نشریه آنالیز سازه - زلزله
سال بیستم شماره 3 (پاییز 1402)

In recent years, self-centering concrete walls have been utilized as modern structures. The mechanism of these structures is such that the focus of energy dissipation is on the dampers, and the role of the concrete wall and tendons is to create stiffness and provide the self-centering capacity in the system resulted in the reduction of residual deformation in the system. The jointed self-centering concrete walls are a type of self-centering wall system where dampers are placed between two concrete wall panels. The most important point that should be considered in these structures is the optimal use of dampers in them. In the present research, a new system has been introduced, which is a combination of self-centering concrete walls with gravity columns. In such a way that the friction dampers were placed in the middle and side positions of the concrete wall. This research aimed to investigate the optimal numerical value for the "slip load of friction dampers" in the middle and side positions of the Self-centering concrete wall based on the "amount of prestressing force" in the friction screws of the dampers. In the current study, the resistance of damper materials, their shape and dimensional size are not considered as variable parameters and they are considered without influence in determining the optimal damping. In total, the optimal sliding load based on the prestressing force in the friction bolts has been simultaneously determined by two-way sensitivity analysis by OpenSEES software. Based on the results, applying the method of determining the percentage of the minimum response coefficient (R) based on parallel (two-way) sensitivity analysis can be recognized as a very efficient method for determining the most optimal friction damper in Self-centering jointed concrete wall systems. Furthermore, the prestressed and optimal force for the dampers indicated that the dampers located between the two walls (set of middle dampers) exhibit a specific optimal value and other dampers (set of side dampers) also present a different optimal value.

The finite element method has been used comprehensively in traditional and academic works. The common finite element method is a powerful method in solving boundary value problems that transforms strong differential form equations into weak form equations using domain discretization. Even though the finite element method has sufficient accuracy in displacements, but calculating the stress field by FEM has low accuracy. This paper uses the modified element-free Galerkin method to solve some numerical elastostatics problems. At first, a one-dimensional elastic bar is considered, which is subjected to a volumetric force with linear changes along the length of the bar. A comparison between the original element-free Galerkin method, the modified element-free Galerkin method and the exact solution has been made to check the accuracy, efficiency and the required time cost. The presented study indicates that these mentioned methods have the same accuracy, but the modified EFG method can be very time-consuming compared to others, mainly when a large number of degrees of freedom is used with a large size of the support domain. The numerical solution of the modified and original element-free Galerkin methods is compared with Timoshenko’s analytical responses for the bending of an elastic beam. This comparison exhibits that modified and original methods have excellent agreements with the analytical ones in calculating displacement values. Despite the same accuracy in estimating the displacements, the calculation of the stress field indicates that the modified method is less accurate than the original method. It is shown that by increasing the number of degrees of freedom, the accuracy of the modified method for estimating the stress field improves. Increased degrees of freedom are used for introducing the domain of the beam. In this study accuracy of the stress solution in the modified EFG method is improved. However, the modified EFG method is yet more time-consuming than others. According to the results, the modified element-free Galerkin method can be nominated as a powerful mesh-free method based on moving least squares that has shape functions with interpolation properties. Having interpolator shape functions in this method makes it possible to combine it with other numerical methods and apply boundary conditions with less computational cost. The results exhibit that the displacement calculation error in the presented method was at most 5% compared to the analytical solution method. Also, the maximum error rate in the presented method for stress estimation was equal to 15%.

Reinforcement of cement-based matrix composites with TRM and FRCM fibers have been utilized to improve the behavioral performance of reinforced concrete beams subjected to destruction in the past decades. Reinforcement and strengthening of the structural surfaces requires the use of fibers and mortar to link between them. The complexity of the interfaces between the fibers and matrix does not allow a simple and accurate model. This research created a numerical analysis approach based on the measuring and evaluating of the strength capabilities of two TRM and FRCM composites under the influence of bending stress conditions in terms of strengthening the external surfaces of the structure. In this regard, six sections of reinforced concrete beams with FLAT, STRIP and U-shaped patterns reinforced by TRM and FRCM composites under three-point loading and one beam were considered as reference. For this purpose, the impact of the link mechanism and bending moment, ultimate load capacity, energy absorption and dissipation, elastic stiffness and finally using the β reduction factor, the ultimate moment and yield stress were calculated by Abaqus software. According to behavioral results, reinforced sections with different FRCM composite patterns exhibit about 18% better performance than TRM composite.

Considering the widespread use of diagrid systems in tall buildings, it is necessary to investigate the behavior of this structural system against the wind and control comfort criteria based on acceleration. According to different regulations, it is evident that there is not much guidance for the design of this structural system and its requirements have not yet been included in the design regulations. Therefore, one of the most important goals of the current research is to investigate and use the Diagrid structural system as one of the modern structural systems in high-rise buildings. Another goal of this research is to compare the performance of the diagrid system with the environmental pipe system. Accordingly, the effect of various parameters including the acceleration of floors and shear of the base under dynamic wind load has been evaluated. It is expected that the performance of the diagonal network will be evaluated with a more detailed understanding of the diagonal network in tall structures and the evaluation of the operation and comfort criteria based on the acceleration against the wind load using dynamic time history analysis applying Cholesky, ergodic and AP methods. The results have been compared with the formulas of the ASCE7 regulation and the AIJ-GBV-2004 and ISO 10137:2007 comfort criteria and the National Building Code of Canada (NBCC). These investigations indicate that the acceleration of the diagrid system floors based on ASCE7 wind dynamic response prediction equations, has exceeded the permissible limit of ASCE 7 regulation by 20 milli-g (20Gal). This is due to the high estimation of ASCE 7 equations compared to the results of wind time history analysis. In such a way that in the 50-, 70-, and 100-story buildings, the maximum accelerations of the roof obtained from the ASCE 7 equation are 1.83, 2.07, and 1.87 times the results of the dynamic analysis of wind time history, respectively.

Passing through the different soil layers, earthquake-induced faulting can reach the ground surface and cause serious damage to infrastructure, especially bridge structures. Therefore, it is necessary to divert the rupture path from the vicinity of the structure using modern techniques. Embedding a barrier wall on the path of rupture propagation and in the vicinity of the structure is an efficient solution to mitigate the secondary effects of this phenomenon (such as displacement of the earth's surface, and rotation of the structure’s foundation). In this paper, a numerical study is carried out on a barrier wall filled with eco-line spheres near a concrete bridge foundation as a novel faulting path diversion technique. Moreover, the effects of different parameters including changes in width, depth, and barrier wall’s distance from bridge foundation on rupture path of the 45-degree reverse dip-slip fault, and changes in the vertical displacement and the rotation of the foundation have been studied. The results indicated that when the barrier wall is placed on the rupture path, it can effectively divert the waves and reduce plastic strains, soil strain energy, and ground surface deflections by up to 100 percent and mitigate structural response by up to 50 percent, hence effectively preventing damage to both the ground surface and the structure. 

The main goal of this research is to evaluate the nonlinear seismic behavior of special RC moment with and without viscous dampers at the floor level. In this research, 2 high-rise three-dimensional RC building frames of 12 and 16 stories, each frame with 8 models, 4 models with and 4 models without viscous damper at the floor level, located in the area with High seismicity on type 3 soil is considered. In order to seismic analysis of frames with and without viscous dampers, nonlinear static analysis method was used according to the second appendix of Iran earthquake regulations, fourth edition. The initial dimensions of the structural elements of the studied frames and the thickness of the roof slabs have been determined in ETABS-V15 and SAFE2014 software, respectively, and finally, modeling, gravity and lateral loading, and nonlinear static analysis of the studied frames have been performed in the SAP2000-V19 software. The results show that the change in the sections of beams and columns from square to rectangle in frames with and without viscous damper causes an increase in the relative lateral displacement of the floors, as well as an increase in the number of openings along the Y axis (model 1 compared to 3), and an increase in the length of the opening along the Y axis (model 1 Compared to 4), in frames with and without viscous damper, it reduces the absolute lateral displacement of floors.

The cost of construction is one of the influencing factors in the design of various structures, and the structure can be designed in such a way that with the same construction cost, it has a better performance against the incoming loads. Various methods for optimal design of structures such as genetic algorithm, biological growth and evolutionary algorithms have appeared. The ability of these methods to find the optimal design of structures is much more than mathematical methods.In this research, using the genetic method, the geometric characteristics and height of a two-dimensional Pratt type truss have been improved to make the design more economical. This truss is designed under the concentrated force in the critical position in such a way that with the minimum amount of steel consumption, the maximum stresses in the members do not exceed the limit value. Then this force is considered in a mobile form along the entire length of the truss and its optimal design has been done with the objective function expressed.Finally, the results of two problems are compared. The results show that with the number of about  17000 calls of the objective function during 50 generations, the results lead to a suitable accuracy and the optimal height of the truss in the fixed load mode is equal to 2.53 meters and the moving load mode is 2.56 meters, which for each Two cases are about 50% of the length of each opening. Also, in the case of moving load, the weight of the optimized truss was about 36% more than that of fixed load.