Sharif Digital Repository

The aim in the current thesis is to introduce a powerful method based on quantitative Acoustic Emission approach for structures health monitoring in a way that the proposed method can be used for industrial purposes. In order to do this, after presenting a survey on moment tensor concept and its relation to crack nucleation in solids, the equivalent forces of crack initiation are calculated. These forces are then applied on the meshed area of a 2D finite element model. The corresponding result is the propagation of acoustic waves which are modeled by using finite element analysis. After waveform data acquisition in the imaginary sensor positions and implying source location analysis, the... 

Karun 4 arch concrete dam with a height of 230 meters is designed and built in one of the most complex natural places. Therefore, monitoring the behavior and evaluating the safety and stability of this dam, both with regard to the height and nature of the dam itself and with regard to its national and international dimensions, is of special importance and sensitivity. This sensitivity is doubled due to some problems and issues encountered in the body of the Karun 4 dam, which of course are considered probable and possible phenomena in arch concrete dams. The Karun 4 Dam construction site is located in the southwest of Iran on the Karun River, immediately upstream of the Karun 3 Dam reservoir... 

Crack detection is a critical task in monitoring and inspection of civil engineering structures. This study proposes a deep-learning-based model for automatic crack detection on the concrete surface. The proposed model is an encoder-decoder model which uses EfficientNetB7, the state-of-the-art convolutional neural network, as encoder and the U Net’s expansion path as decoder. To minimize the training time and maximizing the accuracy, we use transfer learning in our approach. We train our model with a novel training strategy on images from an open-source dataset and achieve 96.44% F1-score for unseen test data. To compare the performance of the proposed method, we evaluate our model on CFD... 

Cardiovascular diseases are currently the most common disease and the first cause of death in Iran and the world. It will increase in the future due to improper diet and lifestyle. Therefore, the prevention and treatment of these diseases is very important for the health of the country. One of the effective ways to diagnose heart diseases is to analyze the electrical signals of the heart and detect heart rhythm irregularities from it. The electrical signal of the heart called ECG is created by the electro-mechanical activity of the atria, ventricles and the valves between them. Therefore, this signal is useful for detecting the correct functioning of different parts of the heart and... 

This research proposes a damage assessment framework based on the visual features of a damaged reinforced concrete shear wall, such as crack pattern distribution, crushing areal density, aspect ratio, and the presence of the boundary condition. The study contains two parts: identifying the performance level of the damaged walls (i.e., Immediate Occupancy, Life Safety, and Collapse Prevention) and estimating the residual strength and drift ratio of the walls. The research database contains 236 images of 72 reinforced concrete shear walls tested in the laboratory under the quasi-static cyclic loadings at various drift ratios between 0.0 to 4.0. To identify the performance level of a damaged... 

The purpose of this paper is to estimate the stiffness and strength of damaged rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. Assessing the damage severity of buildings after an earthquake is an important part of the emergency inspection operation of buildings. Expert inspectors tag buildings into two categories of safe or unsafe that are usually affected by subjective decisions, which may result in catastrophic events reported in previous earthquakes. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls (RCSWs) is collected and used to develop predictive equations for updated stiffness and... 

Damage and collapse in structural systems due to structural loads are considered as a threat to human lives. Therefore, using structural health monitoring methods in order to estimate structural damages and preventing structural collapse, have drawn a lot of attention. Due to the importance of considering random vibration, a nondestructive damage detection method using power spectral density function has presented in this study. This method is based on model updating and solving the sensitivity equations and it is also a model based method. The mentioned method can be classified as a vibration-based health monitoring method in frequency domain which includes dynamic excitation in some... 

Structural system identification from vibration data is one of the most interesting research topics in the structural health monitoring area. Recently, realization and detection of the effects of damage when a structure is subjected to strong ground motion has become a great concern in earthquake and structural engineering communities. Seismic signal processing is one of the most reliable methods of detecting the structural damage during earthquakes. The structural responses during earthquakes are nonstationary with respect to both amplitude and frequency. The state-of-the-art time-frequency distributions when applied to vibration records were studied. Different methods of analysis for... 

In recent years health monitoring and prognostics of complex systems have been considered more than ever.. In the present researh, data - based approach has been selected among various prognostics and health monitoring approaches. One of the most challenging issues in data-based methods is how to map system sensor information to its health status. In this research, different methods of mapping are discussed. The results show that sensor fusion by principal component analysis (PCA) offers acceptable performance. This pattern produces a single-dimensional signal for health monitoring with high reliability.The second challenge is to predict the status and design of the prognostics module. For... 

Pipelines are the preferred means for transporting of liquid or gas phase materials. The economy of many countries is extremely dependent upon a large network of pipelines systems to transport and distribute the nation’s energy resources. Damages to the pipe structure may cause leakage and result in economic losses or even loss of life. Developing methods for detecting the anomalies and damages to the structure before they lead to catastrophic events is vital. Multiple pipeline misadventures over the past several years have resulted in hundreds of fatalities and billions of dollars in property damages. These accidents demonstrate that the current monitoring methods are not sufficient... 

Nowadays, the structural health monitoring is considered as an essential element in improving the performance of the structures. The role and importance of the issues in this area have been reached to the point that different ideas and policies are developed for the safety margin over the useful life of the structures. To analyze more accurately, a real model of a turbine blade is required. This issue would be taken into more consideration when the scale of the turbine gets larger. Changing of the design philosophies over time results in effective changes in the design process and maintenance procedures. Any single of these inspections has different importance according to users' demands. In... 

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... 

In this thesis selection criteria are present for types, numbers and locations of sensors for structural health monitoring of offshore jacket platform in the Persian Gulf. The selection criteria are chosen by studying structural health monitoring of various structures in civil and aerospace industries. Knowing the types of sensors that can be used, a new approach of inverse vibration problem is introduced for structural health monitoring of offshore jacket platforms. In the previous studies, significant numbers of frequencies and mode shapes are usually used to detect damages by updating components of stiffness matrix. Considering the fact that offshore platforms are composed of a heavy... 

High construction and installation costs of offshore platforms, and also harsh environments in which they operate, make health monitoring of these structures more important. Conventional methods to solve the health monitoring problem are deterministic, whereas much uncertainties are imposed to the problem. In most methods of health monitoring methods we try to identify natural frequencies and mode shapes of structures by using its dynamic response. This set of data is then compared to results of modal analysis performed on a finite element model of structure in order to detect any possible damage. In deterministic methods each response of structure is pertained to one damage state, in a... 

Damage and collapse of structural systems due to externally applied loadings, are inevitable, which cause financial and human losses. Therefore, the application of structural health monitoring (SHM) strategies has attracted a lot of attention in order to estimate structural damages, optimal maintenance and preventing structural collapse. Hence, in recent decades, the development of research activities in the field of structural health monitoring and its application in civil engineering, has led to the invention of various techniques and methods in assessing the safety of structures. These methods not only should be accurate enough for confidently identifying diverse severity of damages, but... 

Structural Health Monitoring (SHM) of pipelines is an important task for economic/safety reasons which depends on the method of study of the integrity profile of the pipeline structure. Process pipes, particularly, pipelines in thermal power plants are susceptible to stress corrosion cracking (SCC). Failure of these pipes may result in catastrophic damages, thus, require systematic regular inspections. The damage assessment may demand embedding of appropriate sensors and specific data analysis techniques. According to what is reported from the respective experiments, data analysis of a single sensor may not be adequate to provide a reasonable damage assessment, and in turn to making a... 

Today, considering the structural health monitoring system is approximately essential for aerospace structure due to more safety and reduction of maintenance costs. In this manner, aircraft designers and manufactures have recently attempted to usage of the monitoring system on their new products to maintain the superirority of them among the competitors. Furtheremore, installation of these systems on the aircraft will also becom one of the requirements of the aviation regulation in near future which must be complied.The lap joints are one of the major and inevitable components of the metallic airframe structure and the multisite damage such as fatigue cracks are the high probable damages... 

Structural health monitoring is a process that aims to provide accurate and immediate information about the condition and performance of the structure. Processed is a very important eld in the eld of civil, aerospace and marine engineering, because the use of structural health monitoring allows us to increase human and environmental safety while reducing economic damage. e main component of the health monitoring process is the real-time reconstruction of displacement and three-dimensional stress in the structure using a network of strain gauges and other sensors. e inverse nite element method is a relatively new method and stress measurement that has been shown to be fast and accurate for... 

Application of composite patches in repair of damaged/aged aircraft structures is one of the most popular repairing methods in aerospace engineering and because of its advantages the use of this type of repair is increasing today. However, to use these patches in life extension of aged aircraft, the added weight to the structure should be strictly controlled. This could be best done if achieving the optimum and smart design by using optimization and structural health monitoring methods. These two concept about pre-designed of composite patch repair are investigated in this thesis. The simulation by Abaqus software and experimental results and tests will be used for this purpose. In first... 

Damage detection by Piezoelectric Wafer Active Sensors is one of the emerging efficient and dominant Structural Health Monitoring (SHM) methods. These sensors assess the health state of the structure due two strategies: a) near-field damage detection, b) far-field damage detection. The far-field damage detection is based on the high frequency Lamb wave propagation. As wave travels in a damaged structure, phase and amplitude of the wave will be changed. So comparison of the received signal from the pristine structure with damaged structure can give useful information about the health state of the structure. As PWAS is the essential part of this method, simulation and modeling of this sensors...