Sharif Digital Repository

In this study, a new type of yielding metal dampers is proposed and evaluated numerically in finite element software. The damper consists of three main components, the core, the surrounding shell and the shear plates. These three components are interconnected in parallel and They are designed in such a way that when the system is under axial loading, the plates are much weaker than the shell and the core to remain in operation and elastic behavior until the end of the system and only the plates absorb the energy of the incident with their inertial shear behavior. This damper can be installed at the end of the Chevron braces, crossbar and diagonal. The use of the damper at the end of the... 

Tack coat is a layer of asphaltic materials, which is used for binding the surface layer to the current asphalt layer. The appropriate interlayer bonding condition will help different layers form a monolithic structure to resist traffic. The lack of proper interlayer bonding result in slippage between pavement layers, decrease the capability for transferring the load to the underlying layers, rutting, crescent cracking and decreasing the life of the Overlay. This study intends to model a pavement system in three dimensions with ABAQUS software in order to evaluate the amount of shear stress at the interface of asphalt layers. In order to prove the validity of the model, the results of the... 

Usage of masonry materials in a country like Iran is still significantly high. As most of the failures during an earthquake in this system is failure caused by low ductility of cement mortars and also the high rate of carbon dioxide produced by cement. Experiences of Kermanshah earthquake in 2017 in Iran has doubled the importance of this issue. Hence, in the present investigation, an attempt to enhance the shear bond characteristics of structures constructed by masonry using green materials has been made. “Taftan” natural Pozzolan and two types of rice husk ash (RHA) was used in mix design of used mortars as a green material. In this investigation, a direct shear test (DST) device is... 

Properties of biomaterials, especially in application as planting, can be controlled and optimized by alloying and hardening sedimentation. In recent years, the study on the simultaneous improvement of mechanical properties, toughness and corrosion behavior of magnesium composite by carbon nanotubes (CNTs) is very limited. In this study, the behavior of mechanical properties and corrosion of magnesium alloy composites with different percentages of CNTs have been investigated. The production of magnesium alloy composite by powder metallurgy and aging process have been used as effective methods for improving mechanical properties and increasing the corrosion resistance of magnesium alloys. For... 

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... 

Considering the importance of studying dynamic characteristics of soils in the analysis of wave propagation and the design of earth constructions or soil-related structures, as well as the role of Resonant Column-Torsional Shear in determining the dynamic parameters, including shear modulus, damping ratio and wave velocity in soil, this device was designed and developed in this research. The apparatus developed is able to conduct both resonant column and torsional shear tests and also measure dynamic parameters in large ranges of strain. The unsaturated pressure panel built alongside this device and the especial design of the device components have made the above-mentioned experiments... 

In the last decades, noticeable experimental and analytical investigations have been carried out on cast-in-place Reinforced Concrete column to Steel beam (RCS) connections, however rarely have been conducted on the precast RCS. In this reaserch, test results of five half-scale interior precast RCS connections with variable joint configurations are presented. The steel beams were connected to the precast column, using face bearing plates, embedded in the connection zone. The flanges of beams were strengthened with respect to scaled section, in order to increase the load transfer to the joint. All samples were loaded under reversed displacement controlled condition. The failure mode, joint... 

Structures having buckling restrained braces (BRB) as earthquake resisting system, have the qualities of high lateral stiffness and the ability to damp the energy coming from earthquake, at the same time.In addition to new structures, these braces can also be used in rehabilitating old steel or concrete buildings. By using this kind of resisting system, smaller sections are needed in design of buildings and also the cost of repair after earthquake can be highly reduced.The most important advantage of buckling restrained braces is their equal behavior and capacity in both tention and compression, that causes high energy absorption as a result of symmetric and stable cyclic behavior. All these... 

Soils have an anisotropic response, and mechanical and dynamic properties of this material are greatly dependent on the direction and magnitude of principal stresses. A reliable assessment of the soil behavior and a good estimation of the soil parameters need to perform tests in similar condition with in-situ. From all the devices used for studying anisotropy of soils, hollow cylinder apparatus is the only apparatus that enables an independent control of both the direction and magnitude of the principal stresses. Moreover, one of the most controversial topics in the unsaturated soil dynamics is determining the shear modulus and damping ratio which are used for assessing many geotechnical... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

Nowadays, the research of biodegradable alloys with high corrosion and strength properties, along with a modulus of elasticity close to that of bone tissue, especially the magnesium alloys, which has a good biocompatibility and can be used as a biomedical material, has been considered by the medical industry. On the other hand, carbon nanotubes have been used as an reinforcing phase in composites due to their high mechanical properties. The aim of this project is to produce a biocompatible composite with magnesium alloy and carbon nanotube by powder metallurgy. In order to achieve this, first the raw powder of the alloying elements in the matrix without reinforcement and then with weight... 

There is a large, at times contradictory body of investigations relating low back pain and spinal curvature in sagittal plane. The previous studies have not been subject-specified, and they have not considered the active tissues in the models. The mechanical load has a significant impact on the prevalence of low back pain and the geometry of lumbar spine in the sagittal plane is one of the most important characteristics in determining the load sharing of the spine. Thus, it is essential to know how the geometry load affects the load sharing of the lumbar spine. As a matter of fact, the purpose of this project is to know how the geometry of the lumbar spine affects the load sharing. Thus,... 

The purpose of this paper is to quantify the extent of damage of rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. One of the most important tasks after an earthquake is to assess the safety and classify the performance level of buildings. This assessment is usually performed by visual inspection that is prone to significant errors. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls is collected from the literature. This database includes more than 200 images from experimental quasi-static cyclic tests. Using the concept of Fractal geometry, several probabilistic models are developed by... 

The behavior of a new steel shear wall, already devised by the supervisor of this project, and tested by other students, was modeled numerically. Such numerical simulation was carried out using the Finite Element Methods of analysis. Hexagonal solid elements were employed in order to discretize the tested specimens and those parts of the test assembly which had to be included in the models. Both, Monotonic and Cyclic tests were simulated numerically. Comparison of the tests results with those of the numerical models showed fair correlation between them. Percentages of error in the dissipated energy for the three monotonic tests were 6.9%, 6.4% and 11.2%, respectively, whereas that of the... 

Softening and liquefaction of granular soils due to earthquakes have been a major cause for much destruction in preceding decades. This phenomenon mostly occurs in sandy soils, yet its occurrence has also been reported in gravelly soils in the last three decades. Despite the numerous researches which have investigated the undrained cyclic behavior of gravelly soils during earthquakes, there are still some aspects that need further study.This research investigates the effect of initial static shear stress on undrained cyclic resistance of a well graded, medium dense gravelly soil by conducting a series of cyclic triaxial tests. The 23 performed tests are categorized into 5 groups with... 

So far many systems have been proposed to withstand the lateral loads. For example in a concrete structure, the two concrete moment frame and moment frame with shear wall are commonly used.in the latter case, the shear walls are used to bear a large part of lateral forces.one of the disadvantages of this system is the high consumption of materials and lack of maneuver on their shape. The curved concrete shear wall is a new seismic system that, due to the curvature on the plan, will have the ability to provide the hardness, strength, and ductility required to withstand lateral loads. The goal of this project is to investigate the seismic performance of these types of walls against cyclic... 

One of the major challenges in construction of rubber modified asphalt mixtures is determination of mixing and compaction temperature (MCT). In order to estimate MCT according to Superpave volumetric mix design procedure, a temperature-viscosity relationship for the binder should be developed using ASTM D2493. This approach provides reasonable temperatures for unmodified binders which are Newtonian fluids at high temperatures and their viscosity is independent of shear rate. However, this method often yields excessively high temperatures for modified binders which exhibit non-Newtonian pseudoplastic behavior. The reason is that viscosity of modified binders depend on not only temperature but... 

Lateral spreading is defined as finite lateral displacement of mildly sloping grounds or those ending in free faces induced by liquefaction. Severe damages of pile groups due to lateral spreading in past earthquakes has been reported. Since earthquake is unavoidable, it is necessary to study the response of piles, especially pile groups, to liquefaction induced lateral spreading. Until now, a number of methods have been developed by researchers for design of deep foundations against lateral spreading, but reported failure of piles in last earthquakes indicates that these methods are associated with high uncertainties. This is due to the lack of laboratory and experimental data to evaluate... 

On average there are to resistance spot welding connections per vehicle. The quality of these welding directly affects the quality of the finished product and the strength of the vehicle against various loads, including road roughness, different maneuvers and even sudden impacts from accidents. During the spot welding process, unintentional failures occur due to the wrong choice of current, force and time. The aim of this study is to investigate the fatigue strength of three-sheets welding joints in numerical and laboratory methods, considering the defects of (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT) . For this purpose, a healthy spot welding model was first... 

2024 Aluminum alloy has an abundant application in the aerospace and automobile industries. One of the most important problems of the alloy is hot cracking during the fusion welding process. It is stated that the solidified grains can be refined by a static magnetic field and an alternative electric field applied simultaneously during solidification. To make the alternative electric field, an alternative current was passed through the specimen. In order to prevent hot cracking, electromagnetic vibration was used. Then the effect of intensity of the static magnetic field and alternative electric current on joint was examined. Joining was carried out at electric currents of 40, 60, and 80A and...