Analysis of Non-Symmetric Cross-Sections Relative to the Provisions of AISC 360-10

Non-symmetric sections are used for a variety of applications that range from the main member of a large portal frame, to tee-sections in trusses, to angles for supporting new penetrations in steel structures. These non-symmetric sections complicate the structural analysis process with complex displacements, rotations, and stability limits compared to doubly symmetric cross-sections due to non-concentric shear centers and centroids. The ability, or most likely inability, of various structural analysis software programs to capture the response of singly and point symmetric cross-sections in the framework of the current analysis requirements of the AISC specification including the Direct Analysis Method specified in Chapter-C and Design by Advanced Analysis specified in Appendix-1 is investigated. In particular, the effects of second-order twisting and torsional effects are analyzed and the error in the analysis is quantified. Initial modeling consists of single members with single and point symmetric cross-sections that have published results to compare against for load and deflections, including benchmark problems provided in the AISC Manual. Beam-element finite element models are created in various structural analysis programs to determine how the effects of twisting and warping are considered compared to both published results and to advanced shell finite element models. Additionally, two assemblies of mono-symmetric I-beams are modeled to address the ability to transfer forces between members in different orientations. Future work in this project will address more complex structural systems that consist of non-symmetric cross-sections including angles, channels, and tees to further assess the provisions of the AISC specification.

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