Modeling of Crumb Rubber Concrete for a Structural Column by Evaluating the use of FRP

, M.Sc. Thesis Sharif University of Technology Ghaznavi Doozandeh, Soheil (Author) ; Khaloo, Alireza (Supervisor)

Abstract

The research shows that the compressive strength of concrete reduced by replacing crumb rubber in concrete mix design compared to normal concrete mix design. However, there have been a couple of utilizations investigated to date for the structural utilization of these materials. Crumb rubber is usually provided from recycled rubber from automotive and truck scrap tires. During the recycling process steel and triviality are removed, leaving tire rubber with a granulose cohesiveness. The additional crumb-rubber aggregate has a significant effect on concrete mix porosity which affects both the plastic state workability and hardened state mechanical properties. This research depicts an...

The Seismic Assessment of the Low Rise Steel Structures with Irregular Plans

, M.Sc. Thesis Sharif University of Technology Doozandeh, Pourya (Author) ; Mofid, Masoud (Supervisor)

Abstract

Abstract
In this research, the effect of irregularity in the plan floor of structures, including geometric and torsional irregularity on the seismic behavior of steel moment frames braced with chevron knee braces (CKBs) has been investigated. To achieve this, three–dimensional 5-, 8-, 12-story steel buildings models with regular and irregular plan floors were built in OpenSees software and subjected to nonlinear static (pushover) and nonlinear incremental dynamic analysis (IDA) under 22 ground motion records. The performance of each model was then examined by calculation of three seismic design parameters: response modification (R), structural over strength (Ω), and structural ductility...

Studying the Problem of Maximum Matching in Stochastic Environments

, M.Sc. Thesis Sharif University of Technology Soheil, Farehe (Author) ; Ghodsi, Mohammad (Supervisor)

Abstract

The problem studied in this research is the online stochastic bipartite matching. In this problem the vertices of one side of the given graph arrive in an online manner, with respect to a probability distribution. Also the edges of the graph exist according to a given probability distribution and one should perform queries from an oracle to know about the existence of an edge. The given graph shall be weighted or unweighted. The goal here is to find a maximum matching in the graph that is as close to the omniscient optimum as possible, while the number of queries performed per vertex is limited. In the general case of the problem, there are no specific conditions, but in other versions,...

Effect of solidification mechanism on microstructure and mechanical properties of joint in TLP bonded Al2024-T6 alloy

, Article Science and Technology of Welding and Joining ; Volume 16, Issue 2 , Nov , 2011 , Pages 174-180 ; 13621718 (ISSN) Ghaznavi, M. M ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology

2011

Abstract

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium (Ga) interlayer, has been investigated. Bonding process was carried out at 470°C for 6 min, and homogenising temperature and time were 495°C and 2 h respectively. Conventional TLP bonding using Ga interlayer was not an appropriate method for joining of Al2024. In this method, the boundary between two Al2024 specimens was not fully eliminated during bonding because of solidification with planar front. In addition, bonding zone was depleted of copper, and as a result, tensile and shear strength of joint decreased to 200 and 110 MPa respectively. TLP bonding under temperature gradient offered very good results in bonding of...

HAZ softening behavior of strain-hardened Al-6.7Mg alloy welded by GMAW and pulsed GMAW processes

, Article International Journal of Advanced Manufacturing Technology ; Volume 92, Issue 5-8 , 2017 , Pages 2255-2265 ; 02683768 (ISSN) Hadadzadeh, A ; Mahmoudi Ghaznavi, M ; Kokabi, A. H ; Sharif University of Technology

2017

Abstract

Gas metal arc welding (GMAW) process was used to weld plates of strain-hardened Al-6.7Mg alloy. It was observed that HAZ softening issue occurred extensively for the current material using the GMAW process. So, as a solution, pulsed current was employed and the plates were welded by pulsed GMAW (PGMAW) process. The effects of peak current (93, 120, 140, and 160 A) and pulse frequency (0.5, 2.0, and 5.0 Hz) on the strength of the weldments were investigated. For high peak currents (160 A), catastrophic defects were formed in the weld metal. It was observed that for the lowest pulse frequency (0.5 Hz), increasing the peak current increased the weld strength. The peak current did not change the...

Prediction of Myocardial Infarction Complications using Machine Learning Methods

, M.Sc. Thesis Sharif University of Technology Zojaji, Sahar (Author) ; Rafiee, Majid (Supervisor) ; Hemmati, Soheil (Co-Supervisor)

Abstract

Accurate prediction of myocardial infarction complications is one of the major challenges in the management of cardiac patients, as the occurrence of such complications can lead to severe consequences for quality of life, length of hospitalization, treatment costs, and mortality. This study aims to develop a data-driven, machine learning-based framework to predict 12 critical post-infarction outcomes using modern algorithms. In the first step, patients were stratified into more homogeneous groups based on treatment effects through a causal clustering algorithm. Subsequently, machine learning models, including logistic regression, random forest, and gradient boosting, were trained and...

Modelling of Frictional Cracks by the Extended Finite Element Method Considering the Effect of Singularity

, M.Sc. Thesis Sharif University of Technology Saeed Monir, Saeed (Author) ; Khonsari, Vahid (Supervisor) ; Mohammadi, Soheil (Co-Advisor)

Abstract

When a crack is subjected to a compression field, it will close and its edges will get into contact with each other. Depending on the direction and magnitude of the loads and also the coefficient of friction, ‘stick’ or ‘slip’ situationsbetween the edges will occur. This type of crack is known as ‘frictional crack.’ In this project, first these cracks are studied analytically and the order of singularity is derived using asymptotic analysis and also the analytical fields are determined for both ‘isotropic’ and ‘orthotropic’ materials. Then, numerical simulations are carried out using extended finite element method which is considered as the most powerful means for analyzing the problems...

Theoretical and Numerical Analysis of Shock Waves Propagation in Porous Medium

, Ph.D. Dissertation Sharif University of Technology Nemati Hayati, Ali (Author) ; Ahmadi, Mohammad Mehdi (Supervisor) ; Mohammadi, Soheil ($item.subfieldsMap.e)

Abstract

Particulate porous mateials have always been of interest in terms of reducing shock waves effects in different protective applications. Therefore, the physics governing the flow in porous media is especially significant for which different models have been presented by the researchers. The complexities of these media have caused many existing models to be unable to properly predict the behavior of granular media under shock loadings. On the other hand, the complexity of the equations makes the numerical solution of them cumbersome and costly in a way that many researchers do not solve the whole coupled equations and reduce their number. In addition, current high-resolution TVD solutions of...

Robust Learning to Spurious Correlation without Access to Side Information of the Environment

, M.Sc. Thesis Sharif University of Technology Ghaznavi, Mahdi (Author) ; Rohban, Mohammad Hossein (Supervisor) ; Soleymani Baghshah, Mahdieh (Supervisor)

Abstract

Traditionally, machine learning models for classification tasks rely on statistical methods to find correlations between patterns in the input data and their correspond- ing labels. However, these correlations are not necessarily consistent across different data partitions and may change at test time. Such unstable correlations are referred to as spurious correlations. When the spurious correlation relied upon during training changes at test time, the model’s accuracy can degrade. To improve robustness to shifts in spurious correlations, most research in this area assumes that group annota- tions based on different values of the spurious attribute are available during training or validation....

Reducing the Number of Elements in Order to Enhance the Speed of the Ultrasound Tomographic Imaging Systems

, M.Sc. Thesis Sharif University of Technology Rasouli Jokandan, Fatemeh (Author) ; Kavehvash, Zahra (Supervisor) ; Hakakzadeh, Soheil (Co-Supervisor)

Abstract

Transmission-mode ultrasound computed tomography (USCT) has emerged as a novel, safe, and cost-effective method for quantitative imaging of biological tissues, especially in breast screening. Despite technological advancements, challenges such as reduced accuracy in heterogeneous media, incomplete acoustic field coverage, sensitivity to initial conditions, and phenomena like cycle skipping still limit image quality and reconstruction speed in these systems. In this thesis, aiming to improve the speed and performance of USCT imaging, three reconstruction algorithms have been designed, implemented, and evaluated: a travel-time-based Gauss-Newton method, frequency-domain full waveform inversion...

Transient Liquid phase Bonding of AL2024 Alloy and Evaluation of Joint Properties

, Ph.D. Dissertation Sharif University of Technology Mahmoodi Ghaznavi, Majid (Author) ; Kokabi, Amir Hossein (Supervisor) ; Ekrami, Ali Akbar (Supervisor)

Abstract

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in...

The effects of combining high-top shoes with twister wrap orthoses on balance parameters of children with spastic diplegic cerebral palsy

, Article Journal of Biomedical Physics and Engineering ; Volume 12, Issue 1 , 2022 , Pages 91-100 ; 22517200 (ISSN) Davoudi, M ; Farsani, M. K ; Ba-Baee, T ; Ranjbar, H ; Shok-Ouhyan, S. M ; Ghaznavi, A ; Rezaei, M ; Sharif University of Technology

Shriaz University of Medical Sciences 2022

Abstract

Background: Cerebral palsy (CP) is a non-progressive encephalopathy before, dur-ing, or after childbirth with almost the most common type, i.e. spastic diplegic, leading to a frequent walking problem, In-toeing. Orthoses can reduce the consequences of CP. Objective: This study aimed to evaluate the effect of combining twister wrap orthoses (TWO) with high-top shoes on the balance parameters of children with spastic diplegic CP. Material and Methods: In this quasi-experimental study, twenty children (aged 6.8 ± 0.5 years) with spastic diplegic CP with in-toeing gait participated. The tests were conducted in three conditions: 1) in bare-foot, 2) with high-top shoes, and 3) with high-top shoes...