土木工程畢業(yè)設計外文翻譯10

1、<p>　　4.1 INVESTIGATION OF STRUCTURAL BEHAVIOR</p><p>　　Investigating how structures behave is an important part of structural design: it provides a basis for ensuring the adequacy and safety of a desi

2、gn, In this section I discuss structural investigation in general. As I do throughout this book. I focus on material relevant to structural design tasks. </p><p>　　Purpose of Investigation </p><p

3、>　　Most structures exist because they are needed. Any evaluation of a structure thus must begin with an analysis of how effectively the structure meets the usage requirements. </p><p>　　Designers must con

4、sider the following three factors: </p><p>　　Functionality. or the general physical relationships of the structure's form. detail. durability. fire resistance. deformation resistance. and so on. </p&

5、gt;<p>　　Feasibility. including cost. availability of materials and products. and practicality of construction. </p><p>　　Safety. or capacity 10 resist anticipated loads. </p><p><b&g

6、t;　　Means </b></p><p>　　An investigation of a fully defined structure involves the following: </p><p>　　Determine the structure's physical being-materials, form, scale. orientation. l

7、ocation. support conditions, and internal character and detail. </p><p>　　Determine the demands placed on the structure-that is. loads. </p><p>　　Determine the structure's deformation limits

8、. </p><p>　　Determine the structure's load response-how it handles internal forces and stresses and significant deformations. </p><p>　　Evaluate whether the structure can safely handle the r

9、equired structural tasks. </p><p>　　Investigation may take several forms. You can </p><p>　　Visualize graphically the structure's deformation under load. </p><p>　　Manipulate m

10、athematical models. </p><p>　　Test the structure or a scaled model, measuring its responses to loads. </p><p>　　When precise quantitative evaluations are required. use mathematical models based

11、 on reliable theories or directly measure physical responses. Ordinarily. mathematical modeling precedes any actual construction-even of a test model. Limit direct measurementto experimental studies or to verifying unte

12、sted theories or design methods. </p><p>　　Visual Aids </p><p>　　In this book, I emphasize graphical visualization; sketches arc invaluable learning and problem-solving aids. Three types of grap

13、hics are most useful: the free-body diagram. the exaggerated profile of a load-deformed structure. and the scaled pial. </p><p>　　A free-body diagram combines a picture of an isolated physical clemen I with

14、representations of all external forces. The isolated clement may be a whole structure or some part of it. </p><p>　　For example. Figure 4.1a shows an entire structure-a beamand-eolumn rigid bent-and the ext

15、ernal forces (represented by arrows). which include gravity. wind. and the reactive resistance of the supports (called the reactions). Note: Such a force system holds the structure in static equilibrium. </p><

16、p>　　Figure 4.lb is a free-body diagram of a single beam from the bent. Operating on the beam are two forces: its own weight and the interaction between the beam ends and the columns 10 which the beam is all ached. The

17、se interactions are not visible in the Ireebody diagram of the whole bent. so one purpose of the diagram for the beam is to illustrate these interactions. For example. note that the columns transmit to theendsofthe beam

18、s horizontal and vertical forces as well as rotational bending act</p><p>　　Figure 4.lc shows an isolated portion ofthe beam length. illustrating the beam's internal force actions. Operating on this fr

19、ee body arc its own weight and the actions of the beam segments on the opposite sides of the slicing planes. since it is these actions that hold the removed portion in place in the whole beam. </p><p>　　Figu

20、re 4.ld. a tiny segment. or particle. of the beam material is isolated, illustrating the interactions between this particle and those adjacent to it. This device helps designers visualize stress: in this case. due to its

21、 location in the beam. the particle is subjected to a combination of shear and linear compression stresses. </p><p>　　An exaggerated profile of a load-deformed structure helps establish the qualitative natur

22、e of the relationships between force actions and shape changes. Indeed. you can infer the form deformation from the type of force or stress. and vice versa. </p><p>　　FIGURE 4.1 Free-body diagrams.</p>

23、;<p>　　For example. Figure 4.la shows {he exaggerated deformation of the bent in Figure 4.1 under wind loading. Note how you can determine the nature of bending action in each member of the frame from this figure

24、. Figure 4.2b shows the nature of deformation of individual particles under various types of stress. </p><p>　　FIGURE 4.2 Structural deformation</p><p>　　The scaled plot is a graph of some mat

25、hematical relationship or real data. For example, the graph in Figure 4.3 represents the form of a damped ibration of an elastic spring. It consists of the plot of the displacements against elapsed time t. and represents

26、 the graph of the expression.</p><p>　　FIGURE 4.3 Graphical plot of a damped cyclic motion.</p><p>　　Although the equation is technically sufficient to describe the phenomenon, the graph illust

27、rates many aspects of the relationship. such as the rate of decay of the displacement. the interval of the vibration. the specific position at some specific elapsed time. and so on..</p><p>　　4.2 METHODS OF

28、 INVESTIGATION AND DESIGN </p><p>　　Traditional structural design centered on the working stress method. a method now referred to as stress design or allowable stress design (ASD). This method. which relies

29、on the classic theories of elastic behavior, measures a design's safety against two limits: an acceptable maximum stress (called allowable working stress) and a tolerable extent of deformation (deflection. stretch.

30、 erc.). These limits refer to a structure's response to service loads-that is. the loads caused by normal usage c</p><p>　　To convincingly establish stress. strain. and failure limits, tests were perform

31、ed extensively in the field (on real structures) and laboratories (on specimen prototypes. or models). Note: Real-world structural failures are studied both for research sake and to establish liability. </p><

32、p>　　In essence. the working stress method consists of designing a structure to work at some established percentage of its total capacity. The strength method consists of designing a structure tofail. but at a load co

33、ndition well beyond what it should experience. Clearly the stress and strength methods arc different. but the difference is mostly procedural.</p><p>　　The Stress Method (ASD) </p><p>　　The stre

34、ss method is as follows: </p><p>　　Visualize and quantify the service (working) load conditions as intelligently as possible. You can make adjustments by determining statistically likely load combinations (i

35、.e , dead load plus live load plus wind load). considering load duration. and so on. </p><p>　　Establish standard stress. stability, and deformation limits for the various structural responses-in tension. b

36、ending, shear, buckling. deflection, and so on. </p><p>　　Evaluate the structure's response. </p><p>　　An advantage of working with the stress method is that you focus on the usage condition

37、 (real or anticipated). The principal disadvantage comes from your forced detachment from real failure conditions-most structures develop much different forms of stress and strain as they approach their failure limits. &

38、lt;/p><p>　　The Strength Method (LRFD) </p><p>　　The strength method is as follows: </p><p>　　Quantify the service loads. Then multiply them by an adjustment factor'( essentially

39、a safety factor) to produce thejaclOred load. </p><p>　　Visualize the various structural responses and quantify the structure's ultimate (maximum, failure) resistance in appropriate terms (resistance to

40、 compression, buckling. bending. etc.). Sometimes this resistance is subject to an adjustment factor, called theresistancefacror. When you employ load and resistance factors. the strength method is now sometimes calle

41、d foad and resistancefaaor design (LRFD) (see Section 5.9). </p><p>　　Compare the usable resistance ofthe structu re to the u ltirnatc resistance required (an investigation procedure), or a structure with

42、an appropriate resistance is proposed (a design procedure). </p><p>　　A major reason designers favor the strength method is that structural failure is relatively easy to test. What is an appropriate working

43、condition is speculation. In any event, the strength method which was first developed for the design of reinforced concrete structures, is now largely preferred in all professional design work. </p><p>　　N

44、evertheless, the classic theories of clastic behavior still serve as a basis for visualizing how structures work. But ultimate responses usually vary from the classic responses, because of inelastic materials, secondary

45、effects, multi mode responses, and so on. In other words, the usual procedure is to first consider a classic, elastic response, and then to observe (or speculate about) what happens as failure limits are approached. <

46、/p><p><b>　　中文翻譯</b></p><p>　　4. 1結構特性分析 </p><p>　　研究結構的特性在結構設計中是一個很重要的部分，它是保證設計安全性和適用性的 基礎。本節(jié)討論常用的結構分析方法。正如貫穿本書所討論的一樣，本章集中講述與鋼結 構設計相關的材料問題。</p><p><b>　　

47、1.分析的目的 </b></p><p>　　絕大數的結構是因需而生的。因此，任何一個結構的評價都是從分析結構如何有效地滿足使用要求開始的。 </p><p>　　設計人員必須考慮以下三個因素：</p><p>　?。?）實用性指結構的形式、構造、耐久性、抗火性以及抗變形能力等的一般物理關系。</p><p>　　（2）可行性包括

48、造價、材料及產品的實用性和結構的實用性。 </p><p>　?。?）安全性指抵抗設計荷載的能力。 </p><p><b>　　2.方法 </b></p><p>　　一個完整的結構分析包括以下幾點：</p><p>　?。?）確定結構的物理特性一一材料、形式、尺寸、方向、位置、支承條件以及內部特征和構造。</p

49、><p>　?。?）確定施加在結構上的負荷.即荷載. </p><p>　?。?）確定結構的變形極限。 </p><p>　　（4）確定結構的荷載效應，即荷載作用對結構的內力、應力和主要變形的影響。 </p><p>　?。?）評定結構是否能夠安全地承擔所需的結構要求。 </p><p>　　結構研究可以采用以下三種方法:

50、 </p><p>　?。?）圖解表示街載下結構的變形。 </p><p>　　（2）使用數學模型。 </p><p>　　（3）對結構或比例模型進行試驗，測量其在荷載下的效應. </p><p>　　當需要精確的定量評定時，可以采用基于可靠度理論的數學模型或直接測量物理效 應。-般地.建立數學模型先于實際結構.甚至是先于試驗模型。括號直接測

51、定限制在試驗 研究上或是限定在驗證未被檢驗過的理論上或是限定在設計方法土。 </p><p><b>　　3.直觀法 </b></p><p>　　本書強調圖解法，草圖是一種非常有價值的學習及解決問題的建助工具。最有用的三 種圖解法是:隔離體圖解法、荷載變形結構放大示意圖和比例圖. </p><p>　　隔離體圖解法是用圖解的方法表示一個隔離單

52、元所受的所有外力.這個隔離單元可以 是整體結構或是結構的一部分。 </p><p>　　例如，圖4. 1（a）為一整體結構——梁—柱剛性框架——和框架研受外力(由箭頭表示)。結構所受的外力包括自重、風荷載和支座反力(即反力)。注意：結構所受的力系使結構處于靜力平衡狀態(tài)。 </p><p>　　圖4. 1 （b）為從框架上隔離出來的單個梁的隔離體圖。該梁承受兩種力：自重以及梁端部和與梁相連碼

53、在之間的相互作用力。梁和柱之間的相互作用力在框架隔離體圖中是看不到的。因此梁的隔離體圖目的之一是闡明此相互作用力。注意：柱子傳遞給梁端的不僅有彎距，還有水平力和豎向力。 </p><p>　　圖4.1（c）為沿梁長度方向上部分梁的隔離體，給出了梁的內力作用。在該隔離體上作用有自重和剖面相反一側對該梁段所施加的作用力，正是由于此內力使得整個梁的剩余部分保持平衡。</p><p>　　圖4.1

54、（d）為梁截面隔離體中的一小段或一部分，該圖顯示了這部分與相鄰部分間的作用力。此圖有助于設計人員了解結構所受的應力。既然這樣，由于它是梁的一部分，因此受到剪應力和線性壓應力 的作用。</p><p>　　荷載—變形結構放大示意圖有助于定性確定作用力和形狀改變之間的關系。實際上，可以從力或應力的類型來推斷變形的形式，反之亦然。 </p><p>　　例如，圖4. 2（a）表示的是圖4. 1所

55、示框架在風荷載作用下的變形放大示意圖。應注意從圖中如何確定框架的每個構件的彎曲作用特性。圖4.2 （b）給出了在不同類型應力下，單個隔離體的變形特性。 </p><p>　　比例圖為一些數學關系或實測數據的圖形。例如，圖4. 3代表一彈性彈簧阻尼振動的形式。該圖是位移-時間（s-t）關系圖，其關系式如下: </p><p>　　雖然方程已經足夠描述位移-時間的關系，但是圖示還可以表示位移-

56、時間關系的很多方面，比如位移衰減的比率，振動周期以及在某一特定時間里振動的具體位置等。 </p><p>　　4.2分析與設計方法 </p><p>　　傳統(tǒng)的結構設計方法是圍繞著工作應力法展開的，此方法現在稱為應力設計或容許應力設計（allowable stress design， ASD)。此方法依賴于經典的彈性特性理論，用兩個極限值來衡量設計的安全性:可接受最大應力(稱為容許工作應力

57、)和容許的變形極限值(撓度、伸長等)。這兩個極限值是結構在使用荷載下的效應，即正常使用條件下的荷載效應。 同時，承載力法是用來衡量設計是否足以抵抗其絕對荷載極限，即當結構必須破壞時，結構抗力是否大于結構效應。 </p><p>　　為了得到令人信服的應力極限值、應變極限值以及破壞極限，大量進行現場(在實際結構上)和試驗室(在結構樣本原型或模型上)試驗。 </p><p>　　提示 研究

58、實際結構的破壞是為了研究和確定結構的可靠性。 </p><p>　　實際上，工作應力法是指設計一個結構，使其在工作狀態(tài)下只發(fā)揮部分承載力。承載力法是設計一個結構使其發(fā)生破壞，但是當實際荷載沒有超過破壞荷載時，結構不會發(fā)生破壞。顯而易見，應力法和承載力法是不同的，但是這種不同主要是設計程序上的不同。</p><p>　　應力法（ASD法） </p><p>　　應力法

59、應遵循以下規(guī)則： </p><p>　?。?） 盡可能合理地假設和確定使用（工作）荷載的狀況?？梢酝ㄟ^確定可能的統(tǒng)計荷載組合（如恒載+活載+風載）來調整荷載狀況，同時考慮荷載的持久性等。</p><p>　?。?） 確定不同結構效應下——受拉、受彎、受剪、屈曲及變形等的標準應力、應變和 變形極限值結構效應。 </p><p>　?。?） 評定結構效應。 </p

60、><p>　　使用應力法的優(yōu)點是集中于結構的使用狀態(tài)（真實的或期望的）。主要的不足之處在于人為的把破壞狀態(tài)分離出來——大多數結構接近破壞極限時，應力和應變很不相同。 </p><p>　　承載力法（LRFD法） </p><p>　　承載力法應遵循以下規(guī)則: </p><p>　?。?） 確定使用荷載值。然后乘以一修正系數（本質上是一安全系數），

61、即得到設計荷載。 </p><p>　?。?） 假設結構的各種效應，并確定結構在適當效應下的極限（最大或破壞）抗力（如受壓、屈曲及受彎等的抗力）。有時該抗力受到某一修正系數的影響，即抗力系數。在設計中使用了荷載和抗力系數，則承載力法有時又被稱為荷載抗力系數設計法(load and resistance factor design， LRFD) （見第4. 9節(jié)）。 </p><p>　?。?/p>

62、3） 對照結構的使用抗力與極限設計抗力（分析過程），或建議采用適當抗力的結構 （設計過程）。 </p><p>　　設計人員比較愿意使用承載力法的主要原因是結構的破壞比較容易檢驗。什么樣的工 作狀況才合適是一個值得思考的問題。無論如何，最初被用于設計鋼筋混凝土結構的承載力法，現在己用于各專業(yè)設計。 </p><p>　　不過，經典彈性理論作為基本方法仍然用于結構工作狀況的假設上。但是，由于