（選自書籍）土木工程外文翻譯---在梁和薄壁桿件中的剪應(yīng)力（原文）

1、 383 have just seen, a normal stress sx and a shearing stress txy are exerted on each of the two faces perpendicular to the x axis. But we know from Chap. 1 that, when shearing stresses txy are exerted on the vertica

2、l faces of an element, equal stresses must be exerted on the horizontal faces of the same element. We thus conclude that longi- tudinal shearing stresses must exist in any member subjected to a transverse loading. This

3、 can be verified by considering a cantilever beam made of separate planks clamped together at one end (Fig. 6.3a). When a transverse load P is applied to the free end of this composite beam, the planks are observed to

4、 slide with respect to each other (Fig. 6.3b). In contrast, if a couple M is applied to the free end of the same composite beam (Fig. 6.3c), the various planks will bend into concentric arcs of circle and will not sli

5、de with respect to each other, thus verifying the fact that shear does not occur in a beam subjected to pure bending (cf. Sec. 4.3).While sliding does not actually take place when a transverse load P is applied to a b

6、eam made of a homogeneous and cohesive material such as steel, the tendency to slide does exist, showing that stresses occur on horizontal longitudinal planes as well as on vertical transverse planes. In the case of t

7、imber beams, whose resistance to shear is weaker between fibers, failure due to shear will occur along a longitudinal plane rather than a transverse plane (Photo 6.1).In Sec. 6.2, a beam element of length Dx bounded by

8、 two trans- verse planes and a horizontal one will be considered and the shearing force DH exerted on its horizontal face will be determined, as well as the shear per unit length, q, also known as shear flow. A formula

9、 for the shearing stress in a beam with a vertical plane of symmetry will be derived in Sec. 6.3 and used in Sec. 6.4 to determine the shearing stresses in common types of beams. The distribution of stresses in a nar

10、row rectangular beam will be further discussed in Sec. 6.5.The derivation given in Sec. 6.2 will be extended in Sec. 6.6 to cover the case of a beam element bounded by two transverse planes and a curved surface. This w

11、ill allow us in Sec. 6.7 to determine the shearing stresses at any point of a symmetric thin-walled member, such as the flanges of wide-flange beams and box beams. The effect of plastic deformations on the magnitude a

12、nd distribution of shearing stresses will be discussed in Sec. 6.8.6.1 Introduction(a)(b)PM(c)Fig. 6.3 Beam made from planks.Photo 6.1 Longitudinal shear failure in timber beam.bee80288_ch06_380-435.indd Page 383 10/28

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