Development of Interaction Curve for Composite Column

Abstract

Composite Columns like Concrete Filled Tube, Concrete Encased Steel Section and Concrete Encased and Filled Steel Tube Section are most widely adopted, worldwide, in Tall Buildings and Heavy Structures. These Sections are primarily designed for axial load due to gravity and uniaxial/bi-axial moments. Realizing complexity in analytical solution for column design, mostly they are designed using force-moment (P-M) interaction curve given by various codes like Eurocode-4, AISC-2010, ACI-381-05, and AIJ-2001. Amongst all the design codes, Eurocode-4 and AISC-2010 provides a most simplified method for the development of P-M interaction curve that can be used for composite column design. In India, use of composite column is quite limited and when used design of complete column is carried out by other country’s code, as no dedicated Indian Standard code is available till date. Thus, design engineers practice in India do not have P-M interaction curve for steel section available in Indian market. Therefore, there is a need to develop P-M interaction curve for steel section pertaining to Indian market using simplified method as described in Eurocode-4. In the major project work, P-M interaction curves for different types of composite column sections like Rectangular & circular Concrete Filled Tube, Rectangular & Circular Full Concrete Encased Steel Section and Rectangular & Circular Concrete Encased and Filled Steel Tube are developed through computer programming in Visual Basics-2012. The Computer Program is developed using Eurocode EN 1994-1-1:2004, where in plastic stress axis moves across the cross-section of the composite column. P-M interaction curve is developed by determining plastic axial load resistance and plastic moment resistance with reference to plastic stress axis. Check for safety and stability of the composite column is an integral part of the program developed. Program is also capable to generate design report for composite column design and stability against local buckling. The project work also includes experimental investigation on behavior of medium Circular & Square Concrete Filled Tube subjected to Axial (P) and Eccentric (P-M) loading. Ten numbers of test specimens, five each of Circular and Square Concrete Filled Tube, are prepared for the Axial and Eccentric loading. Test specimen with Eccentricities of 10 mm, 20 mm, 30 mm, and 35 mm are fabricated for the testing. It has been found that all specimens shows failure mode as Buckling. Wherein outer fiber of composite column shows Tension, while other side of composite column shows compression and hence undergoes local buckling. Apart, comparison among experimental values of P-M curve and analytical values, former yields higher P-M values which are 34% and 15% higher as compared to analytical solution respectively. A slenderness effect on composite columns is also investigated. Two numbers of test specimens for medium and slender composite column are also prepared and tested under pure axial gravity loading, while slender column shows predominantly buckling behavior, medium column shows a bulging failure.