Sharif Digital Repository

The use of braced frames has become more popular in seismic design of buildings because of the simplicity in design and construction. The first event that occurs in the earthquake for a concentrically brace frame (CBF), is the buckling of the strut. The inelastic behavior of CBF systems is dominated by brace buckling, yielding and the post buckling behavior. The Inelastic performance of the brace is nonsymmetrical, because of the difference in the tensile and compressive strength of the brace and the deterioration in the resistance after buckling. so we have too complexity in modeling the inelastic performance of brace members. Also the subject of the near fault ground motion and design of... 

In this thesis, the nonlinear seismic behavior of typical Iranian building is evaluated. The evaluation results indicated that these building, which were designed, based on first edition of 2800 standard and before, due to ductility and stiffness deficiency, don’t satisfy the 3th edition of 2800 standard and FEMA356 requirements, then retrofit of the most old structures is recommended. Selected samples include ordinary moment resistant concrete frames. The effectiveness of three retrofit schemes, concentric steel bracing (CBF), Eccentric steel bracing (EBF) and buckling restrained bracing, are studied and compared. The results of investigation indicated that although CBF retrofit scheme is... 

In order to reduce structural and nonstructural damages and associated financial losses during intense seismic events such as Bam earthquake, seismic retrofitting of existing structures should be considered as a special issue. In this regard, for quantifying the seismic performance of structures a guideline termed “instruction for seismic rehabilitation of existing building No.360” is issued which is mainly borrowed from performance-based assessment procedures FEMA 356. In contrast to conventional seismic design methods which are based on controlling stress ratio for different load combinations, in performance-based earthquake engineering methodology, the displacement control of structural... 

One of the most common failure modes of structures in earthquakes is soft story failure which causes by discontinuity of lateral force resisting elements like braces. so the ground floor acts as a soft floor. In this case columns are imposed to large deformation and plastic hinges are formed at top and bottom of the columns. This case is named as story mechanism (severe drift of the story). In most of this case building collapsed or going to collapse. To resolve this problem, different solutions are presented. One of the strategies under section (2-10) 2800 code is increase of designed load in columns of the soft floor. This measure cause to Significant increases in the sections of the... 

Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. In the conventional bracing systems, it is assumed that the braces buckle under compressive forces; but Buckling Restrained Brace (BRB) does not buckle under pressure. In this study performance of BRB in jacket platform, with a case study of Resalat platform, has been investigated under earthquake load and powerful wave. The modeling of jacket equipped with this brace has been done in Abaqus software, and results... 

In this thesis, finite element (FE) models were developed to study hysteresis behavior of pipe braces subjected to cyclic loading. Thus steel braces previously tested by other investigators are used. The results of the analysis are in good agreement with the experiments. Besides, the FE analysis could also simulate both the overall and local buckling. As a result, a sharp growth in plastic strains is followed by geometric changes at the mid-span due to local buckling. The sharp growth of plastic strains is entitled as strain rises. In fact, the local buckling triggers rupture of braces at the mid-span. The local buckling initiation is identified by the sharp growth in plastic strains.... 

Snaking Vibration and buckling of drill string in the horizontal well was investigated in this research. Sinusoidal and helical critical buckling load are obtained for a specific drill string.
Drill string is modeled both analytically and numerically (finite element method). Drill pipes are considered as a clamped-clamped beam with constant cross section and the well is considered as a hollow cylinder. The thickness of cylinder was large enough to model the surrounding soil of the well. Buckling is a complex deformation and is somehow a random phenomenon. In addition, the length and the continuous contact between drill pipes and the well make the finite element model very huge and the... 

Characterization and simulation of carbon nanotube-reinforced composites at large scale have been a concern of researchers in the past decade. This is due to the computational complication of considering many embedded carbon nanotubes (CNTs). However a simple meshing of organized CNT distribution in the matrix can ease this obstacle. In this study, a finite element approach is employed to investigate the elastodynamic behavior of a wavy CNT-reinforced composite structure. A three dimensional structure with up to 6400 uniformly distributed wavy CNTs is embedded in a polymer matrix. Each wavy nanotube is represented by a set of beam elements. The effect of nanotube waviness and volume fraction... 

In this research, a new Kirchhoff plate model based on the modified couple stress theory has been utilized to derive the corresponding closed-form expression for the buckling load. Moreover, a numerical mesh-less method, Reproducing Kernel Particle Method (RKPM), in combination with Corrected Collocation Method (CCM) has been employed to model the nano-plate and calculate its buckling load in the framework of the modified couple stress theory. To this end, two kinds of nano-plates have been modeled, the square nano-plates with all edges simply supported 1) in the presence of the nano-void and 2) without the nano-void. It should be noted that the analytical and numerical solutions for the... 

Since previous models can not give a complete description for electrospinning electrical instability, using polymer solutions with diifferent properties, the aim of the existing thesis is to propose a new model that covers a range of materials from non-conducting to conducting and from viscous to elastic and also the initial jet’s tension. In addition, since the previous models have used large wave length approxiamtions, using accurate calculations we showed that the new model has better results for small wavelengths of about two times the jet’s radii. To compare the model to experimental results, we designed and made a proper setup to record the electrospinning process for a PEO solution... 

Due to restrictions on connecting beams to columns in steel structures when moment-resisting connections in two perpendicular directions are employed, the use of ordinary wide-flange sections or fabricated boxes becomes impractical. Application of Cruciform sections, especially when fabricated from two split-I sections (IPE sections) seems to be a reasonable solution to this problem. In this study, using Finite Elements Method and a commercial FEM software, the nonlinear behaviour of a number of cruciform columns, already tested by others, were modeled numerically. After reaching results in acceptable agreement with those of the tests, potentially suitable sections for fabrication of... 

Duringfalling a viscous liquid freely on a surface, the viscous thread bends due to a phenomenon called buckling. The gravity force in this process could be replaced by an electric force in electrospinning process. In the present thesis, we have designed a number of setups in order to investigate the buckling phenomenon in two categories of helical and non-helical buckling by using direct electrospinning process. By making the collector moving, the electrospun fibers show several shapes including coiling, meander, figure of 8 shape, etc. There are three effective forces acting in this process which are viscous force, electric force and inertia. Also there are three distinct regimes defined... 

To keep up with the growing demands for energy, the oil and gas industry ventures into deeper waters. This increases complexity of offshore projects. Part of this complexity is due to the resistance of a pipeline against local buckling collapse due to external pressure that is more significant in higher pipe laying depth and consequently higher external pressure. Pipeline response to external pressure is an important factor in design of marine pipeline.Local buckling of a pipeline is the buckling behaviour within the pipeline cross section. Other types of buckling behaviour such as upheaval and lateralbuckling are not in the scope of this thesis.In this thesis, the installing pipeline is... 

In the present study, the buckling of conical sandwich panel with composite faces and flexible core is investigated. At first, the nonlinear differential equations based on Donnell and Novozhilov theories with relevant boundary conditions for conical shells are derived using energy method and Hamilton principle. In the following, by applying adjacent-equilibrium criterion, the equations are linearized and the equations of conical shell are obtained. Then, the results obtained from these theories are compared, and based on the benefits and application domain of the theories, Novozhilov theory is selected to model composite faces of the sandwich panel. High-order sandwich theory is used for... 

The purpose of this thesis parametric study the natural frequencies and the criti-cal buckling multilayer composites truncated cone with the effect of lateral shear deformation. For this purpose five-bending tensile deformation equation of motion of the truncated cone shell in a suitable coordinate system have been studied. Then solve the five-coordinate movement for power series-are consid-ered. The natural frequencies and critical buckling force for the various truncat-ed cones with four different boundary conditions are calculated and the results with the results of similar conical shells with the same boundary conditions, tak-ing into account the effect of lateral shear deformation and... 

In the present study, the buckling of generally laminated truncated conical shells having thickness variation expressed by a linear function, subjected to axial compression with simply or clamped supports has been considered. To begin with, the fundamental relations for a conical shell with variable thickness have been derived applying thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy; non-linear terms of Donnell equations by the help of adjacent-equilibrium criterion are linearized. Governing equations are solved using power series method and are applicable for all combinations of classical boundary conditions. The results are validated with Galerkin... 

In this dissertation, elasto-plastic analysis of deformation, buckling and stability of sandwich cylindrical shell panel with orthotropic core under axial compression and lateral uniform pressure is perfomed. A new study on behavior of sandwich cylindrical shell panels under elasto-plastic deformation is done. In contrast of available analyses in which the core layer assumed to be isotropic and elastic, present analysis includes the sandwich shell having orthotropic elasto-plastic core. The deformation analysis of sandwich shell is performed based on two different theories; one is adopted for sandwiches having a stiff core and the other is proper for sandwiches having a flexible core. Based... 

In this study, HSS and double angle braces subjected to cyclic loading in order to study the buckling and post buckling behavior have been investigated by Finite Element method. The results of FE analysis are fairly in good agreement with experiments. Analysis demonstrate that when local buckling occurs in middle span, subsequently, strain rises severely. Accordingly, this strain jumping causes early fracture in braces. Therefore, local buckling can be one of the primary reasons of fracture in braces. As a result, local buckling must be considered one of the primary limit state of Performance-Based design of steel braces. In addition, finding a way to predict local buckling can help us to... 

A major concern in directional well drilling is the transport mechanism of cuttings by drilling fluid. This thesis describes the effect of angular velocity and postbuckled vibrations of drillstring on cuttings transport in a directional well drilling. The analysis proceeds in two stages. First, a finite element model is used to predict the dynamic behavior of postbuckled drillstring inside a directional well. Second, a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) approach to simulate the cuttings transport considering the dynamic collision process. In the combined computational fluid dynamics and discrete element method (CFD-DEM), the fluid phase is treated... 

Strong van der Waals (vdW) potential fields of carbon nanotubes (CNTs) makes them capable to encapsulate some nanostructures inside their hollow space, which leads to the construction of new hybrid nanostructures under specific conditions. Carbon nano-peapods, carbon nanowires and the hybrid of DNA and CNT are the main categories of hybrid nanostructures of CNT. Characteristics of hybrid nanotubes are unique and different from those of CNT. In nanostructures, the lattice spacing between individual atoms is considerable with respect to the structural dimensions. Also, the range of internal characteristic length is relatively close to external ones. So that utilizing the classical continuum...