Title: Experimental Validation of Minimum Vertical Reinforcement Requirements for Ductile Concrete Walls

Author(s): Yiqiu Lu, Ronald J. Gultom, Quincy Q. Ma, and Richard S. Henry

Publication: Structural Journal

Volume: 115

Issue: 4

Appears on pages(s): 1115-1130

Keywords: concrete design standards; minimum vertical reinforcement; plastic hinge region; reinforced concrete; reinforcement buckling; reinforcement fracture; seismic design; wall

DOI: 10.14359/51702048

Date: 7/1/2018

Abstract:
Recent experimental and numerical research has confirmed that reinforced concrete (RC) walls with distributed minimum vertical reinforcement in accordance with existing design standard provisions are unlikely to form a large number of distributed cracks and are only suitable for walls designed for low ductility demands. As a result, the minimum vertical reinforcement limits for ductile walls in the New Zealand Concrete Structures Standard (NZS 3101:2006) were recently amended to require additional vertical reinforcement to ensure well-distributed secondary cracking. A series of four large-scale RC walls were tested to investigate the seismic performance of RC walls with additional reinforcement at the end regions of the wall. The test walls were designed to represent flexural-dominant RC walls in multi-story buildings with varied reinforcement ratio, bar diameter, and number of reinforcement bars in the end zone of the wall. The experimental results confirmed that the increased vertical reinforcement in the ends of the test walls resulted in a significant increase in the number and distribution of cracks in the plastic hinge region when compared to previously tested walls with minimum distributed reinforcement. The increased secondary cracks greatly increased the spread of plasticity and helped to delay reinforcement buckling. Furthermore, the additional vertical reinforcement limits proposed for the end region of ductile walls were found to be appropriate at the threshold at which well-distributed secondary cracks form. It is recommended that similar vertical reinforcement limits be adopted in ACI 318 and other concrete design standards.