Effective length factor of columns in flexibly jointed and braced frames

In order to rationally evaluate the stability of columns in flexibly jointed and braced frames, the governing equations for determining the effective length factor (K-factor) of columns are derived considering the effects of the non-linear moment-rotation characteristics of beam-to-column connections. In this study, to derive the equations, the alignment chart approach is used and a recent study on the stability of flexibly jointed frames and the concept of the Shanley's inelastic column buckling theory are applied. With a proper evaluation of the tangent connection stiffness for semi-rigid beam-to-column connections at buckling state and with the introduction of the modified relative stiffness factors, the alignment chart in the present AISC-LRFD specification can be used to find the corresponding column K-factor in flexibly jointed frames. This is described in this paper. Furthermore, using two flexibly jointed and braced portal and one-bay two-story frame examples, the effects of the non-linear moment-rotation characteristics of connections on the K-factor are numerically studied and the K-factors obtained by two simplified methods are compared with the present method. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.