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ductility
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Nonlinear Response of Shear-Flexural MDOF Structures Subjected to Seismic Excitations
, M.Sc. Thesis Sharif University of Technology ; Ghannad, Mohammad Ali (Supervisor)
Abstract
A generic single-span frame has been used to represent a shear-flexural building and the degree of participation of overall shear and flexural behavior in mode shapes, is controlled by dimensionless parameters of α, δk and δp. By evaluation of modal analysis results, one may conclude the extent to which each parameter affects the dominancy of shear/flexural behavior. By understanding the relation between the abovementioned parameters and proportion of shear/flexural behavior of structures, effects of these parameters and consequently trend of modal shapes on the nonlinear analyses results would be investigated. According to nonlinear analyses results of the flexural structures, ductility...
Seismic Behavior Comparison of RC Shear Walls Strengthened Using FRP Composites, Steel Elements, and Concrete Jacket
, M.Sc. Thesis Sharif University of Technology ; Khaloo, Alireza (Supervisor)
Abstract
This paper aims at investigating the seismic behavior of strengthened reinforced concrete (RC) shear walls using a 3D finite element analysis. A series of four different configurations of carbon fiber reinforced polymer (CFRP) composites, four different schemes of steel elements and two different schemes of concrete jacket are utilized to compare the two methods of retrofitting RC shear walls with similar dimensions and reinforcement ratios. Nonlinear simulations of the RC shear walls are conducted under the action of lateral cyclic loading in ABAQUS Explicit software. In addition, the numerical modeling for RC walls strengthened by CFRP composites as well as steel elements are validated...
Retrofitting of Existing Steel Frames using Ductile Bracing Systems
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
Recent earthquakes indicate the importance of retrofitting existing structures to achieve an acceptable level of performance. Use of bracing systems is a cost-effective method for seismic retrofitting of existing steel frames. In particular, Buckling Restrained Braces (BRBs) and Special Concentrically Bracing systems (SCB) are practical choices to be used because of their large energy dissipation capacity especially under moderate to severe earthquakes. Buckling restrained braces which yield in both tension and compression, exhibits stable and predictable hysteretic behavior. In this study several existing steel frames, which are designed based on older versions of the building codes, have...
Investigating the Lowest Amount of Fibers in Improving the Strength and Ductility of Ultra-High-Performance Concrete
, M.Sc. Thesis Sharif University of Technology ; Khaloo, Alireza (Supervisor)
Abstract
It used to be widely accepted as a virtue in engineering society that, fibers are generally used as mechanism to resist cracking and increasing the strength of concrete in some cases. Since 1990, fibers are usually used in concrete to control cracking due to plastic shrinkage and to drying shrinkage. They also reduce the permeability and bleeding of concrete. Some types of fibers produce greater impact, abrasion and shatter-resistance in concrete. Studies turn this notion to cognition that among all types of existing fibers, Steel Fiber and Polypropylene Fiber resulted the highest improved behavior in concrete. The Ultra-High-Performance Concrete which heated the debate in recent papers...
Numerical Study on Bolted End-Plate Connection and The Code Limits
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
Regarding the numerous casualties and financial losses due to intense earthquakes, the ductility is considered of the main importance in addition to stability, stiffness, and strength criteria of the structure’s connections. In order to enhance the seismic behavior of the structures in such severe earthquakes, design codes for steel structures have suggested special types of connections. Among them, bolted end plate connection is considered a conventional type of connection used for creating ductile semi-rigid connection.In this study, in order to simulate the behavior of this joint, a 3-D finite element model is developed in Abaqus software, in which the inelastic behavior of the materials...
Experimental Study of the Hysteretic Behavior of a new Bracing System
, M.Sc. Thesis Sharif University of Technology ; Khansari, Vahid (Supervisor)
Abstract
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...
Experimental and Numerical Studies on Trapezoid Ally Corrugated Steel Shear Walls with Opening under Cyclic Loading
, Ph.D. Dissertation Sharif University of Technology ; Mofid, Masood (Supervisor)
Abstract
Steel shear wall is a lateral load resistance system, which has been taken into consideration in recent decades for designing and reinforcing high-rise buildings. This system is comprised of steel filler panel surrounded by frame members including beams and columns. Steel shear walls are presently fabricated in two types, stiffened and unstiffened. According to numerous conducted research, it can be stated that the stiffened type has better seismic performance. The use of stiffeners with a great number of executive details is required to spend more time and costs on the construction sector. In order to solve these problems, some experimental and numerical studies have been conducted on...
Experimental and Analytical Studies on Hysteretic Behavior of Trapezoidally Corrugated Steel Shear Walls
, Ph.D. Dissertation Sharif University of Technology ; Mofid, Masoud (Supervisor) ; Vafai, Abolhassan (Co-Advisor)
Abstract
Steel shear wall system has been used in recent years as the lateral-load resisting system in the design and retrofit of high-rise buildings. This system consists of infill shear panel is framed by surrounding steel frames. Infill shear panel can be applied in two types: stiffened or unstiffened. Considering to the previous studies, the stiffened type is more convenient in the seismic performance and utility condition. However, in the stiffened system, the construction cost is considerably higher because of the complicated construction details. This dissertation concentrates on the experimental and analytical studies of trapezoidally corrugated steel shear walls as an option for removing the...
Modeling Fracture Problems with X-FEM
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
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...
On the Numerical Modeling of Semi Rigid Steel Beam to Column Connection Subjected to Monotonic and Cyclic Loading using Finite Lements Method
, M.Sc. Thesis Sharif University of Technology ; Mofid, Masood (Supervisor)
Abstract
To investigate the accurate performance of a structure, the knowledge of the way its connections function, is of great importance. Moreover, cognition of the actual behavior of connections which is often semi-rigid can lead to better apprehension of the actual and more accurate behavior of structures, whilst it is often considered to be pinned or fully-rigid.Therefore, in this study a new semi-rigid steel connection of beam to column will be introduced, and its behavior will be investigated using commercial finite element packages along with mathematical approximate modeling methods. One of the features of this connection is that its behavior mainly depends uponfolding of top and bottom...
Dynamic Modelling of Ductile Damage with Extended Finite Element Method
, Ph.D. Dissertation Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
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...
Effective Factors on the Shrinkage Porosity Defect of Ductile Iron in Centrifugal Casting
, M.Sc. Thesis Sharif University of Technology ; Varahram, Naser (Supervisor) ; Davami, Parviz (Supervisor)
Abstract
The present work has been planned to elaborately investigate the key parameters which affect the formation of shrinkage porosities during centrifugal casting of ductile cast iron pipes. The porosity defects can be mostly found in the Hot Mould centrifugal casting products and adversely affect the final mechanical properties of ductile iron pipes namely Ultimate Tensile Strength and Elongation.
In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces...
In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces...
Performance of Steel Beam Connections with Elliptical Opening in Beam Web
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
After the 1994 Northridge earthquake when investigations show clear results for brittle failure near Beam-Column rigid Connections, research on these connections begun and various theories were suggested for better performance under cyclic loads. One of the appropriate ways is shifting yield beam location from beam-column connection to the beams only. Reducing the capacity of the beam through the beam flange or web far enough from the column, creating special ductile region in the beam. In this thesis, weakening is made by creating an elliptical opening in web beams. If the correct design criteria for this type of connection are suggested, it can satisfy the "weak beam - strong column" and...
Simulation of Solidification and Microstructure of Ductile Cast Iron
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Varahram, Naser (Supervisor)
Abstract
In this research, solidification and microstructure of ductile cast iron was simulated using Fourier heat transfer equation. Using Fourier heat transfer equation, distribution of macroscopic temperature with heat transfer coefficient was obtained. The purpose of simulation, forecasting ductile iron microstructure, including grain size, number per unit volume of graphite (NC), microstructure including volume fractions of ferrite and pearlite and graphite phases. Knowing the phases of the microstructure and nodule count and the use of empirical relationships, we can estimate mechanical properties. In this regard, all transformations during cooling of molten ductile iron was simulated. Results...
Fabrication of a Polymer Compound to Increase the Earthquake Resistance of the Building
, M.Sc. Thesis Sharif University of Technology ; Mousavi, Abbas (Supervisor)
Abstract
Every year hundreds of thousands of lives are taken away worldwide by natural disasters such as earthquakes. Walls made of concrete blocks or bricks, are amongst the most vulnerable type of walls, which tend to collapse during an earthquake. Due to their good sound and thermal insulation properties, unreinforced masonry (URM) walls are widely used in partitioning many of the commercial and residential buildings worldwide. URM is considered one of the most common types of partition wall systems in many of the school and hospital buildings and commercial buildings.URM partition walls are known to have very low drift capacity in seismic events and the failure mechanisms are known to be mostly...
Pushover Analysis for Soil-Structure Systems
, M.Sc. Thesis Sharif University of Technology ; Ghannad, Mohammad Ali (Supervisor)
Abstract
Controlling damage level of structures for an earthquake with certain intensity is the main purpose in seismic performance based design. This is done by estimating and confining the structure displacements and related global and local response parameters. Even though nonlinear time history analysis method is the most exact method for predicting seismic behavior of structures, but its application is limited because of being complex. Nonlinear static analysis procedure (Pushover analysis) which is based on analyzing the structure subjected to the incremental lateral load is an alternative method that has been recommended by recent structural codes. In order to consider the soil-structure...
Steel Moment-Resisting Frames with Mixed Ductile Moment-Shear Fuse
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
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...
Combined Fretting Fatigue Life Estimation Based on the Theory of Critical Distances
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
Theory of Critical Distances (TCD) is one of the methods that has attracted the scientists in life estimation of fretting fatigue problems in recent years. Less difficulty and less time consuming features of this method in comparison with other methods like fracture mechanics are the attracting aspects of this theory. In this research, the capability of the Theory of Critical Distances in life estimation of combined bending and tensile loading modes in fretting fatigue for the pads with sharp edges has been evaluated. This included the evaluation of this method in lifetime estimation of 316L stainless steel for fretting fatigue in two different types of heat treatments and the evaluation of...
Microstructural Evolution During Post-Bond Heat Treatment of Brazed Nickel Base Super Alloys
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Kokabi, Amir Hossein (Co-Supervisor)
Abstract
The brazing process is the preferred method for bonding and repairing high temperature resistant superalloys. In this process, filler metals containing MPD elements such as B and Si are used. The presence of these elements causes the formation of brittle and eutectic phases such as borides and silicides in the joint area. These phases reduce the mechanical properties and re-melting temperature of the joint. By increasing the temperature and time of bonding and using the concept of isothermal solidification, the formation of boride and silicide phases can be prevented. In wide gap joints, the time to complete the isothermal solidification is very long, and applying such temperature and time...
On The Behavior of Low-Rise, Irregular, Dual Structures
, M.Sc. Thesis Sharif University of Technology ; Mofid, Masoud (Supervisor)
Abstract
The Response modification factor R represents the behavior of the structure such as ductility, overstrength and the inherent redundancy. This factor shall be defined according to the type of lateral force resisting system. However, there are some complexities and/or uncertainties in codes related to the R factor according to the height, form of irregularities and structural systems. Therefore, from the scientific point of view as well as reliability, it is very clear that the R factor cannot be similar for all kinds of structures, categorized as a specific group. In this investigation, assuming a low-rise, vertically irregular structure with a heliport which has a dual structural system...