IJESC, November 2021 29060 http:// ijesc.org/ ISSN 2321 3361 © 2021 IJESC Behaviour of Concrete-Filled Steel Columns Subjected to Lateral Cyclic Loading Jayam Praveen Kuar 1 , D. Mohammed Rafi 2 , K. Mohammed Rasheed 3 Student 1 , HOD & Assistant Proffessor 2 , Assistant Proffessor 3 Department of Civil Engineering Chiranjeevi Reddy Institute of Technology, Anantapur, Andhra Pradesh, India – 515001 1,2,3 . 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. From the hysteresis behaviour, it is observed that SFRCFT columns produce plump hysteresis loop without significant drop in the lateral force upto a drift ratio of 8% whereas CFT columns exhibit reduced hysteresis loop and are capable of withstanding lateral load only upto 6% drift ratio. SFRCFT columns exhibited an increase in ductility factor and energy absorption capacity compared to CFT columns irrespective of D/t ratio. This is because addition of steel fibres to concrete delayed the local buckling and increased the number of cycles to failure thereby enhancing the ductility and energy-absorption capacity. Third phase consisted of lateral cyclic loading at constant drift ratios of 2%, 4%, and 6%, respectively which focused on the effects of amplitude and number of cycles on damage accumulation of in-filled columns. The energy absorption capacity of in-filled columns decays with drift ratio. The D/t ratio of the steel tube and drift ratio are found to govern the failure modes irrespective of the type of in-fill and loading pattern. A more complete understanding of the cumulative damage process is possible with the establishment of damage model for the columns evaluated in the experimental study. An expression suggested by Krawinker et al for the deformation of structural components has been used as reference for the development of cumulative damage model of in-filled columns. The simplified cumulative damage model proposed in this study in conjunction with the application of Miner’s linear damage accumulation rule provides a reasonable estimation of the damage index. To verify the applicability of the damage model, a comparative study was carried out using the experimental data available in the literature. The damage indices of the CFT columns were found to be estimated within a margin of 9%. It is concluded that the proposed equation is capable of predicting the damage index reasonably well and can be used as a reliable means of predicting the cumulative damage of new and existing columns. In order to assess the regular distribution adapted to different phases of damage upto failure, energy-based damage index was also calculated and compared with the proposed simplified cumulative damage model. Numerical investigation carried out for CFT and SFRCFT columns using the finite element software package ABAQUS version 6.5 (2005) was found to closely simulate the hysteretic behaviour of the columns obtained from experiments. The deflected shapes of the columns from the numerical results matched very closely with the experimental failure modes. The load- displacement behaviour predicted by the numerical model agrees well with the experimental behaviour. From the extensive investigations carried out, the proposed simplified damage index developed for in–filled columns subjected to lateral cyclic load combined with constant axial load is found to be capable of predicting the damage of in-filled columns reasonably well. Keywords: Concrete Filled Steel Tube (CFT), Steel Fiber Reinforced Concrete Filled Steel Tube (SFRCFT), Lateral Cyclic Loading, D/t Ratio, Hysteresis behaviour under variable amplitude cyclic loading, Drift Ratio, Research Article Volume 11 Issue No.11
Behaviour of Concrete-Filled Steel Columns Subjected to Lateral Cyclic Loading
May 30, 2023
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