Story stability of braced, partially braced, and unbraced frames: Classical approach

The stability equations for plane frames with prismatic columns according to the buckling mode (as sidesway inhibited, partially inhibited, and uninhibited frames) are derived in a classical manner. In addition, an approach that evaluates the effective length K-factor, the critical axial load, and the sway-magnification factor delta(s) for an entire story in plane framed structures is presented. The three-way frame classification and the proposed corresponding stability equations overcome the paradoxes of the current two-way classification of ''braced'' and ''unbraced'' frames. Moreover, the proposed equations are applicable to the stability analyses of multistory multibay plane frames with rigid, semirigid, and simple connections. It is shown that the stability equation of frames with sidesway partially inhibited has been the ''missing link'' to a full understanding of the elastic stability behavior of frames, and is the key to solving the paradoxes of current methods. Four detailed examples are presented that demonstrate the effectiveness and accuracy of the proposed method and the complete classical stability equations for plane framed structures.