Review of Confinement Requirements for the Seismic Design of Rectangular RC Walls in Australia

The majority of low, mid and high-rise buildings in Australia are RC wall buildings, which rely on walls or building cores as the primary lateral load resisting system. The seismic design approach in Australia, like many regions of lower seismicity, typically consists of undertaking a force-based equivalent static or pseudo dynamic analysis method, where inelastic behaviour of the building is indirectly accounted for using force-reduction factors. The force-reduction factors are used to reduce the seismic design actions the structure is designed for under the premise that the earthquake forces acting on the structure are predominantly resisted by inelastic responding elements in the structural system (i.e. strength is being traded for ductility). The Australian standard for concrete structures, AS 3600 provides prescriptive detailing requirements, which if adhered to, should allow a structure to have the required amount of inelastic capacity assumed in the design. This paper will initially provide a summary of the boundary element detailing requirements (i.e. confinement steel) in the new 2018 edition of AS 3600. This is followed by a parametric study that was undertaken to assess the effectiveness of confinement reinforcement in RC walls typical of Australian construction practices. The results of the parametric study are then discussed with reference to a series of AS 3600 compliant boundary element reference examples that were developed. The paper concludes with a general discussion on the role of boundary elements and the effectiveness of confinement steel in the context of limited ductile and moderately ductile wall design.