Free vibration analysis of non-prismatic beams under variable axial forces

Saffari, H.,Mohammadnejad, M.,Bagheripour, M.H. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.5

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of non-prismatic beams under variable axial forces. The governing differential equation is first obtained and, according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

Free vibration analysis of non-prismatic beams under variable axial forces

H. Saffari,M. Mohammadnejad,M.H. Bagheripour 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.5

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of nonprismatic beams under variable axial forces. The governing differential equation is first obtained and,according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

Theoretical modeling and numerical solution of stratified condensation in inclined tubes

Hamid Saffari,Vahid Naziri 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.12

The heat transfer phenomenon occurring during stratified condensation inside an inclined tube is investigated theoretically and numerically. Differential equations governing the kinematic, dynamic, and thermal aspects for vapor condensation inside inclined tubes,which are derived from a thin film flow modeling, are solved simultaneously. These solutions are achieved by applying an explicit finite difference numerical method to predict the condensation heat transfer coefficient variations along the tangential and axial coordinates. The inclination angle is found to have a significant effect on condensation heat transfer coefficient inside inclined tubes. In addition, in accordance with the given physical and thermal condition of working fluids, there is a specific optimum inclination angle. In this study,the 30°–50° range from the horizontal position is found to be the range of the optimum inclination angle for achieving the maximum condensation heat transfer coefficient, with R134a, R141b, and R11 as the working fluids. The results of the present study are compared with experimental data, and a good agreement is observed between them.

Application of Cubic Spline on Large Deformation Analysis of Structures

H. Saffari,S. Shojaee,S. Rostami,M. Malekinejad 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.1

This paper presents a new method for non-linear analysis of structures using an iterative method originated from quadraturerule based on spline function. At first, the above-mentioned method is developed for solving systems of non-linear algebraicequations and then it is implemented on structural problems. In this procedure like many other state of the art methods, thenon-linear equations are linearized by evaluating the non-linear terms with the known solution from the preceding iteration. Theproposed method is constructed as a predictor–corrector one, must frequently taking Newton's method in the first iteration. Forthis method, a simple step-by-step algorithm was implemented and presented to calculate non-linear analysis of structures. Itshould be noted that currently, the proposed method is incapable of tracing the equilibrium curve after passing the limit points. The presented method incorporates the known information at each stage of the loading process to determine the subsequentunknown variables. Compared with the classic Newton–Raphson algorithm and a recently proposed two-point method, it offersa strategy that can be deployed to reduce the number of the iterations to trace the equilibrium path in non-linear analysis ofstructures.

The Effect of Earthquake Characteristics on the Seismic Performance of Steel Moment Resisting Frames

Hamed Saffari,Mohammad Javad Zahedi,Nafise Ebrahimpour,Atefeh Soleymani 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.6

The magnitude, distance from the epicenter, effective duration, fault mechanism, and soil conditions influence the structural consequences of earthquakes. Variations in these characteristics cause structures to behave differently during seismic events. This study investigated the influence of some of these parameters on the seismic performance of moment-resistant frames. This was accomplished by simulating various well-known structures while accounting for panel zone and nonlinear component behaviour. Following that, these structures were exposed to several classified earthquake records. The distance from the fault, the soil type, and the fault mechanism were considered while classifying earthquakes. The findings revealed that the median value of story drift in strike-slip fault mechanism holds a greater level of significance when compared to reverse fault mechanism specifically in the context of far-field records. Also applying the near-field records has a greater impact on drifts in taller frames on stiff soils, and increasing the height of the frame has less impact on the fault mechanism effect on structures built on soft soils.

Educational Intervention Based on the Health Belief Model to Modify Risk Factors of Cardiovascular Disease in Police Officers in Iran: A Quasi-experimental Study

Mohsen Saffari,Hormoz Sanaeinasab,Hassan Jafarzadeh,Mojtaba Sepandi,Keisha-Gaye N. O’Garo,Harold G. Koenig,Amir H. Pakpour 대한예방의학회 2020 예방의학회지 Vol.53 No.4

Objectives: Police officers may be at a greater risk for cardiovascular disease (CVD) than the general population due to their high-stress occupation. This study evaluated how an educational program based on the health belief model (HBM) may protect police officers from developing CVD. Methods: In this single-group experimental study, 58 police officers in Iran participated in a 5-week intervention based on HBM principles. Outcomes included changes in scores on an HBM scale, time spent on moderate to vigorous physical activity (International Physical Activity Questionnaire), body mass index (BMI), blood lipid profile, blood glucose, and blood pressure. The intervention consisted of 5 HBM-based educational sessions. Follow-up was conducted at 3 months post-intervention. The paired t-test was used to examine differences between baseline and follow-up scores. Results: All aspects of the HBM scale improved between baseline and follow-up (p<0.05), except the cues to action subscale. Self-efficacy and preventive behaviors improved the most. BMI decreased from 26.7±2.9 kg/m2 at baseline to 25.8±2.4 kg/m2 at follow-up. All components of the lipid profile, including triglycerides, cholesterol, high-density lipoprotein, and low-density lipoprotein, showed significant improvements post-intervention. Blood glucose and blood pressure also decreased, but not significantly. Nearly 25% of participants who were not physically active at baseline increased their physical activity above or beyond the healthy threshold. Conclusions: A relatively brief educational intervention based on HBM principles led to a significant improvement in CVD risk factors among police officers. Further research is needed to corroborate the effectiveness of this intervention.

A mathematical steel panel zone model for flanged cruciform columns

Hamed Saffari,Sina Sarfarazi,Ali Fakhraddini 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.4

Cruciform sections are an appropriate option for columns of orthogonal moment resisting frames for equal bending strength and stiffness about two main axes and the implementation is easier for continuity plates. These columns consist of two I-shaped sections, so that one of them is cut out in middle and two generated T-shaped sections be welded into I-shaped profile. Furthermore, in steel moment frames, unbalance moment at the beamcolumn connection leads to shear deformation in panel zone. Most of the obtained relations for panel zone strength derived from experimental and analytical results are on I-shaped columns with almost thin flanges. In this paper, a parametric study has been carried out using Finite Element Method (FEM) with effective parameters at the panel zone behavior. These parameters consist of column flange thickness, column web thickness, and thickness of continuity plates. Additionally, a mathematical model has been suggested to determine strength of cruciform column panel zone and has been shown its accuracy and efficiency.

Suggesting double-web I-shaped columns for omitting continuity plates in a box-shaped column

Hamed Saffari,Amir A. Hedayat,Nasrin Soltani Goharrizi 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.15 No.6

Generally the required strength and stiffness of an I-shaped beam to the box-shaped columnconnection is achieved if continuity plates are welded to the column flanges from all sides. However,welding the forth edge of a continuity plate to the column flange may not be easily done and is normallyaccompanied by remarkable difficulties. This study was aimed to propose an alternative for box columnswith continuity plates to diminish such problems. For this purpose a double-web I-shaped column wasproposed. In this case the strength and rotational stiffness of the connection was provided by nearing thecolumn webs to each other. Finite element studies on about 120 beam-column connections showed that theoptimum proportion of the distance between two column webs and the width of the column flange(parameter β) was a function of the ratio of the beam flange width to the column flange width (parameter α). Hence, based on the finite element results, an equation was proposed to estimate the optimum value ofparameter β in terms of parameter α to achieve the highest connection performance. Results also showed thatthe strength and ductility of post-Northridge connections of such columns are in average 12.5 % and 54%respectively higher than those of box-shaped columns with ordinary continuity plates. Therefore, adouble-web I-shaped column of optimum arrangement might be a proper replacement for a box column withcontinuity plates when beams are rigidly attached to it.

Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites

Jilla Saffari,Davood Ghanbari,Noshin Mir,Khatereh Khandan-Barani 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.6

CoFe2O4 (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. Forpreparation of magnetic polymeric films, CoFe2O4 nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM),and transmission electron microscopy (TEM). Magnetic properties of the samples were investigatedusing an alternating gradient force magnetometer (AGFM). CoFe2O4 nanoparticles exhibit aferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe atroom temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe2O4(10%) nanocomposites is higher than that obtained for PS/CoFe2O4 (30%).

Jalal Al-e Ahmad’s Gharbzadegi and the Spirit of Bandung: A Decolonial Reimagination of Development in Mid-Twentieth Century Iran

Siavash Saffari 서울대학교 아시아연구소 2022 아시아리뷰 Vol.12 No.1

Sixty years after the original publication of Gharbzadegi (1962) by dissident Iranian writer Jalal Al-e Ahmad, the controversial book remains an important marker in the formation of the mid- and late-twentieth century perceptions of Iranian intellectuals about the relationship between their country’s past, present, and future. Building on the recent scholarship which considers Gharbzadegi as an alternative vision of the future rather than a nostalgic call for a return to the past, this article situates the book’s piercing critique of the Pahlavi state’s modernization and development agenda in a decolonial register. This is done through a reading of Gharbzadegi against the background, on the one hand, of the 1955 Bandung Conference at which representatives from various Asian and African nations gathered to discuss the futures of their countries after colonialism, and on the other hand, of the local experiences of semicoloniality and dependent development. This reading helps to foreground an alternative conception of modernity in Gharbzadegi, and a decolonial vision in the book of development through delinking from Eurocentric designs. Reading it against the background of the Bandung Conference further helps to situate Gharbzadegi’s engagements with the Islamic tradition in the wider context of a postcolonial turn to religion. The article thus argues that Al-e Ahmad’s turn to Islam reflects a postcolonial sentiment that in developing alternatives to Europe’s colonial modernity the peoples of the Third World ought to reengage with the ways of life and modes of knowledge and norm production which were dismissed and suppressed by the dominating colonial structures and knowledge systems.