Overstrength and ductility of limited ductile RC walls: from the design engineers perspective

Force-based seismic analysis of a structure requires knowledge of its overstrength and displacement ductility. Local earthquake standards provide typical values for both of these parameters for common types of construction in that region. This paper presents the findings of a recent study to determine the overstrength and displacement ductility of limited ductile reinforced concrete (RC) walls in Australia using the static non-linear pushover analysis method introduced in the latest version of the Australian earthquake code. This activity was performed from the ‘perspective of a design engineer’, i.e. by using simple analysis methods presented in well-known texts without having to rely on the use of specialised finite element packages, while following and complying with the Australian earthquake loading and material standards. For this purpose a mean stress-strain curve of Australian and New Zealand reinforcement was determined by analysing test data from an independent industry materials testing laboratory. A proposed model for the actual stress-strain curve of 500 MPa L, N and E grade reinforcement is presented in this paper. The long term mean in-situ strength of concrete is also discussed and recommendations put forward.