Health monitoring of civil infrastructures by subspace system identification method: an overview

Structural health monitoring (SHM) is the main contributor of the future's smart city to deal with the need for safety, lower maintenance costs, and reliable condition assessment of structures. Among the algorithms used for SHM to identify the system parameters of structures, subspace system identification (SSI) is a reliable method in the time-domain that takes advantages of using extended observability matrices. Considerable numbers of studies have specifically concentrated on practical applications of SSI in recent years. To the best of author's knowledge, no study has been undertaken to review and investigate the application of SSI in the monitoring of civil engineering structures. This paper aims to review studies that have used the SSI algorithm for the damage identification and modal analysis of structures. The fundamental focus is on data-driven and covariance-driven SSI algorithms. In this review, we consider the subspace algorithm to resolve the problem of a real-world application for SHM. With regard to performance, a comparison between SSI and other methods is provided in order to investigate its advantages and disadvantages. The applied methods of SHM in civil engineering structures are categorized into three classes, from simple one-dimensional (1D) to very complex structures, and the detectability of the SSI for different damage scenarios are reported. Finally, the available software incorporating SSI as their system identification technique are investigated

A comparative study of the data-driven stochastic subspace methods for health monitoring of structures: a bridge case study

Subspace system identification is a class of methods to estimate state-space model based on low rank characteristic of a system. State-space-based subspace system identification is the dominant subspace method for system identification in health monitoring of the civil structures. The weight matrices of canonical variate analysis (CVA), principle component (PC), and unweighted principle component (UPC), are used in stochastic subspace identification (SSI) to reduce the complexity and optimize the prediction in identification process. However, researches on evaluation and comparison of weight matrices' performance are very limited. This study provides a detailed analysis on the effect of different weight matrices on robustness, accuracy, and computation efficiency. Two case studies including a lumped mass system and the response dataset of the Alamosa Canyon Bridge are used in this study. The results demonstrated that UPC algorithm had better performance compared to two other algorithms. It can be concluded that though dimensionality reduction in PC and CVA lingered the computation time, it has yielded an improved modal identification in PC

Comparative analysis of different weight matrices in subspace system identification for structural health monitoring

Subspace System Identification (SSI) is considered as one of the most reliable tools for identification of system parameters. Performance of a SSI scheme is considerably affected by the structure of the associated identification algorithm. Weight matrix is a variable in SSI that is used to reduce the dimensionality of the state-space equation. Generally one of the weight matrices of Principle Component (PC), Unweighted Principle Component (UPC) and Canonical Variate Analysis (CVA) are used in the structure of a SSI algorithm. An increasing number of studies in the field of structural health monitoring are using SSI for damage identification. However, studies that evaluate the performance of the weight matrices particularly in association with accuracy, noise resistance, and time complexity properties are very limited. In this study, the accuracy, noise-robustness, and time-efficiency of the weight matrices are compared using different qualitative and quantitative metrics. Three evaluation metrics of pole analysis, fit values and elapsed time are used in the assessment process. A numerical model of a mass-spring-dashpot and operational data is used in this research paper. It is observed that the principal components obtained using PC algorithms are more robust against noise uncertainty and give more stable results for the pole distribution. Furthermore, higher estimation accuracy is achieved using UPC algorithm. CVA had the worst performance for pole analysis and time efficiency analysis. The superior performance of the UPC algorithm in the elapsed time is attributed to using unit weight matrices. The obtained results demonstrated that the process of reducing dimensionality in CVA and PC has not enhanced the time efficiency but yield an improved modal identification in PC

Why Iranian married women use withdrawal instead of oral contraceptives? A qualitative study from Iran

<p>Abstract</p> <p>Background</p> <p>Withdrawal as a method of birth control is still used in Iran. The aim of this study was to explore married women's perspectives and attitudes on withdrawal use instead of oral contraceptive (OC) in Tehran, Iran.</p> <p>Methods</p> <p>This was a qualitative study. Participants were 50 married women, not currently pregnant, not desiring pregnancy and who had been using withdrawal for contraception. Face-to face interviews were conducted to collect data. Content analysis was performed to analyze the data.</p> <p>Results</p> <p>Four major themes were extracted from the interviews: advantages, disadvantages, barriers for OC use, and husband-related factors. Advantages of withdrawal use were identified as: easy to use, convenient, ease of access, natural. Even those participants who had experienced unwanted pregnancy while using withdrawal, relied on withdrawal as their contraceptive method. Disadvantages of OC included concerns about side effects. Barriers related to use of OC included the need for medical advice, vaginal examination and daily use. Husband-related factors included: the husband wanted to be the primary decision maker on the number of children and that he preferred withdrawal.</p> <p>Conclusion</p> <p>Health providers should address misunderstandings that exist about OC and highlight the non-contraceptive health benefits of OC to balance the information provided for women. We suggest that not only women but also their spouses be advised in family planning programs.</p

"Assessment of retinopathy of prematurity among 150 premature neonates in Farabi eye hospital "

The aim of this study was to estimate the incidence of retinopathy of permaturity (ROP) and to evaluate possible neonatal risk factors for ROP. The main study was a cross-sectional study including 150 high-risk neonates born at teaching hospitals of Tehran universities referring to to Farabi Eye Hospital. The chossing critertia were birth weight less than 2500 g or gestational age younger than 37 weeks. ROP was present in 9(6%) newborns, all of whom aged less than 32 weeks a birth. There was also strong association between ROP and birth weight, oxygen administration, respiratory distress syndrome and intraventricular hemorrhage. There also seems to be a higher risk for developing ROP in female neoates, those who were born by multiple gestaional pregnancies or were treated by phototherapy or transfusion and those who had suffered from bronchopulmonary dysplasia or seiss.Prematurity per se remains the strongest risk factof for ROP. Suitable criteria for screening of ROP seems to be gestational age younger than 32 weeks or birth weight less than 1500

MICROCHAETE GOEPPERTIANA KIRCHNER, A NEW MORPHOSPECIES OF NOSTOCALEAN CYANOPHYTA FOR ALGAL FLORA OF IRAN

Jafari, E., Shokravi, S., Soltani, N. 2014. 06. 31: Microchaete goeppertiana Kirchner, a new morphospecies of nostocalean cyanophyta for algal flora of Iran.-Iran. J. . Tehran. A new morphospecies, Microchaete goeppertiana Kirchner (Nostocales, Microcheataceae) has been reported for algal flora of Iran. Collection was done at 2011 from oil polluted regions of Khuzestan province. Identification performed using light, epifluoresence and phase contrast microscopy, in addition of behavioral analysis both in liquid and solid cultures. Observation and description were done in a multidisciplinary way including morphological variations in relation to pH and salinity concentration fluctuations at limited irradiance (2 µE m -2 s -1 ). Regarding to biological versatility of cyanophyta, it has been tried to emphasize on most prominent traits for identification and determination. A new description of the species has been presented regarding to morphological characterization