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A case study was conducted to investigate the applicability of the equivalent frame modelling for the nonlinear time-history analysis of unreinforced masonry buildings with flexible diaphragms. The dynamic responses calculated from the equivalent frame models were compared against shake table test results of a full-scale two-storey stone masonry building. The investigated modelling approach reflected the simplifications commonly assumed for the global analysis of buildings; namely, considering the diaphragms to behave elastically and neglecting the stiffness and strength contributions of the out-of-plane responding walls. The sensitivity of the analysis to different idealisations of the equivalent frame, as well as to the diaphragm stiffness values, were also investigated. Discussions are provided on the accuracies and limitations of the investigated modelling approach, which may serve as a useful guidance for practical application.
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The majority of current procedures used to deduce liquefaction potential of soils rely on empirical methods. These methods have been proven to work in the past, but these methods are known to overestimate the liquefaction potential in certain regions of Christchurch due to a whole range of factors, and the theoretical basis behind these methods cannot be explained scientifically. Critical state soil mechanics theory was chosen to provide an explanation for the soil’s behaviour during the undrained shearing. Soils from two sites in Christchurch were characterised at regular intervals for the critical layers and tested for the critical state lines (CSL). Various models and relationships were then used to predict the CSL and compared with the actual CSL. However none of the methods used managed to predict the CSL accurately, and a separate Christchurch exclusive relationship was proposed. The resultant state parameter values could be obtained from shear-wave velocity plots and were then developed into cyclic resistance ratios (CRR). These were subsequently compared with cyclic stress ratios (CSR) from recent Christchurch earthquakes to obtain the factor of safety. This CSL-based approach was compared with other empirical methods and was shown to yield a favourable relationship with visual observations at the sites’ locations following the earthquake.
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The goal of this study is to develop a racking model of plasterboard-sheathed timber walls as part of the efforts towards performance-based seismic engineering of low-rise light timber-framed (LTF) residential buildings in New Zealand.
Residential buildings in New Zealand are primarily stand-alone low-rise LTF buildings, and their bracing elements are commonly plasterboard-sheathed LTF walls. It is an essential part of performance-based seismic designs of LTF buildings to be able to simulate the racking performance of plasterboard walls. In this study, racking test results of 12 plasterboard walls were collected and studied to gain insight into the seismic performance of plasterboard-sheathed LTF walls. The racking performance of these walls was examined in terms of stiffness/strength degradation, displacement capacity, superposition applicability and failure mechanisms. Subsequently, a mathematical analysis model for simulating racking performance of LTF plasterboard walls is developed and presented. The developed racking model is a closed-form wall model and could be easily used for conducting three-dimensional non-linear push-over studies of seismic performance of LTF buildings.
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Axial elongation has been observed during tests of reinforced concrete (RC) members subjected to either monotonic or cyclic loading. The implications of elongating plastic hinges in beams on the seismic performance of RC frame buildings, and in particular the floor systems, has been extensively studied. However, few investigations have addressed axial elongation of RC walls. To expand on the existing knowledge of axial elongation in RC members, the measured axial elongations of 13 previously tested RC walls were investigated. These tests included a wide range of vertical reinforcement ratios, vertical reinforcement layouts, and axial loads. The procedures to estimate wall elongation that were proposed in the Public Comment Draft Amendment No. 3 of the New Zealand Concrete Structures Standard (NZS 3101:2006) were also evaluated and compared against the measured elongations from the tests. The experimental results showed that elongation magnitudes in the analysed walls were between 0.4-0.8% of the wall length at 1.5% lateral drift, and that the elongation equations proposed for NZS 3101:2006 provided an acceptable estimation of the expected elongation in RC walls. Additionally, numerical models were developed using distributed-plasticity fibre-based elements in OpenSees and membrane elements in VecTor2 to verify the ability of these commonly used modelling techniques to capture wall elongation. The numerical simulations were able to represent the global and local behaviour with good accuracy and both models were able to capture the peak elongations. However, the more sophisticated concrete material models in OpenSees allowed the fibre element models to more accurately represent the experimental wall elongations, especially when considering residual elongations.
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A new structural system consisting of precast concrete frames and steel shear walls (SSW's) is introduced and studied numerically in this paper. Two different models, first using ''exact'' FEM and second using approximate equivalent strip model (ESM), are utilized for analysis of such a system with nonlinear static (pushover) procedure. In the FEM model use is made of shell elements while the ESM benefits from simple links that replace the wall panels in the model and are oriented such that they work in tension. Because of good agreement observed between the results of the models in smaller structures, for taller buildings only the ESM approach is followed where computationally applying the FEM approach is impractical. The lateral behaviour of the systems under consideration is investigated with regard to parameters such as number of stories and beam-column connection type. As a result, the ductility, overstrength and response modification factors are calculated for this new structural system as quantities required for their practical design.
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This study aims to provide a comparison and identify the key distinctions between the New Zealand Standard – Earthquake Actions (NZS 1170.5: 2004) seismic design spectra and the hysteresis-damped seismic demand spectra specified by either the New Zealand Society for Earthquake Engineering (NZSEE) “Assessment and Improvement of the Structural Performance of Buildings in Earthquakes” (AISPBE) Guidelines, or the “Displacement-Based Seismic Design of Structures” (DBSDS) textbook by Priestley et al. (2007). The damping provided by the draft document, “The Seismic Assessment of Existing Buildings” (TSAEB), was also briefly discussed. The seismic design spectrum was calculated for various levels of ductility using all three methods and compared against each other. This was performed for structural elastic periods from 0.1 to 4.5 seconds. For a given set of requirements based on the NZS 1170.5 parameters, a representative acceleration-displacement hysteresis loop has been generated. The equivalent viscous damping was then calculated based on the area under this hysteresis using the recommendations of either the AISPBE or through the damping equations based on the DBSDS. The final damped spectra were then compared with each other and against the NZS 1170.5 design spectrum. Results indicate good correlation between the NZS 1170.5 design spectra and the damped design spectra at low levels of ductility but show significant disparities at higher levels of ductility.
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This paper reports on a theoretical student design project to seismically upgrade buildings in a historic precinct of Wellington. The unique feature of the structural upgrading, heritage retention and adaptation, and new building interventions in the precinct was that all retrofitting designs were applied to pairs or clusters of buildings in order to develop new strategies for their seismic retrofit.
The tying of buildings together as part of retrofitting is rarely encountered in earthquake engineering practice but this can be an important retrofitting approach as shown by the following design outcomes and case-study example. The main finding from the architectural design and seismic retrofit of 70 clusters of two to three buildings was the diversity of the retrofitting strategies that were applied. Two primary categories of retrofitting were identified; tying existing buildings together, and tying existing buildings to new buildings, with each category incorporating several variants. This paper highlights the advantages of retrofitting clusters of buildings to prevent seismic pounding, and for other economic and architectural reasons.
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The New Zealand Strong Motion Database provides a wealth of new strong motion data for engineering applications. In order to utilise these data in ground motion prediction, characterisation of key site parameters at each of the ~497 past and present GeoNet strong motion stations represented in the database is required. Here, we present the compilation of a complete set of site metadata for the New Zealand database, including four key parameters: i) NZS1170.5 site subsoil classification, ii) the time-averaged shear-wave velocity to a depth of 30 m (Vs30), iii) fundamental site period (Tsite) and iv) depth to a shear-wave velocity of 1000 m/s (Z1.0, a proxy for depth to bedrock). In addition, we have assigned a quality estimate (Quality 1 – 3) to each numerical parameter to provide a qualitative estimate of the uncertainty. New high-quality Tsite, Vs30 and Z1.0 estimates have been obtained from a variety of recent studies, and reconciled with available geological information.
This database will be used in efforts to guide development and testing of new and existing ground motion prediction models in New Zealand, allowing re-examination of the most important site parameters that control site response in a New Zealand setting. Preliminary analyses, using the newly compiled data, suggest that high quality site parameters can reduce uncertainty in ground motion prediction. Furthermore, the database can be used to identify suitable rock reference sites for seismological research, and as a guide to more detailed site-specific references in the literature. The database provides an additional resource for informing engineering design, however it is not suitable as a replacement for site-specific assessment.
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An important component of seismic hazard assessment is the prediction of the potential ground motion generated by a given earthquake source. In New Zealand seismic hazard studies, it is commonplace for analysts to only adopt one or two models for predicting the ground motion, which does not capture the epistemic uncertainty associated with the prediction. This study analyses a suite of New Zealand and international models against the New Zealand Strong Motion Database, both for New Zealand crustal earthquakes and earthquakes in the Hikurangi subduction zone. It is found that, in general, the foreign models perform similarly or better with respect to recorded New Zealand data than the models specifically derived for New Zealand application. Justification is given for using global models in future seismic hazard analysis in New Zealand. Although this article does not provide definitive model weights for future hazard analysis, some recommendations and guidance are provided.
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This article summarises work that has been undertaken to compile the New Zealand Strong Motion Database, which is intended to be a significant resource for both researchers and practitioners. The database contains 276 New Zealand earthquakes that were recorded by strong motion instruments from GeoNet and earlier network operators. The events have moment magnitudes ranging from 3.5 to 7.8. A total of 134 of these events (49%) have been classified as occurring in the overlying crust, with 33 events (12%) located on the Fiordland subduction interface and 7 on the Hikurangi subduction interface (3%). 8 events (3%) are deemed to have occurred within the subducting Australian Plate at the Fiordland subduction zone, and 94 events (34%) within the subducting Pacific Plate on the Hikurangi subduction zone. There are a total of 4,148 uniformly-processed recordings associated with these earthquakes, from which acceleration, velocity and displacement time-series, Fourier amplitude spectra of acceleration, and acceleration response spectra have been computed. 598 recordings from the New Zealand database are identified as being suitable for future use in time-domain analyses of structural response. All data are publicly available at http://info.geonet.org.nz/x/TQAdAQ.
