Bulletin of the New Zealand Society for Earthquake Engineering

The Shaking Layers project: Near-real time shaking intensity maps for New Zealand earthquakes: Project overview

2024-04-18T08:41:08+12:00

Following a damaging earthquake, emergency managers and decision-makers require reliable shaking information to be able to make decisions and prioritise interventions. Until now, in New Zealand, these decisions needed to be made with incomplete geographical information, relying solely on observed data points from either strong-motion stations or felt reports. The New Zealand Shaking Layers project has been designed to fill that gap. Using the ShakeMap software, configured to satisfy New Zealand’s characteristics, a tool is now available to end-users that provides shaking intensity maps for Peak Ground Acceleration, Peak Ground Velocity, Modified Mercalli Intensity and spectral acceleration at different periods. The Shaking Layers tool covers the entire country, helping decision-makers make better-informed decisions. The maps are generated for magnitude 3.5 or above earthquakes in New Zealand and use strong-motion data from the GeoNet network, as well as intensity derived from felt report data, and fault rupture information when available. To ensure scientific robustness, the tool has been developed with the support of a Science Advisory Panel and has been designed with similar configuration as the updated 2022 National Seismic Hazard Model. Moreover, to ensure the tool is fit-for-purpose, it has been co-designed with an End-User Advisory Panel comprising emergency managers, response engineers, city councils, risk analysts, duty officers and Civil Defence, amongst others. This paper provides the project overview, as well as the tool’s main components and functionalities.

Benefits of site-specific hazard analysis for seismic design in New Zealand: Revisited

2025-03-18T16:36:21+13:00

This paper revisits the sentiments expressed in a 2015 paper published by the author regarding site-specific seismic hazard analysis in New Zealand (NZ) [1]. While many of the general principles expressed remain the same, the completion of the 2022 NZ National Seismic Hazard Model (NSHM), and accompanying Draft Technical Specification TS1170.5:2024 have significantly altered how such analyses are performed in NZ, and the incremental value that they can provide beyond a code-based approach. This paper identifies instances where site-specific analyses remain valuable (and where they do not), where they will likely depart from the ‘baseline’ 2022 NZ NSHM (and TS1170.5:2024) results to a practically significant degree, and past practices for seismic source and ground-motion modelling choices which are now considered unviable. Lastly, challenges for practitioners and researchers are briefly addressed in order to further advance the practice of site-specific seismic hazard analysis over the next decade.

Ground motion simulations for Dunedin and Mosgiel, Otago, New Zealand

2025-03-04T17:33:22+13:00

We develop large scenario earthquakes on active faults in the vicinity of Dunedin and use them to develop ground motion simulations for a site in Dunedin (St Kilda – St Clair area, referred to as “St Beach”) and Mosgiel (centre of Mosgiel, referred to as “Taieri Basin”). The scenarios are developed to represent large Akatore Fault (within 15 km of Dunedin and Mosgiel) and Hyde Fault (within 40-50 km) earthquakes. The simulations utilise the Southern California Earthquake Centre Broadband Simulation Platform and the Graves–Pitarka simulation method. Site response analysis is conducted with two-dimensional basin models, and the nonlinear finite element software OpenSees. The dynamic response characteristics of the soft sedimentary layers are modelled with a pressure-independent multi-yield plasticity model. Some confidence in the simulation method is gained by undertaking historical validations, using the only instrumentally recorded earthquake of significance in the region (the M_w 4.7 2015 Lees Valley earthquake). The simulations provide close matches to the amplitudes and durations of the recorded time histories. The Akatore and Hyde fault earthquake simulations show peak ground accelerations of up to 0.8 g and 0.3g respectively, with durations of strong shaking of around 10 to 20 seconds. Uncertainty in the simulated ground motions due to source is quantified by comparing the spectra for repeated simulations, in which the range of source parameters are sampled. The resulting range of simulations shows a spread of as much as 0.5g. The Akatore – St Beach spectra are also compared to NZS1170.5 and New Zealand national seismic hazard model 2022 (NZ NSHM 2022) spectra, for site classes relevant to those of the St Beach site. In general, the simulated spectra exceed the NZS1170.5 spectra at the 0.1-0.3 second periods, but are similar to the mean NZ NSHM 2022 spectra at these periods. Future updates to NZS1170.5 based on NZ NSHM 2022 will therefore be expected to produce design spectra that are more consistent with the results of our study. The study represents the first ground motion simulations developed for southern New Zealand, and the simulation methods could be used to further advance understanding of seismic hazard in the region.

Standardised timber moment-resisting frames for multistorey buildings: Experimental testing

2024-05-30T12:18:51+12:00

The paper presents experimental results and findings from several large-scale prototype moment-resisting timber frames. The overarching objective of this research was to provide standardised moment-resisting timber frame connections to support the increased application of timber in multistorey structures in NZ, akin to the ‘Steel Connect’ guide by SCNZ. The project was led by Red Stag Timberlab with support and funding by Callaghan Innovation. Enovate provided structural engineering design/detailing services for several prototype internal beam-column joint subassemblies, consulted on the experimental test set-up, apparatus, loading protocol and preliminary findings. Experimental testing on the sub-assemblies was performed by BRANZ.

The prototype sub-assemblies incorporated either Glue-laminated (Glulam) or Laminated Veneer Lumber (LVL) beams/column elements, and capacity-designed connections consisting of ductile steel plastic hinges/fuses designed to suppress brittle failure in the timber elements and provide energy dissipation/damping. This paper presents findings from the experimental testing to-date, highlights some critical design/detailing issues (identified through experimental testing), compares predicted versus observed frame flexibly, and makes recommendations for future design and research.

Tuning procedure for the resilient slip-friction joint (RSFJ)

2025-01-15T13:42:31+13:00

Self-centering friction dampers like the Resilient Slip-Friction Joint (RSFJ) are increasingly relevant for their ability to (1) damp earthquake-induced vibrations without degradation, and (2) prevent residual deformations after earthquakes, thus reducing both damage and downtime. One of their main advantages is a highly customizable load-deformation behaviour, which makes them versatile across various structural applications. Taking advantage of this, however, requires a degree of intuition and iteration to obtain suitable designs. This paper derives an objective and systematic procedure to generate all possible combinations of damper parameters that can produce a custom flag-shaped hysteresis. Equations are obtained to calculate the parameters explicitly and the procedure is validated with existing experimental data. A modelling example is included to demonstrate how the dampers in a three-storey structure can be tuned automatically to provide the global response required. Nonlinear time-history analyses show that the procedure is effective at tuning the dampers simultaneously to achieve the displacement targets and linear deformation profile specified from a displacement-based design.

Seismic fragility of masonry infilled reinforced concrete frames under in-plane loading: A hybrid experimental and numerical approach

2025-02-17T21:32:48+13:00

Many experimental studies have been conducted to understand the in-plane behaviour of reinforced concrete frames infilled with masonry walls (IM-RC). However, detailed analyses of those experimental studies have revealed that the in-plane behaviour of certain IM-RC frame configurations (e.g. different masonry strengths, wall aspect geometries, high strength masonry infills with ductile frames) are not well explored. Therefore, an attempt has been made to extend the understanding of the in-plane behaviour of IM-RC frames by analysing different IM-RC frame configurations using experimental and numerical data. Focus was given in this study to analyse the in-plane behaviour of single storey-single bay IM-RC frames. The numerical analyses were conducted on specific IM-RC frame cases, where experimental results are not available. For that purpose, a numerical modelling method employing fibre-element based RC frames with multi-diagonal struts for IM walls was used. The established numerical modelling method of IM-RC frames has been validated with different experimental datasets, thus proving its ability to accurately predict the in-plane behaviour of different IM-RC frames. Using the experimental and numerical datasets created, a set of seismic fragility functions have been developed. Four damage states incorporating evolution from IM to RC failures have been defined. The fragility functions are given in terms of compressive strengths of IMs (≤ 5MPa, > 5 & ≤15 MPa, and >15 MPa), and type of RC frame used (non-ductile and ductile). The derived fragility functions clearly show the importance of designing ductile frames for IM-RC building types; and the combinations of high strength IM walls with non-ductile RC frame configurations are shown to be more vulnerable than the other IM-RC frame configurations analysed.