Behaviour of externally confined high-strength concrete columns under eccentric loading J. Li, M.N.S. Hadi * Faculty of Engineering, University of Wollongong, Wollongong NSW 2522, Australia Abstract Previous studies proved that the application of FRP can eliminate some unwanted properties of high-strength concrete, such as the brittle behaviour of high-strength concrete. However, research studies conducted so far on external confinement of concrete columns have mainly concentrated on concentric loading. This paper experimentally investigates the performance of externally confined high-strength concrete columns subjected to eccentric loading and evaluates the effectiveness of two confinement materials- carbon fibre and E-glass. Plain columns were wrapped with either carbon fibre or E-glass with different number of layers. Two reference columns were internally reinforced and tested. The enhancement of the strength of the plain column specimens under eccentric loading is not so pronounced as for the concrete specimens under concentric loading, especially for the high strength concrete specimens. However, when wrapped, the columns achieved a considerable gain in strength compared to plain concrete columns. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: External confinement; High-strength concrete; Fibre-reinforced polymers; Eccentricity; FRP; Carbon fibre; E-glass 1. Introduction With the development of technology, the use of high- strength concrete members has proved most popular in terms of economy; superior strength; stiffness and du- rability. With the increase of concrete strength, the ul- timate strength of the columns increases, but a relatively more brittle failure occurs. The lack of ductility of high- strength concrete results in sudden failure without warning, which is a serious drawback. Previous studies have shown that addition of compressive reinforcement and confinement will increase the ductility as well as the strength of materials effectively. Concrete, confined by transverse ties, develops higher strength and to a lesser degree ductility. Studies conducted by some investiga- tors on the improvement of the ductility of high-strength concrete members have proven that the use of the spiral confinement is more effective and beneficial in the im- provement of performance of concrete members [1,2]. In recent years, FRP wrapping in lieu of a steel jacket has become an increasingly popular method for external reinforcement in which the FRP offers improved cor- rosion and fatigue resistance compared to the steel re- inforcement. The high tensile strength and low weight make FRP ideal for use in the construction industry. Another attractive advantage of FRP over steel straps as external reinforcement is its easy handling, thus minimal time and labour are required to implement them [3]. However, research studies conducted so far on external confinement of concrete columns have mainly concen- trated on concentric loading. In practice, structural concrete columns axially compressed (i.e., concentri- cally) rarely occur. Even in a column nominally carrying only axial compression, bending action is almost always present due to unintentional load eccentricities and possible construction error. Also, there are many col- umns where an eccentric load is deliberately applied. Therefore, the studies for concrete columns under ec- centric loading are essential for practical applications. 2. External confinement with FRP The application of FRP in the construction industry can eliminate some unwanted properties of high-strength concrete, such as the brittle behaviour of high-strength * Corresponding author. Tel.: +61-2-4221-4762; fax: +61-2-4221- 3238. E-mail address: mhadi@uow.edu.au (M.N.S. Hadi). 0263-8223/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0263-8223(03)00109-0 Composite Structures 62 (2003) 145–153 www.elsevier.com/locate/compstruct