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Multidisciplinary optimization of a stiffened shell by genetic algorithm
, Article Journal of Mechanical Science and Technology ; Volume 26, Issue 2 , February , 2012 , Pages 517-530 ; 1738494X (ISSN) ; Jafari, A. A ; Azadi, M ; Sharif University of Technology
2012
Abstract
Vibration analysis of simply supported rotating cross-ply laminated stiffened cylindrical shell is performed using an energy approach which includes variational and averaging method. The stiffeners include rings and stringers. The equations are obtained by Rayleigh-Ritz method and Sander's relations. To validate the present method, the results are compared to the results available in other literatures. A good adoption is observed in different type of results including isotropic shells, rotating laminated shells, stiffened isotropic shells and stiffened laminated shells. Then, the optimization of parameters due to shell and stiffeners is conducted by genetic algorithm (GA) method under weight...
Obtaining optimal performance with ring stiffeners on strength for submarine pipeline
, Article World Applied Sciences Journal ; Volume 15, Issue 11 , 2011 , Pages 1494-1502 ; 18184952 (ISSN) ; Shamsai, A ; Rahmani, K ; Showkati, H ; Sharif University of Technology
Abstract
Submarine pipelines as the principal structural components are prone to fail by circumferential buckling under the effect of hydrostatic external pressure. Basically, the buckling capacity of a thin-walled pipe is dependent on "radius to thickness" ratio. At least two modes of local and overall buckling are possible in any pipeline system, which could be developed in pipe wall. A method of strengthening of pipes is developed in this paper to stop the failure. A total of 21 stiffened models are generated and analyzed using the well-known finite element program ABAQUS. In this study, the buckling and post-buckling behaviour of stiffened pipes are investigated by carrying out linear and...
Analysis and Modeling of Base Plates Under the Effect of Different Loads
, M.Sc. Thesis Sharif University of Technology ; Mofid, Masoud (Supervisor)
Abstract
In steel structured buildings the connection of columns to foundations is of practical significance. This connection customarily is performed by a base plate, which is connected to the foundation with bolts. The columns and base plates are usually prepared separately, and later are welded together by contractors. Due to the errors in the process of fabrication, these plates are proposed with larger dimensions than those suggested by the designers. However, it is believed that the utilization of stiffeners, which are welded to the columns in a perpendicular state, reduces the stress field inside the base plates significantly. Therefore, by use of stiffeners the thickness of base plates can be...
Method of Estimating the Response Modification Factor for Stiffened Steel Shear Wall Systems
, M.Sc. Thesis Sharif University of Technology ; Bakhshi, Ali (Supervisor)
Abstract
Steel shear wall systems have been introduced as a lateral load resisting system since 1970s. Based on the designer’s choice, this system can be used with or without stiffeners. Employing stiffeners prevents the elastic buckling of steel plates which can enhance the system to absorb more energy. The design code for using stiffners has not developed yet in Iran since this kind of systems is not common practice. In this study, the Response Modification Factor (R), as an important factor in the design procedures of structures, is investigated for 2 to 10-story building structures which have steel shear walls with 3 and 6 millimeters thickness with 3, 4 and 6 meters spans.To this end, the...
Smeared rotating crack model for reinforced concrete membrane elements
, Article ACI Structural Journal ; Volume 107, Issue 4 , 2010 , Pages 411-418 ; 08893241 (ISSN) ; Kazemi, M. T ; Sharif University of Technology
2010
Abstract
A set of stress-strain relations for normal-strength concrete and mild steel bars embedded in concrete is presented in this paper. The salient features of the proposed constitutive laws are: 1) considering the effect of reinforcement ratio on average stressstrain relationships of cracked concrete; and 2) considering the gradual reduction of average stiffness of steel bars embedded in concrete. Equilibrium, compatibility, and constitutive relationships were incorporated into an algorithm to obtain a procedure for analyzing reinforced concrete membrane elements. Corroboration with data from panel test specimens shows that the presented model provides good predictions for the entire...
Numerical Study of Stiffener Effects on Composite Shear Wall Performance
, M.Sc. Thesis Sharif University of Technology ; Khaloo, Alireza (Supervisor)
Abstract
Concrete filled double-steel-plate (CFDSP) composite wall is a new lateral resisting system that recently used in design and strengthening of high-rise buildings. This CFDSP composite wall is composed of concrete filled steel tubular columns at the two boundaries and concrete filled double-steel-plate wall body. The main advantage of this system is the interaction between steel and concrete which delays local buckling of steel plates. Also, steel jacket increases the strength of concrete in result of confinement effects. Furthermore, these systems have lower thickness compared to ordinary concrete shear walls. Hence, they have less structural weight which reduces the earthquake force....
Free vibration analysis of functionally graded cylindrical shells stiffened by uniformly and non-uniformly distributed ring stiffeners
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 15 , 2010 , Pages 367-375 ; 9780791843888 (ISBN) ; Rahaei Fard, M ; Ahmadian, M. T ; Movahhedy, M. R ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
Abstract
Free vibration analysis of a transversely stiffened circular thin hollow cylinder made of functionally graded materials (FGMs) is analytically evaluated. Functionally graded materials are inhomogeneous composites which are usually made from a mixture of metal and ceramic. The gradient compositional variation of the constituents from one surface to the other provides an elegant solution to the problem of high transverse shear stresses induced when two dissimilar materials with large differences in material properties are bonded. In this paper, application of an FGM made of two different materials is investigated by applying Ritz method. While cylinder is assumed to be thin, strain energy...
Probabilistic analysis of stress concentration factors in tubular KT-joints reinforced with internal ring stiffeners under in-plane bending loads
, Article Thin-Walled Structures ; Volume 99 , 2016 , Pages 58-75 ; 02638231 (ISSN) ; Yeganeh, A ; Mohammadi, A. H ; Zavvar, E ; Sharif University of Technology
Elsevier Ltd
Abstract
In the present research, results from the finite element (FE) stress analysis of 108 models, validated using test data obtained from the experimental investigation, was used to propose probability distribution models for stress concentration factors (SCFs) in internally ring-stiffened tubular KT-joints under four types of in-plane bending (IPB) loads. The SCF is one of the crucial parameters in the fatigue reliability analysis of tubular joints. It exhibits considerable scatter which calls for greater emphasis in accurate derivation of its governing probability function. According to the knowledge of the authors, no comprehensive research has been carried out on the probability distribution...
Analysis and design recommendations for diagonally stiffened steel plate shear walls
, Article Thin-Walled Structures ; Volume 103 , 2016 , Pages 72-80 ; 02638231 (ISSN) ; Joghataie, A ; K. A. Attari, N ; Sharif University of Technology
Elsevier Ltd
Abstract
This paper presents a comparison of analytical and experimental results of an investigation on the diagonally stiffened steel plate shear walls (SPWs). Experimental studies were carried out on three 1/3-scaled, one story single bay shear walls. The first specimen was a control specimen which was unstiffened and the other two specimens were diagonally stiffened using different stiffener configurations. Finite-element models of full SPWs are developed using finite element model. The results are compared with experimental results to investigate the influence of stiffeners on the behavior of the specimens. Good agreement between analytical and experimental models is found in point of failure...
An Analitical Model for Grid Stiffened Structures of Various Patterns
, M.Sc. Thesis Sharif University of Technology ; Kouchakzadeh, Mohammad Ali (Supervisor)
Abstract
Structural efficiency is a primary concern in today’s aerospace and aircraft industries. This brings about the need for strong and light weight structures. To increase the strength of a panel without considerable increase in its weight, we may use a lattice of stiffeners which may have shells connected to one side of the lattice or both sides of it. These structures are usually called grid stiffened structures. Aircraft fuselage and launch vehicle fuel tanks are some of the many applications of these structures in aerospace and aircraft industries. These structures include two major groups; isogrids (grid stiffened structures with equivalent isotropic properties) and orthogrids (grid...
Investigating of the Behavior of the Column Base Plate with Eccentirisity Using FEM
, M.Sc. Thesis Sharif University of Technology ; Vafaei, Abolhassan (Supervisor) ; Mofid, massoud (Co-Advisor)
Abstract
Base plate is one of the crucial elements in steel structures which transfer force from column to foundation and also prevent stress concentration in jointing area between them. For investigating the behavior of base plate under different caseloads such as axial, transverse and earthquake loads, it is necessary to consider all the involved elements including column, base plate, foundation, anchor rods and also interaction between these elements. In this study the connection between column and base plate, base plate and foundation are analyzed thoroughly. The behavior of base plate with a box type column with and without stiffener under the static loads is analyzed using finite element...
Free Vibration Analysis of Circumferentially Stiffened Micro-Cylinder Made of the Functionally Graded Material
, M.Sc. Thesis Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor) ; Firouzbakhsh, Kekhosro (Co-Advisor)
Abstract
Micro-Structures, especially cylindrical shells, has been widely used in different high tech industries, that this extreme usage emphasis, analyze of the vibration behavior of these structures. For gain an appropriate characteristics for a known purpose we can stiffen cylindrical shells with some rings that lids to improvement in mechanical properties of them. With advent of new materials, such as Functionally Graded Materials (FGM) and unique properties of these materials investigation of vibration behavior and characteristics of micro cylinders which has been made of FGM can be very important and essential. By using FGM materials many mechanical characteristics of these structures can be...
Study on Behavior of Diagonally Stiffened Steel Plate Shear Walls
,
Ph.D. Dissertation
Sharif University of Technology
;
Joghataie, Abdolreza
(Supervisor)
;
Khajeh Ahmad Attari, Nader
(Supervisor)
Abstract
In this study, the behavior of diagonally stiffened steel plate shear wall systems which have a new configuration of stiffeners is investigated. This dissertation is divided into three main sections which contain experimental studies, finite element analysis and developing design equations. In the section on experimental studies, 5 single-bay, single-story, one-third scale specimens were tested. An unstiffened specimen as a control sample and two other specimens with different configuration of stiffeners were constructed and tested to study the effect of diagonal stiffeners. Based on the observations during the tests, it was decided to add and study two other specimens too, including one...
High Frequency Vibration Analysis of Two Connected Plates by a Beam Interface via EFEA Method
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor) ; Mohammad Navazi, Hossein (Co-Advisor)
Abstract
In this study, high frequency vibration analysis of two connected plates by a beam interface is carried out using Energy Finite Element Analysis (EFEA). In structural vibration analysis at low frequencies, classical methods such as Finite Element Method or Boundary Element Method present accurate results. But, using these methods at high frequencies requires expense of high calculation cost and time. Therefore, using of statistical methods that are based on average estimates of vibrations, at high frequencies is most popular. EFEA is a method that gives average response of structure at a certain point and frequency band. This method is developed on the basis of finite element analysis of...
Analysis of Slabs Stiffened by Cables and Pedestals
, M.Sc. Thesis Sharif University of Technology ; Eskandari, Morteza (Supervisor)
Abstract
In this study, a new concrete slab stiffened by concrete pedestals and steel cables is introduced. The slab system is studied by employing both analytical and numerical methods. The steel cables are connected to the edges of slab and the concrete pedestals mounted at the bottom face of slab act as the middle supports of cables. The tension force in the cable and its inclination results in upward forces acting at the bottom face of slab. With the aims of classical theory of thin plates and the superposition technique, the problem of a simply supported rectangular slab stiffened by cables is studied analytically. The obtained results are verified by a numerical modelling implemented in SAP2000...
Structural Health Monitoring of Aerospace Stiffened Panels Using Lamb Wave Propagation
, M.Sc. Thesis Sharif University of Technology ; Abedian, Ali (Supervisor)
Abstract
In recent years world countries faced with the ageing aircraft fleet problem which increased the repair and maintenance costs of these aircrafts. The non-destructive inspection methods are common inspection methods of old aircrafts. To do this, the aircraft must test with a certain time scheduled inspection programme in a hangar. This method not only increased the repair and maintenance costs but also affects the flight schedule. To overcome this problem, the structural health monitoring can use to online monitoring the structure and when it needs for repair, the aircraft send to hanger. So, repair and maintenance costs minimize while the flight schedule less affected. One of the structural...
Free vibration analysis of functionally graded stiffened micro-cylinder based on the modified couple stress theory
, Article Scientia Iranica ; Volume 25, Issue 5B , 2018 , Pages 2598-2615 ; 10263098 (ISSN) ; Ahmadian, M. T ; Sharif University of Technology
Sharif University of Technology
2018
Abstract
In this paper, free vibration of the micro-cylinder made by functionally graded material stiffened in circumferential direction was investigated based on modified couple stress and first-order shear deformation theories. Modified Couple Stress Theory (MCST) was used to catch size effects in micro scales. By using first-order shear deformation theory and Hamilton's principle, the general equations of motion and corresponding boundary conditions were derived. Free vibration of the structure was investigated by implementing simply-supported boundary condition as a common case. The effects of different parameters, such as dimensionless length scale parameter, distribution of FGM properties,...
3D wind buckling analysis of long steel corrugated silos with vertical stiffeners
, Article Engineering Failure Analysis ; Volume 90 , 2018 , Pages 156-167 ; 13506307 (ISSN) ; Moazezi Mehretehran, A ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Thin-walled cylindrical steel silos are susceptible to instability under wind pressure when they are empty or only partially filled. This paper investigates numerically the wind buckling behavior of a real steel corrugated silo with 8.02 m diameter and 17.62 m height, strengthened by open-section vertical stiffeners. Accordingly, comprehensive 3D finite element models were used and detailed linear and non-linear buckling analyses were conducted. The effects of sinusoidal corrugated sheet profile dimensions on this issue were specially explored. Wind load vertical and circumferential distributions were adopted from Eurocode. Two proposed circumferential pressure distributions for an isolated...
On the Parametric Analysis of Structural Response of Base Plate Connections through FEM
, M.Sc. Thesis Sharif University of Technology ; Mofid, Masoud (Supervisor)
Abstract
Base plate is one of the important and sensitive elements of a structure which roles as a connector of force and moment in column to foundation joint and prevents from stress concentration in the joint area. As until now there has been several numerical and experimental researches conducted about base plate connections, but in practice for design, base plate is considered as a cantilever beam which undertakes compressive force and bending moment. In this method of design many important factors such as separation and deflection of base plate, interaction of base plate with bolts and foundation aren’t taken into consideration. Therefore there is an urgent need to design base plates considering...
Structural similitude in free vibration of orthogonally stiffened cylindrical shells
, Article Thin-Walled Structures ; Volume 47, Issue 11 , 2009 , Pages 1316-1330 ; 02638231 (ISSN) ; Navazi, H. M ; Jafari, A. A ; Bagheri, M ; Sharif University of Technology
2009
Abstract
In this paper, the necessary similarity conditions, or scaling laws, for free vibrations of orthogonally stiffened cylindrical shells are developed using the similitude theory. The Donnell-type nonlinear strain-displacement relations along with the smearing theory are used to model the structure. Then the principle of virtual work is used to analyze the free vibration of the stiffened shell. After non-dimensionalizing the derived formulations, the scaling laws are developed, using the similitude theory. Then, different examples are solved to validate the scaling laws numerically and experimentally. The obtained results show the effectiveness of the derived formulations. © 2009 Elsevier Ltd....