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1、1.外文资料翻译译文 梁 梁是结构中最常见的构件。这些构件，使携带的载荷，作用于以纵向轴线 。这些荷载使导致梁弯曲弯曲。在这一章里,我们学习梁的轴向力。图1-1a,和1-1c说明了一些梁的典型例子。当我们假设梁(或任何结构构件)为达到分析或设计的目的时,可以简单的认为理想化的形式。这种理想化的形式尽可能代表实际结构构件,但它的优点是,它可以在数学上进行处理。例如,在图4-1a显示了简支梁。这些支撑，左边是较连接（刀口上的对铰链）右边也是铰连接。创造这样他的条件,我们可以很容易处理，然后找到梁的约束反应。弯矩和挠度的分配使这些简支梁可以成为数学化。回想一下，销支撑将提供垂直和水平的反应（但没有旋
2、转阻力）辊销将只提供一个垂直反应。在桥梁上作用是特别明显的，为温度变化引起的膨胀和收缩提供空间。在建筑物的每个支撑一般能够提供垂直和水平的反力。所以，既然梁被认为是简支的自然要求简单的支持是允许自由旋转。在图4-1B悬臂梁具有在左侧的固定支撑。这种类型的支撑提供垂直和水平的反力，以及弯矩。所以在固定支撑足够提供梁的静力使之平衡。在实际结构中虽然一般不会存在理想化条件所以理想的条件应该足够接近允许一个合理的分析和设计。 在梁设计的过程中，应将先考虑梁中的弯曲。梁中所支持的负载因此产生这弯曲力矩。其他的一些形式，例如剪切和偏心，最终有可能控制梁的设计所以同样要检查，验证。这个时候这些形式通常是重要
3、的，因此它一开始就被关注。 梁有时反映一些专门功能所以也被称为其他名称（S） 桁梁：一个主要的，或深的梁，往往为其他横梁支撑 框梁：主纵梁，通常在桥楼 横梁：在桥楼的横梁 托梁：一轻梁，支撑地板 过梁：梁跨越的开口（门或窗），通常在砖石建筑 拱肩：支持在其它负载之间，外墙的建筑物的外周界的梁 檩条：支撑屋架之间或在支撑件如屋架或刚架屋顶和框架梁 顶梁：通常，一个梁，支撑建筑物轻型的外侧（最典型的是在预设计的钢结构建筑物中） 在图4-2中的简支梁a承受两个对称放置的荷载，它弯曲所表现出来的是梁的变形形状。剪力（V）和弯矩（M）的示意图示于图4-2b和C。这些图表忽略梁的重量，只考虑两个集中荷载（
4、P）。假定读者已经完全熟悉剪力图和弯矩图。从材料的发展实力。我们考虑其中的一个部分，在中跨（或两个集中负荷之间的任何位置），力矩为最大，如图4-2c中。在梁的最大应力处，弯矩可以通过使用弯曲公式确定： FB= MC/ I = M / S FB =计算的弯曲应力（最大在顶部和/或底部） M =最大弯矩 C =距离中性轴到极致外的截面积 I=关于弯曲的中性轴的横截面的转动惯量 S =截面模量（S = I/ c）约弯曲中性轴的横截面的 图4-2的荷载，简支梁的剪力图和弯矩图的。基本假定和弯曲公式的推导，在大多数的教科书可能找到相应的材料强度。实际使用的弯曲公式很简单，但是单位必须仔细考虑。任何换算因
5、素必须认真考虑，使公式兼容性的存在。例如，在式FB = M / S，通常的单位可写为米/秒。考虑使用单位的兼容性，压力产生的FB作为KSI，1in./ft的转换。比如说对于这个文本制定出来的数值问题，这些必要的转换系数表明使用的人没有进一步解释。应当指出，对于经验公式，如在第4-3章所讨论的，单位是有时是不兼容。精确地在ASDM中定义的单位数值的这些公式，必须谨慎使用。假设图4-2的梁是一个典型的宽翼缘梁（W形），如图4-3所示的横截面，描绘了由此产生的弯曲应力图。图中的形状是在任何点沿着梁的弯曲应力的几个典型的应注意的要点。1.对于宽翼缘梁，X-X轴的转动惯量。大于惯性约在Y-Y轴的动惯量。
6、梁这样取向的弯曲发生在有关X-X轴。这是对的，除非在非常罕见的情况。 2.在这种情况下，由于对称性，中性轴是在横截面的中心。这个c的距离是相等的不论是在拉伸或压缩的一面。3.该梁中的最大应力发生在顶部和横截面的底部。图4-2的梁的弯曲，使中性轴上产生压缩，中性轴以下出现张拉（通常，这就是所谓的正弯矩） 4. 一般情况下，只要考虑最大弯曲应力。因此，除非另有说明，FB被假定为最大应力。弯曲公式也可以通过C代替中性轴到到相应位置的合适的距离，用来寻找应力代替横截面的任何位置。 2.外文原文BeamBeams are among the most common members that one wi
7、ll find in structures. They are structural members that carry loads that are applied at right angles to the longitudinal axis of the member . These load cause the beam to bend . In this chapter we consider beams that carry no axial force . figure 1-1a,b and c illustrates some typical examples of bea
8、m application . when visualizing a beam (or any structural member)for the purposes of analysis or design, it is convenient to think of the member in some idealized form. This idealized form represents as closely as possible the actual structural member, but it has the advantage that it can be dealt
9、with mathematically . For instance ,in Figuer4-1a the beam is shown with simple supports. These supports, a pin(knife-edge on hinge)on the left and a roller on the right, create conditions that are easily treated ,mathematically when it becomes necessary to find beam reaction, shares, moments and de
10、flections. Recall that the pin support will provide vertical and horizontal reactions ( but no resistance to rotation ), and the roller pin will provide only a vertical reaction .This is particularly significant for bridges, where provisions must be made for expansion and contraction due to temperat
11、ure changes. In buildings each support is generally capable of furnishing vertical and horizontal reactions . The beams, however, are still considered to be simply supported since the requirement are simply support is to permit freedom of rotation .In figure 4-1b the cantilever beam has a fixed supp
12、ort on the left side . This type of support provides vertical and horizontal reactions as well as resistance (or a reaction) to rotation .The on fixed support is sufficient for static equilibrium of the beam. Although the idealize conditions generally will not exist in the actual structure ,the actu
13、al conditions will approximate the ideal conditions and should be close enough to allow for a reason able analysis or design. In the process of beam design, will be concerned initially with the bending moment in the beam. The bending moment is produced in the beam by the load it supports. Other effe
14、cts ,such as shear and deflection, may eventually control the design of the beam and will have to be checked .But usually moment is critical，and it is，therefore，of initial concern Beams are sometimes called by other names that are indicative of some specialized function(s)： Girder：a major，or deep，be
15、am that often provides support for other beams Stringer：a main longitudinal beam，usually in bridge floors Floor beam：a transverse beam in bridge floors Joist：a light beam that supports a floor Lintel：a beam spanning an opening(a door or a window)，usually in masonry ConstructionSpandrel：a beam on the
16、 outside perimeter of a building that supports，among other loads，the exterior wall.Purlin：a beam that supports a roof and frames between or over supportssuch as roof trusses or rigid frames Girt：generally，a light beam that supports only the lightweight exterior sides of a building(typical in pre eng
17、ineered metal buildings)When the simply supported beam of Figure 42a is subjected to two symmetrically placed loads，it bends as shown by the deflected shapeThe diagrams of the induced shear(V)and moment(M)are as shown in Figure 4-2b and c These diagrams neglect the weight of the beam and consider th
18、e two concentrated loads(P)only. It is assumed that the reader is completely familiar with the development of shear and moment diagrams from strength of materials. We consider a section at mid span（or anywhere between the two concentrated loads)where the moment is maximum as shown in Figure 4-2c The
19、 maximum stress due to flexure(bending)in the beam may be determined by use of the flexure formula： fb=Mc/I=M/S whereFb=computed bending stress(maximum at top andor bottom) M = maximum applied momentC=distance from the neutral axis to the extreme outside of the Cross sectionI= moment of inertia of t
20、he cross section about the bending neutral axisS=section modulus(S=Ic)of the cross section about the bending neutral axis FIGURE 4-2 Load，shear，and moment diagrams for a simply supported beamThe fundamental assumptions and the derivation of the flexure formula may be found in most textbooks on stren
21、gth of materials The actual use of the flexure formula is straightforward，although the units must be carefully consideredAny conversion factors must be applied so that come patibility of units existsFor example，in the formula fb=MS，the usual units are fb：kipsin2 or ksi(stress) M：ftkips(moment) S：in.
22、3(section modulus)The units for the calculation of MS may be written Fb=M/S: ft-kips/in.3For compatibility of units，with stress fb resulting as ksi，a conversion factor of 1inft must be used For numerical problems worked out in this text，necessary conversion factors al shown without further explanati
23、on It should be noted that for empirical formulas, such as those discussed in Section 4-3，units are sometimes not compatible In these formulas numeric values with units precisely as defined in the ASDM must be used carefullyAssuming that the beam of Figure 4-2 is a typical wide flange(W shape)，Figur
24、e 4-3 shows the cross section and depicts the resulting bending stress diagramThe shape of the diagram is typical for bending stress at any point along the beamSeveral points should be noted1.For wide-flange beams，the moment of inertia about the x-x axis IX-IX is greater than the moment of inertia a
25、bout the y-y axisThe beam is oriented so that bending occurs about the x-x axisThis is true except in very rare situations 2.In this case，due to symmetry，the neutral axis is at the center of the cross section. The c distance is equal whether on the tension or compression side3.The maximum stress occ
26、urs at the top and the bottom of the cross sectionThe beam of Figure 4-2 bends so that compression occurs above the neutral axis and tension occurs below the neutral axis(commonly，this is called positive moment)4.Generally，only the maximum bending stress is of interestTherefore, unless otherwise stated，fb is assumed to be the maximum stressThe flexure formula may also be used to find the stress at any level in the cross section by substituting in place of C the appropriate distance to that level from the neutral axis