Browsing by Author "Mashayekhi, Mohammadreza"

Now showing 1 - 2 of 2

Citation Count: 6
Modified endurance time method for seismic performance assessment of base-isolated structures
(Elsevier, 2023) Movahhed, Ataallah Sadeghi; Shirkhani, Amir; Zardari, Saeid; Mashayekhi, Mohammadreza; Farsangi, Ehsan Noroozinejad; Majdi, Ali
Endurance time (ET) method is a novel Time History Analysis (THA) approach in which structures are subjected to a set of intensifying excitations called endurance time excitation functions (ETEF). Although various studies show the efficiency of the ET method for the seismic evaluation of fixed base structures, this method has been less employed in isolated structures. The lack of coverage of high-intensity measures by existing ETEFs is the major obstacle to adopting the ET method in high-period structures such as isolated structures. It must be noted that high-intensity measures that are associated with large earthquakes are of paramount importance in performance assessment. This paper introduced a novel method called the modified endurance time (MET) method based on scaling existing ETEFs to alleviate this problem. By averaging multiple scaled ETEFs, the accuracy of the ET method is improved. Three steel structures with a different number of stories (6, 9, and 12), including Intermediate Moment Frames (IMFs), mounted on Triple Friction Pendulum Isolators (TFPIs) are considered to demonstrate the efficiency of the proposed method. These structures are analyzed under ETEFs with intensity multipliers 1 to 4 for three seismic hazard levels with return periods of 72, 475, and 2475 years. The effect of changing parameters such as isolator damping and period is also investigated on the results. The seismic responses obtained from the Endurance Time Analysis (ETA) are compared with the responses obtained from the nonlinear THA and pushover analysis. Results show that increasing the intensity multiplier of ETEFs can greatly improve the accuracy of results. However, it should be careful in the procedure of selecting the appropriate intensity multiplier. Because of the unbalanced changes in some ETEFs parameters such as PGV/PGA, the accuracy of results may also reduce by increasing the intensity multiplier. Therefore, the use of different combinations of results, obtained from several intensity multipliers, is investigated and proposed to reduce the error in results.
Citation Count: 3
On the Influence of Unexpected Earthquake Severity and Dampers Placement on Isolated Structures Subjected to Pounding Using the Modified Endurance Time Method
(Mdpi, 2023) Majdi, Ali; Sadeghi-Movahhed, Ataallah; Mashayekhi, Mohammadreza; Zardari, Saeid; Benjeddou, Omrane; De Domenico, Dario
The aim of this study is to investigate the performance of isolated structures by considering the possibility of impact under severe earthquakes. In the design of isolated structures, the required displacement capacity is determined based on the considered earthquake hazard level. However, there is a possibility of an impact caused by moat walls or adjacent structures under severe earthquakes. Dampers are used in this study to improve the performance of structural and nonstructural components. In this regard, three isolated structures (6, 9, and 12 stories) equipped with Triple Friction Pendulum Isolator (TFPI) are designed under earthquake hazard levels of BSE-1 with return periods of 475 years. Based on the different positions of these three structures relative to each other, four scenarios are defined to investigate the effect of impact. Modified endurance time (MET) method, as a cost-efficient nonlinear time history analysis method, is employed for structural evaluation under variable earthquake hazard levels. The placement of dampers is also taken into account in evaluating the effect of dampers. Therefore, the structures have been retrofitted once by adding damping and stiffness devices (ADAS) on the stories and once by adding fluid viscous dampers (FVD) at the isolated level. Results indicate that structures might collapse under earthquake hazard levels of BSE-2 with return periods of 2475 years. This matter is influenced by the adjacency of two isolated structures next to each other, and the severity of this fact depends on the height of the structures and the displacement capacity of the isolators so that the tall, isolated structures have decreased the performance of the adjacent shorter isolated structure. Moreover, the placement of dampers has a significant influence on the performance of structural and nonstructural components, depending on the reason for the impact.