土木工程外文翻译(外文)框架

《土木工程外文翻译(外文)框架》由会员分享，可在线阅读，更多相关《土木工程外文翻译(外文)框架（6页珍藏版）》请在装配图网上搜索。

1、编号：时间：2021年x月x日书山有路勤为径，学海无涯苦作舟页码：第6页 共6页4.1 INVESTIGATION OF STRUCTURAL BEHAVIORInvestigating how structures behave is an important part of structural design: it provides a basis for ensuring the adequacy and safety of a design, In this section I discuss structural investigation in general. As I do

2、throughout this book. I focus on material relevant to structural design tasks. Purpose of Investigation 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. Designers must consider

3、 the following three factors: l Functionality. or the general physical relationships of the structures form. detail. durability. fire resistance. deformation resistance. and so on. l Feasibility. including cost. availability of materials and products. and practicality of construction. l Safety. or c

4、apacity 10 resist anticipated loads. Means An investigation of a fully defined structure involves the following: 1. Determine the structures physical being-materials, form, scale. orientation. location. support conditions, and internal character and detail. 2. Determine the demands placed on the str

5、ucture-that is. loads. 3. Determine the structures deformation limits. 4. Determine the structures load response-how it handles internal forces and stresses and significant deformations. 5. Evaluate whether the structure can safely handle the required structural tasks. Investigation may take several

6、 forms. You can l Visualize graphically the structures deformation under load. l Manipulate mathematical models. l Test the structure or a scaled model, measuring its responses to loads. When precise quantitative evaluations are required. use mathematical models based on reliable theories or directl

7、y measure physical responses. Ordinarily. mathematical modeling precedes any actual construction-even of a test model. Limit direct measurementto experimental studies or to verifying untested theories or design methods. Visual Aids In this book, I emphasize graphical visualization; sketches arc inva

8、luable learning and problem-solving aids. Three types of graphics are most useful: the free-body diagram. the exaggerated profile of a load-deformed structure. and the scaled pial. A free-body diagram combines a picture of an isolated physical clemen I with representations of all external forces. Th

9、e isolated clement may be a whole structure or some part of it. For example. Figure 4.1a shows an entire structure-a beamand-eolumn rigid bent-and the external forces (represented by arrows). which include gravity. wind. and the reactive resistance of the supports (called the reactions). Note: Such

10、a force system holds the structure in static equilibrium. 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. These interactions are not visib

11、le 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 beams horizontal and vertical forces as well as rotational bending actions. Figure 4.lc shows an isolated portion

12、ofthe beam length. illustrating the beams internal force actions. Operating on this free 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. Figure 4.ld. a tiny s

13、egment. 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 location in the beam. the particle is subjected to a combination of shear and linear compression

14、 stresses. An exaggerated profile of a load-deformed structure helps establish the qualitative nature 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. FIGURE 4.1 Free-body diagrams.For example.

15、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. Figure 4.2b shows the nature of deformation of individual particles under various types of stress. FIGURE 4

16、.2 Structural deformationThe scaled plot is a graph of some mathematical 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 the graph of the

17、 expression.FIGURE 4.3 Graphical plot of a damped cyclic motion.Although the equation is technically sufficient to describe the phenomenon, the graph illustrates many aspects of the relationship. such as the rate of decay of the displacement. the interval of the vibration. the specific position at s

18、ome specific elapsed time. and so on.4.2 METHODS OF INVESTIGATION AND DESIGN 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 on the classic theories of elastic behavior, measure

19、s a designs safety against two limits: an acceptable maximum stress (called allowable working stress) and a tolerable extent of deformation (deflection. stretch. erc.). These limits refer to a structures response to service loads-that is. the loads caused by normal usage conditions. The strength me/

20、hod, meanwhile, measures a designs adequacy against its absolute load limit-that is. when the structure must fail. To convincingly establish stress. strain. and failure limits, tests were performed extensively in the field (on real structures) and laboratories (on specimen prototypes. or models). No

21、te: Real-world structural failures are studied both for research sake and to establish liability. 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

22、 a load condition well beyond what it should experience. Clearly the stress and strength methods arc different. but the difference is mostly procedural.The Stress Method (ASD) The stress method is as follows: 1. Visualize and quantify the service (working) load conditions as intelligently as possibl

23、e. You can make adjustments by determining statistically likely load combinations (i.e , dead load plus live load plus wind load). considering load duration. and so on. 2. Establish standard stress. stability, and deformation limits for the various structural responses-in tension. bending, shear, bu

24、ckling. deflection, and so on. 3. Evaluate the structures response. An advantage of working with the stress method is that you focus on the usage condition (real or anticipated). The principal disadvantage comes from your forced detachment from real failure conditions-most structures develop much di

25、fferent forms of stress and strain as they approach their failure limits. The Strength Method (LRFD) The strength method is as follows: 1. Quantify the service loads. Then multiply them by an adjustment factor( essentially a safety factor) to produce thejaclOred load. 2. Visualize the various struct

26、ural responses and quantify the structures ultimate (maximum, failure) resistance in appropriate terms (resistance to compression, buckling. bending. etc.). Sometimes this resistance is subject to an adjustment factor, called theresistancefacror. When you employ load and resistance factors. the stre

27、ngth method is now sometimes called foad and resistancefaaor design (LRFD) (see Section 5.9). 3. Compare the usable resistance ofthe structu re to the u ltirnatc resistance required (an investigation procedure), or a structure with an appropriate resistance is proposed (a design procedure). A major

28、reason designers favor the strength method is that structural failure is relatively easy to test. What is an appropriate working 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 pro

29、fessional design work. Nevertheless, 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 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. 第 6 页 共 6 页