Development of design spectra for long-duration ground motions from Cascadia subduction earthquakes

1998 ◽  
Vol 25 (6) ◽  
pp. 1078-1090 ◽  
Author(s):  
R Tremblay
Keyword(s):  
Subduction Zone ◽  
Failure Modes ◽  
Ground Motions ◽  
Damage Index ◽  
Cascadia Subduction Zone ◽  
Damage Potential ◽  
Design Spectra ◽  
Subduction Earthquakes ◽  
Long Duration ◽  
Short Period

There is now growing evidence that large-magnitude earthquakes have occurred and could occur again along the Cascadia subduction zone located west of Vancouver Island, Bristish Columbia. Numerical simulations indicate that these earthquakes would produce long-duration ground motions and would thus be capable of inducing a large number of reversals of inelastic deformations in engineered structures. Efforts have now been undertaken to account for this damage potential in building codes. In this paper, inelastic design spectra are developed for Cascadia subduction earthquakes for four sites in British Columbia. These spectra are compared with elastic design spectra that have been developed recently for the same sites based on empirical attenuation relationships for Cascadia events. The approach used to develop the inelastic spectra aims at providing the same level of protection against structural failure for both subduction events and crustal or subcrustal earthquakes. Force modification factors are first determined for structures exhibiting various failure modes and ductility levels when subjected to representative crustal and subcrustal earthquake ground motions. Thereafter, design spectra are developed for the same structures to prevent structural collapse under simulated Cascadia subduction ground motions. The study reveals that the elastic spectra do not reflect adequately the damage potential of Cascadia earthquakes. These elastic spectra generally are unconservative for Tofino and Victoria. For Vancouver and Prince George, the elastic spectra overestimate the demand, especially for short-period structures.Key words: collapse, crustal earthquakes, damage index, design spectrum, ductility, duration, ground motion, subduction zone.

Damage Index for Different Structural Systems Subjected to Recorded Earthquake Ground Motions

2018 ◽  
Vol 34 (2) ◽  
pp. 773-793 ◽  
Author(s):  
Mario E. Rodriguez
Keyword(s):  
Ground Motions ◽  
Damage Index ◽  
Earthquake Ground Motion ◽  
Structural Systems ◽  
Damage Analysis ◽  
Damage Potential ◽  
Structural Wall ◽  
Earthquake Ground Motions ◽  
Frame Buildings ◽  
Earthquake Performance

This study quantifies the damage index previously proposed by the writer ( Rodriguez 2015 ) for different structural systems subjected to a set of earthquake ground motions recorded during 12 strong earthquakes in different countries. Damage spectra were also computed using this seismic damage index. This study revisits the previously proposed index and shows that this index can also be interpreted as a ratio of velocities in the structural system responding to the earthquake demand. In addition, this study gives a more general damage analysis interpretation than that of the previous study since damage spectra were computed to assess the damage potential of a given recorded earthquake ground motion for different types of earthquake-resisting systems. The results from the damage analysis are consistent with the findings from previous research: most structural wall buildings show satisfactory earthquake performance, whereas frame buildings frequently show severe damage and collapse.

Impacts of Simulated M9 Cascadia Subduction Zone Motions on Idealized Systems

2019 ◽  
Vol 35 (3) ◽  
pp. 1261-1287 ◽  
Author(s):  
Nasser A. Marafi ◽  
Marc O. Eberhard ◽  
Jeffrey W. Berman ◽  
Erin A. Wirth ◽  
Arthur D. Frankel
Keyword(s):  
Subduction Zone ◽  
Ground Motions ◽  
High Strength ◽  
Sedimentary Basins ◽  
Cascadia Subduction Zone ◽  
Seismic Resistance ◽  
Spectral Acceleration ◽  
Single Degree Of Freedom ◽  
Conditional Mean ◽  
Subduction Zone Earthquake

Ground motions have been simulated for a magnitude 9 (M9) Cascadia Subduction Zone earthquake, which will affect the Puget Lowland region, including cities underlain by the Seattle, Everett, and Tacoma sedimentary basins. The current national seismic maps do not account for the effects of these basins on the risk-targeted Maximum Considered Earthquake (MCER). The simulated motions for Seattle had large spectral accelerations (at a period of 2 s, 43% of simulated M9 motions exceeded the MCER), damaging spectral shapes (particularly at periods near 1 s), and long durations (5%–95% significant durations near 110 s). For periods of 1 s or longer, the resulting deformation demands and collapse likelihood for four sets of single-degree-of-freedom systems exceeded the corresponding values for motions consistent with the conditional mean spectra at the MCER intensity (MCER). The regional variation of damage was estimated by combining probabilistic characterizations of the seismic resistance of structures and of the effective spectral acceleration, Sa,eff, which accounts for the effects of spectral acceleration, spectral shape, and ground-motion duration. For high-strength, low-ductility systems located above deep basins ( Z2.5 > 6 km), the likelihood of collapse during an M9 earthquake averaged 13% and 18% at 1.0 s and 2.0 s periods, respectively. For low-strength, high-ductility systems, the corresponding likelihoods of collapse averaged 18% and 7%.

scholarly journals Accounting for directivity-induced pulse-like ground motions in building portfolio loss assessment

2020 ◽  
Author(s):  
Roberto Gentile ◽  
Carmine Galasso
Keyword(s):  
Large Scale ◽  
Ground Motions ◽  
Economic Losses ◽  
Loss Assessment ◽  
Damage Potential ◽  
Rc Frames ◽  
Short Period ◽  
Source Directivity ◽  
Moment Resisting ◽  
The Impact

Abstract Earthquake-induced pulse-like ground motions are often observed in near-source conditions due to forward-directivity. Recent worldwide earthquakes have emphasised the severe damage potential of such pulse-like ground motions. This paper introduces a framework to quantify the impact of directivity-induced pulse-like ground motions on the direct economic losses of building portfolios. To this aim, a simulation-based probabilistic risk modelling framework is implemented for various synthetic building portfolios located either in the fault-parallel or fault-normal orientations with respect to a case-study strike–slip fault. Three low-to-mid-rise building typologies representative of distinct vulnerability classes in the Mediterranean region are considered: non-ductile moment-resisting reinforced concrete (RC) frames with masonry infills, mainly designed to only sustain gravity loads (i.e. pre-code frames); moment-resisting RC infilled frames designed considering seismic provisions for high ductility capacity (i.e. special-code frames); special-code steel moment-resisting frames. Monte Carlo-based probabilistic seismic hazard analysis is first performed, considering the relevant modifications to account for the pulse-occurrence probability and the resulting spectral amplification. Hazard curves for sites/buildings located at different distances from the fault are obtained, discussing the spatial distribution of the hazard amplification. A set of pulse-like ground motions and a set of one-to-one spectrally-equivalent ordinary records are used to perform non-linear dynamic analysis and derive fragility relationships for each considered building typology. A vulnerability model is finally built by combining the derived fragility relationships with a (building-level) damage-to-loss model. The results are presented in terms of intensity-based and expected annual loss for synthetic portfolios of different sizes and distribution of building types. It is shown that, for particularly short-period structures (e.g. infilled RC frames), the influence of near-source directivity can be reasonably neglected in the fragility derivation while kept in place in the hazard component. Overall, near-source directivity effects are significant when estimating losses of individual buildings or small portfolios located very close to a fault. Nevertheless, the impact of pulse-like ground motions on losses for larger portfolios can be considered minimal and can be neglected in most of the practical large-scale seismic risk assessment applications.

Evaluation of Damage Potential of Ground Motions during Great Earthquakes

2003 ◽  
Vol 19 (3) ◽  
pp. 713-730 ◽  
Author(s):  
Y. Sunasaka ◽  
K. Toki ◽  
A. S. Kiremidjian
Keyword(s):  
Ground Motions ◽  
Damage Index ◽  
Geological Structure ◽  
Large Area ◽  
Damage Potential ◽  
Seismic Safety ◽  
Great Earthquakes ◽  
Earthquake Resistant Design ◽  
Earthquake Resistant ◽  
Index Value

In order to select appropriate input ground motions for earthquake-resistant design or estimation of seismic safety of structures, their characteristics should be identified. In this paper, damage potential is defined as a spectrum of strength demand required to maintain a damage index less than or equal to a tolerable damage index value. The damage index proposed by Park and Ang (1985) and a bilinear model are used to calculate the strength demand spectrum. The damage index describes the state of the concrete structure from slight damage to severe damage or collapse. Studies of the damage potential of ground motions during the recent great earthquakes, including the 1995 Hyogoken-Nanbu earthquake in Japan and the 1999 Chi-Chi earthquake in Taiwan, show that damage potential may be greatly affected by the location of the fault, the geological structure of the site, and the fault rupture mechanism. Furthermore, an estimation of damage potential of ground motions over a large area, Kawasaki City in Japan, is described.

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