Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Civil Engineering

Major Professor

Mark D. Denavit

Committee Members

T. Truster, N. Wierschem


Steel-concrete composite columns are efficient structural members that possess significant strength, stiffness, and ductility. Accurate methods of assessing the strength of these members are necessary to realize their benefits. Several design codes rely on the plastic stress distribution method (PSD) for computing the cross-sectional strength of composite columns subjected to axial compression and flexural bending. However, there has been limited validation of this method over the wide range of material and geometric properties and loading conditions to which it is permitted to be applied. The first part of this thesis presents a study of the behavior of short composite columns and methods of evaluating their strength. The usage of the PSD method and the strain compatibility method is validated against detailed fiber cross section analyses and published experimental data. The results indicate that the PSD method can yield significantly unconservative strength predictions, especially for encased composite members with high steel yield strengths and high steel ratios. A simple modification factor which can be applied to the results of the PSD method to achieve greater accuracy was derived. This modification factor is suitable for use in design practice and enables better predictions of the strength of short composite columns. The second part focuses on the biaxial strength and design of these members including length effects. Current provisions regarding the strength of composite columns under combined axial compression and biaxial bending are overly simplistic and conservative. This thesis presents a study of the biaxial behavior of composite columns and methods of evaluating their strength. Analyses of composite cross sections confirm the conservative nature of current design provisions and form the basis for modified strength equations that better capture the shape of three-dimensional interaction surface, and confirm that the proposed design equations are suitable for use within the direct analysis method for evaluating members with length effects. The proposed design equations are further validated against published experimental results. This work advances understanding of the behavior of composite columns subjected to axial compression and biaxial bending and present improved yet practical methods of evaluating strength under these conditions that will enable more efficient designs.

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