Sharif Digital Repository

In this paper, the effects of foam density distribution and initial impactor inclination angle on crushing behaviour of metal foam-filled thin-walled square columns have been investigated. The simplified version of an existing pressure dependent self-similar constitutive model with tensile failure for metal foam has been implemented in ABAQUS/Explicit code. Random distribution of cubic regions with normal distribution of density has been created. The analyses have been accomplished for three distinct foam densities, two extreme random distributions (fine and coarse), and five different impactor inclination angles. A local effect on folding patterns of columns filled with low-density foam has... 

Beam, column, plate, and any other structure, under full or partial compressive loading, are prone to failure by the buckling phenomenon. At the instant of failure, the structure may be in unpredictable elastic, elastic–plastic, full plastic, cracked, or other forms of deterioration state. Therefore, in spite of so much study, there is no definite solution to the problem. In this paper a unified, simple, and exact theory is proposed where buckling is considered as the change of state of structure between intact and collapsed states, and then the buckling capacity is innovatively expressed via states and phenomena functions, which are explicitly defined as functions of state variable. The... 

The crushing behaviour of dynamically loaded metal foam-filled square columns has been investigated using an extended version of the existing self-similar pressure dependent constitutive model for metal foams. The model has been implemented in ABAQUS/Explicit and analyses have been conducted using different approaches to model the uniaxial and hydrostatic hardening behaviour of metal foams. A practical and reliable procedure to approximate the observed anisotropic behaviour within the computational framework of isotropic plasticity is introduced. The comparison between the available experimental and newly generated numerical results is presented in order to illustrate the accuracy and... 

This paper presents results of an experimental study to evaluate a retrofit technique for strengthening shear deficient short concrete columns. In this technique a ferrocement jacket reinforced with expanded steel meshes is used for retrofitting. Six short concrete columns, including four strengthened specimens, were tested. Specimens were under a constant compressive axial force of 15% of column axial load capacity based on original concrete gross, A g, and the concrete compressive strength, fc′. Main variables were the spacing of ties in original specimens and the volume fraction of expanded metal in jackets. Original specimens failed before reaching their nominal calculated flexural... 

This paper presents the results of an experimental and analytical study on high-strength, reinforced-concrete (RC) columns with different levels of initial ductility enhanced with carbon fiber reinforced polymer (CFRP) wraps. Six square columns 260 mm wide and 1650 mm long were tested under constant axial load and reversed cyclic lateral load. The test specimens were divided into three groups. Groups I and II were designed and detailed according to the requirements of American Concrete Institute ACI318-02 for intermediate-moment frames. Group I was wrapped with CFRP, group II was control specimens, and group III was designed and detailed according to the requirements of ACI318-02 for... 

The buckling behaviour of compression members is very important in structural engineering especially those that are made from high strength steel (HSS). This paper presents an investigation into the behaviour of four columns which were designed according to EN 1993-1-1 (2005) so that the buckling capacity of both HSS and mild steel column was equal. A finite element model was created which included imperfections due to residual stresses as well as local and global imperfections. It was found that the buckling capacity of the columns made from 460 MPa steel was lower than that for similar capacity mild steel columns with a yield strength of 275 MPa. Accordingly, a buckling curve for HSS is... 

Sudoku puzzle is a logical game which has recently got very popular. Every day various mass media print these puzzles. As a result these puzzles are a suitable alternative for hidden data transfer. SMS (short message service) is one of the popular mobile-phone services. In this service people can write short messages and send it to each other through mobile phones. In this paper a method has been presented for Steganography (hiding data) in Sudoku puzzles and through SMS. In this method after hiding data in a Sudoku puzzle, the puzzle is sent in a way that it does not attract any attention. Steganography algorithm is based on order of place of numbers 1 through 9 in one of the specified row... 

The aim of this paper is to study the influence of the column-to-beam strength ratio on the seismic strengthening of a column with a Fiber-Reinforced Plastic (FRP) wrapping system. FRP wrapped Reinforced Concrete (RC) columns are analyzed to obtain moment-curvature curves using FRP confined concrete characteristics. A pushover analysis of a 2D model was performed on one and three-story moment-resisting frames, with different column-to-beam strength ratios. The results indicate that FRP strengthening is more efficient in frames with a low ratio of column-to-beam strength, due to the type of lateral failure mechanism of the frame. Also, high values of the column-to-beam strength ratio can be... 

An approximate method is presented that can be used to determine the nonlinear behavior of a new structural bracing system called the 'Chevron Knee Bracing' (CKB). In this framing system, an especial form of diagonal brace connected to a knee element instead of a beam-column joint is investigated. The diagonal element provides lateral stiffness during a moderate earthquake. However, the knee element is designed to have three plastic joints or two yielded specimens in flexural and shear yielding mode, respectively, for dissipation of the energy caused by a strong earthquake. This article demonstrates the transformation of a complex problem into a new, practical set of design charts and... 

A new innovative 'universal' structural joint with multiple applications was devised. The two major conceived contexts for the use of this joint are 'joining beams to columns, ' and 'joining diagonal braces to horizontal ones. ' The main features of this joint are its high rotational capacity, its high shear deformation capacity, its high energy-dissipation capacity, its ability to contain damage, and its repalceability. Due to its geometry, it can well lend itself to protection measures against fire, normally practiced by the involving industries. This makes it a good candidate for being used in structures related to oil and gas industry, offshore or onshore. Through numerical modelling of... 

A new 'universal' structural joint with multiple applications was devised. Its application as a 'beam-to-column joint' was already investigated experimentally, and proven to be promising. The results were reported in previous OMAE conferences and elsewhere. Another fruitful application conceived for this joint is in the context of joining (diagonal) braces to the frame members of a structure. In particular, in chevron (inverted V) bracing systems, where the dominating exchanged forces between the combined diagonal braces and the horizontal brace (beam) are 'shear,' the use of the devised joint as a joining member can substantially improve the overall behaviour of the structure under dynamic... 

Bolted Column Base Plate (BCBP) connections are widely used to connect steel columns to the concrete foundations. This paper conducts a parametric study on the initial stiffness of bolted base plate with Square Hollow Section (SHS) column connection, through an extended 3-D Finite Element Modeling (FEM). Different features of the connection such as material behavior, geometric details, typical contact phenomena and large displacements are also considered in the modeling. A comparison between experimental test and FEM is carried out to illustrate the ability of the numerical method to simulate the connection behavior. An analytical explanation on the initial stiffness of the connection is... 

This paper presents analytical part of an investigation on the application of prestressed strips for concrete confinement. In this paper, an analytical model is proposed to predict the compressive stress-strain curve of strapped concrete as a function of the confinement level. The model was calibrated based on the experimental data of compressive tests which were described in part A of this paper. Various parameters are considered in the proposed model including volumetric ratio, yield strength and ultimate strain of confining material, shape of cross section, strength of plain concrete. Three key points were defined on the stress-stress curve of strapped concrete columns and applied in... 

A new structural connection with special unique features was developed. While under bending it showed very high rotational capacity, in shear, unlike other existing connections, it also demonstrated a large shear deformation capacity. The ductile response of this connection stems from its innovative geometry as well as the ductility of the elements embedded in it. Since the previous shear tests on the specimens of this connection were carried out under 'unrestricted' conditions, the tests reported here were all under 'restricted' conditions. These shear tests consisted of 'monotonie' as well as 'cyclic' tests on mild steel specimens. Due to the restrictions imposed on the specimens during... 

In this paper, the axial stability of single-walled carbon nanopeapods is studied based on an elastic continuum shell model. In order to model the non-bonded van der Waals interactions between host carbon nanotube and guest fullerenes, an equivalent pressure distribution is proposed and incorporated in the model. Deriving an explicit equation for the determination of critical axial load, it is concluded that the axial stability of a single-walled carbon nanopeapod is less than that of a carbon nanotube under otherwise identical conditions. In addition, it is shown that applying external pressure to the carbon nanopeapod decreases the axial compressive stability through reducing the critical... 

The liquid-liquid extraction process is well-known for its complexity and often entails intensive modeling and computational efforts to simulate its dynamic behavior. This paper presents a new application of the Genetic Algorithm (GA) to predict the modeling parameters of a chemical pilot plant involving a rotating disc liquid-liquid extraction contactor (RDC). In this process, the droplet behavior of the dispersed phase has a strong influence on the mass transfer performance of the column. The mass transfer mechanism inside the drops of the dispersed phase was modeled by the Handlos-Baron circulating drop model with consideration of the effect of forward mixing. Using the Genetic Algorithm...