Seismic behaviour of reinforced concrete walls with minimum vertical reinforcement

Abstract

Recent research suggested that the current minimum vertical reinforcement limits in NZS 3101:2006 may be insufficient to ensure well distributed cracks in plastic hinge regions. A series of numerical analyses were used to investigate the behaviour of an example RC wall designed according to the minimum requirements in several different concrete design standards. The analysis results confirmed the observed failure mode of an RC wall damaged during the Canterbury earthquakes that had only half the current required minimum vertical reinforcement. Furthermore, RC walls built in accordance with current minimum vertical reinforcement requirements in both ACI 318-11 and NZS 3101: 2006 were shown to still be susceptible to limited flexural cracking and premature bar fracture. In addition to the modelling, six large-scale walls have been tested to examine the effect of axial load, shear span ratio, and reinforcement ties in the end region on RC walls with distributed minimum vertical reinforcement in accordance with NZS 3101:2006. The observed extent of crack distribution, hysteretic behaviour, failure mode, and drift capacity of four of the tested walls are discussed. The experimental results confirmed that current minimum vertical reinforcing limits in NZS 3101:2006 are insufficient to form a large number of secondary cracks. The failure mode for all walls was controlled by bar buckling and subsequent fracture. The lateral drift capacity of all four tested walls was 2.5% and both the shear span ratio and the anti-buckling ties had no significant influence on the drift capacity.