The behavior of concrete structures that are exposed to extreme thermo-mechanical loading is an issue of great importance in nuclear engineering. The structural re-safety capacity of concrete is very complicated because concrete materials have considerable variations. CONSTITUTIVE MODELS and relationships for preloaded Normal and High Strength Concrete (NSC and HSC) subjected to fire are needed, which are intended to provide efficient modeling and to specify the fire-performance criteria of the behavior of preloaded concrete structures exposed to fire. In this paper, formulations for estimating the parameters aecting the behavior of uncon ned preloaded concrete at high temperatures are proposed. These formulations include residual compression strength, initial modulus of elasticity, peak strain, thermal strain, transient creep strain and the compressive stress-strain relationship at elevated temperatures. The proposed CONSTITUTIVE MODELS and relationships are veri ed with available experimental data and existing MODELS. The proposed MODELS and relationships are general and rational, and have good agreement with the experimental data. More tests are needed to further verify and improve the proposed CONSTITUTIVE MODELS and relationships.

Linear viscoelastic CONSTITUTIVE laws, such as hyperelasticity with the Prony series, are commonly used in commercial software to simulate polymer materials. However, these MODELS are not accurate regarding large strain problems despite performing well for small strain problems. To gather experimental data for soft adhesives, various shear modes were employed, including monotonic, creep, and low-cycle tests using single-lap shear specimens. These tests were conducted on optically clear adhesives (OCAs). Initially, the validity range for linear viscoelasticity was established, revealing the inability to predict large strains accurately using this approach. Subsequently, the three-network viscoplastic (TNV) model parameters were calibrated experimentally under large strains. The calibration procedures took advantage of variations in loading modes, enhancing the precision and improving the accuracy of the CONSTITUTIVE MODELS. For calibration purposes, it is recommended to utilize the low-cycle loading-unloading test as it offers a suitable and cost-effective means of precision. This approach provides a cost-effective way to accurately predict material behavior, owing to the variations in loading modes. Finally, the characteristic model was used to evaluate the results through the finite element method. The results showed that the proposed model accurately predicts stress values, energy dissipation, and energy loss due to softening.

In the present study static response of cantilever retaining walls have been investigated by consideration of various soil CONSTITUTIVE MODELS by means of finite element method with using PLAXIS 2-D software. Simulations have been performed at heights of 3, 6, and 9 meters retaining walls with considering two types of soils (cohesive and cohesionless) as backfill material. In this study, analysis have been conducted for two kinds of cohesionless backfill (loose and dense sand in dry condition) and at both conditions, saturated and unsaturated, for cohesive backfill. Analysis have been carried out by using three CONSTITUTIVE behavioral methods: Mohr-Coulomb (MC), Hardening-Soil (HS) and Hardening soil model with Small-Strain stiffness (HSS) for cohesionless backfill and additional method, Soft Soil model (SS), for cohesive backfill. The results show that, for cohesionless and cohesive backfill materials the lateral forces acting on the retaining wall are underestimated by the MC and SS CONSTITUTIVE MODELS, respectively.

Numerical modeling is a strong tool for soil deformation in deep excavations. There are some kind of method such as finite element, finite difference and etc. Finite element method help to select the appropriate CONSTITUTIVE soil model with high accuracy. The controversy between simplicity and accuracy is an important issue always has been intrested in by the researchers. By using physical modeling the accuracy of each CONSTITUTIVE soil modeling could be asset. In this paper, four MODELS of geotechnical centrifuges have been uesd to investigate the effect of the overburden distance from the edge of the excavation and the results of various CONSTITUTIVE soil MODELS in the soil nailing wall. The results showed that the overburden distance from the edge of the wall is so effective on the value and pattern of wall deformation. By increasing the overburden distance from the edge of the excavation, the greatest amount of horizontal deformation of the wall leads to the bottom of the excavation. However, the basis of numerical solution, without the overburden distance from the edge of the excavations, this deformation always occurs in the top of the excavation. Also, based on the comparison of the results of centrifuge MODELS and the results obtained from different behavioral MODELS, in order to predict the vertical deformation of the top of the excavation, the result of hardening soil small strain model (HSS) is nearer to real than other investigated CONSTITUTIVE soil model.

Numerical modeling of soil can be used as a complementary or alternative method for laboratory tests. Therefore, in the simulations of geotechnical problems, properly using CONSTITUTIVE MODELS (such as the cap model) requires accurate calibration of the model parameters. In the present study, the draining behavior of Nevada sand at a relative density of 40% was evaluated using Mohr-Coulomb (MC), Drucker-Prager (DP), and modified Drucker-Prager/cap (MDPC) MODELS in Abaqus and compared with laboratory data. In this context, the conventional triaxial compression (CTC) technique was used for finite element modeling of selected drained triaxial tests by keeping the radial stress constant and increasing the axial stress. Based on the results, MC and DP CONSTITUTIVE MODELS, where the behavior of the materials is linear elastic-perfectly plastic, at high confining pressures, due to the inability to simulate soil hardening, showed significant differences with the experimental results. In other words, with increasing confining pressure, the behavior of sand tends to harden, and the ability of the MDPC model, which has a hardening function based on volumetric plastic strain, increased in simulating sand behavior. Proper determination of cap parameters can have a significant effect on the results. In the present study, cap hardening parameters for Nevada sand have been determined based on experimental data.

In this study, the effect of state parameter in elasto-plastic CONSTITUTIVE MODELS on improvement of predicting sand behavior was studied, using DIANA-SWANDYNE II program. The centrifuge test results, which were obtained in VELACS workshop, were used in this study. The mechanical behaviors of centrifuge MODELS under earthquake loading was predicted by using Pastor & Zienkiewicz Mark III CONSTITUTIVE model and the modified model and were compared with experimental results. The results show that the use of current state parameter can have a significant effect on improvement of predicting deformation, water pore pressure and acceleration caused by earthquake loading in soil structures.

Recently, Shape Memory Alloys (SMAs) have been receiving more attention and further study, due to their ability to develop extremely large, recoverable strains and great forces. In this paper, three major MODELS of SMA behavior, used in the literature, for studying the static performance of SMA components attributed to Tanaka, Liang and Rogers, and Brinson, have been analyzed and compared. The major differences and similarities between these MODELS have also been emphasized and presented in this paper, based on the experimental data of the shape memory and superelastic behavior of an SMA wire. It is shown that these MODELS all agree well in their prediction of the superelastic behavior of SMAs at higher temperatures, but the MODELS developed by Tanaka, and Liang and Rogers cannot be used for predicting the shape memory effect behavior of SMAs. It is also shown analytically that the original evolution kinetics, proposed by Brinson, in a specified region, are inadmissible for some thermo mechanical loading and initial conditions. Furthermore, corrected evolution kinetics is addressed here in detail, that is, admissible and valid in this region. According to this research, regarding the validation assessment of three major 1-D CONSTITUTIVE MODELS with experimental data, it will be shown that the Brinson model with the corrected evolution kinetics developed by Chung et al. can be applied for the modeling of SMA smart structures, such as flexible SMA beam structures.

This study investigates the hot deformation behavior of API X80 pipeline steel using modified hyperbolic sine-based CONSTITUTIVE MODELS. Uniaxial compression tests were conducted at temperatures of 950 to 1100 °C and strain rates of 0.001 to 1 s⁻¹. Five CONSTITUTIVE approaches were evaluated: linear-linear Shi (LLS), linear-polynomial Shi (LPS), polynomial-polynomial Shi (PPS), and polynomial-polynomial Yang (PPY). Results indicate that activation energy (Q) varies significantly with deformation conditions. While the constant Q (CAE) model provides reasonable predictive accuracy and remains useful for simplified analysis, the PPY model demonstrates superior performance by capturing complex dependencies between stress, temperature, and strain rate. Zener-Hollomon (Z) maps and Q contours further illustrate the impact of model selection on process prediction. These findings establish a reliable computational framework for accurately modeling and optimizing hot deformation in high-strength steels.

With the advancement of numerical modeling, predicting tunnels' behavior before construction has become possible for designers. Accurate prediction of tunnels' behavior in diverse environments requires the compatibility of numerical simulations with ground conditions. Although several CONSTITUTIVE MODELS have been proposed for simulating ground characteristics, their appropriate utilization is crucial. In this study, the convergence of a tunnel is modeled, and the results are verified using actual convergence monitoring data. Then, a series of finite element simulations are conducted on a hypothetical TBM tunnel to demonstrate the difference in deformations, ground surface settlements, and stresses in the lining resulting from tunnel excavation under seven CONSTITUTIVE MODELS in rock media. The MODELS are categorized into four groups: rock-specified, soil-established, and general. Additionally, parametric studies are performed on specific gravity, Poisson's ratio, and dilation angle. The findings revealed that different CONSTITUTIVE MODELS significantly influence numerical analysis results. Rock-specified MODELS were found to be more sensitive to parameter variation in rock media than soil-established and general MODELS. Moreover, changes in specific gravity and Poisson's ratio had a significant impact on the magnitude of surface settlements. Overall, the study highlights the importance of appropriately selecting CONSTITUTIVE MODELS and accurately defining material parameters in numerical simulations to ensure reliable predictions of tunnel behavior.

Tunnels are used for numerous purposes; therefore, proper evaluation and prediction of tunnel behavior, influenced by the surrounding environment's characteristics, is of great concern for civil engineers. In this regard, two water convey and railway tunnels in rock medium were modelled to investigate the influence of various CONSTITUTIVE MODELS on tunnels’ behaviors prediction. The tunnel convergence predicted by each CONSTITUTIVE model was compared with the reported monitoring data. Then, the most appropriate CONSTITUTIVE MODELS for tunnel analysis in each rock category were proposed according to the strength of each category’s rocks. The results indicated that the Mohr-Coulomb criteria for very weak rocks, the Generalized Hoek-Brown for weak rocks and the Generalized Hoek-Brown with the residual parameter criteria for modelling medium rocks, had more reliable predictions of tunnel convergence. Also, utilizing shear strength parameters correlated from rock mass specific parameters to analyze tunnels in weak and medium rocks was not satisfactory.