外文翻譯--結構設計原理

1、<p><b>　　附錄</b></p><p>　　Philosophy of Structural Design</p><p>　　A structural engineering project can be divided into three phases: planning, design, and construction.</p>

2、;<p>　　Structural design involves determining the most suitable proportions of a structure and dimensioning the structural elements and details of which it is composed. This is the most highly technical and mathem

3、atical phase of a structural engineering project, but it cannot-and certainly should not-be conducted without being fully coordinated with the planning and construction phases of the project. The successful designer is a

4、t all times fully conscious of the various considerations that were involv</p><p>　　Specially, the structural design of any structure first involves the establishment of the loading and other design conditio

5、ns that must be resisted by the structure and therefore must be considered in its design. Then comes the analysis (or computation ) of the internal gross forces (thrust, shears, bending moments, and twisting moments), st

6、ress intensities, strains, deflections, and reactions produced by the loads, temperature, shrinkage, creep, or other design conditions. Finally comes the pro</p><p>　　Depending on the type of structure and t

7、he conditions involved, the stress intensities computed in the analytical model of the actual structure for the assumed design conditions may or may not be in close agreement with the stress intensities produced in the a

8、ctual structure by the actual conditions to which it is exposed. The degree of correspondence is not important, provided that the computed stress intensities can be interpreted in terms of previous experience. The select

9、ion of the service c</p><p>　　The allowable-stress approach has an important disadvantage in that it does not provide a uniform overload capacity for all parts and all types of structures. As a result, there

10、 is today a rapidly growing tendency to base the design on the ultimate strength and serviceability of the structure, with the older allowable-stress approach serving as an alternative basis for design. The newer approac

11、h currently goes under the name of strength design in reinforce-concrete design literature and plastic </p><p>　　Proponents of this latter approach argue that it results in a more realistic design with a mor

12、e accurately provided margin of strength over the anticipated service conditions. These improvements result from the fact that nonelastic and nonlinear effects that become significant in the vicinity of ultimate behavior

13、 of the structure can be accounted for.</p><p>　　In recent decades, there has been a growing concern among many prominent engineers that not only is the term “factor of safety” improper and unrealistic, but

14、worse still a structural design philosophy based on this concept leads in most cases to an unduly conservative and therefore uneconomical design, and in some cases to an unconservative design with too high a probability

15、of failure. They argue that there is no such thing as certainty, either of failure or of safety of a structure but only a </p><p>　　If a good alignment requires a curved bridge-over a part or the total lengt

16、h then all external longitudinal lines or edges of the structure should be parallel to the curved axis, thereby following again the guideline of good order.</p><p>　　The transverse axis of piers or groups of

17、 columns should be rectangular (radial) to the curved axis, unless skew crossings over roads or rivers enforce other directions.</p><p>　　The requirements of traffic design result occasionally in very acute

18、angles or in level branching which cause difficulties for the bridge engineer to find pleasing solutions for the bridges.</p><p><b>　　結構設計原理</b></p><p>　　一個結構設計工程可以被分為三個階段：計劃、設計、施工。

19、</p><p>　　結構設計包含確定結構最合適的比例并且測量單元體的尺寸及其包含的細部。這是一項結構工程中技術性和數學性最強的一個階段，但是如果不能全面的與計劃和施工階段相協(xié)調的話，它是不能被進行的。成功的設計者在任何時候都能全面地考慮到結構初步設計中包含的各種因素，同時還充分考慮到以后施工中可能遇到的各種問題。</p><p>　　尤其，任何一個結構的結構設計首先包括結構所必須抵抗的荷

20、載及其它設計因素的確定，因此，在設計中必須考慮到。然后開始分析（或計算）由荷載、收縮、徐變或其它設計因素引起的總內力（推力、剪力、彎矩和扭矩），應力強度、應變、變形及反力等。最后是比例的確定和選擇構件和連結件的材料，用來充分的抵抗由設計條件帶來的影響效應，這種用來評斷特定的比例是否會帶來想要的結構的標準反映出你的知識的積累程度、直覺以及判斷。常見的土木工程結構例如橋梁、建筑，過去的這種做法是在比較應力強度以及由使用荷載和其它設計因素引起

21、的應力強度的基礎上設計的。這種傳統(tǒng)的設計被稱作彈性設計，因為允許應力強度是按照這樣一種理念進行選擇的，即材料的拉、壓允許應力與屈服強度相同并且不能超過結構的最大應力。當然，考慮到垮塌的可能性及結構的允許變形，對允許應力強度的選擇可作適當的修正。</p><p>　　根據結構的類型和所包含的條件，對于在假定的條件下在實際結構的分析模型中所計算得的應力強度與在實際的承載條件下實際構件所產生的應力強度可能相似也可能不同

22、。當計算得的應力強度可以被先前的經驗所解釋和肯定時，這種相似度就不再重要了。使用條件和允許應力強度的選擇應該相對垮塌留有一定的安全余地，這種安全余地大小的選擇取決于荷載、分析、設計、材料和施工的不確定程度及垮塌將引起的后果。例如：一個允許抗拉強度為20000磅每立方英寸的結構采用抗拉強度為33000磅每立方英寸的鋼材，則相對于抗拉屈服強度的安全余地為33000/20000，即1.65。</p><p>　　允許應

23、力法有一個嚴重的缺陷，也就是它不能為各類結構及其構件給出一個統(tǒng)一的超載能力。因此在今天有這樣一種快速發(fā)展的趨勢，即把設計建立在極限強度和結構實驗基礎之上，將舊的允許應力法作為設計的一種供選擇的方法。這種新的方法在鋼筋混凝土設計文獻和剛結構彈性設計文獻中被稱為強度設計。當在強度設計的基礎確定比例時，參與的實際荷載會首先乘以一個合適的荷載分項系數（大于1），這個荷載的大小取決于荷載的不確定度，它在結構的生命周期內改變的可能性和荷載的聯合作用

24、的可能性，頻率以及特殊的聯合作用的持續(xù)性。當這種方法應用于鋼筋混凝土設計時，鑒于材料在強度、工藝和尺寸上的不利的變化，結構單元的理論承載力會由于乘了一個承載力折減系數而降低。此時結構的比例會由以下主導因素確定，逐步增大的荷載將會導致（1）疲勞、彎曲或脆斷（2）或在某一內部截面產生屈服（3）或使結構產生彈性位移（4）或者使整個結構處于垮塌的邊緣。</p><p>　　后種方法的支持者聲稱它可以產生一個更實際的設計以

25、及提供一個比實際參與的條件更精確的強度留余。這種改進源于這樣一種事實，即在結構的極限附近的非線形和線形可以得到解釋和說明。</p><p>　　近十幾年來，許多杰出的工程師越來越觀注到安全系數這種方法的不合適和不切實際而且基于這一概念的結構的理性設計也變的更加糟糕，導致了許多設計方案的過度的保守，以至于由此產生的不經濟的設計和一些情況下的破壞概率較高的冒險設計。他們宣稱不論是結構的安全或破壞，都不存在確定的事實，

26、而反之是安全的概率或破壞的概率。因此，他們覺得荷載效應的變化和結構抵抗力的變化應該應用統(tǒng)計的方法進行研究，并且對結構的耐用性和使用性進行估計。這種方法也許不適用于單個結構的單元的設計，然而它在框架設計的規(guī)則和規(guī)定中它是適用的。建設法規(guī)和特殊規(guī)定高度的認同并清楚的說明了設計師們所反映的因素和相應的可能性。</p><p>　　如果一個好的線型需要一個曲線橋——一部分或是全部的長度，則所有的外部縱向線或結構的邊緣應當