Browsing by Author "Altun, Selim"

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Citation - WoS: 9
Citation - Scopus: 9
2-D and 3-D basin site effects in Izmir-Bayrakli during the October 30- 2020 Mw7.0 Samos earthquake
(SPRINGER, 2023) Kemal Onder Cetin; Moutasem Zarzour; Elife Cakir; S. Caglar Tuna; Selim Altun; Altun, Selim; Zarzour, Moutasem; Cetin, Kemal Onder; Cakir, Elife; Tuna, S. Caglar
During the October 30 2020 M(w)7.0 Samos Earthquake the Turkiye-Izmir-Bayrakli district was affected the most due to the geometry and the deep-soft alluvial nature of the basin although the district is approximately 70 km away from the epicenter. In this study the seismic response of the Bayrakli basin and the role of the soil stratigraphy and basin geometry on the recorded amplifications and prolonging of seismic shakings are investigated by using 1- 2-and 3-D non-linear finite element-based dynamic response analyses. The assessment results are presented in the form of spectral amplification ratios A(T). The highest A(T) values were estimated at spectral periods T = 0.85 and 1 s. They exceed five in both the east-west and the north-south directions more pronounced in the latter one. A(T) was decomposed into the product of two independent amplification factors namely rock to soil amplifications A(Soil)(T) and 1-D soil column to 3-D soil basin amplifications A(Basin)(T). A(Basin)(T) values for T = 0.85 and 1 s are estimated as high as 1.4 and 1.6 in the east-west and the north-south directions respectively. These values suggest that the 3-D geometry of the Bayrakli basin amplifies the spectral accelerations by 40-60% at T = 0.85 and 1 s. The unique combination of a deep-soft alluvial site with 3-D basin geometry and overlying 7-9 story residential buildings consistently favors and amplifies the seismic energy in the spectral period range of 0.7-1.0 s. This multi-fold increased seismic demand combined with poor structural design and construction details lead to localized structural damage and over 117 life losses.
Probabilistic evaluation of liquefaction analysis in performance based design framework
(Springer Science and Business Media B.V., 2025) Şahin Çaǧlar Tuna; Selim Altun; Altun, Selim; Tuna, Sahin Caglar
Soil liquefaction during earthquakes poses a persistent challenge in geotechnical engineering particularly in translating advanced numerical simulations into reliable performance-based damage predictions. This study presents a novel framework that incorporates the maximum excess pore pressure ratio (PPR_max)—a simulation–derived yet underutilized Engineering Demand Parameter (EDP)—to directly predict liquefaction–induced damage under site–specific seismic loading conditions. Dynamic effective–stress finite element simulations were performed for soft alluvial soils in the seismically active İzmir–Karşıyaka region. Using logistic regression and receiver operating characteristic (ROC) analysis PPR_max thresholds were statistically calibrated against observed damage levels to define transition points between minor and moderate damage. This calibration enabled the derivation of fragility curves linking peak ground acceleration (PGA) to probabilistic damage states within a regional hazard–consistent framework. The study further demonstrates the critical role of liquefiable layer thickness in controlling seismic pore pressure response. Even under identical ground motion intensities variations in stratigraphy produced significantly different damage outcomes—highlighting a major gap in current seismic codes which often neglect subsurface variability. The proposed framework enhances the predictive capacity of liquefaction risk assessments by bridging physics–based numerical modeling and empirical damage observations. It provides a scalable foundation for integrating simulation–compatible EDPs into performance–based seismic design and risk mitigation strategies. © 2025 Elsevier B.V. All rights reserved.
Soil-Structure Interaction Analysis of Shallow Rectangular Tunnels Based on the Performance-Based Design Concepts
(Springer, 2025) Şahin Çaǧlar Tuna; Selim Altun; Altun, Selim; Tuna, Şahin Çağlar
This study analyzed seismic responses of shallow rectangular tunnels within the framework of soil-structure-soil interaction. The idealized soil profile and properties were derived from site-specific investigation reports. Racking curves typically used in design were reevaluated to reflect local soil conditions nonlinear soil behavior and seismic influences. Results differed significantly from traditional literature findings emphasizing the importance of localized factors. Finite element methods enabled nonlinear soil parameter modeling and time-history analysis of soil-structure systems. Literature reviews and case studies identified potential damage states with discrete damage levels. The findings quantified probabilities of these damage states and established recurrence relationships for system damages. Fragility curve analyses widely employed in structural engineering were used to develop graphical representations of damage probabilities. This study’s outcomes provide insights into the seismic behavior of tunnels under localized conditions and enhance reliability in geotechnical and structural engineering designs. © 2025 Elsevier B.V. All rights reserved.