Effect of spiral reinforcement on axial compressive behavior of tubular steel short columns filled with normal and lightweight concretes / Mohammadreza Hamidian

Mohammadreza , Hamidian (2018) Effect of spiral reinforcement on axial compressive behavior of tubular steel short columns filled with normal and lightweight concretes / Mohammadreza Hamidian. PhD thesis, University of Malaya.

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Abstract

Plain or reinforced concrete can be used for the concrete core in concrete filled steel tube (CFT) columns. Although CFT columns with plain concrete exhibit superior performance under static and dynamic loads due to composite action, several recent studies have shown that CFT columns using reinforced concrete containing a steel cage of longitudinal steel bars with hoop shaped shear reinforcement instead of plain concrete provide higher strength and ductility. This is because the double confinement effect of the steel tube and steel reinforcement on the concrete core results in higher strength and ductility in reinforced CFT columns (RCFT). However, ductility and the load drop percentage of RCFT columns are still considered as areas of concern. In addition, it is known that reinforced concrete columns with lateral spiral reinforcement show better ductile behaviour compared to lateral hoop reinforcement, and there have been many investigations that show the advantages of columns with spiral reinforcement. Currently, there is no investigation or literature available on CFT columns with a spirally reinforced concrete core (SRCFT) and their effect on the ductility and load drop percentage. This research focuses on the effect of spiral reinforcement on the axial compressive behaviour of CFT columns with two groups of concrete – normal and lightweight – with spiral reinforcement. The results are compared with CFT columns with plain normal and lightweight concretes. The effects of different grades of normal concrete and lightweight concrete were studied on the behaviour of CFT columns with a plain and spirally reinforced concrete core. Two types of lightweight concrete, namely, oil palm shell (OPS) lightweight concrete and LECA lightweight concrete were used in this investigation. OPS concrete is known to be a sustainable concrete and LECA is a well-established lightweight concrete in the construction industry. Also, the effects of spiral reinforcement characteristics, such as the pitch spacing and percentage of longitudinal steel bars, were investigated. The test results indicated that a SRCFT column has better post-yield behaviour than a CFT column for both normal and lightweight concretes. A reduction in the pitch spacing further improves the post-yield behaviour of the SRCFTs. For the lightweight concretes, spiral reinforcement improved both the strength and the ductility of SRCFT columns with OPS compared to CFT columns with OPS concrete. In addition, the spiral reinforcement significantly decreased the load drop percentage of the SRCFT columns with LECA concrete compared to the CFT columns. Also, the use of EC4 equations gives a good prediction of the test results compared to the ACI.

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