Annexes G and H of the Dutch Seismic Practice Directive NPR9998
Kam, Weng Yuen
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The province of Groningen in the north-east of the Netherlands is currently experiencing a period of induced seismicity as the result of sustained gas extraction from an underlying gas field. These anthropogenic earthquakes have triggered the need to assess, and where necessary retrofit, the relatively vulnerable building stock. As the Netherlands is not historically a seismic country, there was a lack of seismic guidelines and hence the practice directive NPR9998 was developed to meet the needs of this rather unique situation. A key part of NPR9998 is the Annexes G and H, which enable engineers to undertake Nonlinear Pushover Analysis and Nonlinear Kinematic Analysis, respectively. Both annexes are tailored towards expedited assessments and are based on section C8 of New Zealand’s Technical Guidelines for (seismic) Engineering Assessments. The paper starts with an overview of the induced seismicity situation in Groningen and the need to assess and strengthen houses. The development of NPR9998 Annexes G and H is then presented, with a specific focus on how it addresses societal needs in the Groningen region. Following this, discussion is provided around differences to the New Zealand Guidelines before looking into the more innovative aspects of the annexes’ development, which include comparison against shake table tests and calibration to the results of detailed seismic risk analyses.