نشریه مهندسی عمران فردوسی
سال سی و چهارم شماره 1 (بهار 1400)

Wind energy is one of the most hopeful renewable energy sources that is also growing. The wind turbine tower supports the complete wind turbine system, and its damage may cause catastrophic failure of the wind turbine. However, the background to the study of the health monitoring of the wind turbine tower against its mechanical installations is insignificant. Besides, no comprehensive research has been conducted on the health monitoring of the tower with soil-structure interaction included. In this article, the extensive analysis of the multilevel 2D wavelet decomposition approach using orthogonal wavelets and soil-structure interaction is performed numerically. The established finite element model is calibrated and verified with the NREL 5-MW reference onshore wind turbine. Then, while defining several damage scenarios, the 3-dimensional modes of the finite element model of the damaged structure were investigated using the proposed method. The findings imply that the quality of the damage detection in the soil-structure interaction models has increased, generally.

Due to the non-homogeneous nature of cohesionless soils, and the complexity of the parameters related to settlement, generally the exact estimation of the foundation settlement involves many difficulties. This problem has been studied by many researchers and some equations have been proposed for estimating the settlement of shallow foundations. Because of the low accuracy of these equations, researchers are using more modern techniques like finite elements, finite difference, soft computing, and so on, for calculating the settlement. In the current study, a new model is proposed based on artificial intelligence to predict the settlement. The purpose of developing such models is to achieve more accurate and possibly simpler equations. In this paper, the performance of multi expression programming (MEP) method to predict the settlement of shallow foundations on granular soils is evaluated and the values obtained from the developed models are compared with those from the most accurate previous models. Then, the performance analysis, validation, parametric study and sensitivity analysis are performed. As can be seen from the results, the comparison between the MEP model and the most accurate models including ANN, GP, GEP and EPR in the technical literature showed that the model proposed in this study with correlation coefficient of 93.45 percent, performs better than most previously developed models.

The time-dependent behavior of sands is one of the main issues that can influence many projects. In this study nine sand models with different particles shape and sizes and different grain distribution have been used to investigate creep behavior. The samples were prepared at 60% relative density and the constant stresses of 45 kPa for 30 days and 26 to 416 kPa for seven days (with the double increase in stress increment) under dry conditions in the Oedometer apparatus (one-dimensional consolidation) were tested. The results showed that the rotation, slipping, and crushing of the sand grains over time under constant load was the cause of creep deformation in the dry samples. Sand samples exhibit 1.5 to 4.2% creep strains in 30 days, and 0.61 to 2.5% creep strains in seven days’ time interval. Finally, two linear equations are presented to predict the deformation of sands over time. The results were in good agreement with previous studies.

In the present study, the seismic behavior of self-centering rocking wall systems in both types of base-rocking and double-rocking was investigated. To conduct seismic analyses, three sets of seismic records were considered including 22 Far-Field (FF) ground motions and 28 Near-Field (NF) ground motions that half of which are Pulse-like (Pulse). These ground motions were used for nonlinear time-history analysis of structures with 8, 12, 16 and 20 floors. Based on the area of prestressing cables, three types of double-rocking walls are considered and compared with the base-rocking and the fixed base walls. Numerical modelling was conducted via OpenSEES software in two-dimensional space. For the sake of validation, the available experimental data of base rocking and fixed base walls was used. To compare the seismic performance of the structures, some desirability coefficients have been defined. These coefficients were based on the reduction of the higher mode effects and the reduction of the inter-story residual drifts. The results showed that generally, the double-rocking walls provides higher desirability coefficients than the other considered systems. Furthermore, the double-rocking walls by reducing the cable area in the bottom block (R2-H1) are more

The seismic behavior of the on ground bipartite elliptical tanks has been investigated in the current study. Basically, the tank is a structure used to store different types of fluid, and it is also widely used in refineries, sewage treatment plants and factories in the form of on ground and elevated tanks made from concrete and steel. The monoplete and double on ground elliptical tanks have been dinamically analyzed under Cape and Tabas earthquakes simoultaneously in the longitudinal and transverse directions in various conditions of prolateness and slenderness of the tank and the maximum impulsive pressure and the maximum wave height parameters of corresponding cases have been compared with eachother in the current research. By study of the concluded diagrams, it was revealed that the reduction percent of the maximum impulsive pressure and the maximum wave height parameters due to partitioning of the tank is higher in more slender tanks. It also was revealed that the reduction percent of the maximum impulsive pressure and the maximum wave height parameters due to partitioning of the tank is higher in more prolate tanks.

Rock fall is a type of slope instability that occurs in most mountainous areas and causes casualties and severe damage to facilities, residential areas, roads, farms and vehicles. Therefore, to prevent financial damage, it is necessary to predict and model the phenomenon of rock fall in steep walls to take preventive measures. In this paper, in order to assess the risk of falling rocks, first using Rocfall software, the path of rock fall of isolated blocks was analyzed individually and separately in the most critical section of the northwestern heights of Shahrood. In order to consider the interactions between particles in the path, shape, size and weight of the parts, the distinct element method PFC3D was used. Analyzing the simulation results with the help of these two softwares, it was concluded that if the rock falls, a large number of parts will stop in the area of ​​roads and residential areas, which will result in traffic jams and financial-human risks. In other words, considering that the maximum horizontal distance traveled by the plots is 393 meters and the horizontal distance between residential areas is 340 meters, so the probability of an accident due to falling rocks is very high. In the following, suggestions such as installation of metal grids, shock absorbers, reduction of kinetic energy in the parts, change in the dimensions of the parts, change of the slope geometry to reduce the risk and damage caused by falling rock in the desired section are presented.