Stability of slender columns - A study of initial curvature and braces influence on a column’s load bearing capacity

Abstract: Failures due to instability phenomena will happen suddenly and can cause the whole structure to collapse. It’s therefore in the engineer’s best interest to have a good knowledge about these phenomena. One example of instability phenomena is column buckling, which is the main focus of this thesis. The main cases that are being evaluated have a single brace in the middle of a timber column with hinged ends, where a part of the report revolves around a comparison of calculation methods for column buckling in Eurocode and the U.S. Building code. The second part revolves around the influence of the initial curvature shape and magnitude on a column. During this evaluation second order is taken into account in the numerical analysis. Finally the brace stiffness and reaction force on a column is evaluated, to gain a better understanding of its overall influence on a column’s load bearing capacity. In the study it was shown that Eurocode and the U.S. Building code weren’t comparable due to formation of respective building code. A comparison between the two building codes was however done, to get a better understanding of the difference between the two. Results show that a larger initial curvature leads to a larger reduction to the overall load bearing capacity for a column. The assumed shape of the initial curvature has a large impact on the load bearing capacity. There exist a large discrepancy between the simplified shape of the initial curvature and the least beneficial, which depends on the size and shape of the initial curvature. Findings show that an increase of a column’s brace stiffness contributes to the load bearing capacity even though the stiffness might be small. The European standard however demands a minimum stiffness for a brace to be considered acceptable. The study also shows that the brace force is dependent on the initial curvature of the column and the bracing stiffness. Yura’s & Helwig’s brace force expression is studied and compared with the result of a numerical analysis.