Contents lists available at ScienceDirect Structural Safety journal homepage: www.elsevier.com/locate/strusafe Damage index fragility assessment of low-rise light-frame wood buildings under long duration subduction earthquakes Yuxin Pan a,b, ⁎ , Carlos E. Ventura a , Thomas Tannert b a Earthquake Engineering and Research Facility, Department of Civil Engineering, The University of British Columbia, Vancouver, BC, Canada b Wood Engineering, University of Northern British Columbia, Prince George, BC, Canada ARTICLE INFO Keywords: Fragility curve Structural damage Ground motion duration Subduction earthquake Incremental dynamic analyses ABSTRACT This paper presents fragility curves for conventional low-rise light-frame wood buildings in southwestern British Columbia, Canada, for long duration subduction earthquakes. Computational models of four representative two- story houses (two engineered and two non-engineered) are developed and validated using full-scale shake table testing data. Damage states are evaluated using the Park and Ang damage index. Incremental dynamic analyses are employed for calibrating and assessing the index. Duration efects are investigated by using 30 long duration subduction motions and 30 “spectrally equivalent” short duration crustal motions. The results indicate that the considered houses are more vulnerable to damage under subduction motions which increase the median damage indices of both individual shearwalls and entire lateral systems for all four houses at the same level of ground shaking. The correlation between system damage indices with ground motion duration was dependent on the level of ground shaking and the seismic resistance of the systems. The results further demonstrate that exterior stucco fnish greatly reduces the seismic damage and can be used as an efective seismic retroft strategy for conventional non-engineered wood construction. 1. Introduction 1.1. Seismicity in British Columbia The southwestern (coastal) part of British Columbia (BC) lies in one of the most seismically active regions in Canada. This region is char- acterized by three types of earthquakes, namely i) shallow crustal earthquakes (happening within the crust of the North American con- tinental plate), ii) sub-crustal earthquakes (triggered within the sinking oceanic Juan de Fuca Plate), and iii) subduction earthquakes (triggered at the interface between two plates - the Cascadia subduction zone) [1], as shown in Fig. 1. It has been reported that at least 7 large subduction earthquakes (Mw > 9) have occurred in the Cascadia subduction zone over the past 3500 years [2]. The last major event has been dated to January 26th, 1700. Recent studies by Goldfnger [3] indicated that these large earthquakes have a recurrence interval of approximately 430 years. On this basis, some seismologists expect a similar subduction event to hit the west coast of Canada in the near future which could potentially endanger life, structures and infrastructure in southwestern BC [2]. Engineers and researchers are facing many challenges in dealing with subduction earthquakes. Subduction records are normally associated with large magnitude and long duration [1,5]; their long period characteristics could negatively afect base-isolated and high- rise buildings [6]. One aspect of subduction earthquakes which has not been thoroughly investigated is the link of their long duration with structural damage. Typically, shallow crustal ground motions last no longer than tens of seconds, while subduction motions can last several minutes. Recent studies that focused on the collapse capacity of struc- tures have demonstrated that long duration motions can signifcantly increase the collapse rates of various types of building structures, such as reinforced concrete frame, steel moment frame, and masonry buildings [7–10]. However, few studies have been conducted on da- mage states other than collapse, especially for wood structures that have highly nonlinear behavior and signifcant ability to dissipate hysteretic energy. 1.2. Light-frame wood buildings in British Columbia According to the 2016 Census of Canada [11], over 95% of all re- sidential buildings in Canada are of light-frame wood construction. Of the approximately 1.9 million households in BC providing shelter to 4.6 million occupants, about 44% (830,660) of these units are single-family homes and 42% (793,045) are apartment or condominium units https://doi.org/10.1016/j.strusafe.2020.101940 Received 27 May 2019; Received in revised form 25 January 2020; Accepted 26 January 2020 ⁎ Corresponding author. E-mail address: ypan@civil.ubc.ca (Y. Pan). Structural Safety 84 (2020) 101940 0167-4730/ © 2020 Elsevier Ltd. All rights reserved. T