Site Response Study and Amplification Factor for Shallow Bedrock Sites
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ORIGINAL PAPER
Site Response Study and Amplification Factor for Shallow Bedrock Sites Aditya Parihar1
•
P. Anbazhagan2
Received: 1 August 2019 / Accepted: 6 January 2020 Ó Indian Geotechnical Society 2020
Abstract Amplification is a key paramter considered to account modifcation of seimic wave in the soil for earthquake resistance design of structure placed on soil. Initially, earthquake wave amplifications are related with shear wave velocity (Vs) ratio of soil and foundation layer, and then it was related to average value of Vs up to 30 m (V30 s ). Application of V30 s concept to represent amplification in shallow bedrock sites is questionable and has rock velocity added to soil velocity. In this study, shallow bedrock sites in Bengaluru, Chennai, Coimbatore and Vishakhapatnam has been analyzed to understand amplifications and its proximity to V30 s . The site response calculations are done using one-dimensional nonlinear approach. Intraplate recordings from around the world suitable for the study area are selected. For comparison with known data, the amplification factors are evaluated considering the period ranges similar to international codes. Then, considering spectral signatures from response spectra for all site rock and surface motions, the factors are calculated for period range 0.01–0.06 s and 0.05–1.0 s. Based on the study, only one mid-period amplification factor has been proposed. This amplification factor represents the significant amplification of the site. Acceleration spectra show similar trends for different site classes irrespective of the fact that profiles are selected based on Vs values or SPT-N values. This is observed over a wide range of results and indicates shear modulus as an
& Aditya Parihar [email protected]; [email protected]; http://www.thapar.edu/faculties/view/Dr.-Aditya-Parihar/ MTg4/Mw== 1
Department of Civil Engineering, Thapar Institute of Engineering and Technology, Patiala, Punjab 147004, India
2
Department of Civil Engineering, Indian Institute of Science, Bangalore 5600012, India
influencing parameter. Comparison of spectral signatures for different site classes suggests that amplification reduces as the modulus of the soil column increases. Thus, it may be appropriate to classify sites based on shear modulus of soil column. Keywords Site response Amplification factors Shallow bedrock Seismic site classification Shear modulus Peninsular India
Introduction Site response studies are carried out to estimate the modification in ground motion parameters due to local soil conditions when subjected to transient conditions. In general, site period and stiffness of soil column are the most important factors influencing the site response analysis. Site response analysis is performed using frequency-domain equivalent linear analysis or time-domain nonlinear analysis employing nonlinear hysteretic soil models. For classifying a site, the defining parameters are those that affect site response most and are conveniently measurable. As shear stiffness an
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