Ģ017 elements comprise this model, it is pinned at the bottom surface, and all the top nodes are connected with rigid links to a central node which is allowed to move along and rotate around the vertical axis. Figure 2 shows good compatibility between RC and TOSS tests, and also similar behavior to the studies conducted by Seed and Idriss and Vucetic and Dobry. Shear modulus values from TOSS test were obtained from the monotonic one-way curve, as well as the G sec which is the slope of the line that connects the two ends of each of the loops. 2, the maximum shear modulus obtained from RC test is 95,500 kPa, and other RC tests were conducted at higher strains. An irregular load history was scaled to obtain a maximum value of shear stress of 40 kPa for this stress-controlled TOSS test, and the resulted shear stress-strain curve was used for curve fitting and calibrating the model. For this study, only one irregular TOSS test with a shear stress of 40 kPa was used to evaluate the ability of the material models to predict the dynamic behavior of the soil. The tests were conducted on dry sand, a set of resonance column tests in addition to cyclic and irregular tests were performed up to a stress level of 60 kPa and a confining stress of 94 kPa. The testing device was described in detail by Szilvágyi in his thesis. Then it was rebuilt and calibrated in Győr at the Geotechnical Laboratory of the Department of Structural and Geotechnical Engineering at Széchenyi István University for the purpose of the PhD study of Zsolt Szilvágyi in 2013. The combined Resonant Column-Torsional Simple Shear Device (RC-TOSS device) related to this study was originally built by Prof Richard Ray at University of Michigan in the 1980s Ray,, Ray and Woods. 1).ģ Combined resonant column and torsional shear test The shear modulus degradation curve can be obtained from the torsional simple shear test, which generates stress-strain hysteresis loops, from which values of the secant shear modulus G sec are computed with the increasing strain level ( Fig. In this phase, the shear modulus reduction curve is usually used to describe this property, which is important for the analysis of different dynamic problems where the strain is of high amplitude (e.g., strong ground motion during earthquakes). Furthermore, the shear modulus decreases as the shear strain amplitude increases, and the soil’s behavior becomes nonlinear. Vucetic and Dobry and Ishihara defined a volumetric cyclic threshold shearing strain γ tv, which when exceeded permanent microstructural change of soil occurs and soil stiffness changes permanently. The most used equations are presented by Hardin and Richart, Hardin and Black, and most recently by Wichtmann, Navarrete Hernández, and Triantafyllidis. Other equations can be used as well based on extensive laboratory testing programs to calculate the initial dynamic shear modulus G max, where it is correlated to the confining stress, void ratio, and uniformity coefficient C U. It can be determined by using seismic methods in the field to obtain in situ shear wave velocity, where the strain level is very low and the soil still behaves elastically. The shear stiffness of the soil is usually represented by the shear modulus G, which is the slope of the shear stress-shear strain curve. In this study, the Ramberg-Osgood and the Hardin-Drnevich models were used to predict and simulate the soil behavior in the TOrsional Simple Shear (TOSS) test, and the results were compared with test data for irregular loading patterns. However, the progressive development in computer technology accompanied with the increasing speed of processing complex calculations allowed the use of numerical modeling for easier and faster calibration of models for further use in real and much more complicated geotechnical problems (e.g. This has been a challenge when it comes to irregular loading patterns due to the complex nature of soils’ behavior and its dependence on many factors like the confining stress, void ratio, density and number of cycles, etc. Thus, to be able to study the soil-structure interaction numerically with adequate accuracy, it is important to have a material model that is well representative of the soil in the field conditions. It is agreed that the most important parameters to define this behavior are the dynamic shear modulus and the damping ratio, which contribute to variation in the stiffness and energy dissipation during cyclic loading. Therefore, many researchers in the past few decades focused on studying the behavior of soils subjected to dynamic loads. The response of structures to dynamic loading is directly dependent on the response of soil beneath or around it.
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