Assessment of ultimate drift capacity of RC shear walls by key design parameters

Chanipa Netrattana,Masanobu Sakashita,Rafik Taleb,Susumu Kono,David Mukai,Hidekazu Watanabe,Masanori Tani

doi:10.5459/bnzsee.50.4.482-493

Abstract

The latest version of the Standard for Structural Calculation of Reinforced Concrete Structures, published by the Architectural Institute of Japan in 2010 [1], allows the design of shear walls with rectangular cross sections in addition to shear walls with boundary columns at the end regions (referred to here as “barbell shape”). In recent earthquakes, several reinforced concrete (RC) shear walls were damaged by flexural failures through concrete compression crushing accompanied with buckling of longitudinal reinforcement in the boundary areas. Damage levels have clearly been shown to be related to drift in structures; this is why drift limits are in place for structural design criteria. A crucial step in designing a structure to accommodate these drift limits is to model the ultimate drift capacity. Thus, in order to reduce damage from this failure mode, the ultimate drift capacity of RC shear walls needs to be estimated accurately. In this paper, a parametric study of the seismic behaviour of RC shear walls was conducted using a fibre-based model to investigate the influence of basic design parameters including concrete strength, volumetric ratio of transverse reinforcement in the confined area, axial load ratio and boundary column dimensions. This study focused on ultimate drift capacity for both shear walls with rectangular sections and shear walls with boundary columns. The fibre-based model was calibrated with experimental results of twenty eight tests on shear walls with confinement in the boundary regions. It was found that ultimate drift capacity is most sensitive to axial load ratio; increase of axial load deteriorated ultimate drift capacity dramatically. Two other secondary factors were: increased concrete strength slightly reduced ultimate drift capacity while increased shear reinforcement ratio and boundary column width improved ultimate drift capacity.

Highlights

Slender reinforced concrete walls are an important part of a building’s lateral load resisting systems
This paper provides a simulation of the ultimate drift capacity caused by crushing of concrete and fracture of longitudinal reinforcement assuming other failure modes are not taking place
If the neutral axis is located inside the boundary column, the neutral axis is independent of the column depth, D

Summary

INTRODUCTION

Slender reinforced concrete walls are an important part of a building’s lateral load resisting systems. Their objective was to study effects of boundary columns and confinement on seismic performance of structural walls Their experimental results confirmed that walls with higher transverse reinforcement ratios had larger ultimate drift in both rectangular and barbell shape cross sections. This paper employed the work based on parametric studies by Kono et al [18] who compared eight equations for the equivalent plastic hinge length as shown in Table 1 and eight m’s (1%-8%) Based on their fourteen specimens, three combinations of lp and m that give the best estimate of ultimate drift were found. The ultimate drift of forty-three tested specimens were compared to the ultimate drifts calculated by the proposed model using these three sets of lp and m in order to decide which combination of plastic hinge length and steel strain at the maximum tensile stress give the best estimation of ultimate drift.

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VARIATION OF ULTIMATE DRIFTS

Findings

CONCLUSIONS