In situ conditions affecting the ductility capacity of lightly reinforced concrete wall structures in the Canterbury earthquake sequence

Gareth J Morris,Desmond K Bull,Brendon A Bradley

doi:10.5459/bnzsee.48.3.190-203

Gareth J Morris, Desmond K Bull + Show 1 more

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https://doi.org/10.5459/bnzsee.48.3.190-203

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Abstract

Following the 2010-2011 Canterbury (New Zealand) earthquake sequence, lightly reinforced wall structures in the Christchurch central business district were observed to form undesirable crack patterns in the plastic hinge region, while yield penetration either side of cracks and into development zones was less than predicted using empirical expressions. To some extent this structural behaviour was unexpected and has therefore demonstrated that there may be less confidence in the seismic performance of conventionally designed reinforced concrete (RC) structures than previously anticipated. This paper provides an observation-based comparison between the behaviour of RC structural components in laboratory testing and the unexpected structural behaviour of some case study buildings in Christchurch that formed concentrated inelastic deformations. The unexpected behaviour and poor overall seismic performance of ‘real’ buildings (compared to the behaviour of laboratory test specimens) was due to the localization of peak inelastic strains, which in some cases has arguably led to: (i) significantly less ductility capacity; (ii) less hysteretic energy dissipation; and (iii) the fracture of the longitudinal reinforcement. These observations have raised concerns about whether lightly reinforced wall structures can satisfy the performance objective of “Life Safety” at the Ultimate Limit State. The significance of these issues and potential consequences has prompted a review of potential problems with the testing conditions and procedures that are commonly used in seismic experimentations on RC structures. This paper attempts to revisit the principles of RC mechanics, in particular, the influence of loading history, concrete tensile strength, and the quantity of longitudinal reinforcement on the performance of real RC structures. Consideration of these issues in future research on the seismic performance of RC might improve the current confidence levels in newly designed conventional RC structures.

Highlights

The current understanding of the seismic performance of structural components is largely based on the outcomes and developments of previous research by methods of experimental testing and, in more recent times, numerical modelling techniques
Typical “experimental conditions” that may influence the structural behaviour include: (i) inelastic deformations measured during the application of a gradually increasing symmetric quasi-static loading protocol shown in Figure 4(a); (ii) test specimens containing relatively young concrete with compressive strengths ranging between [25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40] MPa, and; (iii) the use of moderate to high proportions of longitudinal reinforcement where there was no restriction of progressive cracking along the member
The damage to the critical wall in the Gallery Apartments building was described here as a particular example of structural behaviour that is concerning with respect to the “Life-Safety” performance objective at the Ultimate Limit State

Summary

Introduction

The current understanding of the seismic performance of structural components is largely based on the outcomes and developments of previous research by methods of experimental testing and, in more recent times, numerical modelling techniques. Typical “experimental conditions” that may influence the structural behaviour include: (i) inelastic deformations measured during the application of a gradually increasing symmetric quasi-static loading protocol shown in Figure 4(a); (ii) test specimens containing relatively young concrete with compressive strengths ranging between [25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40] MPa, and; (iii) the use of moderate to high proportions of longitudinal reinforcement where there was no restriction of progressive cracking along the member.

Results

Conclusion