## 剪力和弯矩英文文献和中文翻译

2-4-2 Shear and Moment Basic Phenomena.This section begins a study of the type of internal forces and moments generated in a member carrying an external force system that acts transversely to the axis of the member.The concepts of shear and
2-4-2 Shear and Moment Basic Phenomena.This section begins a study of the type of internal forces and moments generated in a member carrying an external force system that acts transversely to the axis of the member.The concepts of shear and moment in structures introduced here are of fundamental importance to an understanding of the behavior of structures undr load.They also provide the basis for developing tools for designing structures.There same concepts are later developed in the context of looking at a particular structural type (trusses,see Section 4-3-5).In succeeding chapters we draw out and elaborate on the theme of shear and moment in connection with other structural elements.Readers new to the subject matter may find it better to skip this section for the time being and pick it up again at a later point,such as directly after truss analysis(Chapter 4) or as part of beam analysis.12354
Consider the loaded cantilever member illustrated in Figure 2-29.There are two primary ways in which the momber might fail as a result of the applied load.One potential type of failure is for the load to cause two contiguous parts of the member to slide relative to each other in a direction parallel to their plane of contact.This is called a shear failure.The internal shear force developed in the member that is associated with this phenomenon is called an internal shear force.This internal shear force is developed in response to the components of the external force system that act transversely to the long axis of the member and tend to cause the type of transverse aliding indicated in Figure 2-29(c).These internal shear forces resist or balance the net external shearing force tending to cause the sliding.Failure of the type illustrated occurs when the member can no longer provide an equilibrating internal force of this type..
FIGURE 2-29  Shear and moment in structures.
The second possible mode of failure is that illustrated in Figure 2-29(c).This type of failure is obviously associared with the tendency of the transverse extemal forces to cause part of the structure to rotate,or bend.Since free rotation cannot occur in a rigid body (unless a pin connection is pressent),an intemal resisting or balancing moment equal and opposite to the applied moment (the moment associated with the rotational tendencies of the extemal forces) must be developed within the struchure. Failure of the type shown occurs when the structure can no longer provide a resisting moment equal to the applied moment.

At any section of the loaded member, internal shear forces and moments are developed simultaneously. It the member is decomposed at this point into two parts, the forces and moments developed intemaily serve to maintain the thanslational and rotational equilibnum of each part. They also represent the intermal actions and reactions of one part of the member on the other part. As will be seen later, one of the objectives of the structural design process is to create a structural configuration capable of providing these intemal shears and moments in an efficient way and with factors of safety sufficient to prevent shear and moment failures.
Internal shear forces and moments of this type deseribed above are developed in any struce carrying transverse loads. Determining the magnitude of these quantities is a straightforward prscess based on the fundamental prorosition that any structure, or any part of any structure, must be in a state of equilibrum under the action of the complete force system (including internal sa well as external forces and moments) acting on it. The extemal force system is typically known. Parts of the force system not initially known, such as reactions at supports, can be readily calculated by methods previously discussed. If the equitibrium of an isolated portion of a sturcture is considered, the unknown internal shears and moments that must be present at the point of decompositiong can be determined through equilibriumm considerations involving known parts of the extemal force system.
Procedures.  The member shown in Figure 2-30 is in equilibrium. Reactions have been determined. Assume that it is desired to know the nature of the intermal forces at some arbitrary location, such as section x-x located at midspan. To find these internal forces, the structure is decomposed into two parts at this location.Consider the left portion of the structure [Figure 2-30(b)].This part of the structure is not in equilibrium if only the effects of the external force system acting on this part are considered.The net effect of the portion of the external force system acting on this part of the structure is to cause it to translate vertically downward and rotate in a clockwise direction.The net downward force is called the external shear force (VE) present at the structure to be in equilibrium,it is evident that the structure must somehow provide an internal resisting shear force (VR) equil in magnitude but opposite in sense.Thus,VE=VR.Hence,VR=P/4↑. 剪力和弯矩英文文献和中文翻译:http://www.lwfree.cn/fanyi/20170810/12095.html
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