• Title/Summary/Keyword: damage conditions

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Vibration-Based Damage Monitoring in Model Plate-Girder Bridges under Uncertain Temperature Conditions (불확실한 온도 조건하의 모형 강 판형교의 진동기반 손상 모니터링)

  • Park, Jae-Hyung;Hong, Dong-Soo;Cho, Hyun-Man;Kim, Jeong-Tae
    • Journal of Ocean Engineering and Technology
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    • v.22 no.1
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    • pp.75-82
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    • 2008
  • A vibration-based damage-monitoring scheme is proposed that would generate an alarm showing the occurrence and location of damage under temperature-induced uncertainty conditions. Experiments on a model plate-girder bridge are described, for which a set of modal parameters was measured under uncertain temperature conditions. A damage-alarming model is formulated to statistically identify the occurrence of damage by recognizing the patterns of damage-driven changes in the natural frequencies of the test structure and by distinguishing temperature-induced off-limits. A damage index method based on the concept of modal strain energy is implemented in the test structure to predict the location of damage. In order to adjust for the temperature-induced changes in the natural frequencies that are used for damage detection, a set of empirical frequency correction formulas is analyzed from the relationship between the temperature and frequency ratio.

Site classes effect on seismic vulnerability evaluation of RC precast industrial buildings

  • Yesilyurt, Ali;Zulfikar, Abdullah C.;Tuzun, Cuneyt
    • Earthquakes and Structures
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    • v.21 no.6
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    • pp.627-639
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    • 2021
  • Fragility curves are being more significant as a useful tool for evaluating the relationship between the earthquake intensity measure and the effects of the engineering demand parameter on the buildings. In this paper, the effect of different site conditions on the vulnerability of the structures was examined through the fragility curves taking into account different strength capacities of the precast columns. Thus, typical existing single-story precast RC industrial buildings which were built in Turkey after the year 2000 were examined. The fragility curves for the three typical existing industrial structures were derived from an analytical approach by performing non-linear dynamic analyses considering three different soil conditions. The Park and Ang damage index was used in order to determine the damage level of the members. The spectral acceleration (Sa) was used as the ground motion parameter in the fragility curves. The results indicate that the fragility curves were derived for the structures vary depending on the site conditions. The damage probability of exceedance values increased from stiff site to soft site for any Sa value. This difference increases in long period in examined buildings. In addition, earthquake demand values were calculated by considering the buildings and site conditions, and the effect of the site class on the building damage was evaluated by considering the Mean Damage Ratio parameter (MDR). Achieving fragility curves and MDR curves as a function of spectral acceleration enables a quick and practical risk assessment in existing buildings.

Theoretical formulation of double scalar damage variables

  • Xue, Xinhua;Zhang, Wohua
    • Computers and Concrete
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    • v.19 no.5
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    • pp.501-507
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    • 2017
  • The predictive utility of a damage model depends heavily on its particular choice of a damage variable, which serves as a macroscopic approximation in describing the underlying micromechanical processes of microdefects. In the case of spatially perfectly randomly distributed microcracks or microvoids in all directions, isotropic damage model is an appropriate choice, and scalar damage variables were widely used for isotropic or one-dimensional phenomenological damage models. The simplicity of a scalar damage representation is indeed very attractive. However, a scalar damage model is of somewhat limited use in practice. In order to entirely characterize the isotropic damage behaviors of damaged materials in multidimensional space, a system theory of isotropic double scalar damage variables, including the expressions of specific damage energy release rate, the coupled constitutive equations corresponding to damage, the conditions of admissibility for two scalar damage effective tensors within the framework of the thermodynamics of irreversible processes, was provided and analyzed in this study. Compared with the former studies, the theoretical formulations of double scalar damage variables in this study are given in the form of matrix, which has many features such as simpleness, directness, convenience and programmable characteristics. It is worth mentioning that the above-mentioned theoretical formulations are only logically reasonable. Owing to the limitations of time, conditions, funds, etc. they should be subject to multifaceted experiments before their innovative significance can be fully verified. The current level of research can be regarded as an exploratory attempt in this field.

Fundamental Research of Early Frozen Damage on Concrete Depending on Various Time Periods of -20℃ Temperature Condition (외기온 -20℃의 유지시간 변화에 따른 초기동해 피해의 기초적 연구)

  • Choi, Yoon-Ho;Han, Jun-Hui;Lee, Young-Jun;Hyun, Seung-Yong;Han, Min-Cheol;Han, Cheon-Goo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2019.05a
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    • pp.197-198
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    • 2019
  • The aim of the research is evaluating the feasibility of inspection for early age frozen damage and for expansion of concrete under the various time periods of -20℃ temperature condition. When the concrete samples were exposed for 12 hours and 24 hours, the frozen depth of the concrete were 10 and 60 mm, respectively, under the wet conditions. From the experiment results of temperature and expansion, only surface area suffered frozen damage for 12 hours exposing conditions while entire area suffered frozen damage for 24 hours exposing conditions.

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Probabilistic Model of Service Life to Evaluate Damage Tolerance of Composite Structure (복합재 항공구조물의 손상허용평가를 위한 운항수명의 확률적 모델)

  • A.스튜어트;A.우샤코프;심재열;황인희
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2000.11a
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    • pp.245-248
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    • 2000
  • Modern aircraft composite structures are designed using a damage tolerance philosophy. This design philosophy envisions sufficient strength and structural integrity of the aircraft to sustain major damage and to avoid catastrophic failure. The only reasonable way to treat on the same basis all the conditions and uncertainties participating in the design of damage tolerant composite aircraft structures is to use the probability-based approach. Therefore, the model has been developed to assess the probability of structural failure (POSF) and associated risk taking into account the random mechanical loads, random temperature-humidity conditions, conditions causing damages, as well as structural strength variations due to intrinsic strength scatter, manufacturing defects, operational damages, temperature-humidity conditions. The model enables engineers to establish the relationship between static/residual strength safety margins, production quality control requirements, in-service inspection resolution and criteria, and POSF. This make possible to estimate the cost associated with the mentioned factors and to use this cost as overall criterion. The methodology has been programmed into software.

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Damage identification in beam-like pipeline based on modal information

  • Yang, Zhi-Rong;Li, Hong-Sheng;Guo, Xing-Lin;Li, Hong-Yan
    • Structural Engineering and Mechanics
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    • v.26 no.2
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    • pp.179-190
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    • 2007
  • Damage detection based on measured vibration data has received intensive studies recently. Frequently, the damage to a structure may be reflected by a change of some system parameters, such as a degradation of the stiffness. In this paper, we apply a method to nondestructively locate and estimate the severity of damage in corrosion pipeline for which a few natural frequencies or mode shapes are available. The method is based on the strain modal sensitivity ratio (SMSR) and the orthogonality conditions sensitivities (OCS) applied to vibration features identified during the monitoring of the pipeline. The advantage of these methods is that it only requires measuring few modal parameters. The SMSR-based and OCS-based damage detection methods are illustrated using computer-simulated and laboratory testing data. The results show that the current method provides a precise indication of both the location and the extent of corrosion pipeline.

Factorial Experiment for Drum-type Secondary Separating Part of Self-propelled Pepper Harvester

  • Nam, Ju-Seok;Kang, Young-Sun;Kim, Su-Bin;Kim, Dae-Cheol
    • Journal of Biosystems Engineering
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    • v.42 no.4
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    • pp.242-250
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    • 2017
  • Purpose: This study was conducted to determine the appropriate operating conditions through a factorial experiment for the secondary separating part of the self-propelled pepper harvester. Methods: An experimental setup that simulates the secondary separating part of the self-propelled pepper harvester was organized. Test samples were classified into three types according to the number of peppers on a stem, and 12 sets were prepared for each type. Among the operating conditions of the secondary separating part, the rotational speed of drum B (four levels), radial clearance between drums and cylindrical teeth (three levels), and speed ratio between the three drums (two levels) were set as the test factors, and tests were repeated three times for different levels of each factor. The appropriate operating conditions were determined by analyzing the separation ratio and damage ratio of the peppers collected through the secondary separating part. Results: The test factors changed the overall separation ratio and overall damage ratio in similar trends. In other words, the conditions that caused high overall separation ratios also exhibited high overall damage ratios. Owing to the high overall damage ratio in the condition with the highest overall separation ratio, the operating conditions should be selected considering both ratios. Conclusions: When the condition with more than 60% of overall separation ratio and less than 15% of overall damage ratio was considered as the appropriate operating condition, 70 rpm of the rotational speed of drum B, 5 mm of the radial clearance between drums and cylindrical teeth, and 7:3:5 for the speed ratio of the three drums A, B, and C should be applied for the secondary separating part used in this study. Supplementary studies will be required in the future to find optimal operating conditions through the actual field test under further divided test factors.

Modeling of damage initiation in singly oriented ply Fiber Metal Laminate under concentrated loading conditions (집중 하중을 받는 일방향 보강 섬유 금속 적층판의 손상 개시 모델링)

  • 남현욱;정성욱;한경섭
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2001.05a
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    • pp.65-68
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    • 2001
  • In this research, damage initiation in singly oriented ply (SOP) FML under concentrated loading conditions was studied. The finite element method (FEM) base on the first order shear deformation theory is used for the analysis of fiber orientation effect on FML under concentrated loading conditions. The failure indices were calculated for the variation of fiber orientation and the results were compared with indentation experiments. The failure indices were well matched with damage initiation of SOP FML. Indentation results shows that the crack initiation of SOP FML is determined by stiffness induced by fiber orientation and tile penetration load of SOP FML are influenced by the deformation tendency and boundary conditions.

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Damage detection for beam structures using an angle-between-string-and-horizon flexibility matrix

  • Yan, Guirong;Duan, Zhongdong;Ou, Jinping
    • Structural Engineering and Mechanics
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    • v.36 no.5
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    • pp.643-667
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    • 2010
  • The classical flexibility difference method detects damage by observing the difference of conventional deflection flexibility matrices between pre- and post-damaged states of a structure. This method is not able to identify multiple damage scenarios, and its criteria to identify damage depend upon the boundary conditions of structures. The key point behind the inability and dependence is revealed in this study. A more feasible flexibility for damage detection, the Angle-between-String-and-Horizon (ASH) flexibility, is proposed. The physical meaning of the new flexibility is given, and synthesis of the new flexibility matrix by modal frequencies and translational mode shapes is formulated. The damage indicators are extracted from the difference of ASH flexibility matrices between the pre- and post-damaged structures. One feature of the ASH flexibility is that the components in the ASH flexibility matrix are associated with elements instead of Nodes or DOFs. Therefore, the damage indicators based on the ASH flexibility are mapped to structural elements directly, and thus they can pinpoint the damaged elements, which is appealing to damage detection for complex structures. In addition, the change in the ASH flexibility caused by damage is not affected by boundary conditions, which simplifies the criteria to identify damage. Moreover, the proposed method can determine relatively the damage severity. Because the proposed damage indicator of an element mainly reflects the deflection change within the element itself, which significantly reduces the influence of the damage in one element on the damage indicators of other damaged elements, the proposed method can identify multiple damage locations. The viability of the proposed approach has been demonstrated by numerical examples and experimental tests on a cantilever beam and a simply supported beam.

Acceleration-based neural networks algorithm for damage detection in structures

  • Kim, Jeong-Tae;Park, Jae-Hyung;Koo, Ki-Young;Lee, Jong-Jae
    • Smart Structures and Systems
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    • v.4 no.5
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    • pp.583-603
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    • 2008
  • In this study, a real-time damage detection method using output-only acceleration signals and artificial neural networks (ANN) is developed to monitor the occurrence of damage and the location of damage in structures. A theoretical approach of an ANN algorithm that uses acceleration signals to detect changes in structural parameters in real-time is newly designed. Cross-covariance functions of two acceleration responses measured before and after damage at two different sensor locations are selected as the features representing the structural conditions. By means of the acceleration features, multiple neural networks are trained for a series of potential loading patterns and damage scenarios of the target structure for which its actual loading history and structural conditions are unknown. The feasibility of the proposed method is evaluated using a numerical beam model under the effect of model uncertainty due to the variability of impulse excitation patterns used for training neural networks. The practicality of the method is also evaluated from laboratory-model tests on free-free beams for which acceleration responses were measured for several damage cases.