finite element method (f.e.m)

Steel shear walls are usually made in two types, hardened and unhardened. Studies have shown that hardened types are more suitable in terms of seismic performance and operational issues, but due to the many operational details, they incur a lot of cost. One of the recent innovations used in steel shear wall is the use of corrugated sheets instead of plain sheets. The idea of replacing the corrugated steel shear wall as a hardened steel shear wall has been proposed in recent years and favorable results have been obtained. In addition to easy implementation and installation, this system has made the structures lighter and justified from the cost perspective. In addition, the use of steel shear wall in the seismic improvement of structures has many advantages such as load capacity, energy dissipation, acceptable hardness and ductility. In this research, nine different models with and without holes were modeled using Abaqus software. Six types of hole arrangements with a diameter of 120 mm were modeled. The results showed that by corrugating the (horizontal) sheet, the final resistance increased by 16%, also, by corrugating the vertical sheet, the final resistance increased by 18%. By creating a hole in the wavy (horizontal) shear wall model, it was observed that the ultimate strength decreased compared to the sample without holes. By corrugating the sheet of the shear wall, the coefficient of behavior increased compared to its traditional type, and the largest increase is related to the horizontal corrugated steel shear wall, which is 4%. Also, the pattern of the hole in the corrugated sheet has an effect on the coefficient of behavior, and by choosing the appropriate pattern, an increase in the coefficient of behavior can be achieved, resulting in more energy absorption and damping of the structure.

Implementation of openings in beams web has been introduced as an innovative method for improving seismic performance of steel moment frames. The limited length of the opening zone and formation of the Vierendeel mechanism in this area causes the reduction of beam horizontal length in nonlinear behavior range. This is while, the rigidity of the structural floor system prevents the reduction of the beam span length. This causes the creation of tensile force in the beam which is known as the second order effect. In this article a numerical study is conducted to evaluate the influence of the second order effects on the cyclic behavior of steel beams with web opening. For this purpose, a perforated steel beam has been modeled in Abaqus software and its results has been validated using laboratory test data. The numerical models have been analyzed considering different opening dimensions and three different profiles for the beam cross-section. This is done once with and once again without considering the second order effects and the results are compared. Based on the results, considering the second order effects changes the behavior of the beam in the reduced area and prevents the stiffness and strength decrease in the post-capping part of the hysteresis curve. The amount of additional strength caused by second order effects is negligible for drift ratios smaller than 2%, but it increases with the increase of loading amplitude. At 6% drift ratio, the amount of this additional strength varies between 44% and 120%, depending on the dimensions of the opening. Determination of this additional strength as a function of lateral drift ratio and opening dimensions for use in the analysis and design of beams with web openings can be considered as the main innovation of this research.

The advancement of technology with an increasing population has led to the requirement for high-speed mobility trains. High-speed transportation by trains requires passing through soft soil conditions, which requires stability. High-speed trains are used nowadays in developed countries to reduce travel time. When the train moves at a critical speed, it can significantly increase the dynamic responses of the components on the railway lines. The present study examines the results of 3D numerical modeling, considering the impact of the high-speed train passing through the mechanical earth wall stabilized by plate anchors. Numerical modeling was carried out using Plaxis 3D finite element software. The impact of various factors such as the speed of the train (180, 200 & 250 Km/h), the number of plates (single, double, and triple), and the number of train tracks (1 & 2 tracks) have been investigated. The Hardening soil with small strain model has been used for modeling the behavior of the backfill soil. In this study, the geometrical characteristics of the Thalys high-speed train were used to model the train passing through the walls of 6 meters that were stabilized with plate anchors. From the results, it was concluded that Increasing train speed from 160 to 250 Km/h increases the settlement under the rails by 11% and increases the horizontal displacement of the wall by 13%. It was confirmed that increasing train speed will result in an increase in the settlement under the rails and increases the horizontal displacement of the wall in all investigated cases. Increasing the number of plates along with decreasing their dimensions has a positive effect on the wall’s performance with regard to the horizontal displacement of the wall. Also, it should be mentioned that by increasing the number of train tracks from 1 to 2, the settlement under the rails increased by 5%, and the horizontal displacement of the wall increased by 20%.

Various bracing systems can be used to withstand lateral displacements caused by earthquakes and wind. One of these systems is Buckling Restrained Braces (BRBs), which consist of a steel core known as a "core plate" and a buckling restraining mechanism (BRM) made of full steel, concrete-steel, or other materials. This study presents a novel method to enhance the performance of all-steel BRBs. In this new method, a lubricated perforated steel plate with roller bearings (small solid steel cylinders) is attached to both sides of the core plate within the BRM. During plastic elongation and contraction of the core plate due to tension or compression loads, these movements occur on the roller bearings, which are housed in a grease-filled space. As a result, the friction between the core plate and the BRM is reduced, preventing the transmission of axial forces to the BRM. Additionally, the reciprocating movement of the core plate inside the BRM is smoothed, eliminating the risk of premature core plate failure. Finite element analysis has been conducted to analyze various types of all-steel BRBs with and without the new method, demonstrating the advantages of the proposed approach. The inclusion of roller bearings in the samples reduces frictional forces on the sheath by at least 45% and up to 63% compared to similar samples without roller bearings.

Tubular structures are made of hollow steel members with circular cross-sections and connecting them is one of the major challenges in their design. So far, some techniques to improve the performance of tubular connections have been proposed. Most of these methods can only be used for structures during the fabrication, but there are only a few techniques that can be applied during both fabrication and operation. Due to the successful experience of using composite materials for the repair and retrofitting of structures, special attention has now been paid to examining the efficacy of these materials in offshore structures.In this research, the effect of CFRP and GFRP wraps on the ultimate strength and deformation of tubular X-joints under compressive load is investigated. For this purpose, the results of the finite element (FE) models were validated with several available experimental tests. After that, the nonlinear static behavior of tubular X-joints strengthened with FRP was studied. In these FE models, the contact between the FRP layers and the steel members (chord, weld, and braces) was considered. Also, the weld profile in the brace/chord intersection was modeled.

Earthen dams have a significant impact on the lives of surrounding communities, so the need for continuous monitoring during the construction and safe operation of these structures when applying dynamic loads, especially explosive loads due to possible sabotage and firefighting has always been considered. The effects of explosive loading, assuming the conditions affecting the performance of earth dams, can be measured using several parameters, the most important of which are the dimensions of the pit caused by the explosion and the stability coefficient of the slopes of the structure. Therefore, in the present study, according to the researches done in the field of dynamic loading of earth dams, while selecting the model and its characteristics, in order to validate the simulation process and apply dynamic loading, the results of numerical solution with the article A reference is compared that provides acceptable consistency. Then the dynamic loading of the explosion in the form of finite element software is simulated in certain parts of the structure and after analysis, the results show that by increasing the explosive charge and increasing the water level of the dam reservoir and also reducing the density of constituents Of the body; The depth and dimensions of the hole created by the explosion in the crown of the dam will increase, which will also indicate local damage. Finally, to investigate the dynamic stability of the slopes, the results are transferred from finite element software to the slope stability analysis software, and the model under pseudo-analysis Static and dynamic, and finally stability analysis. The results indicate that under an explosive charge of 800 kg , the reliability coefficient of slope stability is higher than the reliability coefficient introduced by the publication 624, which indicates no serious damage and instability of the dam structure

In this paper, the main purpose is to investigate the behavior of a reinforced section with vertical stiffeners and circular stirrups of Concrete filled double-skin steel tube (CFDST) columns under cyclic and fixed axial loading. So, the proposed reinforced section with a simple section (not reinforced) in this type of columns with a length of 200 cm has been loaded and examined in the structural laboratory and then modeled in ABAQUS software and their displacement- force cycle diagram has been extracted. In this research, by designing a new reinforced cross section of this type of columns and comparing it with a simple cross section, the improvement of seismic behavior of this type of columns, including ductility, bearing capacity, and energy absorption capacity, has been investigated. To ensure the accuracy of finite element modeling, the results of numerical analysis were compared with laboratory results and the modeling accuracy was also ensured. In addition, the column with reinforced cross section has a significant improvement in its cyclic behavior compared to the simple cross section of this type of column, so that vertical stiffeners and circular stirrups prevent a sharp drop in column strength after the outer wall of the steel pipe deteriorates.

Today, reinforced concrete structures have a special place in the construction industry. To retrofitting some existing concrete buildings, steel braces are used with direct connection to concrete frame. The important issue here is what the details of the connection of the brace to the concrete structure should be. The connections in concrete structures always have the most damage during an earthquake. Therefore, the performance of the connections and the type of steel braces connection to the concrete frames will affect the seismic behavior of them. For this purpose, in this study, three methods of steel brace connection to the concrete frame have been investigated. Models are created as one-story single-span and two-story single-span frames using the finite element method in the Abaqus software. The results indicate that the change in the type of connection causes changes in energy absorption, stress distribution and maximum lateral displacement of the frame. Meanwhile, by applying bilateral loads, first the bolt planting model and then the metal jacket method are considered as selected models. Concerning the performance, which is represented by plasticity and damage of elements, the maximum difference between connection methods is 10 percent and all of them are considered acceptable.

Understanding the performance of reinforced concrete (RC) structures against earthquake load to design them is imperative. One of the fundamental issues determining the performance of concrete structures against earthquake load is investigating the joint behavior and its appropriate ductility. To attain adequate ductility in beams and columns, the joint must have sufficient strength and ductility to withstand the ultimate loads of beams and columns. In many RC structures that have been exposed to severe earthquakes, joint shear failure has been observed. Shear failure of the joint can be due to the weakness of oblique reinforcements in the beam-column joint area of RC structures. The use of high-strength external bolts under axial and cyclic loading in ABAQUS finite element software has been investigated in this paper. The arrangement and the amount of post-tension of the bolts are the parameters investigated in this study. The use of external bolts to retrofit the RC beam-column joints indicates an increase in confinement and consequently improves performance at the joint area. In addition to preventing shear failure in the joint fountain, the proposed method causes a capacity increase of about 44% in post-tension specimens. Also, it increases energy absorption by about 50% in retrofitting specimens.

In general, masonry structures are divided into two categories in terms of the connection between components: mortar-free masonry, which is called dry joint, and structures that use mortar to connect the components. Due to environmental conditions, when the mortar loses its adhesion over time, the components of the wall can be considered as discrete elements. The poor performance of masonry structures leads to the failure of a significant number of these structures even in moderate earthquakes. In particular, in-plane failure in the walls of masonry structures is very common. The results of laboratory research show that shear failure is very likely in lateral loading. One of the characteristics of this failure mode is its ability to resist high shear force and low ductility, which leads to brittle failure in the wall. Previous numerical studies on masonry structures have been mainly based on the finite element method in which the wall components are considered as continuous elements and the local behavior of the constituent parts of the walls is ignored and causes their real function to be misunderstood. In this paper, first, the specifications of unreinforced masonry wall specimens were determined based on the results obtained from previous experiments, and then numerical models were calibrated and analyzed using two software ABAQUS (finite element software) and 3DEC (discrete element software). Then, behavioral diagrams of walls with different characteristics were extracted under different loading conditions. Finally, a comprehensive comparison between the results obtained from the discrete element and finite element methods was presented. Finally, it was concluded that the discrete element approach provides a more accurate prediction of unreinforced masonry walls than finite element one.

The use of multilayer elastomeric bearings in bridges has showed that application of this bearings improved seismic behavior of this types of infrastructures during recent earthquakes. Applications of the elastomeric isolation bearings in long-spans or tall pier bridges can experience rotation due to flexure of the deck or the piers, that it can be effective on their seismic performance. In current study, a two-dimensional mechanical model of elastomeric bearings, under the simultaneous effect of pressure, shear and end rotation is investigated. This mechanical model consists of three layers of axial springs with nonlinear hysteresis behavior that play the role of bending and compressive deformation distribution. The model can take into account end rotations of the bearing, and the overall rotational stiffness includes the effect of the variation of vertical load on the bearing. Comparison of the results of nonlinear static bending tests of this model with the results of laboratory studies shows very well agreement. The results indicate that rotational stiffness increases with higher values of vertical pressure, however decreases with increasing shear deformation. As conclusion, end rotation does not affect the critical displacement appreciably, but it significantly influences on the critical shear force.

Due to population growth in large cities and the growth of cities vertically, in order to facilitate serviceability and provide low-cost and easier access to the needed resources, engineers are forced to build high-rise buildings on less desirable soils. Given the seismic conditions of our dear country Iran and the variety in thickness of soil in different places, it is important to know the structure suffers the most damage under which conditions. In this study, a nonlinear three-dimensional model of soil-structure interaction in tall buildings with finite element method by Abacus software in the time domain is investigated to evaluate the effect of soil-structure interaction. the dynamic implicit used to calculate the problem. Thickness effect with considering soil-structure interaction for 4 different thicknesses by Drucker-Prager modeling method which also considers soil hardening properties under the effect of Lomaprita earthquake which is considered as an earthquake with low frequency content ( Earthquakes with low frequency content have more destructive effects), has been calculated. infinite boundaries used to absorb the reflect of waves. the boundaries The research results show that changes in thickness have significant effects on the analysis results. In this study, for each model, lateral displacement , acceleration, subsidence, acceleration spectrum and stress contours are investigated.