Browsing by Author "Zardari, Saeid"

Now showing 1 - 4 of 4

Citation Count: 8
Effective range of base isolation design parameters to improve structural performance under far and near-fault earthquakes
(Sage Publications inc, 2023) Movahhed, Ataallah Sadeghi; Shirkhani, Amir; Zardari, Saeid; Farsangi, Ehsan Noroozinejad; Pour, Arash Karimi
Triple Friction Pendulum Isolators (TFPIs) have been widely used to enhance the seismic capacity of structures in the recent decade. This study intends to measure the effect of different Ground Motion (GM) sets, including Far-Fault (FF) and Near-Fault (NF) records, on the seismic response of the Triple Friction Pendulum (TFP) isolated structures. For this aim, different Engineering Demand Parameters (EDP), including Inter-story Drift Ratio (IDR), absolute floor acceleration, base shear, residual displacement, and damage energy are measured using numerous Nonlinear Time History (NTH) analyses. A three-dimensional mid-rise special moment resisting frames (SMFs) steel building isolated with TFPIs has been designed as per ASCE 7-16. In addition, the separate and simultaneous effect of raising the damping (beta(b)) and the period (T-b) of the base isolation system on the seismic responses of the superstructure are measured to assess the structural performance and estimate the damage energy. The beta(b) and the T-b are amplified up to 30% and 4.5 times of the superstructure period in incremental steps, respectively. The results show that the damage energy of the superstructure in the Initial Design Parameters' Values (IDPVs) of the isolator under NF records with Forward-Directivity pulses (NF-FD-GMs) is more significant than damping energy, while an inverse trend has occurred for other GM sets. Increasing the IDPVs up to a certain level reduces most EDPs and consequently causes an improvement in the seismic performance of the superstructure. The novel developed empirical relationships can be utilized as useful tools to predict IDRs and the damage states of the superstructure. The variations of the EDPs with respect to simultaneous or separate increasing the IDPVs are also reported for different GM sets.
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.
Citation Count: 4
Seismic performance of a building base-isolated by TFP to with a moat wall
(Techno-press, 2022) Movahhed, Ataallah Sadeghi; Zardari, Saeid; Sadoglu, Erol
Limiting the displacement of seismic isolators causes a pounding phenomenon under severe earthquakes. Therefore, the ASCE 7-16 has provided minimum criteria for the design of the isolated building. In this research the seismic response of isolated buildings by Triple Friction Pendulum Isolator (TFPI) under the impact, expected, and unexpected mass eccentricity was evaluated. Also, the effect of different design parameters on the seismic behavior of structural and non-structural elements was found. For this, a special steel moment frame structure with a surrounding moat wall was designed according to the criteria, by considering different response modification coefficients (RI), and 20% mass eccentricity in one direction. Then, different values of these parameters and the damping of the base isolation were evaluated. The results show that the structural elements have acceptable behavior after impact, but the nonstructural components are placed in a moderate damage range after impact and the used improved methods could not ameliorate the level of damage. The reduction in the RI and the enhancement of the isolator's damping are beneficial up to a certain point for improving the seismic response after impact. The moat wall reduces torque and maximum absolute acceleration (MAA) due to unexpected enhancement of mass eccentricity. However, drifts of some stories increase. Also, the difference between the response of story drift by expected and unexpected mass eccentricity is less. This indicates that the minimum requirement displacement according to ASCE 7-16 criteria lead to acceptable results under the unexpected enhancement of mass eccentricity.