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The presence of environmental and measurement noises and ignoring the input effects are the main sources of error in system identification using ambient vibration test results. Therefore, reducing uncertainty or noise levels from the records has always been one of the main goals of the new techniques in the field of ambient vibration. Among the modal analysis techniques, stochastic subspace identification is considered as a powerful technique. In this study, the modal analysis method based on canonical correlation analysis in stochastic subspace is presented that identifies dynamic properties in optimized space instead of data space by extracting ortho-normal vector of data space. The advantage of this method, due to the nature of canonical correlation analysis, is lower noise which results in greater accuracy in estimating modal properties. Moreover, the presented process is faster due to the smaller space of identification compared to the previous methods. To validate the proposed method, an analytical model of two-dimensional frame excited under Elcentro earthquake acceleration and also the results of ambient vibration tests carried out on the Alamosa Canyon Bridge are used. The results indicate that this method eliminates more noise than other subspace methods and moreover it is faster in solving practical problems. The computation of dynamic properties, natural frequencies and mode shapes, of Alamosa Canyon Bridge with 30 sampling sensors, space matrix size of 750 and 50 excited modes are carried out in less than 150 seconds with a quad-core 2.30 GHz processor.

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The dominant excitation forces are generally measurable during the forced vibration tests of structures unlike the ambient vibration tests. Not considering of input forces in the system identification is one of the main sources for error generation in the Operational Modal Analysis (OMA). Therefore, some non-structural dynamic characteristics obtained due to the excitations effects can be eliminated by considering the input forces. In this paper, a special modal analysis is presented in the subspace method that removes the excitation effect of the measured input forces from the test data using orthogonal decomposition and identifies the system with an optimal subspace method based on canonical correlation analysis (SSI-CCA). To evaluate the proposed method, the seismic response of the Pacoima dam and forced vibration test results of the Alamosa Canyon Bridge are used. Non-structural and noisy pole removal, and increased accuracy of the extracted modal properties, specially damping ratios, can be mentioned as one of the important results of this study. Four non-structural modes are identified using the SSI-Data method while the first two modes without any noises, the same as previous results, are extracted using the proposed method. In addition, the damping ratios of the Alamosa Bridge are obtained by Hammer test, which are not obtained in the previous investigations.

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In the current study, seismic cracking identification of concrete dams is conducted based on extended finite element method (XFEM) and Wavelet (WT) transform. First, the dam is numerically modeled and analyzed using the finite element method (FEM). Then cracking capability to the dam structure is added by applying the XFEM without introducing the initial crack, and the dam is analyzed under the seismic excitation. In fact, the whole dam structure is potentially under damage risk, and any zone reaching the fracture limit, begins to crack, which grows in the structure. This crack is usually unpredictable and is not easy to detect, therefore the structural modal parameters and their variation should be investigated based on structure response by using time-frequency transform. Results show that, investigating time-frequency window of the structure response and model parameters obtained from the numerical model, the history of physical changes occurred in the structure, cracking initiation time and damage localization is performed from comparing the intact and damaged vibration modes. Moreover, investigating the first natural modal indices of the intact and damaged structure, damage initiation and its location on Koyna dam height is easily detected, while for the second indices it is not performable.

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In order to detect damage in a large-scale and complicated structure, there is need to exact nonlinear numerical modeling that its results have been analyzed using a method of system identification. In this way, the extended finite element model (XFEM) based on cohesive crack model (XFEM Based Cohesive Crack Segments) for concrete material as a reliable model is used for investigating real responses of Karun 3 concrete dam against applied loads and damages. In this model, whole of the structure is potentially under damage risk, while there is no initial crack. The dam is numerically modeled and analyzed using the finite element method (FEM) and XFEM Based Cohesive Crack Segments respectively, and the dam is analyzed under the seismic excitation. Then, for specification of crack effects and nonlinear behavior, the structural modal parameters and their variation should be investigated based on structure response for obtaining damage initiation time and its location by using system identification based on continuous Wavelet (CWT) transform. Results show that the dam natural frequencies decrease after the crack is formed, where decrease in longitudinal and vertical responses are more than the transversal response decrease. Moreover, crack width and its exact location are specified precisely from comparing the intact and damaged crest and central cantilever vibration modes. Therefore, the combination of XFEM Based Cohesive Crack Segments and CWT is useful procedure for structural health monitoring of concrete arch dams.

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Finite element model is the conventional method used for static and dynamic analysis of widely used structures such as dams and bridges, since it is cheap and requires no special tools. Nevertheless, these models are not able to describe the accurate behavior of structures against dynamic loads because of simplifying assumptions used in numerical modeling process, including loading, boundary conditions and flexibility. Nowadays, modal testing is used to solve these problems. The dynamic tests used to identify civil structures’ system usually include forced, free and environment vibration tests. Considering either unknown nature of inputs or failure to measure them, some methods have been developed to analyze the results of dynamic tests which are based on measuring only output data and are known as operational modal analysis. Some of such methods are Peak Picking (PP), Frequency Domain Decomposition (FDD) and stochastic subspace methods. However, unknown nature of applied forces, the presence of environmental noise and measurement errors contribute to some uncertainties within the results of these tests. In this article, a modal analysis is presented within a stochastic subspace which is among the most robust and accurate system identification techniques. In contrast to the previous methodologies, this analysis identifies dynamic properties in optimized space instead of data space by extracting ortho-normal vector of data space. Given the optimum nature of the proposed method, more accuracy in detection and removal of unstable poles as well as high-speed analysis can be served as its advantages. In order to evaluate the proposed method in terms of civil systems detection, seismic data (being among the most real and strong environmental vibrations) and steady-state sinusoidal excitation (which is among the most precise forced vibration tests) were used. In the first step, 2001 San Fernando earthquake data were analyzed using SSI-CCA and SSI-data methods, the results of which are presented in the following. Data processing rate in the SSI-CCA method is almost twice that in SSI-data method which is because of processing in an optimum space while lowering the use of least squares method to compute system vector. Furthermore, there is one unstable pole in the results of the proposed method while 4 noisy characteristics were recognized in the results of SSI-Data method. Estimated damping ratios comprised the major difference observed in this analysis using above-mentioned two methods. Modal damping ratios estimated by the proposed method were 60% closer to the previous results when compared to those of the previous subspace method. Mode shapes of both subspace methods with MAC value of 92% and 75% for the first and the second modes, respectively, are well correlated with each other. Due to lack of access to the mode shape vectors of Alves’s method, it was not feasible to calculate the corresponding MAC value. In the following, forced vibration test results of Rajai Dam conducted by steady sine excitation in 2000 and analyzed by a method known as four spectral, are re-processed Using the SSI-CCA method. As results indicate, using the proposed method the first three modes are obtained that were not on the preliminary results. In addition, other modes are of great fit with the values of the finite element.

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Dams are one of the most important structures which are built to prepare water for different usages such as drinking, agriculture, industrial, flood control and hydro power generation. Due to the importance of dams and increasing number of terrorist attack, Stability of dam structures against blast loading is important. Dam responses depend on magnitude of released energy and if the dam structure could not be able to resist and maintain its stability against this energy, irreparable consequences will happen. Explosion is a sudden release of energy which could be like gases combustion, nuclear explosion or any kind of bombs. TNT unit usually used as reference to determine the explosion power. Some of basic properties of an explosion are random location of explosion, transient loading and short time loading (up to few seconds). When blast loading happened, energy will released suddenly and this released energy include thermal radiation and wave scattering in air and earth. The waves which scattered in the air are the main factor to structural damage. These waves move faster than sound wave velocity and impact the structure. Due to reflex from structure surface, the pressure of these waves increased and also some air waves penetrate to structural elements from openings such as doors and windows. This process continues until all available parts of the structure affected by pressure waves. In this research, the effects of blast loading on Karun 4 dam are investigated. To this purpose, dynamic analysis of dam-reservoir-foundation system is performed by finite element model using ABAQUS software. Dam-reservoir-foundation modeled three dimensional in which reservoir length is three times greater than dam height. The foundation modeled as a hemi-sphere with a radius of three times greater than dam height. Non-linear material behavior also considered by using concrete damage plasticity method. The CONWEP theory is used to model blast loading. To verify the blast modeling theory and software abilities, a steel plate which investigated under blast loading in references has been modeled and the results shows same responses with the paper. The responses of dam are investigated under two different reservoir conditions include full and empty conditions. Analysis also done for three different explosion points in three different elevations. Explosion points are near base, mid height of dam and near dam crest respectively. All these points have 10 m distance from dam structure. TNT mass used in each noticed conditions, is the minimum amount of TNT which cause damage in dam body. The results indicate that the responses of the dam is very sensitive to mesh dimensions. The results also show, water level has not great effect on explosive mass which is needed for structural damage of the dam. In both full and empty reservoir conditions, when explosion happened near the dam crest, the displacement is more than other cases. It is noteworthy that when the explosion happened near the crest, the maximum displacement of the crest and the point in front of the explosion point, occur in same time but when the explosion point is in middle and also near the base, theses displacements are not in same time.

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Operational modal analysis (OMA), as a branch of the system identification, plays a very important and practical role in determining the dynamic characteristics of the structures. In the operational approach that is implemented based on the ambient vibration test, the ambient and operation loads are considered as the excitation source of the structure. In the present research, an integrative method composed of frequency domain decomposition (FDD) and wavelet transform (WT) called FDD-WT is proposed in order to identify the natural frequencies and damping ratios of an arch concrete dam. Furthermore, the wavelet transform of the seismic responses is also calculated in order to validate and compare the results. For this purpose, the time and frequency position of the system modes during the different earthquakes is evaluated using the time-frequency representation obtained from wavelet transform. In this paper, Pacoima arch concrete dam located in California, US is selected as the case study and the seismic records related to 1994 Northridge, 2001 San Fernando and 2008 Chino Hills earthquakes are also used to evaluate the dynamic characteristics and structural health monitoring during the period between 1994 to 2008. Investigation of changes in the natural frequencies of the structure indicates that the dam had taken serious damage during 1994 Northridge earthquake (about the fourth second), while the vibrations of the concrete structure has been almost linear during the first 4 seconds of the earthquake and also in 2001 and 2008 earthquakes.

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In recent years, a new approach called transmissibility based operational modal analysis has been propounded.The new approach is able to identify the modal parameters of structural systems based on the transmissibility functions, where, unlike conventional methods of operational modal analysis, there is no limiting assumption about the input excitations. In this paper, an effective form of transmissibility called power spectral density transmissibility is used in order to identify the dynamic characteristics of a 5DOF system. The dynamic system that is modeled using MATLAB/Simulink is excited by the different earthquakes such as El Centro, Northridge and Loma Prieta, and white Gaussian noise is also added to its responses with different signal to noise ratios. The modal parameters (natural frequencies and mode shapes) of the numerical model are calculated and extracted based on the singular values and vectors obtained from singular value decomposition of the power spectral density transmissibility matrix. This matrix, unlike the Fourier spectral transmissibility matrix, can be created based on the transferring outputs obtained from just one loading condition; therefore, there is no need to use the outputs of multiple loading conditions, so that it is possible to identify the dynamic characteristics with only one dynamic test. In this research, the modal identification results are evaluated through comparison with the values obtained from exact solution of the system. The comparison shows that the modal parameters extracted from the system responses with different noise levels have a good agreement with the exact values.

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Recently, a new approach called Transmissibility based Operational Modal Analysis (TOMA) has been presented in order to identify the dynamic characteristics of structural systems that determines the modal parameters of structures using the concept of transmissibility. In the TOMA approach, unlike OMA methods that use the assumption of white noise input, no limiting assumption is considered for the input excitations, and the modal parameters of structural systems are extracted based on the features of transmissibility matrix. The transmissibility methods, like other frequency domain methods, do not present very satisfactory results in identifying the damping values. Therefore, in the present paper, a new combined method called Fourier Spectral Transmissibility-Wavelet Transform (FST-WT) is proposed which, in addition to determining the natural frequencies and mode shapes of the system, also addresses the exact detection of damping values based on the features of wavelet transform. In this research, the capability of the FST-WT method in identifying and extracting the modal parameters of a 5-DOF system under free vibration is investigated using the responses obtained from the MATLAB Simulink model. For this purpose, the frequencies and mode shapes are respectively extracted from the inverse of the second singular value and the first left singular vector of transmissibility matrix, and the damping values are also determined using the single frequency signals (wavelet coefficients) obtained from wavelet transform based on the minimal Shannon entropy criterion. The comparison of the identification results shows a good agreement with the exact values.

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This study was conducted to investigate the response of four barley cultivars (Reyhan03, Yousef, Afzal, and Khatam) to salinity stress at 0 (control), 100, 200 and 300 mM levels as a factorial experiment, within the randomized complete block design in three replications in a greenhouse, using the Hoagland solution. The physiological and biochemical properties including dry weight and RWC, photosynthesis pigments, K⁺/Na⁺, osmotic adjustments (soluble sugars, glycine betaine, proline), hydrogen peroxide and antioxidants enzymes (catalase and peroxidase) in root and shoot of barley cultivars were evaluated in saline and non-saline conditions. To determine the relationship between growth performance and the physiological and biochemical properties, the correlation between the properties and causality analysis was examined. Results obtained from comparing the mean among the treatment combinations showed that the salinity stress reduced the dry weight, photosynthesis pigments, and K⁺/Na⁺, while it increased the soluble sugars, glycine betaine, proline, H₂O₂, catalase and peroxidase in the root and shoot of barley cultivars. Correlation analysis indicated that potassium in the shoot had the most positive and significant correlation coefficient (r= 0.86) with the dry matter of shoot. The stepwise regression analysis showed that the root dry weight, catalase of root and shoot, H₂O₂ of shoot and K⁺/Na⁺ of shoot contributed to the performance. Causality analysis revealed that the root dry weight, K⁺/Na⁺ of shoot, and catalase of shoot were highly important as they had a direct positive and significant impacts on the performance of shoot dry matter.

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Salinity stress is one of the most important environmental stresses that decrease crop growth and yield. Barley is an important crop known as the salt-tolerant plant in cereals. In this study, the salt stress-responsive root transcriptome of tolerant (Afzal) and susceptible (Yusef) cultivars was investigated. The sequencing of mRNA transcripts (termed RNA-Seq) was performed using the Illumina HiSeq platform after filtering for RNA with 3' polyadenylated tails to include only mRNA. The Tuxedo pipeline was used to identify the altered expression of transcripts. Sequencing results showed that, after initial trimming of the reads, more than 20 million reads (92%) remained for all samples, of which 88% were aligned with the barley genome. Bioinformatics analysis showed the altered genes expressions in various processes such as membrane antiporter and transporter activity, an antioxidant, wide range of kinase and phosphatase cascades, internal signal transduction, metabolism of carbohydrates, amino acids, and lipids, binding processes, response to plant hormones, catalytic activity, and cell wall organization. Gene network analysis revealed that key genes, including proteins involved in systemic acquired resistance, peroxidase family proteins, cyclin-dependent protein kinase, phosphatidylinositol kinase, auxin-carrying proteins, mannose 6 phosphate isomerase, helicases and transcription factors play an important role in salt tolerance. These data can be used as a valuable source in future studies for genetic manipulation of barley and development of salinity tolerant cultivars.

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Salt stress, as the most important abiotic stress, limits growth of plants and causes extensive damage to agricultural production worldwide. Therefore, it is necessary to identify genes that play a key role in tolerance to salt stress in plants through the analysis of transcriptome data such as microarray and High-Throughput Sequencing (HTS or NGS). In the present research, the combined analysis of microarray data by R packages for Hordeum vulgare L. under salinity stress identified 685 upregulated meta-DEGs (differentially expressed genes) and 766 downregulated meta-DEGs. The upregulated genes mostly belong to abiotic stress tolerance and hormone biosynthesis, and the downregulated genes pertain to late embryogenesis abundant protein and salinity stress response. GO terms in the upregulated genes are mostly associated with response to external and internal stresses; and in the downregulated genes, they are mostly associated with cellular metabolism. In the up and down meta-DEGs by KEGG, most of the genes connected to salinity stress included PP2C, ABF, AGT, and ChiB and F-box connected to the downregulated genes. Moreover, Transcription Factors (TFs) in the up and downregulated meta-DEGs with high frequency included AP2, ERF, bZIP, and bHLH. Most of the hub upregulated genes acquired from this research were metabolite biosynthesis and photosynthesis-related; and the hub downregulated genes were mainly the tricarboxylic acid cycle and glycolysis processes-related. Finally, a comparison was made between this meta-analysis and data obtained from other investigations. The findings validated their up and down expression. Our results give a new understanding about the molecular mechanism and present many TFs and candidate genes for salt stress tolerance in barley breeding programs.