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Earthquakes and Structures
  Volume 16, Number 6, June 2019, pages 705-714

Seismic fragility and risk assessment of an unsupported tunnel using incremental dynamic analysis (IDA)
Arsham Moayedifar, Hamid Reza Nejati, Kamran Goshtasbi and Mohammad Khosrotash

    Seismic assessment of underground structures is one of the challenging problems in engineering design. This is because there are usually many sources of uncertainties in rocks and probable earthquake characteristics. Therefore, for decreasing of the uncertainties, seismic response of underground structures should be evaluated by sufficient number of earthquake records which is scarcely possible in common seismic assessment of underground structures. In the present study, a practical risk-based approach was performed for seismic risk assessment of an unsupported tunnel. For this purpose, Incremental Dynamic Analysis (IDA) was used to evaluate the seismic response of a tunnel in south-west railway of Iran and different analyses were conducted using 15 real records of earthquakes which were chosen from the PEER ground motion database. All of the selected records were scaled to different intensity levels (PGA=0.1-1.7 g) and applied to the numerical models. Based on the numerical modeling results, seismic fragility curves of the tunnel under study were derived from the IDAcurves. In the next, seismic risk curve of the tunnel were determined by convolving the hazard and fragility curves. On the basis of the tunnel fragility curves, an earthquake with PGA equal to 0.35 g may lead to severe damage or collapse of the tunnel with only 3% probability and the probability of moderate damage to the tunnel is 12%.
Key Words
    seismic response; fragility curve; incremental dynamic analysis; underground structures
Arsham Moayedifar, Hamid Reza Nejati, Kamran Goshtasbi: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Tehran, Iran
Mohammad Khosrotash: Donya Tunnel Saze Consulting Engineering Company, Tehran, Iran

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