Sharif Digital Repository

Bulk metallic glasses (BMGs), in contrast to conventional crystalline materials, are defined as metals with an amorphous and disordered atomic-scale structure. Due to the absence of dislocations and grain boundaries, BMGs have considerably unique mechanical properties such as high strength and elastic strain, high wear resistance and desirable corrosion resistance. However, they generally suffer from poor plasticity caused by an inhomogeneous deformation which leads to catastrophic failure by localization of strain into narrow regions, known as shear bands. This factor has extremely restricted their application as advanced structural materials. Furthermore, the recently discovered phenomenon... 

In this study, the flexural behavior of simple concrete beams with rectangular section (depth 20cm and width 18 cm) reinforced with perforated steel plates is evaluated. Perforated steel plates are used as an alternative for steel bars in the tension region. Because of special geometry, these plates are more integrated with surrounding concrete as compared with steel rebars. The holes in the plates caused local confinement on the surrounding concrete. Concrete beams are modeled with different number of perforated steel plates (one or two or four layer) in Abaqus software. Also beams with different patch lengths are modeled to evaluate patch length of perforated steel plates. Results of... 

Every year, fracture imposes high economic costs and casualties to all societies. Since the beginning of the twentieth century, scientific approach to this issue has lead to invention of a new branch in mechanics, called fracture mechanics. In general, fracture problems fall into two categories. Brittle fracture, like what happens in glass, in which, few plastic deformations and energy absorption occurs and ductile fracture, which is preceded by large plastic deformations and energy absorption. This kind of fracture is usual in ductile metals like low carbon steel. Finite Element which is considered as the most important numerical method in the mechanics of materials, is also, widely used in... 

In this thesis, based on the combination of Extended Finite Element Method (X-FEM) and appropriate material constitutive models, an efficient method is proposed to model ductile fracture under quasi-static, cyclic and dynamic conditions. X-FEM is a novel method in which with the use of appropriate enrichment functions, discontinuity geometry is separated from the computational mesh and hence the need for a remeshing step is alleviated. The non-linear material behavior in the crack tip process zone can best be modeled with methods based on continuum damage mechanics. These methods model the ductile fracture mechanisms, phenomenologically. In this thesis, in order to model the ductile... 

Bracing Systems are usually a set of inclined members that are embedded in structures to resist lateral forces and control lateral displacements. There are different types and behaviors for Bracing Systems depending on the way of assembling and locating them in the structure. Braced Frames, such as Concentrically Braced Frames (CBFs), generally have high stiffness and low ductility. Another Type of Braced Frames is Eccentrically Braced Frames (EBFs) which improves CBFs by establishing suitable ductility as well as stiffness. Inelastic behavior of Links involved with EBFs caused this in EBFs. Nevertheless, these systems have no efficiency in next earthquake, because links are parts of beams... 

The present study looks into the fracture of perforated steel plates and their sensitivity in ductile fracture. It also examines the effects of strain rise phenomenon in these specimens. The main employed fracture model is VGM, which was first introduced by Rice and Tracey, and later enhanced by Kanvinde et al.. The general methodology includes finite element simulation and lab experiments on perforated plates, to determine ductility, strain concentration in hole periphery and model sensitivity. Fot thid purpose 86 steel sheet specimen with different holes and cuts were manufactured and tested. With the acquired data, the impact of strain concentration on the load carrying capabilities and... 

In recent years, steel tub girder superstructures have been exceedingly used in long span superstructures due to their significant torsional and flexural stiffnesses. In such superstructures, end diaphragms made of plates are one of the most important members in transferring seismic forces to the substructure. Despite the importance of end diaphragms, limited number of studies have been conducted on their behaviour and as a result, their design procedure is not clear. In this dissertation, different configurations of end diaphragms in elastic steel tub girder superstructures were evaluated using finite element models and the required equations for stiffness and strength were derived.... 

In this study, the behavior of a new innovative bracing system under cyclic loading and according to AISC code is investigated. An Ideal bracing system, in addition to having sufficient stiffness, should have a suitable ductility. Also, in order to prevent inelastic behavior of other structural members, braces, in addition to possessing high architectural adaptivity, must be able to contain the damage within itself and behave like a fuse. Three specimens with different sections, IPE100, HEA100 and 2UNP100, were designed and tested. The results of these tests represent an elastic- (approximately) perfectly plastic behavior of the brace if an appropriate section is used. Moreover, this bracing... 

These days usage of prestressed structures in civil projects are increased significantly. One of these structures is prestressed concrete beam. Considering of such charactristics as failure loads , maximum loads, ductility and occurence and extension of cracks in prestressed concrete beams are interested by civil engineering so in this project we try to investigate the effect of increasing in nonprestressed bars with different arrangements in six specimens.
The load enters in static way on each specimen and supports are simple. Considering the results of experiments, ductility increases significantly because of adding longitude and transverse bars and brittle behavior of speciments... 

The goal of this project is production of composite laminated sheetswith bimodal microstructure using ARB process. It is planned to produce a laminated sheet having bimodal grain size distribution in microstructure to increase the formability while maintaining the strength. Two different aluminum alloys including AA 1050 and AA5083 were ARB processed up to 9 cycles, Then the ARB samples were annealed under controlled temperatures and times. Due to structural differences like stacking fault energy,stored cold work energy and solute atoms concentration, annealing ofThese two alloys lead to different recrystallized grain sizes. In order to evaluate the recovery and recrystallization behavior of... 

Response modification factor is the most crucial factor in the seismic design of structures in which the nonlinear performance of structures during strong and medium earthquakes is considered. This research tries to evaluate the response modification factors of split-level steel moment-resisting frames, which are designed in accordance with AISC 360-10. Since the response modification factor depends on ductility and overstrength, static nonlinear analysis has been performed on a number of building models and the effects of some parameters influencing it, including the height of building and number and length of spans, are studied. The over-strength, ductility and response modification... 

On the ground, it is necessary to have the values of Response Modification Factor R, Over-strength Factor Ω0, and Deflection Amplification Factor Cd to design seismic-force-resisting systems according to design and loading codes. This study is intended to evaluate these factors for a structural lateral bracing system called Chevron Knee Bracing (CKB). In this type of bracing, the knee elements help the system to dissipate energy through the formation of plastic flexural and/or shear hinges within the presented bracing system. The ap- proach used in this study is according to FEMA P695 based on low probabili- ty of structural collapse and involves nonlinear static and dynamic analyses.... 

A particular kind of concentric bracing system composed of three members arranged in y-shaped geometry is examined in this thesis. The non-straight diagonal strut of this off-centre bracing causes eccentricity to the system and is connected to the frame corner through a third member. Providing adequate openings in braced bays accompanied by improved energy dissipation are resulted in positive attitude toward using y-bracing frame as a lateral load resisting system. However, lacking of specific design codes could be problematic for engineers. To overcome this incompetency, seismic performance factors including the response modification coefficient, the system overstrength factor, and... 

Nowadays, Braced Frames systems are prevalent as a structural resisting lateral loads. One of the most crucial prominent of them is Disposable Knee Bracing (DKB). In such a system, braces provide stiffness, while the link elements play an important role as an energy-absorbing fuse to dissipate energy by plastic deformation. In this research, bracing frames consist of shear and/or flexural link elements. The experimental results reveal that hysteresis behavior of link elements remains constant till specific rotation. After that, sharply decrease due to crack failure of these elements occurs. This specific rotation has been reported between 0.06 to 0.08 Rad. Seismic performance factors such as... 

This thesis presents the seismic performance evaluation of steel MRFs with nonlinear replaceable links. Although existing MRFs can provide life safety during a design level earthquake, they are expected to sustain significant damage at the locations of flexural yielding fuses in the beams .These drawbacks can be mitigated by introducing replaceable links at the locations of expected inelastic action. Codes require that the span-to-depth ratio of the beams in moment resisting frames (MRF) should be limited to guarantee the development of plastic hinges with a sufficient length at beam ends. To overcome the abovementioned limits, in this paper a new replaceable shear structural fuse is... 

Glass Fiber Reinforced Polymer (GFRP) bars with significant corrosion resistance lead to an improvement in the performance of concrete structures and a significant reduction in costs. High ratio of tensile strength to weight, non-conductive, and non-magnetic properties are other features of GFRP bars. Recent international design standards, such as ACI 440.1R-15 do not recommend including FRP reinforcement in compression, so they replace them by concrete in calculations. The purpose of this study was to investigate the effect of concentric and excentric axial loading on the axial capacity and ductility of GFRP reinforced concrete columns compared to steel reinforced concrete columns,... 

Pearlitic Ductile Iron are being used variously for producing different kinds of components in industry. For producing of Pearlitic structure in some kind of components such as crankshaft, copper and tin are being used. In many cases according to conditions and facilities of the replacement, these two elements normally have been used.Despite the fact that mostly components are influenced by the fatigue, the influence of these two elements on the fatigue properties of the components hasn’t been studied comprehensively.In this research, the influence of the copper and tin alloying elements on the fatigue limit of the Pearlitic Ductile Iron has been studied.The samples of ductile iron with... 

A total of four reinforced concrete slabs with dimension of 2200×1000×100 mm strengthened with different layers of GFRP sheets were fabricated and tested. A loading of the slabs was performed using displacement control approach.In addition, nonlinear finite element analysis (NLFEA) using ANSYS package was used to simulate the behavior of the test specimens. After reasonable validation of NLFEA with the experimental test results of companion slabs, NLFEA was expanded to provide a parametric study of sixty two slabs. Forty two numbers of these sixty two slabs were without any opening and were modeled for different type of concrete strength, ratio of length/wide for slabs, type of FRP, number... 

Recent research studies on ductile fracture of metals have shown that the ductile fracture initiation is significantly affected by the stress state. In this study, the effects of the stress invariants as well as the effect of the reverse loading on ductile fracture are considered. To estimate the reduction of load carrying capacity and ductile fracture initiation, a scalar damage expression is proposed. This scalar damage is a function of the accumulated plastic strain, the first stress invariant and the Lode angle. To incorporate the effect of the reverse loading, the accumulated plastic strain is divided into the tension and compression components and each component has a different weight... 

Concrete structures require reinforcement and retrofitting because of possible mistakes in design or calculation, inconformity between plan and implementation, change in occupancy or applied loads, and decay. Development in technology, production of materials, and new methods play important roles in development of structure construction and reinforcement methods. Emerge of new materials creates great demand in studying, surveying, and determining design characteristic and criteria for these materials. One of these materials is FRP composite which is used in concrete structure reinforcement in different ways. In this laboratory research, the effect of external wrapping by GFRP composite...