• Structural Engineering and Mechanics
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• v.91 no.1
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• pp.103-121
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• 2024

The smoothed particle hydrodynamics (SPH) method is a numerical technique used in dynamic analysis to simulate the fluid-like behavior of materials under extreme conditions, such as those encountered in explosions or high velocity impacts. In SPH, fluid or solid materials are discretized into particles. These particles interact with each other based on certain smoothing kernels, allowing the simulation of fluid flows and predict the response of solid materials to shock waves, like deformation, cracking or failure. One of the main advantages of SPH is its ability to simulate these phenomena without a fixed grid, making it particularly suitable for analyzing complex geometries. In this study, the structural damage to a masonry arch bridge subjected to blast loading was investigated. A high-fidelity micro-model was created and the explosives were modeled using the SPH approach. The Johnson-Holmquist II damage model and the Mohr-Coulomb material model were considered to evaluate the masonry and backfill properties. Consistent with the principles of the JH-II model, the authors developed a VUMAT code. The explosive charges (50 kg, 168 kg, 425 kg and 1000 kg) were placed in close proximity to the deck and pier of a bridge. The results showed that the 50 kg charges, which could have been placed near the pier by a terrorist, had only a limited effect on the piers. Instead, this charge caused a vertical displacement of the deck due to the confinement effect. Conversely, a 1000 kg TNT charge placed 100 cm above the deck caused significant damage to the bridge.

• Smart Structures and Systems
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• v.19 no.2
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• pp.195-202
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• 2017

The aim of this paper is to develop a novel method to determine the severity of a damage in a thin plate. This paper presents a novel fault detection and diagnosis approach employing a new electromagnetic acoustic transducer, called EMAT, together with a complex signal processing method. The method consists in the recognition of a fault that exists within the structure, the fault location, i.e. the identification of the geometric position of damage, and the determining the significance of the damage, which indicates the importance or severity of the defect. The main scientific novelties presented in this paper is: to develop of a new type of electromagnetic acoustic transducer; to incorporate wavelet transforms for signal representation enhancements; to investigate multi-parametric analysis for noise identification and defect classification; to study attenuation curves properties for defect localization improvement; flaw sizing and location algorithm development.

• Smart Structures and Systems
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• v.17 no.6
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• pp.1017-1030
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• 2016

This study focuses on the system identification of reinforced concrete bridges using vector autoregressive model (VAR). First, the time series output response from a bridge establishes the autoregressive (AR) models. AR models are one of the most accurate methods for stationary time series. Burg's algorithm estimates the autoregressive coefficients (ARCs) at p-lag by reducing the sum of the forward and the backward errors. The computed ARCs are assembled in the state system matrix and the eigen-system realization algorithm (ERA) computes: the eigenvector matrix that contains the vectors of the mode shapes, and the eigenvalue matrix that contains the associated natural frequencies. By taking advantage of the characteristic of the AR model with ERA (ARMERA), civil engineering can address problems related to damage detection. Operational modal analysis using ARMERA is applied to three experiments. One experiment is coupled with an artificial neural network algorithm and it can detect damage locations and extension. The neural network uses a specific number of ARCs as input and multiple submatrix scaling factors of the structural stiffness matrix as output to represent the damage.

• Structural Engineering and Mechanics
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• v.41 no.5
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• pp.663-673
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• 2012

A number of mode shape-based structure damage identification methods have been verified by numerical simulations or experiments for on-line structure health monitoring (SHM). However, many of them need a baseline mode shape generated by the healthy structure serving as a reference to identify damages. Otherwise these methods can hardly perform well when multiple cracks conditions occur. So it is important to solve the problems above. By aid of the fractal dimension method (FD), Qiao and Wang proposed a generalized fractal dimension (GFD) to detect the delamination damage. As a modification of GFD, Qiao and Cao proposed the approximate waveform capacity dimension (AWCD) technique to simplify the calculation of fractal and overcome the false peak appearing in the high mode shapes. Based on their valued work, this paper combined and applied the AWCD method and curvature mode shape data to detect multiple damages in beam. In the end, the identification properties of the AWCD for multiple damages have been verified by groups of Monte Carlo simulations and experiments.

• Smart Structures and Systems
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• v.28 no.6
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• pp.799-810
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• 2021

When monitoring the structural integrity of a bridge using data collected through accelerometers, identifying the profile of the load exerted on the bridge from the vehicles passing over it becomes a crucial task. In this study, the speed and location of vehicles on the deck of a bridge is reconfigured using real-time video to implicitly associate the load applied to the bridge with the response from the bridge sensors to develop an image-based deep learning network model. Instead of directly measuring the load that a moving vehicle exerts on the bridge, the intention in the proposed method is to replace the correlation between the movement of vehicles from CCTV images and the corresponding response by the bridge with a neural network model. Given the framework of an input-output-based system identification, CCTV images secured from the bridge and the acceleration measurements from a cantilevered beam are combined during the process of training the neural network model. Since in reality, structural damage cannot be induced in a bridge, the focus of the study is on identifying local changes in parameters by adding mass to a cantilevered beam in the laboratory. The study successfully identified the change in the material parameters in the beam by using the deep-learning neural network model. Also, the method correctly predicted the acceleration response of the beam. The proposed approach can be extended to the structural health monitoring of actual bridges, and its sensitivity to damage can also be improved through optimization of the network training.

• Smart Structures and Systems
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• v.20 no.2
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• pp.247-261
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• 2017

In the field of dynamic measurement and structural damage identification, it is generally known that modal frequencies may be measured with higher accuracy than mode shapes. However, the number of natural frequencies within a measurable range is limited. Accessing additional forms of modal frequencies is thus desirable. The present study is concerned about the extraction of artificial boundary condition (ABC) frequencies from modal testing. The ABC frequencies correspond to the natural frequencies of the structure with a perturbed boundary condition, but they can be extracted from processing the frequency response functions (FRF) measured in a specific configuration from the structure in its existing state without the need of actually altering the physical support condition. This paper presents a comprehensive experimental investigation into the measurability of the ABC frequencies from physical experiments. It covers the testing procedure through modal testing, the data processing and data analysis requirements, and the FRF matrix operations leading to the extraction of the ABC frequencies. Specific sources of measurement errors and their effects on the accuracy of the extracted ABC frequencies are scrutinised. The extracted ABC frequencies are subsequently applied in the damage identification in beams by means of finite element model updating. Results demonstrate that it is possible to extract the first few ABC frequencies from the modal testing for a variety of artificial boundary conditions incorporating one or two virtual pin supports, and the inclusion of ABC frequencies enables the identification of structural damages without the need to involve the mode shape information.

• Journal of Environmental Policy
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• v.8 no.2
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• pp.1-23
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• 2009

This study applied satellite radar imagery to identify flooded areas and examined post-flooding conditions using time-series satellite radar imagery for the development of flood damage mitigation strategies. Using time-series satellite radar images, this study constructed a map delineating areas vulnerable to frequent flood damage. The extracted flooded areas were combined with reference land use maps to examine flood damage by land use type. Major landuse types with severe flood damage were agricultural and forested areas. The analysis of the damage conditions, in terms of land use, served as the basis for developing flood damage mitigation policies, in conjunction with land use planning. The policies for flood damage mitigation can be summarized as land use regulations, land use planning, and flood damage mapping. A preventive measure to minimize flood damage of properties, which regulates developing areas with high flooding potential, is highly recommended. Although this study suggested a number of policies for flood damage mitigation, they represent only a small number of possible policies useful for mitigating flood damage and other environmental problems. Based upon the results of this study, it may be concluded that satellite radar imagery has great potential in providing basic data for large-scale environmental problems such as flooding and oil spills. Nevertheless, further examinations should be conducted and the application of satellite radar imagery should be used to examine other environmental problems.

• Korean Journal of Oriental Medicine
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• v.18 no.1
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• pp.25-34
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• 2012

Objective : This study was carried out with focus on written by Joh, Taek-seung (曺澤承) and Joh, Byeong-who(曺秉矦) in the relation of father and son in 1933. This book is a medical book including rare data, which has never been reported to academic circles all this while. Method : First, this study looked into the authors of this book and its history of publication. Further, this study analyzed the composition and contents of this book. Lastly, this study summed up the meaning of this book from the standpoint of medical history. Result : The authors were Confucian doctors who were active in the latter era of the Joseon Dynasty and also in the period of Japanese colonial rule. They lived in Haenam district of Jeonlanam-do, and cured its neighboring local residents while studying. They published the book of by putting together their own medical experiences. The authors suggested their remedial prescription according to gender and age whereas Zhang Zhongjing(張仲景) suggested the remedial prescription according to Six-Meridian Pattern Identification & Syndrome Differentiation(六經辨證). In addition, the authors of gave weight to the relationship with internal damage. Additionally, the authors not only thought much of the relationship between internal damage and external damage but also thought of the weakness and strength of the healthy qi, and the new and the old of a disease as an important clue to medical treatment. It seems that such contents was influenced by (東醫寶鑑). Conclusion : shows the results of the research on which was spontaneously conducted in Joseon.

• Journal of the Society of Disaster Information
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• v.15 no.2
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• pp.186-197
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• 2019

Purpose: This study intends to develop a nonlinear cyclic plasticity damage model in the framework of finite element formulation, which is capable of taking large deformation effects into account, in order to accurately predict the hysteretic behavior of stainless steel structures. Method: The new cyclic constitutive equations that utilize the combined isotropic-kinematic hardening rule for plastic deformation is incorporated into the damage mechanic model in conjunction with the large strain formulation. The damage growth law is based on the experimental observations that the evolution of microvoids yields nonlinear damage accumulation with plastic deformation. The damage model parameters and the procedure for their identification are presented. Results and Conclusion: The proposed nonlinear damage model has been verified by simulating uniaxial strain-controlled monotonic and cyclic loading tests, and successfully applied to a thin-walled stainless steel pipe subjected to constant and alternating strain-controlled cyclic loadings.

• Smart Structures and Systems
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• v.31 no.1
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• pp.13-27
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• 2023

Fatigue crack is a fatal problem for steel structures. Early detection and maintenance can help extend the service life and prevent hazards. This paper presents the ultrasonic guided waves-based (UGWs-based) fatigue crack detection of a steel I-beam. The semi-analytical finite element model has been built to obtain the wave propagation characteristics. Damage indices in both time and frequency domains were analyzed by considering the characteristic variations of UGWs including the amplitude, phase angle, and wave packet energy. The pulse-echo and pitch-catch methods were combined in the detection scheme. Lab-scale experiments were conducted on welded steel I-beams to verify the proposed method. Results show that the damage indices based on the characteristic variations in the time domain can identify and localize the fatigue crack before it enters the rapid growth stage. The damage severity can be reasonably evaluated by analyzing the time-domain damage indices. Two nonlinear damage indices in the frequency domain give earlier warnings of the fatigue crack than the time-domain damage indices do. The identification results based on the above two nonlinear indices are found to be less consistent under various excitation frequencies. More robust nonlinear techniques needed to be searched and tested for early crack detection in steel I-beams in further study.