Sharif Digital Repository

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... 

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 are one of the cheapest ways for distribution and transportation of petroleum and natural gas. The testing of pipes used in the petroleum industry is necessary to avoid unplanned process interruptions, environmental pollution and provide good safety. One of the methods which is used for pipeline inspection is the ultrasonic non-destructive testing (NDT) technique. The use of conventional NDT techniques such as ultrasonic thickness gauging is a slow inspection process, which becomes very expensive when full inspection is needed. Ultrasonic guided waves provide an appropriate fast screening technique. These waves stress the whole pipe wall and propagate along the length of the... 

Structural Health Monitoring (SHM) of civil infrastructures is of paramount importance in ensuring the safety and reliability of these structures. SHM involves the use of sensors and data analysis techniques to continuously monitor the structural condition of infrastructure, detect damage or degradation, and provide insights for maintenance and repair. Concrete cracks are one of the most common and critical types of damage in civil infrastructure, which can compromise the structural integrity and safety of the infrastructure if left undetected and untreated. Therefore, the development of effective and efficient crack detection techniques using computer vision and machine learning can... 

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... 

Nowadays, many offshore jacket platforms have been built in all over the world for excavating oil and gas. Due to cost of construction and maintenance, they are considered as national assets. Jacket platforms are always under various types of loads in their time life, so they cause some damages to them. Hence, on time damage detection can prevent possible extravagant costs of repair and reconstruction. Because many jacket platforms are in Iran, this issue can be very important.Structural health monitoring (SHM) improvised to ensure safety and detect damages of structures uses sensors. They transfer data received from structures to the computers in order that after interpretation of data,... 

In this study, damage detection of brick masonry walls using a unique signal processing technique has been addressed. Firstly, the pushover analysis and the calibration of the model is performed. Then, the dynamic analysis of the wall under earthquake excitation in three cases with different aspect ratios is conducted. Finally the dynamic properties of the system, namely natural frequency and modal damping ratio, are identified using continuous wavelet transform. The advantage of wavelet transform is its fine time-frequency resolution. The Morlet mother wavelet is used since it can provide the best time-frequency resolution based on Heisenberg uncertainty principle. Afterwards, the... 

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... 

This study aims to identify the structural damage using deep learning. Damage to structures reduces their lifespan. Therefore, continuous monitoring of structures is necessary to detect any possible damages that occurred due to various causes. Structural health monitoring systems that use wired sensors to measure signals are costly and time-consuming to install. Whereas, wireless sensor-based damage detection systems are relatively cost-effective. However, one of the most important problems in using them is the loss or non-recording of some data, which severely affects the accuracy of a structural damage detection system. On the other hand, health monitoring using machine learning-based... 

As more structures are equipped with supplemental energy dissipation devices, the assumption of classical damping becomes less accurate. For this reason, development of a general identification method that is accurate enough for response simulation is emparative for such structures. Modal identification of structures can be carried out using either modal or state space approach. In modal methods (such as wavelet transform method), the damping matrix needs to be identified for response simulation. This is sometimes difficult, and may result in simulation inaccuracies. In contrast, direct identification of damping matrix for simulation is not required in state space approach. Hence, the... 

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... 

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... 

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... 

Modal analysis is very important in determining the physical properties of structures and mechanisms. This field is divided into two general parts: Experimental Modal Analysis (EMA) and Operational Modal Analysis (OMA). In the operational modal analysis, there are more challenges for the analyst due to the lack of inputs to identify the system. Many of the mechanical structures can not be analyzed experimentally and under specific loadings, but should be identified under actual operating conditions and in situations where the inputs of the system are not measurable. For this purpose, a modal analysis method called "Random Sub-Space Identification" (SSI) is intoduced, which uses only output... 

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... 

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... 

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... 

Extracting modal parameters is necessary for future vibration-based health monitoring studies of the structures. Due to the reason that it is difficult to measure the input excitation forces acting on a real large structure in its operational condition, it is preferable to use the output-only methods which estimate the modal model by using responses data only. Also, the output-only dynamic testing has advantages of being inexpensive since no equipment is needed to excite the structure and the service condition does not have to be interrupted.This paper presents the results of modal identification of an offshore jacket platform using output-only methods with the assumption of ambient... 

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... 

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....