剖分T型钢压杆的屈曲性能和应用

Buckling Behavior of Hot-rolled Cut-T Section and Application

剖分T型钢由热轧H型钢一分为二得来,属单轴对称截面。在承受轴线压力时,它的屈曲性能有两个特点。其一是绕对称轴屈曲时必然伴随有扭转,从而降低其承载力。另一方面,当压力移至截面剪心时,屈曲不再出现扭转,承载力达到弯曲屈曲荷载。杆件承载力的这种提高,只有在绕另一主轴屈曲有多余承载力,足以承担压力移至剪心产生的偏心力矩时才能加以利用。本文分析表明,截面高宽比不小于1.25的剖分T型钢满足或部分满足这一条件。有时,荷载作用在形心与剪心距离的一半处较为有利。第二个特点表现在压杆腹板局部屈曲承载力和宽厚比限值。本文揭示出腹板的临界应力总是高于杆件弯扭屈曲的临界应力,因此,只要杆件通过弯扭屈曲验算,就不必顾虑腹板屈曲。然而,在工程实践中有些杆件扭转受到约束,从而不去验算其弯扭屈曲。此时,腹板有可能作为一纵边嵌固、另一纵边自由的板件屈曲。建议的腹板宽厚比限值就是为保证在这种情况下的稳定性而给出的。

Cut-T section, obtained by splitting hot-rolled H-section into two halves, is monosymmetric and has two features in its buckling behavior when subjected to concentric compressive force. The first one is the fact that twisting always accompanies flexion upon the onset of buckling with respect to its axis of symmetry and thus reduces the bearing capacity of the strut. On the other hand, by shifting the force to the shear centre of the section, no twisting occurs any more and the buckling load can reach the flexural buckling load. This increase in bearing capacity can only be procured if there is surplus capacity with respect to the other principal axis so that bending moment caused by the eccentric loading can be tolerated. Analysis performed in this article shows that those cut-T struts with section depth not less than 1.25 times section width satisfy this condition in full or in part. Sometimes it is better to locate the force half-way between the centroid and the shear centre. The second feature is relevant to the local buckling capacity of the strut web and its limiting width-thickness ratio. It is revealed in this article that the critical stress of the web is always larger than that of the flexural-torsional buckling of the strut. Therefore, as long as the strut is checked on flexural-torsional buckling, one has nothing to worry about the web buckling. But, in the engineering practice, some struts may be restrained against twisting and are dispensed with such checking, so that the web may buckle locally as a plate with one longitudinal edge fixed and the other edge free. Suggestion on the limiting value of web width-thickness ratio is formulated to guarantee its stability in this situation.