Browsing by Author "Tuna, Sahin Caglar"

Now showing 1 - 4 of 4

Critical Evaluation of Strong Ground Motions in Izmir and Implications for Future Earthquake Simulation Results
(Copernicus Gesellschaft mbH, 2026) Tuna, Sahin Caglar
Izmir, a major city in western Turkey, is located in a highly seismic region, subject to frequent earthquakes due to its proximity to active fault systems. This paper critically evaluates the strong ground motions recorded in Izmir, with a focus on understanding the implications for urban infrastructure and future seismic hazard mitigation. Historically available data is collected and compared with the available ground motion prediction equations (GMPE). Later, the most appropriate prediction equation is selected and used to determine the target response spectrum. 2020 Sisam earthquake is a well-documented seismic event and the data from the stations are then used to further calibrate the 1D site response model. Lastly, possible future events are generated and results are compared with the current Turkish Earthquake Code (TEC). Amplification factors prescribed by code for Izmir Bay have been surpassed by projected future events, highlighting the necessity for reassessment. Therefore, region-specific seismic zoning should be established when standard code practices fall short in accounting for significant site effects. Concrete recommendations about local site modification factors and evaluations on this topic have been provided within the article.
Direct Shear Box Assessment of Sand–Rubber Mixtures: Strength, Ductility, and a Performance Index
(2025) Tuna, Sahin Caglar
The reuse of waste materials in geotechnical engineering promotes sustainability while enhancing soil performance. This study investigates the effect of shredded waste rubber on sand through consolidated drained direct shear tests at two relative densities (Dr ≈ 30% and 70%) with 0–10% rubber content. Rubber inclusion reduced brittleness and improved ductility, with mixtures containing 2.5–5% achieving the most favorable strength–deformation balance. In loose sand, cohesion and friction angle increased up to 5%, while in dense sand cohesion rose slightly but friction angle declined at higher contents. A new Performance Index (PI) is proposed in this study, integrating energy absorption, ductility, and residual-to-peak strength into a unified framework. The PI confirmed the 2.5–5% range as optimum, providing a practical tool for mixture evaluation. These findings indicate that low rubber contents are suitable for seismic embankments, retaining walls, and transportation subgrades, while higher contents may be more effective in lightweight and energy-dissipative applications.
Probabilistic Evaluation of Earthquake-Induced Soil Liquefaction Using 3D Spatial Variability Modeling and Performance-Based Design: A Case Study from I•zmir, Türkiye
(Elsevier Sci Ltd, 2026) Tuna, Sahin Caglar
This study develops a comprehensive probabilistic, performance-based framework for assessing earthquakeinduced soil liquefaction by explicitly incorporating spatial variability through semivariogram-calibrated three-dimensional Gaussian Random Fields (3D GRFs). A dataset of 52 Standard Penetration Test (SPT) boreholes from I(center dot)zmir, Türkiye was processed to generate Monte Carlo simulations that capture the stochastic nature of soil resistance. Liquefaction susceptibility was quantified using three complementary indicators: the Liquefaction Potential Index (LPI), reflecting potential surface deformation; the Damage Severity Index (DSI), linking severity to engineering performance thresholds; and the depth-averaged probability of liquefaction P(Liq), representing occurrence likelihood across different seismic intensities. Fragility functions were developed using both logistic regression and Monte Carlo-GRF simulations, and subsequently coupled with site-specific seismic hazard curves to derive annualized liquefaction risk metrics expressed in return-period format. Results highlight the nonlinear escalation of liquefaction severity with increasing seismic demand, accompanied by a systematic growth of epistemic uncertainty. Scenario-based probabilistic mapping revealed spatial hot spots of susceptibility and variance, underlining the value of incorporating correlation structures in liquefaction hazard assessment. Validation against field evidence from the 2020 Samos Earthquake confirmed the predictive reliability of the framework, with GRF-based simulations producing results consistent with reconnaissance observations in I(center dot)zmir Bay and surrounding coastal sites. Overall, the proposed framework advances methodological clarity and provides actionable contributions for seismic microzonation, regional hazard mapping, and performance-based geotechnical design, supporting the development of more resilient infrastructure in earthquake-prone urban environments.
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.