Articles
Engineering Structures (18737323)327
This study introduces a novel Replaceable Fuses Metallic Damper (RFMD) with a double-stage yield mechanism, aiming to enhance the energy dissipation capacity of structures across multiple seismic levels. The RFMD, designed with two steel pieces as the main body and a series of mild steel round bars as energy absorbers, is intended for installation along the bracing element. The external part of the RFMD must be fixed, while the internal part, with one degree of translational freedom, acts like a sliding piston along its longitudinal axis. During tension and compression in the brace, the movement of the internal part leads to bending and axial plastic deformations in the bars, absorbing energy and providing damping for the structure. Furthermore, shifts in the boundary conditions of the fuses during the loading procedure result in a two-stage yielding mechanism. The performance of a series of full-scale RFMDs was carefully examined through displacement-control monotonic and cyclic tests, demonstrating consistent stable hysteretic behavior and proper ductility over numerous cycles with no sudden decrease in stiffness or strength. The damper enables easy replacement of its fuses, which could prevent the necessity of post-earthquake replacements if engineered to avoid bar failure during intended movement. Serving as a simple, practical, and cost-effective passive energy dissipation device, the RFMD offers adequate ductility and energy dissipation, making it valuable for protecting the key components of structures. © 2025 Elsevier Ltd
Mechanics Based Design of Structures and Machines (15397742)52(11)pp. 9381-9411
One of the significant obstacles in conducting linear and non-linear time history analysis is its time-consuming nature. In this article, a new downsamlping method based on discrete wavelet transform (DWT) and smoothing is proposed to overcome this problem. In order to assess the precision of this approach, 50,000 linear and non-linear dynamic analyses of single degree of freedom (SDOF) systems and 300 nonlinear dynamic analyses of frame structures have been performed. One hundred Fema440 records were utilized to generate approximate waves up to the third level and the outcomes of this method were then contrasted with those of DWT. It has been demonstrated that the third-level approximate wave produced by DWT, previously considered dependable in other research, generates significant errors in results and the average error (absolute error percentage of the acceleration spectrum) of its third-level approximate wave is approximately 17.5%. On the other hand, the proposed method generated approximate waves with an average error of less than 4.5% across all behavior coefficients and periods and the error rate decreases as the period and behavior coefficient increase. Analysis of steel moment-resisting frames indicated that the lowest error in both methods is achieved for the base shear and across different engineering demand parameters, the average error rate for the proposed method was below 7.5%. Furthermore, caution must be exercised when employing the proposed method for structures with periods shorter than 0.5 s. © 2024 Taylor & Francis Group, LLC.
Amirkabir Journal of Civil Engineering (2588297X)56(3)pp. 321-324
It’s important to study the liquid motion and its effect on the tanks. The method of fundamental solution (MFS) is a novel meshless numerical method proposed to solve incompressible inviscid fluid flow problems with moving boundaries. In this paper, this method is developed for two-dimensional rectangular water reservoirs under harmonic and earthquake excitations. For modeling of fluid motion with a moving free surface, Lagrangian formulation is used to pressure equation, like a potential equation and so the geometry is updated in each time step through an implicit algorithm. In recent research, equations are used with linearized boundary conditions, while due to the Lagrangian approach of pressure-based equations; the boundary conditions of the problem are very simple and it’s easy to solve complex problems. The innovation of this study is considering earthquake loads to simulate sloshing water surfaces applied by the Method of fundamental solution (MFS). The nature of earthquake excitation due to frequency content and fast acceleration changes leads to singularity problems in tank corners. So, the solution is expressed as a linear Green basis function in the method of fundamental solutions to avoid the singularity problem and to obtain better results. The numerical results are compared with other numerical and experimental results to show the proposed procedure precisely taking into account the effects of earthquake excitation. © 2024, Amirkabir University of Technology. All rights reserved.
Soil Dynamics and Earthquake Engineering (02677261)175
One of the main problems of nonlinear time history analysis is its high computational effort, especially in structures with large number of structural components, high-rise buildings and complex structural systems. The ground motions recorded in recent years also include more recorded points than in the past, which has also increased the required volume of calculations. In this paper, three downsampling methods for reducing calculation costs of nonlinear time history analysis are presented and their applicability is investigated through practical examples of complex structures. These methods include the discrete wavelet transform, the time step correction, and the wavelet time step correction which is introduced in this paper. The efficiency of these downsampling methods is investigated for near-fault and far-fault earthquake records, as well as for records on different soil types. A comprehensive study is performed on five sets of ground motions consisting of 20 records. Each record is filtered up to three stages using one half, one quarter, and one eighth of the number of the main record points. First the linear and nonlinear response spectra based on the original records and the approximate waves are investigated. Subsequently, to evaluate the performance of the methods on more complex structural systems, two three-dimensional structures of 6-story and 15-story are analyzed. The 6-story structure is equipped with viscous dampers, while the 15-story structure has seismic isolators. The results indicate that the wavelet time step correction method has better performance in most cases, compared to the other two methods. It is shown that careful consideration is needed when dealing with earthquake records with high frequency contents. In such situations, one filtering step for the discrete wavelet transform method and two filtering steps for the other two methods are recommended. Also, in practical applications, it is advisable to choose earthquake records exhibiting the least error based on the results of SDOF systems analyses. Employing this technique can significantly cut down computational effort (up to 90%), while maintaining an average error ranging from 1% to 2% for the wavelet time step correction method. © 2023
