Minimum vertical reinforcement in RC walls

Yiqiu Lu,Richard S Henry

doi:10.5459/bnzsee.50.4.471-481

Abstract

Recent earthquakes and research have shown that the minimum vertical reinforcement requirements in current concrete standards are insufficient to ensure well distributed cracking occurs in ductile reinforced concrete (RC) walls. To address the deficiencies of existing requirements, new theory was proposed to calculate the minimum distributed and end zone vertical reinforcement required for RC walls to meet current performance expectations. The distributed vertical reinforcement requirement was intended to prevent non-ductile behaviour for walls with low ductility demands, and was derived based on the requirement that nominal flexural strength must exceed the cracking moment capacity. The vertical reinforcement required in the ends of the wall was intended to ensure that well distributed secondary cracks form in the plastic hinge region of walls with high ductility demands, and was derived to ensure that the concrete tensile strength could be overcome by the tensile demands imposed when the vertical reinforcement in the ends of the wall yields. The proposed requirements considered the key parameters that influence the behaviour of walls with minimum vertical reinforcement. In addition, the proposed formulas were compared with current minimum vertical reinforcement limits from different concrete design standards by considering the margin of safety between cracking and nominal flexural strength and the secondary cracking behaviour. The deficiencies of the existing requirements were demonstrated and the proposed requirements were proved to be superior for walls with both low and high ductility demands.

Highlights

Minimum vertical reinforcement requirements for reinforced concrete (RC) walls are imposed by most concrete design standards worldwide, in part to mitigate shrinkage and temperature effects, and to prevent non-ductile failure modes [1]
Results indicated that the minimum vertical reinforcement requirements in current concrete standards are insufficient to ensure that well distributed cracking occurs in the plastic hinge region of ductile RC walls
Two new formulas were proposed to calculate the minimum distributed and end zone vertical reinforcement required for reinforced concrete (RC) walls

Summary

INTRODUCTION

Minimum vertical reinforcement requirements for reinforced concrete (RC) walls are imposed by most concrete design standards worldwide, in part to mitigate shrinkage and temperature effects, and to prevent non-ductile failure modes [1]. Following the Canterbury earthquakes, a series of experimental tests and numerical models were conducted to investigate the behaviour of RC walls with minimum vertical reinforcement in accordance with current concrete design standards both in New Zealand and worldwide [4,5,6,7]. Results indicated that the minimum vertical reinforcement requirements in current concrete standards are insufficient to ensure that well distributed cracking occurs in the plastic hinge region of ductile RC walls. The proposed formulas were verified against existing experimental data and numerical modelling results and compared with existing requirements for minimum vertical reinforcement in different concrete design standards. Following the observations in the 2010/2011 Canterbury earthquakes, new amendments were proposed to the

Design Standard

Summary

Drift to East

Findings

CONCLUSIONS