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- 저자 : Ali Andalib (검색결과 4 건)
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Mohammad Bazzaz,Ali Kheyroddin,Mohammad Ali Kafi,Zahra Andalib 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.12 No.5
In order to evaluate the dynamic behavior of passive energy dissipation system, two steps need to be considered for prediction of structural response in the presence of ductile element in an off-centre bracing system. The first is a detailed analysis of the proposed ductile element and the second is the effect of this ductile element on an off-centre bracing system. The use of ductile bracing system is expanding in steel structures in order to increase the force reduction factor. Therefore, regarding the nonlinear behavior of steel material used in an off-centre bracing systems and using ductile element in OBS bracing systems, the seismic evaluation of the mentioned systems seems to be necessary. This paper aims to study linear and nonlinear behavior of steel frames with off-centre bracing system and ductile element, in order to get the best position of these bracing elements. To achieve this purpose, the modeling has been done with ANSYS software. The optimum eccentricity has been obtained by modeling three steel frames with different eccentricities and evaluating the results of them. The analytical results showed that the model OBS-C with 0.3 eccentricities has higher performance among the models.
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Ebrahim Ameri,Ali Andalib,Hossein Vahid Tari,Hasan Ghandhari 대한척추외과학회 2015 Asian Spine Journal Vol.9 No.4
Study Design: Prospective study. Purpose: To determine the role of routine preoperative magnetic resonance imaging (MRI) to detect the incidence and risk factors for intraspinal anomalies in patients with idiopathic scoliosis. Overview of Literature: The incidence and risk factors for intraspinal anomalies in patients with idiopathic scoliosis are controversial, and the indications for preoperative MRI in these patients vary among centers. Methods: Information on patients with idiopathic scoliosis who were surgical candidates over 10 years (age at presentation, sex, magnitude and apex of major curve, intraspinal anomalies detected by MRI, and neurological examination results) were recorded, the patients were grouped according to the intraspinal anomaly, and the data were analyzed. Results: Of the 271 patients with idiopathic scoliosis, 27 had neuroaxial abnormalities (9.9%). Of these 27 patients, 14 (52%) underwent a neurosurgical procedure. Significant differences were observed in the frequency of early disease onset and male sex (p <0.05) between the group of patients with neuroaxial abnormalities on preoperative MRI and those who did not have a cord anomaly. No difference was detected in the magnitude or direction of the curve. Conclusions: Neuroaxial abnormalities in patients with idiopathic scoliosis and a normal neurological examination were highly frequent (9.9%). Missing these abnormalities before surgery could inflict catastrophic postoperative complications. The incidence of neuroaxial abnormalities was higher in male patients and in those with early onset disease. Thus, MRI is essential for all patients with idiopathic scoliosis who require medical intervention.
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Mohammad Bazzaz,Zahra Andalib,Ali Kheyroddin,Mohammad Ali Kafi 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.4
During a seismic event, a considerable amount of energy is input into a structure. The law of energy conservation imposes the restriction that energy must either be absorbed or dissipated by the structure. Recent earthquakes have shown that the use of concentric bracing system with their low ductility and low energy dissipation capacity, causes permanent damage to structures during intense earthquakes. Hence, engineers are looking at bracing system with higher ductility, such as chevron and eccentric braces. However, braced frame would not be easily repaired if serious damage has occured during a strong earthquake. In order to solve this problem, a new bracing system an off-centre bracing system with higher ductility and higher energy dissipation capacity, is considered. In this paper, some numerical studies have been performed using ANSYS software on a frame with off-centre bracing system with optimum eccentricity and circular element created, called OBS_C_O model. In addition, other steel frame with diagonal bracing system and the same circular element is created, called DBS_C model. Furthermore, linear and nonlinear behavior of these steel frames are compared in order to introduce a new way of optimum performance for these dissipating elements. The obtained results revealed that using a ductile element or circular dissipater for increasing the ductility of off-centre bracing system and centric bracing system is useful. Finally, higher ductility and more energy dissipation led to more appropriate behavior in the OBS_C_O model compared to DBS_C model.
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Mohammad Bazzaz,Mohammad Ali Kafi,Ali Kheyroddin,Zahra Andalib,Hamed Esmaeili 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.2
Braced structures with concentric braces are among earthquake resistant systems that are widely used in frames with jointconnections. Ductility, dissipation of energy and decreasing in base shear are the benefits of these bracing systems. Despite thebenefits mentioned limited ductility of concentric braces, however, caused poor functionality against earthquake. Therefore inthis paper, new bracing system using circular element (circular dissipater) has been evaluated, in order to replace damagedmember without needing rehabilitation or repair of general system. So using nonlinear software package ANSYS a frame withoff-centre bracing system with optimum eccentricity (OBS-C-O) and another frame with same specifications without circularelement (OBS) has been created. The function of general system has been studied for the first time. Linear and nonlinearbehavior of these two frames compared to each other so the benefits of this circular element in an off-centre bracing systemare highlighted. The analytical results and comparison between plots of these two models showed that the first model has higherperformance than the others.
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