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一、概述实践经验和理论分析均表明,任何截面形状的梁,只有当垂直于梁轴的外力通过横截面上的一个特定点时,梁才只发生弯曲[图1(a)、(b)],否则在弯曲的同时还将产生扭转变形(图1(c)]。上述特定点称为弯曲中心(图1中的A点)。可以证明,当梁受扭时横截面在自身平面内绕以转动之点,即所谓扭转中心,其位置总是与弯曲中心重合的。箱梁的横截面如果具有两个对称轴,则弯曲中心及扭转中心A即在两对称轴的交点处,此时弯心及扭心的位置又与截面的形心重合。如果箱梁的顶板外伸于腹板之外,或顶板与底板厚度不同,则弯心及扭心就不在截面高度中央,亦不与形心重合。
I. OVERVIEW Practical experience and theoretical analysis show that beams of any cross-section shape only bend when an external force perpendicular to the beam axis passes through a particular point on the cross-section [Figure 1 (a), (b) ], Otherwise the bending will also produce torsional deformation (Figure 1 (c)]. The above-mentioned specific point is called the bending center (point A in Figure 1) .Be able to prove that when the beam is twisted cross-section in its own plane Around the point of rotation, the so-called torsion center, the position always coincides with the center of curvature. If the cross-section of the box girder has two axes of symmetry, the center of curvature and the center of torsion A are at the intersection of the two axes of symmetry, When the bending and torsion of the position coincides with the shape of the cross section of the center.If the roof of the box girder extends outside the web, or the thickness of the roof and floor are different, the bending and twisting of the heart is not in the middle of the section height, nor Coincide with the shape and heart.