نشریه مهندسی سازه و ساخت
سال نهم شماره 4 (پیاپی 57، تیر 1401)

The use of displacement-dependent steel curved dampers as fuse or interchangeable element in the beam-to-column connection region is one of the newest methods for improving the seismic performance of semi-rigid moment steel frames (SRMF). In the present study, performance of low-yield strength steel curved dampers in SRMF has been investigated. These dampers are inactive and install in the beam-to-column connection region. Variable parameters of this study involve the damper width (75, 100 and 125 mm), damper thickness (10, 15, 20, 25 and 30 mm) and the curve damper steel type (SN400YB and LY160). Evaluation of SRMF models were performed using finite element method by ABAQUS software. For validation, a SRMF with steel curve dampers under cyclic loading was modeled that had been experimentally tested and reported in previous experimental research and a good agreement was observed. The results show that the use of low-yield strength steel in curved steel dampers, depending on the damper thickness, can lead to an increase in the ductility parameter and total energy dissipated compared to the steel with higher yield stress. Also, the steel curved damper around the beam-to-column connection zone has caused the plastic hinge to occur in the farther region of the connection.

Nowadays, the use of innovative methods such as cross-sectional reduction method in designing moment connections of steel structures has become widespread among designers. The method of reducing the cross section by deliberately weakening the beam in a part close to the connection of the beam and column reduces the plastic strains of the joint and the formation of a plastic hinge in the beam. In this paper, the effect of reduced beam section (RBS) on joint strength by removing the plastic hinge from the column and also the optimal performance of various reduced beam section shapes through different indicators such as hysteresis curve, pushover diagram, energy dissipation of connection and … are checked. In this research, modelling and nonlinear analysis of 10 examples of reduced beam section with and without beam section reduction using ABAQUS software has been investigated under cyclic loading. The results showed that all models with reduced beam section have the ability to transfer the place of formation of plastic strains or the same plastic hinge into the beam and away from the column. Among all the methods of reducing the cross-section, the method of reducing flange beam section with uneven holes and enlarging inward to the beam has shown a better performance than other samples. The energy dissipation of this method is increased 68% versus the reference sample without reduced section. The flexural capacities of sample with reducing flange beam section with uneven holes and enlarging inward to the beam has shown better cyclic performance. The values of flexural capacity in the mentioned sample is decreased 33% versus the reference sample without reduced section. This subject causes plasticization faster and as a result, more energy dissipation is obtained versus other samples.

With their wide range of applications in the design and construction of steel structures, rigid connections are among the most prevalent types of connections. In many cases, hollow circular columns are used as a component in moment resisting frames. Circular columns have a wide range of applications, primarily due to their high flexural strength around the principal perpendicular axes, their ductility, energy dissipation, and low susceptibility to local buckling. These hollow sections are available and used in two forms: rolled sections and sections manually manufactured using plates. The most important weak point of these sections is when they are used in moment resisting frames and structures located in areas with a high level of seismicity. In these cases, design standards necessitate the use of continuity plates along the beam’s flanges. However, due to the inaccessibility of the inner spaces of these types of columns, using continuity plates is either impossible or very difficult. This study introduces an external diaphragm connection between the I -shaped beam and hollow circular column which uses continuity plates outside the section (column). Through an experimental investigation, the behavior and strength of welded and bolted connections are evaluated under cyclic loading. The results show that the proposed detail possesses suitable strength and ductility, and provides the connection with a suitable level of rigidity. The connection satisfies the specifications of existing seismic codes.

In recent decades, construction of massive structures has increased around the world. These structures which are built for different purposes, should have a useful life-time. Therefore, composite structures can increase the construction costs and useful life of such structures. Therefore, CFDST members can practically increase the efficiency of composite structures. Since the diameter and thickness of the outer tube have the greatest impact on determining the bearing capacity of CFDST columns, this study investigated four different values of D/t for the outer tube including 86, 85.8, 45.6 and 44. Two types of concrete were used to fill CFDST samples including C10 and C20. Besides, a comprehensive formula for estimating the bearing capacity of CFDST columns using artificial intelligence methods is proposed. The results showed that CFDST columns with lower Do / to value have higher load capacity and with increasing Do / to, it is observed that the ductility decreases. As a comparison between the filled concretes in CFDST samples of C10 and C20 grades, the stress-strain curves have shown that with increasing compressive strength, the bearing capacity for CFDST columns increased by about 6%. In the modeling section, the R2 for artificial neural network (ANN), support vector machines (SVM) and model tree (M5-MT) in the testing stage were determined to be 0.95, 0.96 and 0.97, respectively. Accordingly, the M5-MT method in the testing stage, had a better performance than other proposed methods for estimating the bearing capacity of CFDST columns. Comparison of traditional equations and AI models in estimating the bearing capacity of CFDST columns show that the formula presented by M5-MT with an average value of 1.01 and a standard deviation of 0.19 It has performed better in modeling the bearing capacity of CFDST columns than other intelligent models and traditional relationships.

In this paper, an effective joint damage identification method has been proposed. Beam to columns connections modeled as a rotational mass less spring. Joint damage has been presented as a reduction in the connection rigidity or rotational stiffness factor. Because of sensitivity of mode shapes and frequencies on structural stiffness, the first mode shape and frequency of damaged frame has been used as a feature to identify damage in steel frame connections. This data is acquired by the modal analysis of damaged structure applying the finite element method (FEM). The numerical studies are carried out within the MATLAB (2016) environment, which is used for the solution of finite element problems. To identify joint damage, an optimization problem formulated in which the objective functions formulated based on Modal Assurance Criterion (MAC) and MAC flexibility. To solve the optimization problem, an effective meta-heuristic called Grey Wolf Optimizer is employed to detect damage in beam to columns connections. To evaluate the performance of presented method, three examples consists of a seven, twelve and fifteen story steel frames are chosen with two different scenarios of damage in beam to columns connections for each of them for this purpose. Results reveal that the proposed approach is effective to detect and estimate damage in steel frame connections.

The main direction of this research is the effect of using buckling buckle in steel buildings in order to achieve the IO level. The validation has been done by using Abaqus software. After validating the 3D simulation of the BRB braces, its parametric study is performed and the sensitivity of the buckling buckle brace is performed. The modeling phase in 2D bracing space and seismic analysis (history-time) of braced frames was performed under different acceleration mapping records. The parameters of this research are the opening member-radius dimensions, geometric shape of the member, type of brace, The effects of the number of floors and the length of the opening in the frame with BRB brace. The results are presented based on pushover diagrams and time-history and relative drift of stories. The results showed that the parameter that has the most impact on the hardness and ductility index is the cross-sectional area and the parameter that has the most impact on the strength index is the cross-sectional geometry. By changing the cross-sectional geometry from the circle to the square of the BRBF brace, relative percentage reduction in stiffness, strength and ductility were obtained 2%, 16% and 10%, respectively. By changing the type of brace from CBF to BRBF, the relative percentage of increase in stiffness was between 30 to 62%, the relative percentage of increase in strength was between 63 to 69% and the relative percentage of increase in ductility was between 12 to 30%. The amount of drift roof in the analysis of time history under different earthquakes, in BRB 4, 8 and 12 floors in the range of 1.19 to 1.51 times has been achieved. Hardness and ultimate strength and ductility indices decreased with increasing opening, decreased with increasing cross section and decreased with increasing height.

Rock slopes are commonly more stable than soil slopes when subjected to different types of external loadings. Despite the fact that rock masses are commonly stronger than soils, stability analysis is necessary even for rock slopes, since any failure of them may result in a huge loss of lives and wealth. In the present paper, upper bound method of limit analysis is employed for stability analysis of rock slopes obeying Hoek-Brown failure criterion. In many previous studies based on the upper bound method, the nonlinear Hoek-Brown criterion was linearized using a single straight line which resulted in reducing the accuracy of the obtained results. For improving the accuracy of the factor of safety of Hoek-Brown rock slopes, the present paper proposes a multi-tangential technique for linearizing the Hoek-Brown criterion, in which, the nonlinear criterion is replaced by several tangential lines to the main nonlinear criterion. This method results in improving the accuracy of the obtained factor of safety. Using the obtained results, the effect of different important parameters on the factor of safety of rock slopes can be evaluated. Increasing the uniaxial compressive strength of intact rock, Geological strength index and the Hoek-brown constant mi results in increasing the safety factor, while increasing the disturbance factor and the rock mass density, the slope height and the slope inclination results in decreasing the safety factor. Finally, simple charts are presented which are useful for quick determination of factor of safety and stability number of rock slopes in practical applications.

Alkali activated slag concrete, as a new type of concrete in which, conventional Portland cement is not used, due to various advantages such as reducing the amount of CO2 produced, the use of by-products and recycled steel industry and mechanical characteristics comparable to ordinary concrete, in The last decades have been welcomed by various researchers. On the other hand, due to the nature of concrete cracking, it seems necessary to study its fracture characteristics. Two parameters of silicate modulus and alkali concentration are the most important factors affecting the mechanical and fractur properties of this type of concrete. In this experimental study, their effect was studied. For this purpose, 16 different mixes of Alkali activated slag concrete in 4 classes of silicate modulus and 4 classes of alkali concentration and 3 ordinary Portland concrete mixes were selected for comparison. In order to obtain the fracture characteristics of the work-fracture method, a total of 95 three-point bending notched beams were prepared and tested after storage at ambient temperature at the age of 28 days. According to the results, in all values of alkali concentration, with increasing silicate modulus, the specific fracture energy increased and the characteristic length of crack decreased, and with increasing alkali concentration from 4.5 to 6.5%, in all values of silicate modulus, the specific fracture energy increased and the characteristic length of crack decreased. which indicates an increase in the brittleness of concrete. However, by increasing the concentration of alkali from 6.5 to 7.5%, an inverse trend was observed in the fracture parameters. The results showd that at similar values of compressive strength, the fracture energy of alkali activated slag concrete was higher than ordinary portland concrete and the crack characteristic length was lower.

It is necessary to study the responses of underground tunnels to dynamic loads, especially explosive loads at different depths relative to the soil surface, due to the vital importance of these structures and the need for their greater stability compared to surface structures. This requires the analysis of the stability of this type of structures, under the influence of explosive loads, using structural dynamics. In this research, to analyze the dynamic response of the numerical model of the most used sections of tunnels, including circular, horseshoe and rectangular, under the influence of deep projectile explosion scenario with 500, 250 and 1000 kg TNT costs by Ansys LS-Dina finite element software (ANSYNA LS-D). we will pay. In modeling, assuming the tunnels are located at a depth of 50 meters above the ground, the penetration and explosion of the projectile occurs up to 30 meters deep in the soil. In the following, we will examine the velocity of the particles at a specific point in the tunnel crown, the maximum stress created during the explosive loading time and the amount of explosive energy absorbed by the sections of the tunnels and compare each. The results show that the von Mises stress in the tunnel with a rectangular cross section is higher than other tunnels due to the concentration of stress on the sides. Also, the tunnel with a circular cross section with the highest energy absorption resulting from the explosion showed a good performance in comparison with the rectangular and horseshoe sections.

The foundation of offshore wind turbines has various structures at different depths of the sea. At depths between 30 and 50 meters, jacket substructure is recommended as an economical solution for offshore wind turbines. During their life cycle, the substructures of offshore wind turbines are exposed to a couple of damage sources which can reduce their service life. This problem became more severe in sensitive areas such as deck, joints, or splash zone that are prone to failure. Modal strain energy (MSE) method is one of the non-destructive and practical methods in which the location and the severity of the damage is determined using changes in the dynamic properties of the structure. In recent years, some modifications have been made to the original version of this method, one of which is to consider modal frequencies in determining the location of damage. In this paper, the damage location and its severity are identified for members located in deck and splashing zone in tripod substructure of wind turbine using improved modal strain energy method (IMSE). The results showed that the improved method is more accurate in locating the damage than the original method (Stubbs index). Also, single and multiple damages, both with low and high intensity, were predicted with this method with appropriate accuracy.

In this paper, the free vibration behavior of functionally graded thin elliptical plates with simply supported and clamped boundary conditions is investigated using classical laminated plate theory. In contrast to previous studies, the geometry of the plate is considered to be as elliptical and in a more general form as super elliptical. Also, it is assumed that the considered plate is subjected to boundary in-plane preload and is rested on Winkler-type elastic foundation. It is assumed that the mechanical properties of the functionally graded plate vary continuously through the thickness according to a power law of the volume fraction of the constituents. The governing equations of motions are derived by employing the variational approach. The obtained equations are solved using Ritz method. In addition to the analytical modeling, for comparison, the problem is also modeled and analyzed numerically by using finite element software Abaqus. Correctness and accuracy of the present analytical model is confirmed through comparing the present analytical results by the results existed in the literature and by the present numerical results. After that, doing parametric study, the effects of some important parameters such as the boundary conditions, the in-plane forces, the plate geometry and the power-law index on the vibration behavior of the plate are studied and discussed. The results presented in this research are of great importance in design and application of the functionally graded elliptical plates.

Often the decision to choose an appropriate technology for landfill management is one of the main problems in multi-criteria decision analysis. Assessing and prioritizing risks in various projects is a logical way to quantify the quantitative and qualitative risks and to examine the potential consequences of potential accidents on people, materials, equipment and the environment. In fact, this determines the efficiency of multi-criteria decision-making models and provides valuable data for decision-making in risk management, risk identification, control, improvement and modification of control systems and planning to respond to them. In addition, there are significant internal relationships and feedback between different dimensions and criteria. Therefore, it is necessary to conduct environmental risk assessment studies in order to identify the destructive factors and their effects on the environment, and provide a solution for proper control and management. In the present study, using Delphi techniques, network analysis process (ANP) and using TOPSIS technique, the most important risks of landfill projects in the construction and operation phases have been identified. The obtained results show that in the construction and operation phases, the highest probability of risk is related to the environmental sector and the lowest probability of risk is related to the socio-economic and cultural sector. Adverse events have been reported. Also, the results showed that the proposed model is effective in risk assessment in urban waste landfill projects. The results of this study provide new and significant concepts in the design and engineering of municipal landfills.