• Steel and Composite Structures
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• v.31 no.2
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• pp.149-158
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• 2019

The force-deformation behavior, strain distribution and failure modes of a variable damping self-centering brace (VD-SCB) are theoretically analyzed, experimentally studied, and numerically simulated to guide its design. The working principle of the brace is explained by describing the working stages and the key feature points of the hysteretic curve. A large-scale brace specimen was tested under different sinusoidal excitations to analyze the recentering capability and energy dissipation. Results demonstrate that the VD-SCB exhibits a full quasi-flag-shaped hysteretic response, high ultimate bearing capacity, low activation force and residual deformation, and excellent recentering and energy dissipation capabilities. Calculation equations of the strain distribution in different parts of the brace are proposed and are compared with the experimental data and simulated results. The developments of two failure modes are compared. Under normal circumstances, the brace fails due to the yielding of the spring blocking plates, which are easily replaced to restore the normal operating conditions of the brace. A brief description of the design procedure of the brace is proposed for application.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.39 no.5
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• pp.313-319
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• 2021

The national geodetic reference frame of Korea was adopted in 2003, which is referenced to ITRF (International Terrestrial Reference Frame) 2000 at the epoch of January 1, 2002. For precise positioning based on the satellites, it should be thoroughly maintained to the newest global reference frame. Other than plate tectonic motion, there are significant events or changes such as earthquakes, antenna replacement, PSD (Post-Seismic Deformation), seasonal variation etc. We processed three years of GNSS (Global Navigation Satellite System) data(60 NGII CORS stations, 51 IGS core stations) to produce daily solutions minimally constrained to ITRF. From the time series of daily solutions, the sites with unexpected discontinuity were identified to set up an event(mostly antenna replacement). The combined solution with minimum constraints was estimated along with the velocity, the offsets, and the periodic signals. The residuals show that the surrounding environment also affects the time series to a certain degree, thus it should be improved eventually. The transformation parameters to ITRF2014 were calculated with stability and consistency, which means the national geodetic reference frame is properly aligned to the global reference frame.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.4
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• pp.37-44
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• 2019

According to the statistical surveys and studies, insufficient maintenance in the use of existing buildings caused fire and collapse accidents. In this respect, I analyzed the data managed by the current building maintenance and inspection system to find out the actual state of safety management and proposed two significant results. First, regarding the state of the buildings, the safety management status of the small-sized ones, where 20 years or more passed after construction, is the worst and a priority improvement plan is required. Second, there are eight deeply concerning factors for the fire incidents and collapse accidents of buildings. In the order of high risk, these factors are structural strength (seismic design), exterior wall finishing material, basement floor, interior finishing materials, other evacuation facilities, corridors stairs entrances, rooftop, fire partition. We need to have more special designs and management plans regarding high-risk factors as a system to prevent accidents in the building.

• Computers and Concrete
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• v.27 no.1
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• pp.29-39
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• 2021

This study aimed to develop a method for the determination of the damaged story in reinforced concrete (RC) structure with ambient vibrations, based on modified jerk energy methodology. The damage was taken as a localized reduction in the stiffness of the structural member. For loading, random white noise excitation was used, and dynamic responses from the finite element model (FEM) of 4 story RC shear frame were extracted at nodal points. The data thus obtained from the structure was used in the damage detection and localization algorithm. In the structure, two damage configurations have been introduced. In the first configuration, damage to the structure was artificially caused by a local reduction in the modulus of elasticity. In the second configuration, the damage was caused, using the Elcentro1940 and Kashmir2005 earthquakes in real-time history. The damage was successfully detected if the frequency drop was greater than 5% and the mode shape correlation remained less than 0.8. The results of the damage were also compared to the performance criteria developed in the Seismostruct software. It is demonstrated that the proposed algorithm has effectively detected the existence of the damage and can locate the damaged story for multiple damage scenarios in the RC structure.

• 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.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.827-833
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• 2022

In this study, the prediction of the bending angle for the 350 A bellows-type expansion joints and the structural stability according to the load were determined. The stability of the 2km piping system was predicted by applying the allowable bending angle of the expansion pipe joint obtained from the analysis. The maximum bending angle was calculated through bending analysis of the bellows-type expansion joints, and the maximum bending angle by numerical calculation was about 1.8°, and the maximum bending angle of the bellows obtained by comparing the allowable strength of the material was about 0. 22°. This angle was very stable compared to the allowable bending angle (3°) of the expansion pipe joint regulation. By applying the maximum bending angle, the allowable maximum deflection of the 2 km pipe was about 3.8 m. When the seismic load was considered using regression analysis, the maximum deflection of the 2km pipe was about 142.3mm, and it was confirmed that the bellows-type expansion joints and the deflection were stable compared to the allowable maximum deflection of the pipe system. These research results are expected to present design and analysis guidelines for the construction of piping and the development of bellows systems, and to be used as basic data for systematic research.

• Earthquakes and Structures
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• v.22 no.1
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• pp.53-64
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• 2022

This study proposes an intelligent semi-active isolation system combining a variable-stiffness control device and ground motion characteristic prediction. To determine the optimal control parameter in real-time, a genetic algorithm (GA)-fuzzy control law was developed in this study. Data on various types of ground motions were collected, and the ground motion characteristics were quantified to derive a near-fault (NF) characteristic ratio by employing an on-site earthquake early warning system. On the basis of the peak ground acceleration (PGA) and the derived NF ratio, a fuzzy inference system (FIS) was developed. The control parameters were optimized using a GA. To support continuity under near-fault and far-field ground motions, the optimal control parameter was linked with the predicted PGA and NF ratio through the FIS. The GA-fuzzy law was then compared with other control laws to verify its effectiveness. The results revealed that the GA-fuzzy control law could reliably predict different ground motion characteristics for real-time control because of the high sensitivity of its control parameter to the ground motion characteristics. Even under near-fault and far-field ground motions, the GA-fuzzy control law outperformed the FPEEA control law in terms of controlling the isolation layer displacement and the superstructure acceleration.

• Journal of Korean Association for Spatial Structures
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• v.23 no.3
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• pp.57-69
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• 2023

In this study, in order to establish a strategy for developing an fire following earthquake risk assessment method that can utilize domestic public databases(building datas, etc.), the method of calculating the ignition and fire-spread among the fire following earthquake risk assessment methodologies proposed by past researchers is investigated After investigating and analyzing the methodology used in the HAZUS-MH earthquake model in the United States and the fire following earthquake risk assessment methodology in Japan, based on this, a database such as a domestic building data utilized to an fire following earthquake risk assessment method suitable for domestic circumstances (planned) was suggested.

• Proceedings of the KSRS Conference
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• v.1
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• pp.376-379
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• 2006

A numerous oil slicks of natural origin were revealed in the southwest (SW) part of Caspian Sea by the synthetic aperture radar (SAR) images acquired by Envisat satellite in 2003-2004. On the basis of computer processing, visual analysis of SAR images and comparisons with bathymetry, geophysical and seismic data in geographic information system (GIS), a link between these slicks and unloading of liquid hydrocarbons in the SW Caspian is established. Oil slicks are basically concentrated above domes of local geological formations of the sedimentary cover. In total more than 90 seeps and mud volcanoes having a repeating regime and representing an active type were identified; they are distributed across the SW Azerbaijan and West Iranian sectors. Periodical occurrence of slicks can reflect alternation of mud volcanism pulses forced by intensive seismicity with the quiet periods. Seepage rate of oil in the SW part of the Caspian Sea according to SAR images is estimated to be up to 16,000 metric tons per year. The importance of unloading of oils on hydrochemistry and ecological conditions of the Caspian Sea is demonstrated. Conclusion is done that the Envisat SAR to be an excellent tool for studying oil seeps through observation oil slicks floating on the sea surface.

• Steel and Composite Structures
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• v.42 no.5
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• pp.657-669
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• 2022

Structural materials can experience large plastic deformation under extreme cyclic loading that is caused by events like earthquakes. To evaluate the seismic safety of a structure, accurate numerical material models should be used. For a steel structure, the cyclic strain hardening behavior of structural steel should be correctly modeled. In this study, a combined hardening model, consisting of one isotropic hardening model and three nonlinear kinematic hardening models, was used. To determine the values of the combined hardening model parameters efficiently and accurately, the improved opposition-based particle swarm optimization (iOPSO) model was adopted. Low-cycle fatigue tests were conducted for three steel grades commonly used in Korea and their modeling parameters were determined using iOPSO, which was first developed in Korea. To avoid expensive and complex low cycle fatigue (LCF) tests for determining the combined hardening model parameter values for structural steel, empirical equations were proposed for each of the combined hardening model parameters based on the LCF test data of 21 steel grades collected from this study. In these equations, only the properties obtained from the monotonic tensile tests are required as input variables.