• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.549-555
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• 2003

The objective of かis study is to investigate the feasibility of piezoelectric transducers as a damage detection system for civil infrastructures. There have been considerable amount of efforts by the modal analysis community to localize damage and evaluate its severity without looking at a reliable way to excite the structure. The detection of damages by modal analysis and similar vibration techniques depends upon the knowledge and estimation of various modal parameters. In addition to the associated difficulties, such low-frequency dynamic response based techniques fail to detect incipient damages. Smart piezoelectric ceramic (PZT) transducers which act as both actuators and sensors in a self-analyzing manner are emerging to be effective in non-parametric health monitoring of structural systems. In this paper, we present the results of an experimental study for the detection of damages using smart PZT transducers on the steel plate. The method of extracting the impedance characteristics of the PZT transducer, which is electro-mechanically coupled to the host structure, is adopted for damage detection. Two damages are simulated and assessed by the bonded PZT transducers for characterization. The experimental results verified the efficacy of the proposed approach and provided a demonstration of good robustness at the realistic steel structures, emphasizing the great potential for developing an automated in situ structural health monitoring system for application to large civil infrastructures without the need to blow the modal parameters.

• Transactions of Materials Processing
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• v.23 no.3
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• pp.164-170
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• 2014

To predict the deformation and fracture during tube expansion using the finite element (FE) method, a material model is considered that incorporates the damage evolution due to the deformation. In the current study, a Rice-Tracey model was used as the damage model with inclusion of the hydrostatic stress term. Since OFHC Cu is not significantly affected by strain rate, a Hollomon flow stress model was used. The material parameters in each model were obtained by using an optimization method. The objective function was defined as the difference between the experimental measurements and FE simulation results. The parameters were determined by minimizing the objective function. To verify the validity of the FE modeling, cross-verification was conducted through a tube expansion test. The simulation results show reasonable agreement with the experiments. The design for a minimum diameter of expansion tube using the FE modeling was verified by a simplified tube expansion test and simulation results.

• Geomechanics and Engineering
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• v.21 no.3
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• pp.289-300
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• 2020

Estimating the damage induced by an explosion around a blast hole has always been a challenging issue in geotechnical engineering. It is difficult to determine an exact dimension for damage zone since many parameters are involved in the formation of failures, and there are some uncertainties lying in these parameters. Thus, the present study adopted a probabilistic approach towards this problem. First, a reliability model of the problem was established and the failure probability of induced damage was calculated. Then, the corresponding exceedance risk curve was developed indicating the relation between the failure probability and the cracked zone radius. The obtained risk curve indicated that the failure probability drops dramatically by increasing the cracked zone radius so that the probability of exceedance for any crack length greater than 4.5 m is less than 5%. Moreover, the effect of each parameter involved in the probability of failure, including blast hole radius, explosive density, detonation velocity, and tensile strength of the rock, was evaluated by using a sensitivity analysis. Finally, the impact of the decoupling ratio on the reduction of failures was investigated and the location of its maximum influence was demonstrated around the blast point.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.657-666
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• 2020

A reliable and cost-effective technique for the development of corrosion damage model is introduced to predict nonlinear time-dependent corrosion wastage of steel structures. A detailed explanation on how to propose a generalised mathematical formulation of the corrosion model is investigated in this paper (Part I), and verification and application of the developed method are covered in the following paper (Part II) by adopting corrosion data of a ship's ballast tank structure. In this study, probabilistic approaches including statistical analysis were applied to select the best fit probability density function (PDF) for the measured corrosion data. The sub-parameters of selected PDF, e.g., the largest extreme value distribution consisting of scale, and shape parameters, can be formulated as a function of time using curve fitting method. The proposed technique to formulate the refined time-dependent corrosion wastage model (TDCWM) will be useful for engineers as it provides an easy and accurate prediction of the 1) starting time of corrosion, 2) remaining life of the structure, and 3) nonlinear corrosion damage amount over time. In addition, the obtained outcome can be utilised for the development of simplified engineering software shown in Appendix B.

• Structural Monitoring and Maintenance
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• v.7 no.4
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• pp.319-344
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• 2020

Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

• 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.

• Journal of Korean Association for Spatial Structures
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• v.23 no.2
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• pp.79-90
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• 2023

Existing reinforced concrete (RC) frame buildings have seismic vulnerabilities because of seismically deficient details. In particular, since cumulative damage caused by successive earthquakes causes serious damage, repair/retrofit rehabilitation studies for successive earthquakes are needed. This study investigates the repair effect of fiber-reinforced polymer jacketing system for the seismically-vulnerable building structures under successive earthquakes. The repair modeling method developed and validated from the previous study was implemented to the building models. Additionally, the main parameters of the FRP jacketing system were selected as the number of FRP layers associated with the confinement effects and the installation location. To define the repair effects of the FRP jacketing system with the main parameters, this study conducted nonlinear time-history analyses for the building structural models with the various repairing scenarios. Based on this investigation, the repair effects of the damaged building structures were significantly affected by the damage levels induced from the mainshocks regardless of the retrofit scenarios.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.1-8
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• 2024

In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 ℃ for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and service-exposed Gr. 91 steels, the thermal aging effect has been shown to be significant.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.419-434
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• 2020

In this study, the damage parameters of Mazars model for KURT (KAERI Underground Research Tunnel) granite are measured form uniaxial compressive and Brazilian tests under the simulated coupled condition of a deep geological disposal. The tests are conducted in three different temperatures (15℃, 45℃, and 75℃) and dry/saturated conditions. Major model parameters such as maximum effective tensile strain (𝜖_d0), A_t, B_t, A_c, and B_c differ from the typical reference values of concrete specimens. This is likely due to the difference in elastic modulus between rock and concrete. It is found that the saturation of specimens causes an increase in value of B_t and B_c while, the rise in temperature increases 𝜖_d0 and B_t and decreases B_c. The damage model obtained from this study will be used as the primary input parameters in the development of coupled Thermo-Hydro-Mechanical Damage numerical model in KAERI.

• Earthquakes and Structures
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• v.19 no.2
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• pp.79-90
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• 2020

4- and 8-storey reinforced-concrete frame buildings are analyzed under the suites of the near-fault pulse-like, and the corresponding spectrally equivalent far-fault ground-motion records. Seismic fragility curves for the slight, moderate, extensive, and complete damage states are developed, and the damage probability matrices, and the mean loss ratios corresponding to the Design Basis Earthquake and the Maximum Considered Earthquake hazard levels are compared, for the investigated buildings and sets of ground-motion records. It is observed that the spectrally equivalent far-fault ground-motion records result in comparable estimates of the fragility curve parameters, as that of the near-fault pulse-like ground-motion records. As a result, the derived damage probability matrices and mean loss ratios using two suites of ground-motion records differ only marginally (of the order of ~10%) for the investigated levels of seismic hazard, thus, implying the potential for application of the spectrally equivalent ground-motion records, for seismic fragility and risk assessment at the near-fault sites.