Behaviour of concrete filled steel columns subjected to lateral cyclic loading

Abstract

The main objective of this study is to investigate the cumulative damage of circular in-filled columns subjected to quasistatic loading. The test parameters include the diameter-to-thickness ratio (D/t) of the steel tube and two types of in-fill namely Plain Cement Concrete (PCC) and Steel Fibre Reinforced Concrete (SFRC). Loading pattern consists of variable and constant amplitude lateral cyclic load combined with constant axial load. Theoretical, numerical and experimental investigations have been carried out. The entire study is divided into three distinct phases. In the first phase, experimental investigations were carried out to find the ultimate load carrying capacity of Concrete-filled steel tube (CFT) columns and Steel fibre reinforced concrete-filled steel tube (SFRCFT) columns under pure compression. 30% of this ultimate load was applied as constant axial load during lateral cyclic load testing of columns. The hollow steel tubes used were 1m long and were seam welded along the length. For PCC in-fill, M20 grade concrete was chosen and for SFRC in-fills, in the same grade of concrete, crimped shape steel fibres with aspect ratio of 70 were added in three different volume fractions viz. 0.75%, 1.00% and 1.25%. Load versus axial shortening and load versus strain behaviour for all the specimens were studied. It was seen that SFRCFT columns had higher initial stiffness, ductility factor and ultimate load carrying capacity compared to CFT columns. The ultimate loads determined experimentally were compared with the corresponding analytical values obtained using the expressions given in Eurocode 4 (2004), BS5400 (2005), AIJ (1997) and AISC LRFD (2010). Eurocode 4 is found to be most viable to predict the ultimate loads of in-filled columns. The second phase consisted of benchmark tests to establish the hysteresis behaviour under variable amplitude cyclic loading. Tests were carried out by applying three single lateral loading cycles corresponding to an increment of 0.25% peak drift ratio.