Buckling of Pretwisted Steel Columns

A Master of Science thesis in Civil Engineering by Mai Megahed entitled, "Buckling of Pretwisted Steel Columns," submitted in January 2015. Thesis advisor is Dr. Farid H. Abed. Available in both soft and hard copy.

Abstract

Buckling is a mode of failure that is mainly observed in compression members due to structural instability. Inducing a natural pretwist along the length of a column section makes the column have a different resistance at every point along its centroidal axis. A pretwisted column in 3D-space has its strong flexural plane weakened and its weak flexural plane strengthened, leading to a net favorable effect on the buckling strength of the pretwisted column. The proposed research focuses on studying the effect of pretwisting on the buckling capacity of steel columns. Experimental and numerical investigations of pretwisted steel columns with different slenderness ratios were carried out. A linear perturbation analysis was conducted for several universal column cross-sections for various lengths, a set of pretwisting angles ranging 0°-180° and different boundary conditions. A number of pretwisted columns were then tested to examine the elastic and inelastic behavior of one of the universal steel columns. The experimental results were utilized to verify and develop a set of non-linear finite element models including the material and geometric nonlinearities. The validated FE models were then extended to conduct a parametric study to include several more lengths and angles of twist. It was found that pretwisting is most effective with elastic buckling since it is mainly controlled by the moment of inertia of the column in opposition to inelastic buckling, which is additionally affected by material yielding. It was also noticed that fixed-ended conditions ensured better buckling capacity improvement as compared to pinned-ended columns in both elastic and inelastic buckling of pretwisted columns.