finite element

Retaining structure or retaining wall is a wall that acts as supporting structure and the stability of another structure. This wall is used for preventing collapse of soil and generally wherever lateral support is needed. The retaining wall can be designed as gravity, cantilever and supported. Considering that the retaining walls are essential in protecting the related structures to them, therefore, studying the dynamic behavior of these structures is very important due to the financial and human damages. Such structures should be stable against the forces acting on the wall. In addition to static loads, which are always an inseparable part of the calculations of such walls, forces such as cyclic forces caused by the movement of machinery and also dynamic forces caused by earthquake occur on the wall during the period of operation. These forces can be effected on retaining walls and should be investigated and evaluated. Trying to investigate and analyze the dynamic behavior of different retaining walls is one of the most challenging for different researchers. The wavelet theory in the dynamic analysis of the issues related to civil engineering is going to be widespread. This research aims to investigate the effect of using wavelet theory in the dynamic analyses of concrete retaining walls. For this purpose, a soil medium along with concrete retaining walls with different dimensions (heights) are considered. Dynamic analyses are performed based on the finite element method. In the first stage of modeling, the Sarpol-e Zahab earthquake record is filtered during four steps using the discrete wavelet theory. The numerical models are prepared and subjected to the available records. The percentage of the difference in the results of the analyses done with the records obtained from the different steps of filtering record with wavelet compared to the analyses done with the main record, along with the reduction of the time consumption, is evaluated. As expected, the best match of the post-filtering results to the main earthquake results is for the first-step filter. It can be seen that even the first step filter reduces the analysis time by about 60%. Based on the obtained results, the difference between the results obtained with the filtered records becomes less compared to the main earthquake with the increase in the height of the wall. It has also been observed that acceptable results are still obtained, and the analysis time is reduced by almost 80% until the third step filter. It should be noted that the Mohr-Coulomb behavioral model is used in the conducted analyzes in this research. This behavioral model is not inherently able to model hysteresis damping behavior at low strains. Therefore, this issue can affect the results of deformations and stresses obtained from dynamic analysis. However, the purpose of this research is to evaluate the performance of the wavelet in the dynamic analysis of the retaining wall. Considering that in all the analyses (both the performed analysis with the main earthquake and the performed analyzes with the wavelet filtered records) the same structure and trend are used, it can be concluded that the effect of using the wavelet compared to the main earthquake gives an acceptable overview and quality

Although conventional earthquake-resistant systems such as moment frames and braced frames meet the requirements for the safety of a structure when an earthquake occurs, these systems have not guaranteed the prevention of damage to the structure after an earthquake occurs. So that sometimes the repair of some structures seems uneconomic due to these serious damages. Repairing the damage caused by the earthquake was expensive and caused business interruption. A highly effective solution in the new generation of seismic resistance is self-centering systems that eliminate and limit residual drift. The self-centering system's key features affected how the system behaves during earthquakes. The first crucial feature is the amount of post-tensioning (PT) force, which is often used for the standing position after the earthquake. Another one that is played the important role in the behavior of the self-centering system is the energy dissipater element. Employing the damper as a replaceable and cost-effective tool and fuse in self-centering frames to improve energy absorption and damping of structural systems under earthquakes has been considered. A system that can restore the structure to its original state after applying earthquake loads is necessary to minimize damage. Self-centering systems are elements that have the ability to minimize the residual drifts while enduring earthquakes of great intensity. In this study, flexural damper as an energy dissipator system is employed in the self-centering steel moment frame connections to improve energy absorption, post yielding stiffness, and is easily replaceable after the earthquake. Moreover, providing the sufficient stiffness, strength, and ductility, while reducing permanent deformations in the self-centering steel moment frames subjected to seismic loading have been deliberated. In this paper, after validating the results from the FE model with the prior experimental PT connection, the behavior of the self-centering connection with the flexural damper has been analyzed. In the FE modeling, the geometric and material nonlinearities and preloading strands are contemplated in the modeling. Gap opening and closing action beside contact and sliding phenomena are involved in the models. To achieve this goal, a large-scale experimental test program of analyzed and designed models using the finite element method has been planned. Changing the height of the beam has a great effect on the performance of the moment capacity of self-centering connection. This issue has been tested much less in the experiments and researches carried out until today, but the numerical studies have confirmed this issue. In this research, the change in beam height has been evaluated as one of the main factors in the experiments. According to the test results, the beam and column remained in the elastic range. Also the damage is accumulated in the damper. Flexural dampers can enhance the post-yield stiffness and energy absorption of SF-MRF frames, while maintaining minimal permanent deformation at particular damper thicknesses. The obtained results show that in addition to reducing the residual drift to less than 0.5%, the effective energy the dissipation ratio, β, is also improved to 0.25%. Also, this improvement in the seismic performance of self-centering connection with the flexural damper has been achieved with an acceptable ratio of the moment capacity to the beam plastic moment capacity.

Hydraulic fracturing can occur in the fine-grained core of earthen dams. This phenomenon often occurs during the first water intake of the dam when the water pressure suddenly increases. Hydraulic fracturing in Erath dam has investigated laboratory by many researchers (Jaworski, 1981; Jian, 2022; Patel, 2017). In this research, the aim is to investigate numerically the phenomenon of hydraulic fracture and the effect of the dimensions and shape of the clay core section of the Hajiler Chai Dam (an earthen dam with impermeable clay core) located in East Azarbayjan province on the reliability coefficient of hydraulic fracture. For this purpose, first, using Geo-Studio, the phenomenon of hydraulic fracturing has been investigated in two sections in the middle of the core (A-A) and the upstream side of the core (B-B) of the dam for two types of materials CL and CH. Analyzes have been done in the stages of the end of construction, initial dewatering and steady state seepage, and the stages of dam construction have also been considered in the modeling. Also, the possibility of hydraulic fracture in thicker cores and the bottom of the core was also investigated. Finally, the reliability coefficient of hydraulic failure occurrence has been quantitatively calculated for each of the soils in stages and sections and with different criteria, and the suitable soil has been suggested for use in the dam core.

Blast load is a load with a dynamic nature similar to an earthquake, with the difference that its effects take much less time than an earthquake, are more intense, and directly affect the structure itself. Therefore, in this case, in addition to carrying out the usual retrofitting, it is necessary to reduce this explosive effect by changing the architecture of the structure. One of the solutions for this problem is the dual-purpose use of seismic elements such as shear walls, which can not only resist earthquakes but also resist explosive loads. Meanwhile, concrete structures have shown good resistance to explosion compared to steel structures, and one of the design methods in these types of structures is the use of concrete shear walls. One of the solutions to reduce the dimensions of the columns is to use a concrete shear wall. One of the capabilities of this method is the possibility of creating an opening in it, and it reduces the limitations created in the architectural discussion. In this research, the performance of arched concrete shear wall with opening against explosive load has been investigated, and the considered samples with and without opening have been compared. Also, the effect of compressive strength of concrete has been investigated. Finally, it was determined that when creating the opening, full care and inspection should be done and the area around the opening should be reinforced. Arched concrete shear wall with 10 cm thick opening has performed best against explosive load.

In this literature a case study that includes surcharge and prefabricated vertical drains (PVDs) was introduced and verified using finite element program Geostudio 2018R2. Based on the verified model, the lateral displacement and horizontal strains were calculated. It was shown that the safe zone for this special case study is 40 m that is approximately equal to the length of the constructed embankment. In urban areas as a result of the existence of water and wastewater pipes, optical fibers, oil and gas transition lines or trenches and excavations, these infrastructures are in serious danger due to the lateral displacements and horizontal strains. The same case is true for constructions in industrial areas. Since the mentioned infrastructures do have special importance in passive defense doctrine, exclusive attention should be considered by the owners, consultants and contractors in such projects all phases including preliminary investigation, during the construction and after the compilation of the treatment process in the case of permanent embankment. It was shown that due to the obstacles related to surcharge and PVDs treatment, this method is not suitable in urban areas.

Solving the problem with the meshless method is based on selecting a series of points from inside the computational area and boundaries without meshing. In the present study, the phenomenon of seepage below the dam under steady and unsteady flow conditions has been investigated by combining the Meshless method and the Finite Difference Method. Problem solving and calibrating operations were done by coding in MATLAB software. The Meshless method was used for spatial sentences and the Finite Difference Method was used for the discretization of temporal sentences. The results showed that the shape factor (α) for low points is 0.85 and for high points is 0.52, which indicates the proximity of the initial approximations to the main answer. Considering that, the shape factor depends on the geometry and the governing equation, so the same shape factor was obtained for the steady and unsteady conditions equal to 0.52. In the unsteady condition, with the water level behind the dam remaining constant, the water head below the dam also reaches a constant value over time. Also, examination of the results showed that in numerical problem solving, a low error is not a criterion and among the various basic functions, only the MQ function has the better hydraulic performance to draw equipotential lines, so that for 133 points, the shape factor and root mean square error index are 0.52 and 0.0108, respectively.