Strain compatibility method for the design of short rectangular concrete filled tube columns under eccentric axial loads

In many countries, high-rise building construction has been rapidly increasing where steel concrete composite construction is highly preferred. Concrete-filled tube columns have superior constructability and structural performance attributes. The strength and ductility of concrete filled tube can be enhanced by the use of high-strength materials, rectangular column filled tube sections with high strength materials employed by few concrete stress-strain models.

Earlier structural provisions of the rectangular concrete filled tube have limitations in predicting the P-M interaction strength of concrete filled tube columns under various material and geometric combinations. Researchers from Seoul National University in Republic of Korea developed a concrete stress-strain model combined with the strain compatibility method. The previously tested concrete filled tube was used to check whether stress strain model could be used when subjected to eccentric axial loads. The team of authors finally found that concrete stress-strain model can easily predict the P-M interaction strength of rectangular CFT columns under general design conditions.

A concrete stress block is used with a strain compatibility method to predict flexural and axial strengths of concrete-filled tube columns. The accurate stress-strain relations of the confined concrete and steel should be used to get an exact solution while using the strain compatibility method. Hence, no slip is assumed to occur between the materials. The ratio of specified minimum yield stress of the specified concrete compression strength can be high and (b/t) ratio can be low when using the proposed stress-strain model.

The limits of material properties and the (b/t) ratio are expected to be relaxed while the authors proposed model is applied. As Euro code 4’s upper bounds on material properties and/or (b/t) ratios are limited, these upper bounds could be extended accordingly. The reliability of the strain compatibility method is improved, using an empirical stress-strain model which can capture the stress-strain characteristics of the confined concrete of rectangular concrete-filled tube columns.

When using various material properties and plate width-to-thickness ratios, the current structural provisions could not provide satisfactory predictions of the P-M interaction strength of rectangular concrete filled tube columns. With an elasto-plastic model of steel, strain compatibility method was applied with the developed concrete model. The authors found that the test data were well correlated. The concrete crushing strain was found to be a function of the steel-to-concrete strength ratio and width to-thickness ratio of steel tube.

The proposed model is also in part based on the analysis of an extensive existing test database. Professor Cheol-Ho Lee and colleagues here analyzed an updated database of previous and recent test results of rectangular concrete-filled tube columns. The proposed model of the authors predicts the P-M interaction strength of rectangular concrete-filled tube columns under general design conditions for compact sections more accurately and more consistently. 

Strain-compatibility-method-for-the-design-of-short-rectangular-concrete-fil2

Journal Reference

Cheol-Ho Lee, Thomas H.-K. Kang, Sung-Yong Kim, Kiyong Kang, Strain compatibility method for the design of short rectangular concrete filled tube columns under eccentric axial loads, Construction and Building Materials.

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