Preparation of unixaial chart for rectangular concrete-filled steel columns based on rigid plastic principles

Abstract

Composite columns are in an increased usage for construction of high-rise and medium-rise buildings, bridges and other structures. However, their design procedure as proposed by the relevant Ethiopian Building Code Standard, which is also a derivative of the corresponding European Standard Eurocode 4 calls for extensive numerical effort for drawing the moment -axial-force interaction charts. Furthermore, the results obtained following those procedures are based on curve-fitting techniques making use of widely sparse control points and, consequently, they produce approximate results. This paper explores the shortcomings' of the relevant local building code standard for the design process and presents improved design chart procedures for concrete-filled rectangular steel tube columns. The proposed procedure simplifies the design process and, at the same time, considerably increases the accuracy of results.

A unified approach has been presented for the procedure of establishing interaction design charts for concrete-filled steel tubes (CFTs) under uniaxial bending and valuable charts have been prepared for most frequently encountered shapes in practice - rectangular and square shapes. The proposed procedure may also be developed and adapted to facilitate the preparation of similar design charts for other shapes and material types.

Finally, numerical examples will be presented to demonstrate implementation of the proposed procedure and to provide insight into comparative quality of the charts with those generated according to the relevant national code standard.