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Juneau, AK, United States

Yang Z.J.,University of Alaska Anchorage | Dutta U.,University of Alaska Anchorage | Xu G.,State of Alaska DOT and PF Bridge Section | Hazirbaba Kenan K.,University of Alaska Fairbanks | Marx E.E.,State of Alaska DOT and PF Bridge Section
Soil Dynamics and Earthquake Engineering | Year: 2011

Some of the damage to the infrastructure observed in past earthquakes occurred in Alaska could be related to the existence of permafrost. However, only limited research has been carried out so far to investigate the effects of permafrost on the seismic site response. Permafrost with relatively high shear wave velocity (1000-1500. m/s) extensively exists in the interior of Alaska and causes anomaly in the shear wave velocity profile that may alter the site response. In current design practices, permafrost has been treated as bedrock and its potential effects on site response are ignored. A systematic investigation was conducted to understand the effects of permafrost on the ground motion characteristics using one-dimensional equivalent linear analysis for the MCE, AASHTO and IBC Design Earthquake level hazards. The average surface displacement, velocity and acceleration response spectra for a typical permafrost site were obtained and the worst case scenario was identified. The results show that the presence of permafrost can significantly alter the ground motion characteristics and it may not be conservative to ignore the effects of permafrost in the seismic design of civil structures. © 2010 Elsevier Ltd. Source


Xu G.,State of Alaska DOT and PF Bridge Section | Yang Z.,University of Alaska Anchorage | Dutta U.,University of Alaska Anchorage | Tang L.,Harbin Institute of Technology | Marx E.,State of Alaska DOT and PF Bridge Section
Journal of Cold Regions Engineering | Year: 2011

Several large-magnitude earthquakes, including the Prince William Sound earthquake of March 1964 and the Denali earthquake of November 2002, occurred in the state of Alaska and caused considerable damages to its transportation system, including damage to several highway bridges and related infrastructure. Some of these damages are related to frozen soil effects. However, only limited research has been carried out to investigate the effects of frozen soils on seismic site responses. A systematic investigation of seasonally frozen soil effects on the seismic site response has been conducted and is presented in this paper. One bridge site in Anchorage, Alaska, was selected to represent typical sites with seasonally frozen soils. A set of input ground motions was selected from available strong-motion databases and scaled to generate an ensemble of hazard-consistent input motions. One-dimensional equivalent linear analysis was adopted to analyze the seismic site response for three seismic hazard levels, i.e., maximum considered earthquake (MCE), AASHTO design, and service design level hazards. Parametric studies were conducted to assess the sensitivity of the results to uncertainties associated with the thickness and shear-wave velocity of seasonally frozen soils. The results show that the spectral response of ground motions decreases as the thickness of seasonally frozen soil increases, and the results are insensitive to the shear-wave velocity of seasonally frozen soils. In conclusion, it is generally conservative to ignore the effects of seasonally frozen soils on seismic site response in the design of highway bridges. © 2011 American Society of Civil Engineers. Source

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