Buildings that rely on reinforced concrete walls and cores as their primary lateral loading system are prevalent in much of Australia’s building stock. Capacity design principles do not have to be adhered to in most low-to-moderate seismic regions, such as Australia. Consequentially, the level of detailing typically provided in accordance with the current and past concrete material standards, AS 3600 and AS 1480, is regarded as non-ductile from the seismic design point of view. These non-ductile reinforced concrete elements have been known to perform poorly when subjected to large lateral loads, as observed in the Christchurch earthquake in 2011. This paper presents an investigation into the seismic performance of C-shaped reinforced concrete walls acting as a core of a Mid-Rise building using current and past building codes in Australia. The displacement capacity of the building was calculated using a displacement-based assessment. A shear capacity model, which is a function of the curvature ductility of the walls, was also considered in the assessment. The results indicate that the older building is likely to fail in shear in the event of a 1000-year return period earthquake event. The building designed to current standards is vulnerable to a non-ductile failure from premature fracturing of the longitudinal reinforcing steel bars.