Minimum Vertical Reinforcement in Ductile Reinforced Concrete Walls

Abstract eng:
Research into the seismic design of lightly reinforced concrete (RC) walls was initiated following the Canterbury earthquakes in New Zealand when several walls were observed to have formed only a limited number of cracks in the plastic hinge region. Initial investigation highlighted that vertical reinforcement content and distribution were critical parameters that influenced the ductility of lightly reinforced concrete walls. A total of ten half scale walls were tested to investigate the seismic behaviour of multi-story RC walls with minimum vertical reinforcement. Six walls were designed with minimum required distributed vertical reinforcement in accordance with existing New Zealand Concrete Structures Standard (NZS 3101:2006). An additional four test walls were designed with additional vertical reinforcement in the ends of the walls, as is required by some design standards and proposed amendments for ductile RC walls in NZS 3101:2006 (A3 draft). The experimental results of three of these test walls are presented and discussed. The test results indicated that typical minimum distributed vertical reinforcement requirements, such as those in NZS 3101:2006 (A2), were insufficient to ensure that a large number of secondary cracks formed, and are only suitable for walls designed for low ductility demands. Additionally, the concentration of inelastic reinforcement strains at wide cracks resulted in premature reinforcement buckling even when closely spaced transverse reinforcement was used. The RC walls tested with a small amount of additional vertical reinforcement in the ends of the wall displayed significantly greater crack distribution in the plastic hinge region and more evenly distributed reinforcement strains. The test results and analysis have been used to provide recommendations for suitable minimum vertical reinforcement provisions for walls with a range of ductility demands.

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