Assessing the life-safety risk for the proposed technical specification (TS) 1170.5
DOI:
https://doi.org/10.5459/bnzsee.1690Abstract
The current New Zealand seismic design provisions are expected to be updated with a proposed Technical Specification (TS). The update is motivated primarily by the recent release of the 2022 National Seismic Hazard Model, with new seismic hazard estimates across the country. The updates are being carried out by the Seismic Risk Working Group (SRWG). One of the SRWG’s primary intentions for the proposed TS was to maintain the Building Code objective of safeguarding people from injury in light of these hazard changes. While previous code development in New Zealand has not explicitly assessed whether the life-safety risk was tolerably low, the SRWG sought to implement a new life-safety risk assessment methodology. The risk assessment takes an Ultimate Limit State (ULS) design spectrum as input and provides an expected distribution of the fatality risk, representing the variety of buildings that could be designed in accordance with the minimum requirements associated with ULS. The methodology is made up of four modules representing (A) the shaking hazard, (B) the building performance (collapse fragility), (C) the probability of fatality given collapse, and (D) the variability in performance among code-conforming buildings. The first three modules quantify fatality risk for a single building, while the fourth module iterates over many buildings to produce a full risk distribution. Using this methodology, the SRWG found that for Importance Level 2 (IL2) buildings, a ULS design spectrum with an annual probability of exceedance (APoE) of 1/500 typically corresponds to an annual individual fatality risk (AIFR) ranging between 10−6 and 10−5. Comparison with the ULS design spectra from the current NZS 1170.5:2004 provisions shows that the proposed spectra result in more uniform risk across the country, across different site classes, and across different periods. Additionally, the IL3 ULS design spectrum with an APoE of 1/1000 was considered, demonstrating that increasing the importance level to mitigate mass casualty events in high occupancy buildings is functionally equivalent to reducing the tolerable AIFR level. In summary, the risk assessment methodology can provide valuable information to the code development process by evaluating and comparing the life-safety risk associated with various options for the ULS design spectra.
References
Gerstenberger MC, Bora S, Bradley BA, DiCaprio C, Kaiser A, Manea EF, Nicol A, Rollins C, Stirling MW, Thingbaijam KKS, Dissen RJV, Abbott ER, Atkinson GM, Chamberlain C, Christophersen A, Clark K, Coffey GL, de la Torre CA, Ellis SM, Fraser J, Graham K, Griffin J, Hamling IJ, Hill MP, Howell A, Hulsey AM, Hutchinson J, Iturrieta P, Johnson KM, Jurgens VO, Kirkman R, Langridge RM, Lee RL, Litchfield NJ, Maurer J, Milner KR, Rastin S, Rattenbury MS, Rhoades DA, Ristau J, Schorlemmer D, Seebeck H, Shaw BE, Stafford PJ, Stolte AC, Townend J, Villamor P, Wallace LM, Weatherill G, Williams CA and Wotherspoon LM (2023). “The 2022 Aotearoa New Zealand National Seismic Hazard Model: Process, Overview, and Results”. Bulletin of the Seismological Society of America: 7–36. https://doi.org/10.1785/0120230182 DOI: https://doi.org/10.1785/0120230182
Standards New Zealand (2004). NZS 1170.0:2004 Structural Design Actions Part 5: Earthquake Actions - New Zealand. www.standards.govt.nz
Elwood K and Dhakal R (2025). “Background to proposed changes to NZS 1170.5:2004”. Bulletin of the New Zealand Society for Earthquake Engineering, 58(1): i–ii. https://doi.org/10.5459/bnzsee.1734 DOI: https://doi.org/10.5459/bnzsee.1734
Francis T, Sullivan T, Hulsey AM and Elwood KJ (2025). “Recommendations for the shape of the design response spectrum in the New Zealand seismic loadings technical specification”. Bulletin of the New Zealand Society for Earthquake Engineering, 58(2): 83–97. https://doi.org/10.5459/bnzsee.1692 DOI: https://doi.org/10.5459/bnzsee.1692
Lee R, CubrinovskiMand Bradley B (2025). “Site classification methodology for TS 1170.5 design spectra”. Bulletin of the New Zealand Society for Earthquake Engineering, 58(1): 11–39. https://doi.org/10.5459/bnzsee.1686 DOI: https://doi.org/10.5459/bnzsee.1686
New Zealand Government (1992). “The New Zealand Building Code”. https://www.legislation.govt.nz/regulation/public/1992/0150/latest/DLM162576.html
Luco N, Ellingwood BR, Hamburger RO, Hooper JD, Kimball JK and Kircher CA (2007). “Risk-Targeted versus Current Seismic Design Maps for the Conterminous United States”. Structural Engineering Association of California 2007 Convention Proceedings: 1–13.
Silva V, Crowley H and Bazzurro P (2016). “Exploring risk targeted hazard maps for Europe”. Earthquake Spectra, 32: 1165–1186. https://doi.org/10.1193/112514EQS198M DOI: https://doi.org/10.1193/112514eqs198m
Horspool N, Hulsey AM, Elwood KJ and Gerstenberger MC (2023). “Risk-targeted hazard for seismic design in New Zealand considering individual and societal risk targets”. Earthquake Spectra, 39: 1007–1036. https://doi.org/10.1177/87552930231156947 DOI: https://doi.org/10.1177/87552930231156947
Standards New Zealand (2002). AS/NZS 1170.0:2002 Structural Design Actions Part 0: General Principles. www.standards.govt.nz
EQC TTA (2023). “Natural Hazard Risk Tolerance Literature Review”. Technical report, Toka T¯u Ake EQC. https://www.eqc.govt.nz/assets/Publications-Resources/Risk-Tolerance-Literature-Review.pdf
Jonkman SN, Gelder PHV and Vrijling JK (2003). “An overview of quantitative risk measures for loss of life and economic damage”. Journal of Hazardous Materials, A99: 1–30. https://doi.org/10.1016/S0304-3894(02)00283-2 DOI: https://doi.org/10.1016/S0304-3894(02)00283-2
Clarke LB, Kelly SD, FitzGerald T, Pondard N and Wilson-Rooy M (2021). “Stocktake of Existing Risk Tolerance Frameworks”. Technical report, GNS Science Consultancy Report 2021/71.
ISO 2394:2015 (2015). “General Principles on Reliability for Structures”. Technical report, International Organization for Standardization (ISO).
Douglas J, Ulrich T and Negulescu C (2013). “Risk-targeted seismic design maps for mainland France”. Natural Hazards, 65: 1999–2013. https://doi.org/10.1007/s11069-012-0460-6 DOI: https://doi.org/10.1007/s11069-012-0460-6
Baker JW, Bradley B and Stafford P (2021). Seismic Hazard and Risk Analysis. Cambridge University Press, ISBN 9781108348157. https://doi.org/10.1017/9781108425056 DOI: https://doi.org/10.1017/9781108425056
FEMA P695 (2009). “Quantification of Building Seismic Performance Factors”. Technical report, Applied Technology Council. www.ATCouncil.org
Eads L, Miranda E and Lignos DG (2015). “Average spectral acceleration as an intensity measure for collapse risk assessment”. Earthquake Engineering & Structural Dynamics, 44: 2057–2073. https://doi.org/10.1002/eqe.2575 DOI: https://doi.org/10.1002/eqe.2575
Eads L, Miranda E and Lignos D (2016). “Spectral shape metrics and structural collapse potential”. Earthquake Engineering & Structural Dynamics, 45: 1643–1659. https://doi.org/10.1002/eqe.2739 DOI: https://doi.org/10.1002/eqe.2739
Zhong K, Chandramohan R, Baker JW and Deierlein GG (2022). “Site-specific adjustment framework for incremental dynamic analysis ( SAF-IDA )”. Earthquake Spectra, 38: 1893–1917. https://doi.org/10.1177/87552930221083688 DOI: https://doi.org/10.1177/87552930221083688
Bradley BA (2010). “A generalized conditional intensity measure approach and holistic ground-motion selection”. Earthquake Engineering & Structural Dynamics, 40. https://doi.org/10.1002/eqe.995 DOI: https://doi.org/10.1002/eqe.995
FEMA P-58 (2012). “Seismic Performance Assessment of Buildings: Volume 1 (Methodology)”. Technical report, Applied Technology Council.
Zareian F and Krawinkler H (2007). “Assessment of probability of collapse and design for collapse safety”. Earthquake Engineering & Structural Dynamics, 36: 1901–1914. https://doi.org/10.1002/eqe.702 DOI: https://doi.org/10.1002/eqe.702
Horspool N, Elwood KJ, Johnston D, Deely J and Ardagh M (2020). “Factors influencing casualty risk in the 14th November 2016 MW7.8 Kaikoura, New Zealand earthquake”. International Journal of Disaster Risk Reduction, 51. https://doi.org/10.1016/J.IJDRR.2020.101917 DOI: https://doi.org/10.1016/j.ijdrr.2020.101917
Horspool N (2022). “Life-safety risk in earthquakes: Investigating risk factors and development of risk management tools”. Ph.D. Thesis, The University of Auckland, New Zealand. https://hdl.handle.net/2292/62613
FEMA (2001). “HAZUS MH-2.1 Advanced Engineering Building Module (AEBM)”. Technical report, Federal Emergency Management Agency, Mitigation Division.
Zaidi F, Elwood KJ and Hulsey AM (2024). “A Framework For Incorporating Fatality Risk In Seismic Assessment Methodology In New Zealand”. 18th World Conference on Earthquake Engineering.
FEMA (2012). “Hazus Multi-hazard Loss Estimation Methodology, Earthquake Model, Hazus-MH 2.1 Technical Manual”. Technical report, Federal Emergency Management Agency, Mitigation Division.
So E (2016). Estimating Fatality Rates for Earthquake Loss Models. Springer, ISBN 978-3-319-26837-8, 71 pp. DOI: https://doi.org/10.1007/978-3-319-26838-5
Yeow TZ, Orumiyehei A, Sullivan TJ, MacRae GA, Clifton GC and Elwood KJ (2018). “Seismic performance of steel friction connections considering direct-repair costs”. Bulletin of Earthquake Engineering, 16: 5963–5993. https://doi.org/10.1007/s10518-018-0421-x DOI: https://doi.org/10.1007/s10518-018-0421-x
John L, Williamson MB and Sullivan TJ (2023). “Investigating the Impact of Design Criteria on the Expected Seismic Losses of Multi-Storey Office Buildings”. Bulletin of the New Zealand Society for Earthquake Engineering, 56: 11–28. https://doi.org/10.5459/bnzsee.56.1.11-28 DOI: https://doi.org/10.5459/bnzsee.56.1.11-28
Orumiyehei A (2022). “Probabilistic Displacement Based Seismic Assessment”. Ph.D. Thesis, University of Canterbury, Christchurch, New Zealand.
