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    A numerical study on the estimation of liquefaction-induced free-field settlements by using PM4Sand model
    (Korean Society of Civil Engineers, 2021) Subaşı, Ozan; Koltuk, Serdar; İyisan, Recep
    The present paper treats the estimation of liquefaction-induced, free-field settlements using two-dimensional, fully coupled, finite element (FE) analyses. The PM4Sand model is used to simulate the liquefaction behavior of a homogeneous sand layer with three different relative densities of 35%, 55%, 75% under eleven different strong ground motions. The results of FE analyses are compared with those obtained from the well-known, semi-empirical methods in the literature. The numerical analyses show that, in case of a relative density of 35%, in general, the majority of earthquake-induced settlements occur in the period, in which the excess pore water pressure resulting from the strong ground motion begins to dissipate. The liquefaction-induced settlements are influenced by not only the moment magnitude and peak ground acceleration, but also other parameters of the ground motion. Furthermore, it has been shown that the evaluation of the liquefaction potential using finite element and semi-empirical methods gives similar results. However, the semi-empirical methods yield mostly larger settlements than those obtained from the FE analyses.
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    Assessment of liquefaction potential during earthquakes by using SPT-number of blows and two-dimensional finite element analyses
    (Springer, 2022) Koltuk, Serdar; Subaşı, Ozan; Fernandez-Steeger, Tomas; İyisan, Recep
    For the planning and design of buildings in earthquake zones with high groundwater levels, the liquefaction potential of the building site has to be investigated and evaluated. In DIN EN 1998-5:2010-12 (2010), the diagrams based on SPT-number of blows are given for the assessment of liquefaction potential. In the present study, this method is first described according to the current state of knowledge. Subsequently, the liquefaction potential of a sandy soil is analyzed using SPT-number of blows and two-dimensional finite element analyses (2D-FEA) with the sand-plasticity model PM4Sand. With respect to the assessment of liquefaction potential, a good agreement between the results obtained from both methods is found. Furthermore, the use of 2D-FEA with the PM4Sand model allows the estimation of earthquake-induced deformations on the soil surface.
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    Öğe
    Comparison of one dimensional dynamic analysis and microtremor measurement results
    (Turkish Chamber Civil Engineers, 2019) Subaşı, Ozan; Haşal, M. Emre; Özaslan, Bilal; İyisan, Recep; Yamanaka, Hiroaki; Chimoto, Kosuke
    The deformation level of the surface soil layer due to strong ground motion has a considerable effect in soil-structure interaction problems. The shear strain values of the near surface soil deposits which are calculated by one dimensional (1D) seismic site response analyses can also be estimated by incorporating the results obtained from Horizontal to Vertical Spectral Ratio (HVSR) analysis of microtremor data and peak horizontal acceleration value of design ground motion. In this study, the seismic behaviors of soil layers at a site located in the vicinity of North Anatolian Fault were estimated by using the results of both 1D equivalent linear seismic site response analyses for 14 different seismic excitation records and HVSR analyses of ground ambient noise-microtremor measurement data. A correlation is proposed for elastic and elasto-plastic deformation levels of surface soil layers in order to estimate the value of shear strain due to strong ground motion.
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    Seismic microzonation of Bursa/Güzelyalı in Turkey: a study on the compatibility of 1d dynamic analysis and microtremor measurements
    (CRC Press/Balkema, 2019) Subaşı, Ozan; Haşal, Murat Emre; Özaslan, Bilal; İyisan, Recep
    Estimation of soil behavior under dynamic loading has great importance in reducing the damage that may occur in an earthquake. For this reason, microtremor measurements were performed in a specific site to define dynamic behavior in terms of shear strain. The study area was divided into square shaped cells with 200m‘X’200m dimensions in order to implement the seismic microzonation criterion. Within the scope of microzonation studies, to 75 separate single station microtremor measurements, 7 microtremor array measurements were carried out and 75 boreholes data are collected. These field measurements were analyzed according to the Nakamura Method and estimated effective shear strain. One-dimensional (1D) equivalent linear seismic ground response analyses were performed for the sites where the microtremor array measurements were conducted. The results of microtremor analyses and 1D dynamics analysis were presented by Geographic Information System (GIS) and compared for research area. © 2019 Associazione Geotecnica Italiana, Rome, Italy.