Behavior and design of multi-sided composite sections

Composite construction is advantageous due to the combination of steel and concrete materials in structural members. Composite column's cross-section types such as hexagonal, octagonal, and decagonal and high diameter-to-thickness (D/t) ratios are highly desirable in transmission towers, yet not covered in the applicable codes. Therefore, the objective of this study is to investigate the behavior of composite columns with various characteristics including cross-section types, and height and propose a design procedure based on Force - Moment (P-M) Interaction diagrams and related equations. Three-dimensional non-linear finite element models were developed using a nonlinear finite element software to simulate and verify the behavior of the composite towers against prior experimental work. Concrete Damage Plasticity and Steel Bilinear Elasto-Plastic Model were calibrated and used in capturing the realistic nonlinear behavior of the materials and their interaction. Based on the computational models, a concrete reduction factor, needed for the development of design equations, was derived. Conclusively, typical normalized P-M Interaction diagrams were constructed for various polygonal shapes with high D/t ratios beyond code limitations. The corresponding derived design equations play a significant role in the applicability of the composite columns in transmission towers.