Frame Design without Using Effective Column Length

by Francois Cheong-Siat-Moy, (A.M.ASCE), Asst. Prof. of Civ. Engrg.; Dept. of Civ. and Mineral Engrg., Univ. of Minnesota, Minneapolis, Minn.,

Serial Information: Journal of the Structural Division, 1978, Vol. 104, Issue 1, Pg. 23-33

Document Type: Journal Paper


The pitfalls underlying the use of the effective column length concept in frame design are illustrated. It is shown that such a concept can be unsatisfactory for both braced and unbraced fromes whether they are loaded predominantly by gravity loads or by combined gravity and lateral loads. The basis for the development of a rational design method based upon the story stiffness concept is then presented. This design procedure can eliminate the use of the K-factor, if all secondary effects are included in the calculation of the real forces acting on the members. In the light of the unconservative nature of present design specifications, some fundamental formulation is proposed for their possible modifications. In particular, it is recommended that calculation of story stiffness be a clearly stated requirement in design codes.

Subject Headings: Gravity loads | Lateral loads | Frames | Effective length | Columns | Stiffening | Conceptual design | Bracing

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