外文翻譯---鋼筋混凝土結構設計制約因素（部分）

1、<p><b>　　外文資料翻譯</b></p><p>　　The constraintion of reinforced concrete structure design ( part)</p><p>　　Part 1. Reinforced Concrete</p><p>　　Plain concrete is forme

2、d from a hardened mixture of cement ,water ,fine aggregate, coarse aggregate (crushed stone or gravel),air, and often other admixtures. The plastic mix is placed and consolidated in the formwork, then cured to facilitate

3、 the acceleration of the chemical hydration reaction lf the cement/water mix, resulting in hardened concrete. The finished product has high compressive strength, and low resistance to tension, such that its tensile stren

4、gth is approximately one tenth lf its</p><p>　　It is this deviation in the composition of a reinforces concrete section from the homogeneity of standard wood or steel sections that requires a modified approa

5、ch to the basic principles of structural design. The two components of the heterogeneous reinforced concrete section are to be so arranged and proportioned that optimal use is made of the materials involved. This is poss

6、ible because concrete can easily be given any desired shape by placing and compacting the wet mixture of the constituent</p><p>　　The techniques necessary for placing concrete depend on the type of member to

7、 be cast: that is, whether it is a column, a bean, a wall, a slab, 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 a

8、fter cleaning them, and the reinforcement should be cleared of 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

9、>　　Hydration of the cement takes place in the presence of moisture 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

10、is too rapid, surface cracking takes place. This would result 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 num

11、ber of parameters have to be dealt with in proportioning a reinforced concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on. Consequently, trial

12、 and adjustment is necessary in the choice of concrete sections, with assumptions based on conditions at site, availability of the constituent materials, particular demands of the owners, architectural and headroom requi

13、rements, the applicable codes, a</p><p>　　A trial 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 streng

14、th is adequate to carry the applied factored load. Since more 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.<

15、/p><p>　　The trial-and –adjustment procedures for the 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 availabil

16、ity of handbooks, charts, and personal computers and programs supports this approach as a more efficient, compact, and speedy instructional method compared with the traditional approach of treating the analysis of reinfo

17、rced concrete separately from pure design.</p><p>　　Part 2 Safety of Structures</p><p>　　The principal scope of specifications is to provide general principles and computational methods in order

18、 to verify safety of structures. The “ safety factor ”, which according to modern trends is independent of the nature and combination of the materials used, can usually be defined as the ratio between the conditions. Thi

19、s ratio is also proportional to the inverse of the probability ( risk ) of failure of the structure. </p><p>　　Failure has to be considered not only as overall collapse of the structure but also as unservice

20、ability or, according to a more precise. Common definition. As the reaching of a “ limit state ” which causes the construction not to accomplish the task it was designed for. There are two categories of limit state :<

21、/p><p>　　(1)Ultimate limit sate, which corresponds to the highest value of the load-bearing capacity. Examples include local buckling or global instability of the structure; failure of some sections and subsequ

22、ent transformation of the structure into a mechanism; failure by fatigue; elastic or plastic deformation or creep that cause a substantial change of the geometry of the structure; and sensitivity of the structure to alte

23、rnating loads, to fire and to explosions.</p><p>　　(2)Service limit states, which are functions of the use and durability of the structure. Examples include excessive deformations and displacements without i

24、nstability; early or excessive cracks; large vibrations; and corrosion.</p><p>　　Computational methods used to verify structures with respect to the different safety conditions can be separated into:</p&g

25、t;<p>　　(1)Deterministic methods, in which the main parameters are considered as nonrandom parameters.</p><p>　　(2)Probabilistic methods, in which the main parameters are considered as random paramete

26、rs.</p><p>　　Alternatively, with respect to the different use of factors of safety, computational methods can be separated into:</p><p>　　(1)Allowable stress method, in which the stresses comput

27、ed under maximum loads are compared with the strength of the material reduced by given safety factors.</p><p>　　(2)Limit states method, in which the structure may be proportioned on the basis of its maximum

28、strength. This strength, as determined by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load ( ultimate state ).</p><p&g

29、t;　　The stresses corresponding to working ( service ) conditions with unfactored live and dead loads are compared with prescribed values ( service limit state ) . From the four possible combinations of the first two and

30、second two methods, we can obtain some useful computational methods. Generally, two combinations prevail:</p><p>　　(1)deterministic methods, which make use of allowable stresses.</p><p>　　(2)Pro

31、babilistic methods, which make use of limit states.</p><p>　　The main advantage of probabilistic approaches is that, at least in theory, it is possible to scientifically take into account all random factors

32、of safety, which are then combined to define the safety factor. probabilistic approaches depend upon : </p><p>　　(1)Random distribution of strength of materials with respect to the conditions of fabrication

33、 and erection ( scatter of the values of mechanical properties through out the structure );</p><p>　　(2)Uncertainty of the geometry of the cross-section sand of the structure ( faults and imperfections due

34、to fabrication and erection of the structure );</p><p>　　(3)Uncertainty of the predicted live loads and dead loads acting on the structure;</p><p>　　(4)Uncertainty related to the approximation

35、of the computational method used ( deviation of the actual stresses from computed stresses ).</p><p>　　Furthermore, probabilistic theories mean that the allowable risk can be based on several factors, such a

36、s :</p><p>　　(1)Importance of the construction and gravity of the damage by its failure;</p><p>　　(2)Number of human lives which can be threatened by this failure;</p><p>　　(3)Poss

37、ibility and/or likelihood of repairing the structure;</p><p>　　(4)Predicted life of the structure.</p><p>　　All these factors are related to economic and social considerations such as：</p>

38、;<p>　　(1)Initial cost of the construction; </p><p>　　(2)Amortization funds for the duration of the construction; </p><p>　　(3)Cost of physical and material damage due to the failure o

39、f the construction; </p><p>　　(4)Adverse impact on society; </p><p>　　(5)Moral and psychological views.</p><p>　　The definition of all these parameters, for a given safety factor,

40、 allows construction at the optimum cost. However, the difficulty of carrying out a complete probabilistic analysis has to be taken into account. For such an analysis the laws of the distribution of the live load and its

41、 induced stresses, of the scatter of mechanical properties of materials, and of the geometry of the cross-sections and the structure have to be known. Furthermore, it is difficult to interpret the interaction betwe</p

42、><p>　　鋼筋混凝土結構設計制約因素（部分）</p><p>　　第一部分：鋼筋混凝土</p><p>　　混凝土是由水泥、水、細骨料、粗骨料（碎石或；卵石）、空氣，通常還有其他外加劑等經過凝固硬化而成。將可塑的混凝土拌合物注入到模板內，并將其搗實，然后進行養(yǎng)護，以加速水泥與水的水化反應，最后獲得硬化的混凝土。其最終制成品具有較高的抗壓強度和較低的抗拉強度。其抗拉強

43、度約為抗壓強度的十分之一。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件中較弱的受拉區(qū)的強度。</p><p>　　由于鋼筋混凝土截面在均質性上與標準的木材或鋼的截面存在著差異，因此，需要對結構設計的基本原理進行修改。將鋼筋混凝土這種非均質截面的兩種組成部分按一定比例適當布置，可以最好的利用這兩種材料。這一要求是可以達到的。因混凝土由配料攪拌成濕拌合物，經過振搗并凝固硬化，可以做成任何一種需要的

44、形狀。如果拌制混凝土的各種材料配合比恰當，則混凝土制成品的強度較高，經久耐用，配置鋼筋后，可以作為任何結構體系的主要構件。</p><p>　　澆筑混凝土所需要的技術取決于即將澆筑的構件類型，諸如：柱、梁、墻、板、基礎，大體積混凝土水壩或者繼續(xù)延長已澆筑完畢并且已經凝固的混凝土等。對于梁、柱、墻等構件，當模板清理干凈后應該在其上涂油，鋼筋表面的銹及其他有害物質也應該被清除干凈。澆筑基礎前，應將坑底土夯實并用水浸濕

45、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，混凝土都應在水平方向分層澆筑，并使用插入式或表面式高頻電動振搗器搗實。必須記住，過分的振搗將導致骨料離析和混凝土泌漿等現象，因而是有害的。</p><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行，必須具備上述條件。如果干燥過快則會出現表面裂縫，這將有損與混凝土的強度，同

46、時也會影響到水泥水化作用的充分進行。</p><p>　　設計鋼筋混凝土構件時顯然需要處理大量的參數，諸如寬度、高度等幾何尺寸，配筋的面積，鋼筋的應變和混凝土的應變，鋼筋的應力等等。因此，在選擇混凝土截面時需要進行試算并作調整，根據施工現場條件、混凝土原材料的供應情況、業(yè)主提出的特殊要求、對建筑和凈空高度的要求、所用的設計規(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場澆注的合成材料，它與在工廠中制

47、造的標準的鋼結構梁、柱等不同，因此對于上面所提到的一系列因素必須予以考慮。</p><p>　　對結構體系的各個部位均需選定試算截面并進行驗算，以確定該截面的名義強度是否足以承受所作用的計算荷載。由于經常需要進行多次試算，才能求出所需的截面，因此設計時第一次采用的數值將導致一系列的試算與調整工作。</p><p>　　選擇混凝土截面時，采用試算與調整過程可以使復核與設計結合在一起。因此，當

48、試算截面選定后，每次設計都是對截面進行復核。手冊、圖表和微型計算機以及專用程序的使用，使這種設計方法更為簡捷有效，而傳統(tǒng)的方法則是把鋼筋混凝土的復核與單純的設計分別進行處理。</p><p>　　第二部分：結構的安全度</p><p>　　規(guī)范的主要目的是提供一般性的設計原理和計算方法，以便驗算結構的安全度。就目前的趨勢而言，安全系數與所使用的材料性質及其組織情況無關，通常把它定義為發(fā)生破

49、壞的條件與結構可預料的最不利的工作條件之比值。這個比值還與結構的破壞概率（危險率）成反比。</p><p>　　破壞不僅僅指結構的整體破壞，而且還指結構不能正常的使用，或者，用更為確切的話來說，把破壞看成是結構已經達到不能繼續(xù)承擔其設計荷載的“極限狀態(tài)”。通常有兩種類型的極限狀態(tài)，即：</p><p>　?。?）強度極限狀態(tài)，它相當于結構能夠達到的最大承載能力。其例子包括結構的局部屈曲和整

50、體不穩(wěn)定性；某此界面失效，隨后結構轉變?yōu)闄C構；疲勞破壞；引起結構幾何形狀顯著變化的彈性變形或塑性變形或徐變；結構對交變荷載、火災和爆炸的敏感性。</p><p>　?。?）使用極限狀態(tài)，它對應著結構的使用功能和耐久性。器例子包括結構失穩(wěn)之前的過大變形和位移；早期開裂或過大的裂縫；較大的振動和腐蝕。</p><p>　　根據不同的安全度條件，可以把結構驗算所采用的計算方法分成：</p&

51、gt;<p>　　（1）確定性的方法，在這種方法中，把主要參數看作非隨機參數。</p><p>　?。?）概率方法，在這種方法中，主要參數被認為是隨機參數。</p><p>　　此外，根據安全系數的不同用途，可以把結構的計算方法分為：</p><p>　?。?）容許應力法，在這種方法中，把結構承受最大荷載時計算得到的應力與經過按規(guī)定的安全系數進行折減后

52、的材料強度作比較。</p><p>　?。?）極限狀態(tài)法，在這種方法中，結構的工作狀態(tài)是以其最大強度為依據來衡量的。由理論分析確定的這一最大強度應不小于結構承受計算荷載所算得的強度（極限狀態(tài)）。計算荷載等于分別乘以荷載系數的活載與恒載之和。</p><p>　　把對應于不乘以荷載系數的活載和恒載的工作（使用）條件的應力與規(guī)定值（使用極限狀態(tài)）相比較。根據前兩種方法和后兩種方法的四種可能組合

53、，我們可以得到一些實用的計算方法。通常采用下面兩種計算方法：</p><p>　　確定性的方法，這種方法采用容許應力。</p><p>　　概率方法，這種方法采用極限狀態(tài)。</p><p>　　至少在理論上，概率法的主要優(yōu)點是可以科學的考慮所有隨機安全系數，然后將這些隨機安全系數組合成確定的安全系數。概率法取決于：</p><p>　?。?）

54、制作和安裝過程中材料強度的隨機分布（整個結構的力學性能數值的分散性）；</p><p>　　（2）截面和結構幾何尺寸的不確定性（由結構制作和安裝造成的誤差和缺陷而引起的）；</p><p>　　對作用在結構上的活載和恒載的預測的不確定性；</p><p>　　所采用的近似計算方法有關的不精確性（實際應力與計算應力的偏差）。</p><p>　

55、　此外，概率理論意味著可以基于下面幾個因素來確定允許的危險率，例如：</p><p>　　建筑物的重要性和建筑物破壞造成的危害性；</p><p>　?。?）由于建筑物破壞使生活受到威脅的人數；</p><p>　?。?）修復建筑的可能性；</p><p>　?。?）建筑物的預期壽命。</p><p>　　所有這些因素

56、均與經濟和社會條件有關，例如：</p><p>　?。?）建筑物的初始建設費；</p><p>　?。?）建筑物使用期限內的折舊費；</p><p>　?。?）由于建筑物破壞而造成的物質和材料損失費；</p><p>　?。?）在社會上造成的不良影響；</p><p>　?。?）精神和心理上的考慮。</p>

57、<p>　　就給定的安全系數而論，所有這些參數的確定都是以建筑物的最佳成本為依據的。但是，應該考慮到進行全概率分析的困難。對于這種分析來說，應該了解活載及其所引起的盈利的分布規(guī)律、材料的力學性能的分散性和截面的結構幾何尺寸的分散性。此外，由于強度的分布規(guī)律和應力的分布規(guī)律之間的相互關系是困難的。這些實際困難可以采用兩種方法來克服。第一種方法對材料和荷載采用不同的安全系數，而不需要采用概率準則；第二種方法是引入一些而簡化假設