A semi-analytical technique for bending analysis of cylindrical panels with general loading and boundary conditions

Rahbar Ranji A,Rostami Hoseynabadi H 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.6

Cylindrical panels are structural elements widely used in engineering structures for high value of strength to weight ratio. Exact solutions of cylindrical panels are available only for a very limited number of cases. The main target of this paper is to utilize a semianalytical technique to study bending behavior of cylindrical panels with different boundary conditions under general distributed loading. The solution of the partial differential equations was reduced to an iterative sequential solution of a double set of ordinary differential equations using extended Kantorovich method. The competence and accuracy of the method is established by comparison with available results in the literature and finite element analyses which shows good agreement.

Flexural-torsional buckling analysis of angle-bar stiffened plates

Rahbar-Ranji Ahmad 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.9

The interaction of flexural-torsional buckling modes is critical for stiffened plates with asymmetric stiffeners. However, this interactionis ignored in all design rules because it is complex to characterize. In the literature, the presence of an attached plate is ignored, and stiffenedplate is treated as an ordinary asymmetric beam. In the flexural buckling mode, stiffener and the attached plate buckle together; inthe torsional buckling mode, the attached plate cannot freely rotate with stiffener. Basic equations of the flexural-torsional bucklingmodes are deduced based on hybrid beam concept and a new strain distribution assumption for sideway bending of stiffeners. Elasticbuckling stresses of different angle-bar stiffened plates are calculated and compared with those generated by the Finite element method(FEM) and those available in the literature. The present method has better agreements with FEM.

Ultimate strength of stiffened plates with pitting corrosion

Rahbar-Ranji, Ahmad,Niamir, Nabi,Zarookian, Arvin The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.3

Predicting residual strength of corroded plates is of crucial importance for service life estimation of aged structures. A series of nonlinear finite element method is employed for ultimate strength analysis of stiffened plates with pitting corrosion. Influential parameters, including plate thickness, type and size of stiffeners, pit depth and degree of pitting are varied and more than 208 finite element models are analyzed. It is found that ultimate strength is reduced by increasing pit depth to thickness ratio. Thin and intermediate plates have minimum and maximum reduction of ultimate strength with stronger stiffeners, respectively. In weak stiffener, reduction of ultimate strength in thin and intermediate plates depends on DOP. Reduction of ultimate strength in thick plates depends on thickness of plate and DOP. For intermediate plates, reduction for all stiffeners regardless of shape and size are the same.

A semi-analytical solution for forced vibrations response of rectangular orthotropic plates with various boundary conditions

Rahbar Ranji A,Rostami Hoseynabadi H. 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.1

Orthotropic plates form an essential part of many marine, aerospace, and automobile structures. The recent increase in the use of composite materials for plate-type structures intensified the need for solutions utilizing orthotropic plates. These structural components, in many instances, are subjected to vibration. The main purpose of this paper is to present a semi-analytical analysis of the response of orthotropic plates to forced vibrations with different combinations of boundary conditions subjected to a general distributed excitation. The solution of the partial differential equation was reduced to an iterative sequential solution of ordinary differential equations using extended Kantorovich method. The efficiency and accuracy of the proposed method were examined through comparison with available literature and was in good agreement with them.

Ultimate strength of stiffened plates with pitting corrosion

Ahmad Rahbar-Ranji,Nabi Niamir,Arvin Zarookian 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.3

Predicting residual strength of corroded plates is of crucial importance for service life estimation of aged structures. A series of nonlinear finite element method is employed for ultimate strength analysis of stiffened plates with pitting corrosion. Influential parameters, including plate thickness, type and size of stiffeners, pit depth and degree of pitting are varied and more than 208 finite element models are analyzed. It is found that ultimate strength is reduced by increasing pit depth to thickness ratio. Thin and intermediate plates have minimum and maximum reduction of ultimate strength with stronger stiffeners, respectively. In weak stiffener, reduction of ultimate strength in thin and intermediate plates depends on DOP. Reduction of ultimate strength in thick plates depends on thickness of plate and DOP. For intermediate plates, reduction for all stiffeners regardless of shape and size are the same.

Elastic tripping analysis of corroded stiffeners in stiffened plate with irregular surfaces

Ahmad Rahbar-Ranji 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.9

Tripping of stiffeners is one of the buckling modes of stiffened panels which could rapidly lead to its catastrophic failure. Loss ofthickness in the web and flange of stiffeners due to corrosion reduces elastic buckling strength. It is common practice to assume a uniformthickness reduction for corroded surfaces. To estimate the remaining strength of a corroded structure, a much higher level of accuracyis required since corroded surfaces are irregular. Finite element method is employed to analyze elastic tripping stress of corrodedstiffeners with irregular surfaces. Comparing the results with elastic tripping stress of un-corroded stiffener, a reduction factor is introduced. It is found that for flat-bars and angle-bars the reduction factor increases by increasing corrosion loss; however, for tee-bars remainsalmost unchanged. Surface roughness has no significant effect on reduction of tripping Euler stress of angle-bars and flat-bars;however, it has an effect on reduction of tripping Euler stress of small flat-bars. For high values of corrosion loss, reduction of trippingEuler stress is higher in flat-bars than angle-bars. Corrosion at the mid-length or ends of flat-bars is more detrimental than full length. Corrosion at the ends of angle-bars is more detrimental than full length and mid-length.

Eigenvalue Analysis of Flexural-torsional Buckling of Angle-bar Stiffened Plates

Ahmad Rahbar-Ranji 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.3

Equilibrium method is employed to analyze interaction of flexural and torsional buckling of angle-bar stiffened plates. The cross sectional areas of the angle-bar stiffened plate for these two modes are different (hybrid beam). In flexural buckling mode, angle-bar and attached plate buckle together, however in torsional buckling mode only angle-bar would be buckled. Basic equations of equilibrium for flexural and torsional buckling modes of angle-bar stiffened plates are deduced based on hybrid beam concept and new strain distribution assumption for sideway bending of stiffeners. Elastic buckling stress of different angle-bar stiffened plates are calculated and compared with finite element method and those available in the literature. It is shown that present method has very good agreements with finite element method for isolated rigid angle-bar and isolated rigid angle-bar with rigid attached plate. For isolated rigid angle-bar with pin connected to rigid attached plates it has better agreement than previously proposed method.

Blast response of corroded steel plates

Alireza Eslami-majd,Ahmad Rahbar-Ranji 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.5

Numerical results for one- and both-sided corroded steel plates subjected to blast loading are presented. Finite element analysis, withABAQUS software, is employed to determine the deformation and stress distributions. The results for the case of triangular pulse pressureon un-corroded plates are validated against literature-based data and then, detailed parametric studies are carried-out. The effects ofinfluential parameters including, plate aspect ratio, degree of pit and different ratio of pit depth at each sides of the plate are investigated. The results show that position of pitted surface in respect to applied pressure is the most influential parameter on reduction of dynamicload carrying capacity of pitted plates. By increasing degree of pitting, reduction of dynamic load carrying capacity decrease more.

Free vibration analysis of corroded steel plates

Alireza Eslami-majd,Ahmad Rahbar-Ranji 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6

Vibration analysis of unstiffened/stiffened plates has long been studied due to its importance in the design and condition assessmentsof ship and offshore structures. Corrosion is inevitable in steel structures and has been so far considered in strength analysis of structures. We studied the free vibration of pitted corroded plates with simply supported boundary conditions. Finite element analysis, withABAQUS, was used to determine the natural frequencies and mode shapes of corroded plates. Influential parameters including plateaspect ratio, degree of pit, one-sided/both-sided corroded plate, and different corrosion patterns were investigated. By increasing the degreeof corrosion, reduction of natural frequency increases. Plate aspect ratio and plate dimensions have no influence on reduction ofnatural frequency. Different corrosion patterns on the surface of one-sided corroded plates have little influence on reduction of naturalfrequency. Ratio of pit depth over plate thickness has no influence on the reduction of natural frequency. The reduction of natural frequencyin both-sided corroded plates is higher than one-sided corroded plates with the same amount of total corrosion loss. Mode shapesof vibration would change due to corrosion, except square mode shapes.