英汉双语材料力学4.pptVIP

三、对称性与反对称性的应用： 对称结构在对称载荷作用下，Q图反对称，M图对称；对称结构在反对称载荷作用下，Q图对称，M图反对称。 Example 7 Plot internal-force diagrams of the beams shown in the following figure. P PL P PL L L L L L L 0.5P 0.5P 0.5P 0.5P P 0 Q x Q1 x Q2 x – 0.5P 0.5P 0.5P – + – P [例7] 作下列图示梁的内力图。 P PL P PL L L L L L L 0.5P 0.5P 0.5P 0.5P P 0 Q x Q1 x Q2 x – 0.5P 0.5P 0.5P – + – P P PL P PL L L L L L L 0.5P 0.5P 0.5P 0.5P P 0 M x M1 x M2 x 0.5PL PL 0.5PL – + + 0.5PL + P PL P PL L L L L L L 0.5P 0.5P 0.5P 0.5P P 0 M x M1 x M2 x 0.5PL PL 0.5PL – + + 0.5PL + Example 8 Correct the mistakes in the following internal-force diagrams. a 2a a q qa2 A B Q x x M – – + + qa/4 qa/4 3qa/4 7qa/4 qa2/4 49qa2/32 3qa2/2 5qa2/4 RA RB [例8] 改内力图之错。 a 2a a q qa2 A B Q x x M – – + + qa/4 qa/4 3qa/4 7qa/4 qa2/4 49qa2/32 3qa2/2 5qa2/4 Example 9 Knowing Q-diagram, determine external loads and M-diagram (Therefore no concentrated force couples acted on the beam). M(kN·m) Q(kN) x 1m 1m 2m 2 3 1 5kN 1kN q=2kN/m + – + x + 1 1 1.25 – [例9] 已知Q图，求外载及M图（梁上无集中力偶）。 Q(kN) x 1m 1m 2m 2 3 1 5kN 1kN q=2kN/m + – + M(kN·m) x + 1 1 1.25 – §4–6 THE INTERNAL-FORCE DIAGRAMS OF THE PLANAR RIGID FRAMES AND CURVED RODS 1、Planar rigid frame 1). Planar rigid frame ：Structure made from rods of different direction that are mutually connected in rigidity at their ends in the same plane. Characteristics：There are internal forces Q, M and N in each rod. 2). Conventions to plot diagram of internal forces： Bending-moment diagram：Plot it at the side where fibers are elongated and not mark the sign of positive or negative. Shearing-force and axial-force diagrams：May be plotted at any side of the frame（In common the diagram with positive value is plotted outside the frame ），but must mark the signs of positive and negative. §4–6 平面刚架和曲杆的内力图 一、平面刚架 1. 平面刚架：同一平面内，不同取向的杆件，通过杆端相 互刚性连接而组成的结构。 特点：刚架各杆的内力有：Q、M、N。 2. 内力图规定： 弯矩图：画在各杆的受拉一侧，不注明正、负号。