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Unexpected failure modes were observed in RC walls in the 2010 Chile and 2011 New Zealand earthquakes. A peculiar failure mode, not previously reported in the structural engineering literature, was the brittle collapse of one of the structural walls of the 28-story Grand Chancellor Hotel in Christchurch, New Zealand. As one of the first steps toward the understanding of this failure mode, three rectangular RC walls were tested under bidirectional quasi-static cyclic loading. The only parameter varied among the three specimens was the structural detailing associated to various level of ductility design of the wall cross section. It was found that whereas the wall with nominal ductility section detailing (μ=1.25) experienced an out-of-plane shear-axial failure, those with higher ductility section detailing (1.25<μ<3 and μ>3) performed reasonably well. However, a relatively abrupt axial crushing failure was observed in the ductile walls at higher drift levels that needs further investigation. The bidirectional loading, rarely adopted in experimental tests or in numerical simulation due to its inherent complexity, was found to be one of the key factors in the development of out-of-plane shear-axial failure. Moreover, it was observed that walls with 0.3Agfc′ axial load, which is the maximum limit of the current New Zealand standard for concrete structures, and designed according to nominal ductile detailing might be prone to out-of-plane shear-axial failure. [ABSTRACT FROM AUTHOR]

On 22 February 2011, one of the main structural walls of one of the tallest buildings in Christchurch, New Zealand (Grand Chancellor Hotel), had an extremely brittle and unusual failure that significantly damaged the building, severely compromising its structural stability. To this date, this peculiar failure mode has not yet been fully investigated and understood. Moreover, currently, it is not possible to identify and assess walls that are prone to this failure mode. Following recent findings based on experimental investigations, this failure mode was identified as out‐of‐plane shear‐axial failure. A Finite Element (FE) model was developed in DIANA to capture this failure mode, and through a numerical parametric study, the key parameters that contribute to the development of this failure mode in rectangular reinforced concrete (RC) walls were identified. Solid elements were used for the concrete material and embedded truss elements for the steel reinforcement. Bar buckling was not included in this investigation due to the limitation of DIANA in implementing the bar buckling and Menegotto‐Pinto models together, among which the latter was found to be more influential on the behaviour of RC walls investigated in this study. Based on the numerical and experimental studies conducted, an analytical method is proposed to: (1) identify rectangular walls prone to out‐of‐plane shear‐axial failure as a first‐level check for both design and assessment purposes; and (2) determine the out‐of‐plane drift capacity of rectangular walls prone to out‐of‐plane shear‐axial failure. Design recommendations are provided for rectangular walls prone to out‐of‐plane shear‐axial failure. [ABSTRACT FROM AUTHOR]

Observations of out-of-plane (OOP) instability in the 2010 Chile earthquake and in the 2011 Christchurch earthquake resulted in concerns about the current design provisions of structural walls. This mode of failure was previously observed in the experimental response of some wall specimens subjected to in-plane loading. Therefore, the postulations proposed for prediction of the limit states corresponding to OOP instability of rectangular walls are generally based on stability analysis under in-plane loading only. These approaches address stability of a cracked wall section when subjected to compression, thereby considering the level of residual strain developed in the reinforcement as the parameter that prevents timely crack closure of the wall section and induces stability failure. The New Zealand code requirements addressing the OOP instability of structural walls are based on the assumptions used in the literature and the analytical methods proposed for mathematical determination of the critical strain values. In this study, a parametric study is conducted using a numerical model capable of simulating OOP instability of rectangular walls to evaluate sensitivity of the OOP response of rectangular walls to variation of different parameters identified to be governing this failure mechanism. The effects of wall slenderness (unsupported height-to-thickness) ratio, longitudinal reinforcement ratio of the boundary regions and length on the OOP response of walls are evaluated. A clear trend was observed regarding the influence of these parameters on the initiation of OOP displacement, based on which simple equations are proposed for prediction of OOP instability in rectangular walls. [ABSTRACT FROM AUTHOR]

The 2017 New Zealand Society for Earthquake Engineering (NZSEE) guidelines for seismic assessment of buildings recommends using Simple Lateral Mechanism Analysis (SLaMA) before implementing numerical analyses. The method and the NZSEE guidelines have been enhanced from the 2006 version, resulting into an efficient procedure, balancing simplicity and accuracy. This paper presents a numerical study, initiated as part of the development of the SLaMA-2017 method, to investigate the accuracy of the analytical approach via comparison with numerical 2D-pushover on 40 RC frames. SLaMA is effective in capturing the plastic mechanism of the frames, including global or soft-story mechanisms. Further-yet-simple refinements of the procedure are suggested. [ABSTRACT FROM AUTHOR]

The new guidelines for the seismic assessment of existing buildings recently introduced by the New Zealand Society for Earthquake Engineering (NZSEE) recommend the Simple Lateral Mechanism Analysis (SLaMA) as an "analytical" first phase of any other numerically-based analysis. This article illustrates the development of the SLaMA method and its validation with reference to an existing RC building severely damaged during the Christchurch earthquake (2011). The capacity of the lateral resisting systems is assessed from component/subassembly to system level. The comparison of the results with observed damage and with the outcomes of refined numerical analyses confirms the effectiveness of this method. [ABSTRACT FROM AUTHOR]

The research presented here seeks to address the key parameters influential on out-of-plane (OOP) instability of rectangular walls, which was observed in the 2010 Chile and the 2011 New Zealand earthquakes in some well-confined modern walls. For this purpose, a finite element model, previously verified for its capability to reliably simulate different failure modes of this type of structural walls, was adopted. The parametric matrix included a series of specimens designed to be tested by the authors and other specimens already tested by other researchers. The effect of slenderness (unsupported height-to-thickness) ratio, reinforcement ratio, length and axial load on the OOP response of these specimens is scrutinized using the predicted response of the boundary region longitudinal reinforcement at the elevation corresponding to the maximum OOP displacement in each case. For a given slenderness and longitudinal reinforcement ratio, development of a critical average tensile strain over a certain height can lead to formation of OOP instability in walls. Therefore, the effect of these parameters on the strain history, strain gradient along the wall height, as well as the stress–strain response of the longitudinal bars throughout the cyclic loading are evaluated and the variation of the OOP response attributable to the effect of each parameter is discussed. This parametric study indicated that the initiation of OOP displacement in doubly reinforced walls after unloading from a peak displacement and during reloading in the opposite direction is in line with the significant reduction of compressive stiffness (yielding in compression) in the boundary region longitudinal bars along a specific height (at least 60% of the wall height). Based on the findings of this study, an experimental campaign was designed and four of the parametric models were experimentally tested under in-plane cyclic loading. In addition to the parameters noted above, the effects of shear strength, boundary conditions and eccentricity of material properties across the wall thickness on the OOP response of the benchmark parametric model are also briefly discussed. The experimental observations as well as the numerical versus experimental comparisons are presented in a companion paper. [ABSTRACT FROM AUTHOR]

A wide range of reinforced concrete (RC) wall performance was observed following the 2010/2011 Canterbury earthquakes, with most walls performing as expected, but some exhibiting undesirable and unexpected damage and failure characteristics. A comprehensive research programme, funded by the Building Performance Branch of the New Zealand Ministry of Business, Innovation and Employment, and involving both numerical and experimental studies, was developed to investigate the unexpected damage observed in the earthquakes and provide recommendations for the design and assessment procedures for RC walls. In particular, the studies focused on the performance of lightly reinforced walls; precast walls and connections; ductile walls; walls subjected to bi-directional loading; and walls prone to out-of-plane instability. This paper summarises each research programme and provides practical recommendations for the design and assessment of RC walls based on key findings, including recommended changes to NZS 3101 and the NZ Seismic Assessment Guidelines. [ABSTRACT FROM AUTHOR]

The concept of post-tensioned rocking structures was successfully applied to timber in 2005, in prestressed laminated timber (Pres-Lam) technology. When applied to moment-resisting frames, the technology relies on unbonded post-tensioning tendons passing through hollow beams and the supporting column to provide beam–column connections with moment capacity. Supplemental dissipation devices can be included in the design, resulting in a recentring/dissipative system. Since seismic movements are accommodated through a control rocking mechanism between the beam and the column, the detailing of the beam–column joint can significantly affect the seismic performance of the structure. Among the main concerns, the shear transfer system should be able to transfer shear forces without interfering with the rocking motion, and ignoring the face friction and joint deformation should not compromise the drift activation of the gap opening. Attention should also be paid to minimizing post-tensioning losses while providing access for potential retensioning. As a result of the continuous and rapid development of Pres-Lam frame systems, a wide range of alternative solutions for connection detailing has been tested in the laboratory or implemented in existing buildings. This paper presents an overview of the beam–column detailing implemented in the five Pres-Lam frame buildings currently operative in New Zealand. [ABSTRACT FROM AUTHOR]

The simple lateral mechanism analysis (SLaMA) is an analytical method to assess the force–displacement capacity curve of Reinforced Concrete (RC) structures composed of frames, cantilever walls or dual wall/frame systems. The current version of the method was proposed in the 2017 New Zealand guidelines for the seismic assessment (NZSEE in New Zealand Society for Earthquake Engineering, the seismic assessment of existing buildings—technical guidelines for engineering assessments, Wellington, 2017). Regarding frame structures, the possible influence of infill walls is currently considered locally with checks on the RC members. However, it is universally known that infills have a major effect on the global capacity curve of the frame. In this paper, a comprehensive SLaMA method for infilled frames is proposed, which allows considering the influence of the infills on the global force–displacement curve without any numerical algorithm. The extended SLaMA method is herein formalised and it is validated in a companion paper (part 2) through an extensive parametric analysis. The extended SLaMA is based on the possibility to separately calculate the base shear contributions of the frame and the infills, in turn based on global equilibrium considerations. Such considerations also allow defining a novel procedure to post-process the results of pushover or time-history analyses where infills are modelled as diagonal struts, or to interpret experimental tests. This allows, within a single numerical analysis, to decouple the frame and infills contributions to the base-shear capacity. The decoupling procedure is herein demonstrated for an ideal two-storey, one-bay masonry-infilled frame with different infills configurations. [ABSTRACT FROM AUTHOR]

The transport infrastructure was majorly affected by the 14th November 2016 Kaikōura Earthquake. Severe vertical and horizontal peak ground accelerations generated high inertial forces, land-slides, and liquefaction. Most of the bridges in the Hurunui, Malborough and Kaikōura districts were critical nodes to the railway and road networks. In total, 904 road bridges across those districts were affected. Two reached the life safety limit state, suffering severe damage, however, most of the affected bridges experienced only minor to moderate damage. This paper describes the structural performance of the most severely damaged bridges based on observations made from site inspections. In addition to this, several performance issues have arisen from this event and are posed in this paper, hopefully to be addressed in the near future. [ABSTRACT FROM AUTHOR]

Base isolation is arguably the most reliable method for providing enhanced protection of buildings against earthquake-induced actions, by virtue of a physical separation between the structure and the ground through elements/devices with controlled force capacity, significant lateral deformation capacity and (often) enhanced energy dissipation. Such a design solution has shown its effectiveness in protecting both structural and non-structural components, hence preserving their functionality even in the aftermath of a major seismic event. Despite lead rubber bearings being invented in New Zealand almost forty years ago, the Christchurch Women's hospital was the only isolated building in Christchurch when the Canterbury earthquake sequence struck in 2010/11. Furthermore, a reference code for designing base-isolated buildings in New Zealand is still missing. The absence of a design standard or at least of a consensus on design guidelines is a potential source for a lack of uniformity in terms of performance criteria and compliance design approaches. It may also limit more widespread use of the technology in New Zealand. The present paper provides an overview of the major international codes (American, Japanese and European) for the design of base-isolated buildings. The design performance requirements, the analysis procedures, the design review process and approval/quality control of devices outlined in each code are discussed and their respective pros and cons are compared through a design application on a benchmark building in New Zealand. The results gathered from this comparison are intended to set the basis for the development of guidelines specific for the New Zealand environment. [ABSTRACT FROM AUTHOR]

The magnitude 6.3 earthquake that struck Christchurch on 22 February 2011 caused widespread damage throughout Christchurch's central business district (CBD), where a large proportion of the building stock consists of reinforced concrete (RC) buildings. Damage to the façades of these buildings was a clear contributor to overall building damage. This paper presents the damage assessment of the façade systems of these RC buildings. A survey of 173 RC buildings in the Christchurch CBD is conducted here, focusing on the damage to the façade systems of the buildings. The survey covers only buildings greater than three storeys in height, excluding the majority of unreinforced masonry façades, the damage to which has been well documented. The façade type and modularity is classified for each system, as well as the connection type where possible. The level of damage to each façade is determined in terms of the following performance levels: Operational, Immediate Occupancy, Life Safety and High Hazard. Further investigation is also made into three precast concrete panel systems. These case studies examine the damage, detailing and construction practice of each particular system. [ABSTRACT FROM AUTHOR]

• The increase in yield strength for Grade 300E is not dependent on the pre-strain. • At room temperatures, changes in mechanical properties are completed within 90 days. • Increase in UTS and reduction in ductility are proportional to the prestrain. • The increase in yield strength due to long term strain ageing is about 55 MPa. • Microalloyed high strength steel Grade 500E is not affected by strain ageing. Modern seismic codes are based on capacity design and hierarchy of strength principles that allow the formation of plastic hinges in sacrificial elements within a structure. An accurate estimation of the mechanical properties of the steel reinforcement is required to achieve a ductile failure mechanism. After being subjected to plastic deformation, many types of low-carbon steel experience a time- and temperature-dependent phenomenon known as strain-ageing. This phenomenon causes changes in the mechanical properties such as increase in yield and reduction in ductility. Therefore, in the aftermath of an earthquake event, the hierarchy of strength between beams and columns in a subassembly and/or between flexure and shear within the same structural element of a damaged structural system could potentially be compromised. In this paper, the extent of strain-ageing in New Zealand Grade 300E and Grade 500E reinforcement is investigated through experimental testing in which reinforcing bar samples were pre-strained up to selected strain limits and then subjected to natural (at 15 °C) and accelerated ageing (at 100 °C), at different time intervals, up to one year. The changes in mechanical properties were monitored and quantified. These changes must be accounted for during post-earthquake assessments and repairing design and are recommended to be incorporated in future code provisions. [ABSTRACT FROM AUTHOR]