container over the front axle on large rubber-tyred wheels, and the container tips forwards on most types, though in articulated dumpers the direction of tip can be

48、 widely varied. The smallest dumpers have a capacity of about 0.5 m ³, and the largest standard types are of about 4.5 m ³. Special types include the self-loading </p><p>　　3.Safety of Structures&l

49、t;/p><p>　　The principal scope of specifications is to provide general principles and computational methods in order to verify safety of structures. The “ safety factor ”, which according to modern trends is in

50、dependent of the nature and combination of the materials used, can usually be defined as the ratio between the conditions. This ratio is also proportional to the inverse of the probability ( risk ) of failure of the stru

51、cture. </p><p>　　Failure has to be considered not only as overall collapse of the structure but also as unserviceability or, according to a more precise. Common definition. As the reaching of a “ limit state

52、 ” which causes the construction not to accomplish the task it was designed for. There are two categories of limit state :</p><p>　　(1)Ultimate limit sate, which corresponds to the highest value of the load-

53、bearing capacity. Examples include local buckling or global instability of the structure; failure of some sections and subsequent transformation of the structure into a mechanism; failure by fatigue; elastic or plastic d

54、eformation or creep that cause a substantial change of the geometry of the structure; and sensitivity of the structure to alternating loads, to fire and to explosions.</p><p>　　(2)Service limit states, which

55、 are functions of the use and durability of the structure. Examples include excessive deformations and displacements without instability; early or excessive cracks; large vibrations; and corrosion.</p><p>　　

56、Computational methods used to verify structures with respect to the different safety conditions can be separated into:</p><p>　　(1)Deterministic methods, in which the main parameters are considered as nonran

57、dom parameters.</p><p>　　(2)Probabilistic methods, in which the main parameters are considered as random parameters.</p><p>　　Alternatively, with respect to the different use of factors of safet

58、y, computational methods can be separated into:</p><p>　　(1)Allowable stress method, in which the stresses computed under maximum loads are compared with the strength of the material reduced by given safety

59、factors.</p><p>　　(2)Limit states method, in which the structure may be proportioned on the basis of its maximum strength. This strength, as determined by rational analysis, shall not be less than that requi

60、red to support a factored load equal to the sum of the factored live load and dead load ( ultimate state ).</p><p>　　The stresses corresponding to working ( service ) conditions with unfactored live and dead

61、 loads are compared with prescribed values ( service limit state ) . From the four possible combinations of the first two and second two methods, we can obtain some useful computational methods. Generally, two combinatio

62、ns prevail:</p><p>　　(1)deterministic methods, which make use of allowable stresses.</p><p>　　(2)Probabilistic methods, which make use of limit states.</p><p>　　The main advantage o

63、f probabilistic approaches is that, at least in theory, it is possible to scientifically take into account all random factors of safety, which are then combined to define the safety factor. probabilistic approaches depen

64、d upon : </p><p>　　(1)Random distribution of strength of materials with respect to the conditions of fabrication and erection ( scatter of the values of mechanical properties through out the structure );<

65、;/p><p>　　(2)Uncertainty of the geometry of the cross-section sand of the structure ( faults and imperfections due to fabrication and erection of the structure );</p><p>　　(3)Uncertainty of the p

66、redicted live loads and dead loads acting on the structure;</p><p>　　(4)Uncertainty related to the approximation of the computational method used ( deviation of the actual stresses from computed stresses ).&

67、lt;/p><p>　　Furthermore, probabilistic theories mean that the allowable risk can be based on several factors, such as :</p><p>　　(1)Importance of the construction and gravity of the damage by its

68、failure;</p><p>　　(2)Number of human lives which can be threatened by this failure;</p><p>　　(3)Possibility and/or likelihood of repairing the structure;</p><p>　　(4)Predicted life

69、 of the structure.</p><p>　　All these factors are related to economic and social considerations such as：</p><p>　　(1)Initial cost of the construction; </p><p>　　(2)Amortization fu

70、nds for the duration of the construction; </p><p>　　(3)Cost of physical and material damage due to the failure of the construction; </p><p>　　(4)Adverse impact on society; </p><p>

71、;　　(5)Moral and psychological views.</p><p>　　The definition of all these parameters, for a given safety factor, allows construction at the optimum cost. However, the difficulty of carrying out a complete p

72、robabilistic analysis has to be taken into account. For such an analysis the laws of the distribution of the live load and its induced stresses, of the scatter of mechanical properties of materials, and of the geometry o

73、f the cross-sections and the structure have to be known. Furthermore, it is difficult to interpret the interaction betwe</p><p><b>　　建筑結(jié)構(gòu)</b></p><p>　　建筑師必須從一種全局的角度出發(fā)去處理建筑設(shè)計(jì)中應(yīng)該考慮到的實(shí)用

74、活動(dòng)，物質(zhì)及象征性的需求。因此，他或他試圖將有相互有關(guān)的空間形式分體系組成的總體系形成一個(gè)建筑環(huán)境。這是一種復(fù)雜的挑戰(zhàn)，為適應(yīng)這一挑戰(zhàn)，建筑師需要有一個(gè)分階段的設(shè)計(jì)過程，其至少要分三個(gè)“反饋”考慮階段：方案階段，初步設(shè)計(jì)階段和施工圖設(shè)計(jì)階段。</p><p>　　這樣的分階段涉及是必需的，它可使設(shè)計(jì)者避免受很多細(xì)節(jié)的困惑，而這些細(xì)節(jié)往往會(huì)干擾設(shè)計(jì)者的基本思路。實(shí)際上，我們可以說一個(gè)成功的建筑設(shè)計(jì)師應(yīng)該具備一種從很

75、多細(xì)節(jié)中分辨出更為基本的內(nèi)容的能力。</p><p>　　概念構(gòu)思階段的任務(wù)時(shí)提出和斟酌全局場(chǎng)地規(guī)劃，活動(dòng)相互作用及房屋形式方案。為實(shí)現(xiàn)這些，建筑師必須注意場(chǎng)地各部分的基本使用，空間組織，并應(yīng)用象征手法確定其具體形式。這就要求建筑師首先按照基本功能和空間關(guān)系對(duì)一項(xiàng)建筑設(shè)計(jì)首先構(gòu)思并模擬出一個(gè)抽象的建筑物，然后再對(duì)這一抽象的總體空間進(jìn)行深入探究。在開始勾畫具體的建筑形似時(shí)，應(yīng)考慮基本的場(chǎng)所跳進(jìn)加以修改。</p

76、><p>　　在方案階段，如果設(shè)計(jì)者能夠形象的預(yù)見所作方案的結(jié)構(gòu)整體性，并要考慮施工階段可行性及經(jīng)濟(jì)性，那將是非常有幫助的。這就要求建筑師或者過問工程是能夠從主要分體系之間的關(guān)系而不是從構(gòu)建細(xì)節(jié)去構(gòu)思總體結(jié)構(gòu)方案。這種能夠易于反饋以改進(jìn)空間形式方案。</p><p>　　在初步設(shè)計(jì)階段，建筑師的重點(diǎn)工作應(yīng)是詳細(xì)化可能成為最終方案的設(shè)計(jì)，這是建筑師對(duì)結(jié)構(gòu)的要求業(yè)轉(zhuǎn)移到做分體系具體方案的粗略設(shè)計(jì)上

77、。在這一階段應(yīng)該完成對(duì)結(jié)構(gòu)布置的中等程度的確定，重點(diǎn)論證和設(shè)計(jì)主要分體系已確定它們的主要幾何尺寸，構(gòu)件和相互關(guān)系。這樣就可以依據(jù)全局設(shè)計(jì)方案，確定并解決各分體系的相互影響以及設(shè)計(jì)難題。顧問工程師在這一過程中作用重大，但各細(xì)部的考慮還留有選擇余地。當(dāng)然，這些初步設(shè)計(jì)階段所作的決定仍可以反饋回取使方案概念進(jìn)一步改善，或甚至可能有重大變化。</p><p>　　當(dāng)設(shè)計(jì)者和顧問工程師對(duì)初始階段設(shè)計(jì)方案的可行性滿意時(shí)，就意

78、味著全部設(shè)計(jì)的基本問題已經(jīng)解決，不會(huì)再因細(xì)節(jié)問題而發(fā)生大的變化。這是工作重點(diǎn)將再次轉(zhuǎn)移，進(jìn)入細(xì)部設(shè)計(jì)。在這一階段將重點(diǎn)完善各分體系的細(xì)節(jié)設(shè)計(jì)。此時(shí)包括結(jié)構(gòu)工程在內(nèi)的各個(gè)領(lǐng)域的專家的作用將十分突出，應(yīng)為所有施工的細(xì)節(jié)都必須設(shè)計(jì)出來。這一階段的決定，可能會(huì)反饋到第二階段并導(dǎo)致一些變化。如果第一階段和第二階段的設(shè)計(jì)做的深入，那么在最初兩個(gè)階段所得到的總體結(jié)論和最后階段的細(xì)節(jié)的重新設(shè)計(jì)不再是問題。當(dāng)然，整個(gè)實(shí)際過程應(yīng)該是逐步發(fā)展的過程，從創(chuàng)造和

79、細(xì)化（改進(jìn)）總體設(shè)計(jì)概念直到做出精確的結(jié)構(gòu)設(shè)計(jì)和細(xì)部構(gòu)造。</p><p>　　綜上所述：在第一階段，建筑師必須首先用概念的方式來確定基本方案的全部空間形式的可行性。在第一階段，專業(yè)人員的合作是有意義的，但僅限于行程總的構(gòu)思方面；在第二階段，建筑師應(yīng)該能夠用圖形來確定各分體系的需求，并且通過估計(jì)關(guān)鍵構(gòu)件的性能來證明其相互作用的可行性。也就是說，主要分體系的性能只須做到一定深度，需要驗(yàn)證他們的基本形式和相互關(guān)系是協(xié)

80、調(diào)一致的。這需要與工程師進(jìn)行更加詳細(xì)與明確的合作；在第三階段，建筑師和專業(yè)人員必須繼續(xù)合作完成所有構(gòu)件的設(shè)計(jì)細(xì)節(jié)，并制定良好的施工文件。</p><p>　　當(dāng)然，這些設(shè)計(jì)的成功來源于建筑材料的發(fā)展與革新。</p><p><b>　　1.鋼筋混凝土</b></p><p>　　素混凝土是由水泥、水、細(xì)骨料、粗骨料（碎石或；卵石）、空氣，通常還

81、有其他外加劑等經(jīng)過凝固硬化而成。將可塑的混凝土拌合物注入到模板內(nèi)，并將其搗實(shí)，然后進(jìn)行養(yǎng)護(hù)，以加速水泥與水的水化反應(yīng)，最后獲得硬化的混凝土。其最終制成品具有較高的抗壓強(qiáng)度和較低的抗拉強(qiáng)度。其抗拉強(qiáng)度約為抗壓強(qiáng)度的十分之一。因此，截面的受拉區(qū)必須配置抗拉鋼筋和抗剪鋼筋以增加鋼筋混凝土構(gòu)件中較弱的受拉區(qū)的強(qiáng)度。</p><p>　　由于鋼筋混凝土截面在均質(zhì)性上與標(biāo)準(zhǔn)的木材或鋼的截面存在著差異，因此，需要對(duì)結(jié)構(gòu)設(shè)計(jì)的基

82、本原理進(jìn)行修改。將鋼筋混凝土這種非均質(zhì)截面的兩種組成部分按一定比例適當(dāng)布置，可以最好的利用這兩種材料。這一要求是可以達(dá)到的。因混凝土由配料攪拌成濕拌合物，經(jīng)過振搗并凝固硬化，可以做成任何一種需要的形狀。如果拌制混凝土的各種材料配合比恰當(dāng)，則混凝土制成品的強(qiáng)度較高，經(jīng)久耐用，配置鋼筋后，可以作為任何結(jié)構(gòu)體系的主要構(gòu)件。</p><p>　　澆筑混凝土所需要的技術(shù)取決于即將澆筑的構(gòu)件類型，諸如：柱、梁、墻、板、基礎(chǔ)，

83、大體積混凝土水壩或者繼續(xù)延長(zhǎng)已澆筑完畢并且已經(jīng)凝固的混凝土等。對(duì)于梁、柱、墻等構(gòu)件，當(dāng)模板清理干凈后應(yīng)該在其上涂油，鋼筋表面的銹及其他有害物質(zhì)也應(yīng)該被清除干凈。澆筑基礎(chǔ)前，應(yīng)將坑底土夯實(shí)并用水浸濕6英寸，以免土壤從新澆的混凝土中吸收水分。一般情況下，除使用混凝土泵澆筑外，混凝土都應(yīng)在水平方向分層澆筑，并使用插入式或表面式高頻電動(dòng)振搗器搗實(shí)。必須記住，過分的振搗將導(dǎo)致骨料離析和混凝土泌漿等現(xiàn)象，因而是有害的。</p><

84、;p>　　水泥的水化作用發(fā)生在有水分存在，而且氣溫在50°F以上的條件下。為了保證水泥的水化作用得以進(jìn)行，必須具備上述條件。如果干燥過快則會(huì)出現(xiàn)表面裂縫，這將有損與混凝土的強(qiáng)度，同時(shí)也會(huì)影響到水泥水化作用的充分進(jìn)行。</p><p>　　設(shè)計(jì)鋼筋混凝土構(gòu)件時(shí)顯然需要處理大量的參數(shù)，諸如寬度、高度等幾何尺寸，配筋的面積，鋼筋的應(yīng)變和混凝土的應(yīng)變，鋼筋的應(yīng)力等等。因此，在選擇混凝土截面時(shí)需要進(jìn)行試算并

85、作調(diào)整，根據(jù)施工現(xiàn)場(chǎng)條件、混凝土原材料的供應(yīng)情況、業(yè)主提出的特殊要求、對(duì)建筑和凈空高度的要求、所用的設(shè)計(jì)規(guī)范以及建筑物周圍環(huán)境條件等最后確定截面。鋼筋混凝土通常是現(xiàn)場(chǎng)澆注的合成材料，它與在工廠中制造的標(biāo)準(zhǔn)的鋼結(jié)構(gòu)梁、柱等不同，因此對(duì)于上面所提到的一系列因素必須予以考慮。</p><p>　　對(duì)結(jié)構(gòu)體系的各個(gè)部位均需選定試算截面并進(jìn)行驗(yàn)算，以確定該截面的名義強(qiáng)度是否足以承受所作用的計(jì)算荷載。由于經(jīng)常需要進(jìn)行多次試算

86、，才能求出所需的截面，因此設(shè)計(jì)時(shí)第一次采用的數(shù)值將導(dǎo)致一系列的試算與調(diào)整工作。</p><p>　　選擇混凝土截面時(shí)，采用試算與調(diào)整過程可以使復(fù)核與設(shè)計(jì)結(jié)合在一起。因此，當(dāng)試算截面選定后，每次設(shè)計(jì)都是對(duì)截面進(jìn)行復(fù)核。手冊(cè)、圖表和微型計(jì)算機(jī)以及專用程序的使用，使這種設(shè)計(jì)方法更為簡(jiǎn)捷有效，而傳統(tǒng)的方法則是把鋼筋混凝土的復(fù)核與單純的設(shè)計(jì)分別進(jìn)行處理。</p><p><b>　　2.土

87、方工程</b></p><p>　　由于和土木工程中任何其他工種的施工方法與費(fèi)用相比較，土方挖運(yùn)的施工方法與費(fèi)用的變化都要快得多，因此對(duì)于有事業(yè)心的人來說，土方工程是一個(gè)可以大有作為的領(lǐng)域。在1935年，目前采用的利用輪胎式機(jī)械設(shè)備進(jìn)行土方挖運(yùn)的方法大多數(shù)還沒有出現(xiàn)。那是大部分土方是采用窄軌鐵路運(yùn)輸，在這目前來說是很少采用的。當(dāng)時(shí)主要的開挖方式是使用正鏟、反鏟、拉鏟或抓斗等挖土機(jī)，盡管這些機(jī)械目前仍然

88、在廣泛應(yīng)用，但是它們只不過是目前所采用的許多方法中的一小部分。因此，一個(gè)工程師為了使自己在土方挖運(yùn)設(shè)備方面的知識(shí)跟得上時(shí)代的發(fā)展，他應(yīng)當(dāng)花費(fèi)一些時(shí)間去研究現(xiàn)代的機(jī)械。一般說來，有關(guān)挖土機(jī)、裝載機(jī)和運(yùn)輸機(jī)械的唯一可靠而又最新的資料可以從制造廠商處獲得。</p><p>　　土方工程或土方挖運(yùn)工程指的是把地表面過高處的土壤挖去（挖方），并把它傾卸到地表面過低的其他地方（填方）。為了降低土方工程費(fèi)用，填方量應(yīng)該等于挖方

89、量，而且挖方地點(diǎn)應(yīng)該盡可能靠近土方量相等的填方地點(diǎn)，以減少運(yùn)輸量和填方的二次搬運(yùn)。土方設(shè)計(jì)這項(xiàng)工作落到了從事道路設(shè)計(jì)的工程師的身上，因?yàn)橥练焦こ痰脑O(shè)計(jì)比其他任何工作更能決定工程造價(jià)是否低廉。根據(jù)現(xiàn)有的地圖和標(biāo)高，道路工程師應(yīng)在設(shè)計(jì)繪圖室中的工作也并不是徒勞的。它將幫助他在最短的時(shí)間內(nèi)獲得最好的方案。</p><p>　　費(fèi)用最低的運(yùn)土方法是用同一臺(tái)機(jī)械直接挖方取土并且卸土作為填方。這并不是經(jīng)?？梢宰龅降?，但是如果

90、能夠做到則是很理想的，因?yàn)檫@樣做既快捷又省錢。拉鏟挖土機(jī)。推土機(jī)和正鏟挖土機(jī)都能做到這點(diǎn)。拉鏟挖土機(jī)的工作半徑最大。推土機(jī)所推運(yùn)的圖的數(shù)量最多，只是運(yùn)輸距離很短。拉鏟挖土機(jī)的缺點(diǎn)是只能挖比它本身低的土，不能施加壓力挖入壓實(shí)的土壤內(nèi)，不能在陡坡上挖土，而且挖。卸都不準(zhǔn)確。</p><p>　　正鏟挖土機(jī)介于推土機(jī)和拉鏟挖土機(jī)的之間，其作用半徑大于推土機(jī)，但小于拉鏟挖土機(jī)。正鏟挖土機(jī)能挖取豎直陡峭的工作面，這種方式對(duì)

91、推土機(jī)司機(jī)來說是危險(xiǎn)的，而對(duì)拉鏟挖土機(jī)則是不可能的。每種機(jī)械設(shè)備應(yīng)該進(jìn)行最適合它的性能的作業(yè)。正鏟挖土機(jī)不能挖比其停機(jī)平面低很多的土，而深挖堅(jiān)實(shí)的土壤時(shí)，反鏟挖土機(jī)最適用，但其卸料半徑比起裝有正鏟的同一挖土機(jī)的卸料半徑則要小很多。</p><p>　　在比較平坦的場(chǎng)地開挖，如果用拉鏟或正鏟挖土機(jī)運(yùn)輸距離太遠(yuǎn)時(shí)，則裝有輪胎式的斗式鏟運(yùn)機(jī)就是比不可少的。它能在比較平的地面上挖較深的土（但只能挖機(jī)械本身下面的土），需要

92、時(shí)可以將土運(yùn)至幾百米遠(yuǎn)，然后卸土并在卸土的過程中把土大致鏟平。在挖掘硬土?xí)r，人們發(fā)現(xiàn)在開挖場(chǎng)地經(jīng)常用一輛助推拖拉機(jī)（輪式或履帶式），對(duì)返回挖土的鏟運(yùn)機(jī)進(jìn)行助推這種施工方法是經(jīng)濟(jì)的。一旦鏟運(yùn)機(jī)裝滿，助推拖拉機(jī)就回到開挖的地點(diǎn)去幫助下一臺(tái)鏟運(yùn)機(jī)。</p><p>　　斗式鏟運(yùn)機(jī)通常是功率非常大的機(jī)械，許多廠家制造的鏟運(yùn)機(jī)鏟斗容量為8 m³，滿載時(shí)可達(dá)10 m³。最大的自行式鏟運(yùn)機(jī)鏟斗容量為19立方

93、米（滿載時(shí)為25 m³），由430馬力的牽引發(fā)動(dòng)機(jī)驅(qū)動(dòng)。</p><p>　　翻斗機(jī)可能是使用最為普遍的輪胎式運(yùn)輸設(shè)備，因?yàn)樗鼈冞€可以被用來送混凝土或者其他建筑材料。翻斗車的車斗位于大橡膠輪胎車輪前軸的上方，盡管鉸接式翻斗車的卸料方向有很多種，但大多數(shù)車斗是向前翻轉(zhuǎn)的。最小的翻斗車的容量大約為0.5立方米，而最大的標(biāo)準(zhǔn)型翻斗車的容量大約為4.5m³。特殊型式的翻斗車包括容量為4 m³

94、的自裝式翻斗車，和容量約為0.5 m³的鉸接式翻斗車。必須記住翻斗車與自卸卡車之間的區(qū)別。翻斗車車斗向前傾翻而司機(jī)坐在后方卸載，因此有時(shí)被稱為后卸卡車。</p><p><b>　　3.結(jié)構(gòu)的安全度</b></p><p>　　規(guī)范的主要目的是提供一般性的設(shè)計(jì)原理和計(jì)算方法，以便驗(yàn)算結(jié)構(gòu)的安全度。就目前的趨勢(shì)而言，安全系數(shù)與所使用的材料性質(zhì)及其組織情況無關(guān)，

95、通常把它定義為發(fā)生破壞的條件與結(jié)構(gòu)可預(yù)料的最不利的工作條件之比值。這個(gè)比值還與結(jié)構(gòu)的破壞概率（危險(xiǎn)率）成反比。</p><p>　　破壞不僅僅指結(jié)構(gòu)的整體破壞，而且還指結(jié)構(gòu)不能正常的使用，或者，用更為確切的話來說，把破壞看成是結(jié)構(gòu)已經(jīng)達(dá)到不能繼續(xù)承擔(dān)其設(shè)計(jì)荷載的“極限狀態(tài)”。通常有兩種類型的極限狀態(tài)，即：</p><p>　?。?）強(qiáng)度極限狀態(tài)，它相當(dāng)于結(jié)構(gòu)能夠達(dá)到的最大承載能力。其例子包

96、括結(jié)構(gòu)的局部屈曲和整體不穩(wěn)定性；某此界面失效，隨后結(jié)構(gòu)轉(zhuǎn)變?yōu)闄C(jī)構(gòu)；疲勞破壞；引起結(jié)構(gòu)幾何形狀顯著變化的彈性變形或塑性變形或徐變；結(jié)構(gòu)對(duì)交變荷載、火災(zāi)和爆炸的敏感性。</p><p>　　（2）使用極限狀態(tài)，它對(duì)應(yīng)著結(jié)構(gòu)的使用功能和耐久性。器例子包括結(jié)構(gòu)失穩(wěn)之前的過大變形和位移；早期開裂或過大的裂縫；較大的振動(dòng)和腐蝕。</p><p>　　根據(jù)不同的安全度條件，可以把結(jié)構(gòu)驗(yàn)算所采用的計(jì)算方法

97、分成：</p><p>　　（1）確定性的方法，在這種方法中，把主要參數(shù)看作非隨機(jī)參數(shù)。</p><p>　?。?）概率方法，在這種方法中，主要參數(shù)被認(rèn)為是隨機(jī)參數(shù)。</p><p>　　此外，根據(jù)安全系數(shù)的不同用途，可以把結(jié)構(gòu)的計(jì)算方法分為：</p><p>　　（1）容許應(yīng)力法，在這種方法中，把結(jié)構(gòu)承受最大荷載時(shí)計(jì)算得到的應(yīng)力與經(jīng)過按規(guī)定

98、的安全系數(shù)進(jìn)行折減后的材料強(qiáng)度作比較。</p><p>　?。?）極限狀態(tài)法，在這種方法中，結(jié)構(gòu)的工作狀態(tài)是以其最大強(qiáng)度為依據(jù)來衡量的。由理論分析確定的這一最大強(qiáng)度應(yīng)不小于結(jié)構(gòu)承受計(jì)算荷載所算得的強(qiáng)度（極限狀態(tài)）。計(jì)算荷載等于分別乘以荷載系數(shù)的活載與恒載之和。</p><p>　　把對(duì)應(yīng)于不乘以荷載系數(shù)的活載和恒載的工作（使用）條件的應(yīng)力與規(guī)定值（使用極限狀態(tài)）相比較。根據(jù)前兩種方法和后兩