Browsing by Author "Shirkhani, Amir"

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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.