• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.165-171
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• 2009

This research developed two semi-active MR dampers whose gaps in the orifice area were different from each other, and evaluated their damping performance by loading tests. The Damping performance of MR dampers characteristically depends on various factors like their material and mechanical ones, but most importantly on the size of gap in the orifice area. For this research, we designed the orifice gaps of two dampers as each 1.0mm and 2.0mm, both with the 80mm outer diameter of the orifice. We also designed two loading test sets with different input currents, and acquired different control ability from them. The acquired test results were analyzed and evaluated with their maximum and minimum damping force and also their dynamic range from the force-displacement hysteresis loops and the force-input current relationship curve. This research clearly proved how the damping performance of control devices depends on the gap effect, and also presented a possibility that the two dampers developed in this research could be used for the smart control of construction structures by effectively adapting the input current and the number of coil turns.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.172-180
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• 2009

Normally in order to build a semi-active control system equipped with MR damper, the dynamic modeling of the damper is required to numerically predict its dynamic damping force and also its behavioral characteristics. For the dynamic modeling of the MR damper, this paper attempts to predict and evaluate its dynamic behavior by applying specifically both a power model and a Bingham model. Dynamic loading tests were performed on the squeeze type of damper specially designed for this research, and force-displacement hysteresis loops confirmed the effectiveness of the damper as a semi-active control device. In the meantime, in order to evaluate the effectiveness of each model applied, the model parameter for each model was identified. On the basis of the parameter, we derived the error ratio of the force-velocity relationship curve and the dynamic damping force, which was contrasted and compared with the experimental results of the squeeze type of damper. Finally, the squeeze type of MR damper developed in this research was proved to be valid as a semi-active control device, and also the evaluation of the two dynamic models showed they were working fine so that they were likely to be easily utilized to numerically predict the dynamic characteristics of any dampers with MR fluid as well as the squeeze type of MR damper.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.30-39
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• 2022

Maintaining structural integrity of major apparatuses in a nuclear power plant, including piping system, is recognized as a critical safety issue. The integrity of piping system is also a critical matter related to the safety of a nuclear power plant. The actual failure mode of a piping system due to a seismic load is the leakage due to a fatigue crack, and the structural damage mechanism is the low-cycle fatigue due to large relative displacement that may cause plastic deformation. In this study, in-plane cyclic loading tests were conducted under various constant amplitudes using specimens composed of steel straight pipes and a steel pipe tee in the piping system of a nuclear power plant. The loading amplitude was increased to consider the relative displacement generated in the piping system under seismic loads, and the test was conducted until leakage, which is the limit state of the steel pipe tee, occurred due to fatigue cracks. The limit state of the steel pipe tee was expressed using a damage model based on the damage index that used the force-displacement relationship. As a result, it was confirmed that the limit state of the steel pipe tee can be quantitatively expressed using the damage index.

• Steel and Composite Structures
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• v.47 no.1
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• pp.91-102
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• 2023

To study the evaluation standard and control limit of mortar filling layer void length, in this paper, the train sub-model was developed by MATLAB and the track-bridge sub-model considering the mortar filling layer void was established by ANSYS. The two sub-models were assembled into a train-track-bridge coupling dynamic model through the wheel-rail contact relationship, and the validity was corroborated by the coupling dynamic model with the literature model. Considering the randomness of fastening stiffness, mortar elastic modulus, length of mortar filling layer void, and pier settlement, the test points were designed by the Box-Behnken method based on Design-Expert software. The coupled dynamic model was calculated, and the support vector regression (SVR) nonlinear mapping model of the wheel-rail system was established. The learning, prediction, and verification were carried out. Finally, the reliable probability of the amplification coefficient distribution of the response index of the train and structure in different ranges was obtained based on the SVR nonlinear mapping model and Latin hypercube sampling method. The limit of the length of the mortar filling layer void was, thus, obtained. The results show that the SVR nonlinear mapping model developed in this paper has a high fitting accuracy of 0.993, and the computational efficiency is significantly improved by 99.86%. It can be used to calculate the dynamic response of the wheel-rail system. The length of the mortar filling layer void significantly affects the wheel-rail vertical force, wheel weight load reduction ratio, rail vertical displacement, and track plate vertical displacement. The dynamic response of the track structure has a more significant effect on the limit value of the length of the mortar filling layer void than the dynamic response of the vehicle, and the rail vertical displacement is the most obvious. At 250 km/h - 350 km/h train running speed, the limit values of grade I, II, and III of the lengths of the mortar filling layer void are 3.932 m, 4.337 m, and 4.766 m, respectively. The results can provide some reference for the long-term service performance reliability of the ballastless track-bridge system of HRS.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.281-291
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• 2010

In this study, a five-story steel frame was designed in accordance with KBC2005 to evaluate the effects of the beam-column connection on the structural behavior. The connections were designed as fully rigid and semi-rigid. The fiber model was used to describe the moment-curvature relationship of the steel beam and the column, the power model for the moment-rotation angle of the semi-rigid connection and the three-parameter model for the hysteretic behavior of the steel beam, column, and connection. The structure was idealized as separate 2-D frames and as connected 2-D frames. The peak ground accelerations of four earthquake records were modified in a time-history analysis for the levels of the mean return period and for the maximum base-shear force in a pushover analysis. The top story displacement, base-shear force, story drift, demanded ductility ratio for the semi-rigid connection, maximum bending moment of the column, beam, and connection, and distribution of the plastic hinge were examined in the time-history analysis. The frame with the semi-rigid connection yielded a lower base-shear force, less magnitude, and increasing ratio in the bending moment of the column, beam, and connection than the frame with a fully rigid connection. The TSD connection was deemed to have secured the economy and safety of the sample structure that was subjected to seismic excitation for the Korean design level.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.219-228
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• 2011

In this paper, the design procedure of substructure of the steel-type breakwater was described and the actual foundation design was performed for the test bed. The site investigation was executed at the Osan-port area, in Uljin, Gyeongbuk, where the steeltype detached breakwater is constructed. The foundation mainly depends on the lateral load and uplift force due to the wave force. Since the superstructure is stuck out about 9.0m from the ocean bed, the foundation must resist on the lateral force and bending moment. After considering various factors, the foundation type of this structure was determined by the steel pipe pile(${\varphi}711{\times}t12mm$). On the stability of pile foundation, the safety factors of the pile on the compressive, lateral and uplift forces were grater than the minimum factor of safety. The displacements of pile under the working load were evaluated as the values below the permissible ones. Based on the subgrade reaction method, we evaluated the relationship of subgrade reaction and displacement for the lateral and the vertical directions in the layers. The structural analyses along with the foundation were perfomed and the effect of pile foundations were compared quantitatively.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.633-641
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• 2012

In this study, the effects of the inelastic shear behavior of beam-column joint on the response of RC OMRF are evaluated in the inelastic time history analysis. For an example, a 5-story structure for site class SB and seismic design category C was designed in accordance with KBC2009. Bending moment-curvature relationship for beam and column was evaluated using fiber model and bending moment-rotation relationship for beam-column joint was calculated using simple and unified joint shear behavior model and moment equilibrium relationship. The hysteretic behavior was simulated using three-parameter model suggested in IDARC program. The inelastic time history analysis with PGA for return period of 2400 years showed that the model with inelastic beam-column joint yielded smaller maximum base shear force but nearly equivalent maximum roof displacement and maximum story drift as those obtained from analysis using rigid joint. The maximum story drift satisfied the criteria of KBC2009. Therefore, the inelastic shear behavior of beam-column joint could be neglected in the structural design.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.189-198
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• 2006

The composition of most engineering materials is heterogeneous at some degree. It is simply a question of scale at which the level of heterogeneity becomes apparent. In the case of cementitious granular materials such as concrete the heterogeneity appears at the mesoscale where it is comprised of aggregate particles, a hardened cement paste and voids. Since it is difficult to consider each separate particle in the topological description explicitly, numerical models of the meso-structure are normally confined to two-phase matrix particle composites in which only the larger inclusions are accounted for. 2-D and 3-D concrete blocks(Representative Volume Element, RVE) are used to simulating heterogeneous concrete meso-structures in the form of aggregates in the hardened mortar with nearly zero-thickness linear or planar interfaces. The numerical sensitivity of these meso-structures are Investigated with respect to the different morphologies of heterogeneity and the different level of coupling constant among fracture mode I, II and III. In addition, a numerically homogenized concrete block in 3-D using Hashin-Shtrikman variational bounds provides an evidence of the effective cracking paths which are quite different with those of heterogenous concrete block. However, their average force-displacement relationship show a pretty close match each other.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.3
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• pp.44-51
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• 2016

This paper presents the characteristics of the energy absorption in an expansion tube type impact absorber that is applied to a high weight drop tester and the use of a response surface methodology to predict the impact energy absorption. In order to identify the characteristics of the energy absorption, a set of finite element analysis was conducted with Abaqus Explicit. Moreover, the ISCD-II sampling method and a first order polynomial were used to build a response surface. As a result, we demonstrated that the impact energy could be controlled by four main design variables, namely an expansion pipe's thickness, inner radius, pressing die's expansion angle and expansion ratio. Additionally, we observed the relationship between the four main design variables and the impact energy absorbing time, displacement, and maximum impact force.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.2 s.48
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• pp.11-19
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• 2006

In this paper the seismic performances of 4, 10, and 30-story staggered truss systems (STS) were evaluated by observing the force-displacement relationship up io failure. The results were compared with the seismic performance of conventional moment resisting frames and braced frames. According to the analysis results, the STS showed relatively satisfactory lateral load resisting capability. However, in the mid- to high-rise STS, plastic hinges formed first at the chords were transferred to vertical members of the vierendeel panels, which formed a week link and subsequently leaded to brittle collapse of the structure. Therefore to enhance the ductility of STS it would be necessary to reinforce the vertical bracing members of the virendeel panels so that the plastic hinges, once toned in cord members of a virendeel panel, spread out to virendeel panels of neighboring stories.