Seismic performance of wood‐frame houses in south‐western British Columbia

Abstract

The seismic performance of conventional wood-frame structures in south-western British Columbia is analytically investigated through incremental dynamic analysis by utilizing available UBC-SAWS models, which were calibrated based on experimental test results. To define an adequate target response spectrum that is consistent with information from national seismic hazard maps, record selection/scaling based on the conditional mean spectrum (CMS) is implemented. Furthermore, to reflect complex seismic hazard contributions from different earthquake sources (i.e. crustal events, interface events, and inslab events), we construct CMS for three earthquake types, and use them to select and scale an adequate set of ground motion records for the seismic performance evaluation. We focus on the impacts of adopting different record selection criteria and of using different shear-wall types (Houses 1-4; in terms of seismic resistance, House 1 > House 2 > House 3 > House 4) on the nonlinear structural response. The results indicate that the record selection procedures have significant influence on the probabilistic relationship between spectral acceleration at the fundamental vibration period and maximum inter-story drift ratio, highlighting the importance of taking into account response spectral shapes in selecting and scaling ground motion records. Subjected to ground motions corresponding to the return period of 2500 years, House 1 is expected to experience very limited extent of damage; Houses 2 and 3 may be disturbed by minor damage; whereas House 4 may suffer from major damage occasionally. Finally, we develop statistical models of the maximum inter-story drift ratio conditioned on a seismic intensity level for wood-frame houses, which is useful for seismic vulnerability assessment.is relatively high, in comparison with other regions of Canada, and hence, potential urban seismic risk is a serious concern. More than 50% of the population in BC lives in the Lower Mainland region, and residential wood-frame buildings are the most prevalent construction type. About 40% of the wood-frame buildings were built before 1970, 25 and 21% were built in the 1970s and 1980s, respectively, and about 14% were constructed after 1990 [1]. Many wood-frame buildings in the region are non-engineered and may lack sufficient post-yield seismic resistance, as the adoption of the National Building Code of Canada (NBCC) by municipalities in BC was not approved until 1973. Thus vulnerability assessment of wood-frame buildings provides home owners, business proprietors, and emergency officials in local municipalities with valuable information about regional urban seismic risk.The main objectives of this study are twofold: (1) to assess the seismic performance of typical wood-frame houses in south-western BC, and (2) to develop a probabilistic prediction model of the inelastic seismic demand for these houses. For analysis, we adopt structural models that were developed by White and Ventura [2] based on the computer program SAWS [3]. It should be emph...

Seismic loss estimation of wood-frame houses in south-western British Columbia

“…Specifically, we incorporate: (i) an updated seismic hazard model for western Canada [16,17], (ii) a spatial correlation model of peak ground motions and response spectra for subduction earthquakes [18,19], in addition to a counterpart for shallow crustal earthquakes [20], and (iii) prediction models of the maximum interstory drift ratio of wood-frame houses with different shear-wall types [21]. The latter models were developed by carrying out incremental dynamic analysis (IDA) of the UBC-SAWS structural models, which were made for conventional wood-frame houses in south-western British Columbia (BC) [22] (see [23] for descriptions of the SAWS model).…”

Incremental dynamic analysis of wood-frame houses in Canada: Effects of dominant earthquake scenarios on seismic fragility

“…Such distinction may be effective in capturing source and path effects simultaneously; for instance, the Cascadia subduction events are associated with a specific combination of magnitude and distance for a given site. The consideration of multiple CMS leads to more variation of the expected response spectral shape, and consequently results in increased variability of the final IDA results [5]. Similarly, distinction in terms of magnitude may be applicable to eastern Canada, where large characteristic events (M w 7.5 class) are likely to be originated from the St. Lawrence rift zone, while local smallto-moderate events (M w 5.0-6.5) occur elsewhere.…”

“…In eastern Canada, magnitudes of major scenarios are smaller in comparison with western Canada, yet potentially large destructive earthquakes from the St. Lawrence rift zone might be expected [17], affecting many cities and towns in eastern Canada. Importantly, this work extends the previous work [5] in two aspects: (1) impact of different IDA-CMS-based approaches is assessed in terms of regional seismic risk for a group of wooden houses (beyond the comparison of fragility curves), and (2) seismic hazard estimates as well as dominant earthquake scenarios varying across the territory significantly are taken into account. Systematic investigations of IDA-CMS-based fragility models by considering detailed seismic characteristics across Canada are highlighted.…”

“…The IDA repeatedly carries out nonlinear dynamic analysis of a structural model subjected to scaled accelerograms. It is a viable numerical procedure to develop a probabilistic model of EDP for a given IM and to assess collapse capacity of a structure, and has been applied to various types of structures, including wood-frame houses [4,5]. Recent developments of the IDA have focused upon quantification of uncertainty associated with the IDA-based fragility models by taking into account uncertain structural parameters [6,7].…”

“…The effect of using multiple target CMS, reflecting real situations more closely, is increased variability of the predicted EDP for a given IM. Goda and Atkinson [5] showed how such detailed seismic hazard information from probabilistic seismic hazard analysis (PSHA) can be incorporated in defining multiple target CMS for crustal, interface, and inslab events in western Canada.…”