Cyclic Testing of Reinforced Concrete Walls with Distributed Minimum Vertical Reinforcement

Abstract

During the 2010/2011 Canterbury earthquakes in New Zealand, several reinforced concrete (RC) walls in multistory buildings formed only a limited number of cracks at the wall base with a fracture of vertical reinforcement observed. Recent research suggests that walls designed with minimum vertical reinforcement in accordance with current New Zealand standards may not exhibit large ductility during earthquakes. To investigate this theory further, a total of six flexure dominant RC walls with two layers of distributed vertical reinforcement in accordance with minimum requirements were tested. The test walls were typical of multistory RC walls in regions with moderate seismicity in New Zealand and were used to examine the effect of shear span ratio, axial load, and reinforcement ties in the wall end region. The experimental results confirmed that the current minimum vertical reinforcement limits are insufficient to ensure that a large number of secondary flexural cracks will occur in the plastic hinge region. The lateral-load response of the walls was controlled by one or two main large flexural cracks at the wall base. This behavior greatly reduced the spread of plasticity and resulted in several potential issues, such as limited drift capacity and premature reinforcement buckling or fracture. Recommendations are provided related to minimum vertical reinforcement requirements, plastic hinge length assumptions, ultimate drift capacity, and antibuckling reinforcement.