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1、本外文文献来自Simplified Design of Steel Structures（钢结构简化设计丛书 第七版）,作者James Ambrose（詹姆斯安布罗斯）。 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 str
2、uctural investigation in general. As I do 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 u
3、sage requirements. Designers must consider 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 pr
4、acticality of construction. l Safety. or capacity 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.
5、2. Determine the demands placed on the structure-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 struct
6、ural tasks. Investigation may take several 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 mo
7、dels based 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 untested theories or design methods. Visual Aids In this book, I emphasize
8、graphical visualization; sketches arc invaluable 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
9、representations of all external forces. The 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 su
10、pports (called the reactions). Note: Such 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 a
11、ll ached. These 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 beams horizontal and vertical forces as well as rotational bending actio
12、ns. Figure 4.lc shows an isolated portion 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 plac
13、e in the whole beam. Figure 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 location in the beam. the particle is subjected to a c
14、ombination of shear and linear compression 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. F
15、IGURE 4.1 Free-body diagrams.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. Figure 4.2b shows the nature of deformation of individual particl
16、es under various types of stress. FIGURE 4.2 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 expression.FIGURE 4.3 Graphical plot of a dam
