2345 Modification of Column Effective Length Factor

The determination of column strength is of primary importance in the design of framed structures. The strength and stability of a frame and its columns are interrelated. The effective-length concept for evaluating column strength in rigid frames used to be the primary method to evaluate the stability of columns of frames. According to this concept, the strength of a column is evaluated from that of an equivalent pin-ended member of length KL, subject to axial load only, by means of a so-called K factor found as

V Pcr where Pe = p2 EI/L2is the Euler buckling load of the pinned-end column, in which L is the length of the column and I is the moment of inertia of the column section about the axis of bending, and Pcr is the buckling load of the end-restrained column. For a laterally braced semirigid column, the corresponding effective-length factor based on Newmark's approximation [23] can be expressed in terms of column end-fixity factors r1 and r2 defined in Equation 23.7 as

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