6 INTRODUCTION TO COLUMN BUCKLING - （6介绍柱屈曲-）.pdf

INTRODUCTION TO COLUMN BUCKLING 6 INTRODUCTION TO COLUMN BUCKLING 1.0 INTRODUCTION AND BASIC CONCEPTS There are many types of compression members, the column being the best known. Top chords of trusses, bracing members and compression flanges of built up beams and rolled beams are all examples of compression elements. Columns are usually thought of as straight vertical members whose lengths are considerably greater than their cross- sectional dimensions. An initially straight strut or column, compressed by gradually increasing equal and opposite axial forces at the ends is considered first. Columns and struts are termed “long” or “short” depending on their proneness to buckling. If the strut is “short”, the applied forces will cause a compressive strain, which results in the shortening of the strut in the direction of the applied forces. Under incremental loading, this shortening continues until the column squashes. However, if the strut is “long”, similar axial shortening is observed only at the initial stages of incremental loading. Thereafter, as the applied forces are increased in magnitude, the strut becomes “unstable” and develops a deformation in a direction normal to the loading axis. (See Fig.1). The strut is in a “buckled” state. Buckling behaviour is thus characterized by deformations developed in a direction (or plane) normal to that of the loading that produces it. When the applied loading is increased, the buckling deformation also increases. Buckling occurs mainly in members subjected to compressive forces. If the member has high bending stiffness, its buckling resistance is high. Also, when the member leng