The Effects of Accurate Boundary Condition Modeling on Column Stability

Idealization of real-world boundary conditions as either “free,” “pinned,” or “fixed” is common in engineering practice. Standard generalization of end restraints can lead to conservative designs. However, certain instances may merit the additional calculation effort for a more realistic boundary condition for a higher degree of accuracy. Some examples include: the optimization of hundreds of similar connections, verification of as-built details, or a detailed understanding of the moment transfer at the base of a structure. This paper explores the effect on column stability of an example connection through rigorous finite element analysis and nonlinear, load-deflection models. Abaqus is used to assess the moment-rotation capacity of a suite of connections representing commonly encountered boundary conditions. Parameters such as variable axial loads, contact or bearing within the connection, and component yielding are incorporated into the FEA model. The results of the FEA are used in OpenSees to determine the column capacity through a large-displacement, inelastic analysis. Finally, a comparison of the column capacity is made between the in-situ and ideal connection models to provide engineering insight into the importance of accurately modeling connections.

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