架構の復元力特性に及ぼす柱軸力変化の影響について

Abstract

An analytical study is made of the effects of axial force variation on the inelastic horizontalrestoring-force characteristics of a rectangular frame. The example considered is a portal framewhich is composed of two identical columns and a rigid beam, and is subjected to a constantvertical load and to a varying horizontal force. The relation between the horizontal force andthe displacement is sought when the latter increases monotonously. Large elastic-plastic de-formation causes the interaction of plastic collapse and the instability which is due to change ingeometry. The beam shear increases the compressive axial force in one column and decreasesin the other, so that the axial force variation gives rise to the addition of folds in the horizontalforce-displacement diagram. In the case of a small vertical load, an initially compressive axial forceeven becomes tensile in the course of horizontal force application. If the axial force remainscompressive in both columns, the axial force variation little influences the frame behavior afterthe frame reduces to a mechanism with a sufficient number of plastic hinges. If one of thecolumn axial forces changes the sign, however, the axial force variation reduces the maximumhorizontal force the frame can carry. It is found, among other things, that the importance ofaxsal force variation depends on the ratio of the column depth to the span. This effect can beneglected when the ratio is sufficiently smaller than unity.