Sharif Digital Repository

The ultimate goal of this study is to evaluate the condition of concrete structures using computer vision methods and using powerful tools such as machine learning methods based on visual information. This assessment is performed by detecting damage in these structures. With the aging of structures such as dams, bridges and tall buildings, structural health monitoring is an important task in ensuring their safety and stability. Therefore, rapid assessment of the health of structures and diagnosis of damage after destructive events is of great value in terms of providing resilience of structures. Visual inspection of structures by experts is one of the basic methods of evaluating structures.... 

Structural Health Monitoring (SHM) is a multidisciplinary emerging research field. SHM assesses the health state of the structure through processing and interpreting of signals and can predict remain life of the structure. Damage detection with Piezoelectric Wafer Active Sensors (PWAS) is one of the effective and emerging methods of SHM. One of the most critical parts of aerial structures is lap joints in which SHM could be very effective. In this research, damage detection of lap joints using lamb wave propagation has been studied. A 3D model of an aluminum lap joint presented. The PWAS are modeled separately and bonded to the host structure and coupled electromechanically with the... 

The goal of this research is to study the effect of local microcracking due to step by step pressure loading on the durability properties of geopolymer concrete. To better understand the behavior of GGBS-based GPC under different pressure stress levels, some experiments such as water permeability and water absorption conducted on the samples at each state of damage. Also, non-destructive tests such as ultrasonic waveform and pulse velocity (UPV) was used to quantify the extent of damage at each step. GGBFS and a blend of sodium silicate solution and 10 molar sodium hydroxide solution with SSSH⁄ ratio of 2 were used for production of GPC samples. GPC, OGPC and OPC samples with water to binder... 

This study aimed to develop a method for locating damages in the early stages of damage expansion in plate components of the structure using a one-dimensional discrete wavelet function. Continuous monitoring of the health of structures to preserve and repair them to protect the lives and property of individuals and national capitals and to lower the direct and indirect economic costs imposed on society is vital and inevitable for society's decision-makers. Because the damage to the structure caused by earthquakes occurring during the lifetime of the structure, exhaustion of structural components, improper implementation of the structure at the time of construction, and other events that... 

Structures face various loadings and confront different circumstances as they are built and used. This situation causes the aging structures to deteriorate, which would lead to a decrease in reliability and safety. In the recent decades, the need for systems to assure the integrity of structures in terms of their age, usage and level of safety when experiencing infrequent and extreme forces such as earthquakes, tornados, hurricanes, large waves has deeply been recognized. These systems are often referred to as structural health monitoring (SHM) in the literature. The main objective of such system is to increase reliable operating lifetime. In the case of offshore structures, utilizing... 

Pipeline systems have a major role in civil infrastructure for transportation of energy sources including, petroleum, natural gas, and water. As most pipelines are located in hard-access location such as underground and sea as well as mountains, they are vulnerable to corrosion, cracks and thus, unpredictable failure. Failure of pipelines not only costs millions of dollars but also causes environmental damage, requiring continuous health monitoring systems to provide early detection and early warning of flaws such as corrosion and leaks. Structural health monitoring based on ultrasonic guided waves is used in structures as plates, composites, rods, piping and tubing. This research aims to... 

In presence of epistemic and aleatoric uncertainties of the structural systems, it is better to investigate the events in probabilistic manner. Bayesian inference is an approach that can update the current knowledge of probabilities with new evidence. The main objective of this study was evaluating the advanteges of using Bayesian approach in two main area of structural health monitoring, model calibration and decision making. In each of these two areas, one case study was conducted. First case study was prediction of crack growth life in a pre-cracked aluminum plate and the results showed that using Bayesian approach in calibration of crack growth model and measurement model of health... 

This study presents the best layout with optimal number of sensors for an arbitrary monitoring area based on reference free damage detection and localization. In recent years, damage detection approaches with the concept of instantaneous baseline measurements in Structural Health Monitoring (SHM) with lamb wave propagation are being developed. An array of spars transducers is obligatory in SHM with lamb wave propagation, so that designing the best one is a concern for many researchers. To obtain the best sensors layout, damage localization process should be done for all definable sensors layouts in many different crack positions. Obviously, doing this seems not practical as wave propagation... 

Structural Health Monitoring (SHM) is an effective method for the early detection of structural damage, and this method can reduce the maintenance costs of structures. In this thesis, the use of artificial one-way and multi-layer artificial neural network is evaluated to determine the damage to the structure. The neural network method used in this thesis is a post-propagation method. Finally, the numerically damage determine will be evaluated using a two-dimensional frame structure and a three-dimensional frame structure by finite element method. In this method, the dynamic properties of the structure are used only in the form of the modules. For this purpose, the finite element model is... 

Civil structures are on the verge of changing which leads energy dissipation capacity to decline. Structural Health Monitoring (SHM) as a process in order to implement a damage detection strategy and assess the condition of structure plays a key role in structural reliability. Earthquake is a recognized factor in variation of structures condition, inasmuch as inelastic behavior of a building subjected to design level earthquakes is plausible. In this study Hilbert Hunag Transformation (HHT) is superseded by Ensemble Empirical Mode decomposition (EEMD) and Hilbert Transform (HT) together. Albeit this method is closely resemble HHT, EEMD brings more appropriate Intrinsic Mode Functions (IMFs).... 

The purpose of the study: The purpose of this study is to identify the crack position in homogeneous plates through health monitoring methods based on vibration. Identifying structural damage is one of the issues that attention can prevent the sudden collapse of structures and causing heavy loss of life and property. For this reason, extensive studies have been conducted in this field in recent decades. In this study, plates are examined as one of the most used structural members, and their damage is identified through a proposed method based on wavelet transform. Research method: In this study, through the wavelet transform method, the dynamic responses of a homogeneous plate excited by a... 

Bridges are among the crucial elements of transportation networks, and play an important role in facilitating emergency relief efforts following earthquakes. For this reason, it is emparative to monitor their damages to ensure about their performace in earthquakes. The structure of a bridge is divided into two parts, namely the superstructure and substructure. Due to the relatively high rigidity and strength of superstructures, most of structural damage is usually concentrated in substructures, which may ultimately affect the overall stability of the bridge. Therefore, assessing the level of damage in the substructure is of utmost concern. This research attempts to evaluate the damage in the... 

Along with improvement of technology and need for access to energy resources, existence of pipelines such as gas, oil and water pipes is vital for our lives. These pipes will be eroded and damaged over time. With the prediction of the defects and tracking of pipeline paths, the probability of sudden damages is greatly reduced. In this research, at first various non-destructive methods of monitoring the pipelines are investigated and it is shown that the laser method is the most comprehensive and non-destructive inspection method and then the background of the chosen method is examined. Also, the hardware aspect of the system and the proper layout of the laser sensors are determined on the... 

This thesis presents a probabilistic framework for prioritizing the highway bridge network for seismic retrofitting and structural health monitoring. The basis of this framework is the risk analysis of the bridge network, which includes bridges and the links connecting them in the transportation network. Risk is defined as the probability of exceeding the sum of all losses incurred to the community in the event of a hazard. These losses include the direct economic cost of bridge repairs and damage to vehicles due to bridge failure, the socioeconomic cost of increased travel time for transportation network users, the indirect economic cost of excess fuel consumption and depreciation of... 

In recent years world countries faced with the ageing aircraft fleet problem which increased the repair and maintenance costs of these aircrafts. The non-destructive inspection methods are common inspection methods of old aircrafts. To do this, the aircraft must test with a certain time scheduled inspection programme in a hangar. This method not only increased the repair and maintenance costs but also affects the flight schedule. To overcome this problem, the structural health monitoring can use to online monitoring the structure and when it needs for repair, the aircraft send to hanger. So, repair and maintenance costs minimize while the flight schedule less affected. One of the structural... 

Structural health monitoring (SHM) has been motivated in aircraft and civil industries over the two last decades. Ultrasonic guided wave propagation technique is one of the best damage detection methods in airplane thin wall structures because of their large distance traveling and low attenuation.
In fact by efficient design of sensors pattern one can effectively pick up the changes that happen in propagated signals due to presence of any kind of structural damage. This could be effectively achieved by numerical simulation techniques like finite element modeling. To obtain a damage detection algorithm based on instantaneous baseline data, here, finite element technique is employed for... 

The main purpose of this dissertation is to investigate and improve the efficiency of Sparse Reconstruction method for structural health monitoring application in order to solve the challenges including; finding multiple simultaneous damages, damage detection and location in anisotropic structures and real engineering complex structures. The main approach of this research is based on presenting theoretical concepts and developing practical methods based on the presented concepts, as well as evaluating and implementing the developed methods using numerical simulations and experimental tests. In this work, the finite element method is used for numerical simulation. In the experimental test,... 

Principal component analysis (PCA) is a conventional tool for dynamic system analysis. In this paper, a new damage diagnosis method is presented based on sensitivities of principal components obtained from PCA of Frequency response functions (FRFs). Damage identification, determination of its location and estimation of the damage severity are conducted by an innovative well established sensitivity relation of PCA results. Then, sensitivity matrix is obtained by using measured frequency of damaged structure, and comparison of PCA of the intact structure with PCA from FRFs which are measured at sensors locations. Damage location and its severity are calculated by model updating procedure. This... 

Nowadays a major part of energy, fresh water and sewer water in over the world are transmitted by buried pipe, and always these lines are under the loads and different stresses such as corrosion, earth quick and etc.
In many countries the age of these lines are more than 30 years which causes corrosion of the pipe wall and the necessity of health investigating of transmission lines has a special importance for the governments and leak detection can also keep the natural environment healthyand the costs will come down significantly, scientists and researchers have always tried different ways to check the health of the pipes.
In the field of leak detection and the problems of age... 

The main goal of this research is detection, localization, and determining the severity of structural damages. The importance of this objective is to prevent abrupt destruction and severe human and financial losses. Damage detection is divided into local and global detection, and global detection contains static and vibration-based methods. In this research, the vibration-based method is used. Due to the complexity of this method, accurate and powerful tools are required for detecting effective features in damages; Deep Learning (DL), which is part of a broader family of machine learning methods based on artificial neural networks (ANN), could be used. Accordingly, in this project, the...