Rizwan, Muhammad (2022) Nonlinear Analysis of Rectangular Double-Skin Concrete-Filled Steel Tubular Columns. Research Master thesis, Victoria University.

Abstract

Rectangular double-skin concrete-filled steel tubular (RDCFST) composite columns are increasingly utilized in the construction of buildings, bridges, transmission towers and offshore structures due to their high structural behavioral properties, including stiffness, ductility, energy absorption, and strength. The hollow internal steel tube used in a RDCFST column not only makes the column economical but also reduces its weight which is highly favorable for seismic design. However, the inner and outer rectangular tubes with a large depth to thickness ratio may undergo local buckling. This kind of composite columns is significantly different from conventional concrete-filled steel tubular (CFST) columns. Only very limited studies have been undertaken on the behavior of RDCFST columns. Therefore, this research develops an efficient and accurate numerical model for predicting the behavior of thin-walled RDCFST short columns under axial loads. The effects of localized buckling and high strength materials are incorporated in the numerical formulations for short RDCFST columns. The measurements from experiments documented elsewhere are used to verify the developed numerical model. Parametric investigations are carried out to quantify the effects of important parameters on the fundamental behavior of short RDCFST columns. Based on the parametric studies, a design formula is proposed for the strength calculations of short RDCFST columns including the post-local buckling strength of steel sections. Thin-walled RDCFST slender columns composed of non-compact or slender steel sections loaded eccentrically may undergo local and global interaction buckling. There are no computational modeling schemes that have been developed for the determination of the performance of slender RDCFST columns, accounting for interaction buckling. In this research, a computational modeling program of thin-walled RDCFST slender columns loaded eccentrically is developed, incorporating the interaction of local and global buckling failure modes. The modeling method also accounts for the effects of initial geometric imperfections, seconder order, and material nonlinearities. To compute the interaction buckling behavior of slender RDCFST columns, an incremental-iterative computational algorithm is designed, which implements Müller’s method to solve the nonlinear equilibrium functions of slender RDCFST columns. The developed computer program is verified by experimentally obtained data documented elsewhere and utilized to analyze nonlinear RDCFST slender columns with important parameters to ascertain their structural behavior. It has been confirmed that the computer program predicts well the interaction responses of the local and global buckling of RDCFST slender columns. This research makes significant contributions to the knowledge base by means of developing robust and efficient computational algorithms that can predict the responses of RDCFST short and slender columns and producing benchmark computational results on the performance of RDCFST columns incorporating interaction buckling, steel yielding and concrete crushing. The established mathematical and design models are efficient modeling and design tools, which can be used by structural engineers and researchers to accurately simulate the structural responses of RDCFST columns.

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