• Geotechnical Engineering
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• v.14 no.3
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• pp.47-62
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• 1998

The disturbed state concept (DSC) proposed here is based on the idea that a deforming material element can be treated as a mixture of two constituent parts in the relative intact (Rl) and fully adjusted (FA) states, referred to as reference states. Based on this idea, DSC provides a unified constitutive model for the characteristics of saturated sands under cyclic loading. The model parameters for saturated sands are evaluated by using data from truly triaxial test device, The laboratory test results are also used for the verification of D SC model. In general, the model predictions are found to provide satisfactory correlation with the test results. From the results of this research, it can be stated that the DSC model is capable of characterizing the cyclic behavior of saturated sands under dynamic loading.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.226-234
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• 2021

The objective of this study is to establish the fundamental design data for axial load-displacement relationship under axial monotonic or cyclic responses of seismic damping·isolation (SDI) units developed for ceiling structures. The main parameters include the installation of a spring, the number of rubber layer, prestress stress of bolts for connector between the spring and rubbers, and loading type. Test results showed that SDI units with a spring in the core and higher prestress stress of bolts tended to be higher stiffness at the ascending branch and more ductile behavior at the descending branch. This trends more notable for the specimens under monotonic load rather than cyclic loads. Consequently, the energy dissipation of SDI unit can be optimally designed with the following conditions: installation of a spring within 3-layer rubbers and prestress applied to the bolts at 10% of their yielding strength . When compared with the experimental tension capacity of the developed SDI units, the predictions by JIS B 2704-1 and KDS 31 00 are conservative under monotonic loading but higher by approximately 10% under cyclic loading.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.22-29
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• 2023

In the evaluation of seismic performance for structural materials and components, the loading rate and axial force can have a significant impact. Due to time-delay effects between input and output displacements, It is difficult to apply high-rate displacement in cyclic tests and hybrid simulations. Additionally, the difficulty of maintaining a consistent vertical load in the presence of lateral displacement has limited fast and real-time tests performed while maintaining a constant vertical load. In this study, slow, fast cyclic tests and real-time hybrid simulations were conducted to investigate the rate dependency and the influence of vertical loads of Isolation Bearing. In the experiment, the FLB System including an Adaptive Time Series (ATS) compensation and a state estimator was constructed for real-time control of displacement and vertical load. It was found that the vertical load from the superstructure and loading rate can have a significant impact on the strength of the seismic isolation bearing and its behavior during an earthquake. When conducting experiments for seismic performance evaluation, they must be implemented to be similar to reality. This study demonstrates the excellent performance of the system built and used for seismic performance evaluation and enables accurate and efficient seismic performance evaluation.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.1071-1084
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• 2022

The present study aims to investigate the dynamic properties of a novel isolation system composed of separate rubber and wire isolators. The testing program comprised pure compressive, pure-shear, compressive-stress dependence, and shear-strain dependence tests that used full-scale test specimens according to ISO 22762-1. A total of 22 test specimens were fabricated and investigated. Among the tests, the pure compressive test was a destructive test that reached up to the failure stage, whereas the others were nondestructive tests before the failure stage. Similar to the pure-shear test, at each compressive-stress level in the compressive dependence test or at each shear-strain level in the shear-strain dependence test, the cyclic loading was conducted for three cycles. In the nondestructive tests, examination of the dynamic shear properties in the X-direction was independent of the Y-direction. The test results revealed that the increase in the shear strain increased the energy dissipation but decreased the damping ratio, whereas the increase in the compressive stress increased the damping ratio. In addition, a macro model was developed to simulate the load-displacement response of the isolation systems, and the prediction results were consistent with the experimental results.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.289-301
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• 2008

Double skin composite (DSC) wall is a structural wall that is filed with concrete between two steel plate skins connected by tie bars. This type of wall was developed to enhance the structural performance of wall, to reduce wall thickness, and to enhance constructibility, eliminating the use of formwork and re-bars. In this study, cyclic tests were performed to investigate the inelastic behavior and earthquake resistance of isolated and coupled DSC walls with rectangular and T-shapedcross-sections. The DSC walls showed stable cyclic behaviors, exhibiting excellent energy dissipation capacity. The te st specimens failed by the tensile fracture of welded joints at the wall base and coupling beam and by the severe local buckling of the steel plate. The deformation capacity of the walls varied with the connection details at the wall base and their cross-sectional shapes. The specimens with well-detailed connections at the wall base showed relatively god deformation capacity ranging from 2.0% to 3.7% drift ratio. The load-carrying capacities of the isolated and coupled wall specimens were evaluated considering their inelastic behavior. The results were compared with the test results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1227-1234
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• 2012

In this study, fatigue tests were carried out using real-scale pipe bend specimens with wall-thinning defects under a cyclic bending load together with a constant internal pressure of 10 MPa. The wall-thinning defect was located at the extrados and the intrados of the pipe bend specimens. A fully reversed cyclic in-plane bending displacement was applied to the specimens. For the pipe bends with wall thinning at the extrados, an axial crack occurred at the crown of the pipe bend rather than at the extrados where the defect was located. In addition, the fatigue life was longer than that of a sound pipe bend predicted from the design fatigue curve in ASME Sec.III, and it was less dependent on the axial length of the wall-thinning defect. For the pipe bends with wall thinning at the intrados, a circumferential crack occurred at the intrados. In this case, the fatigue life was much shorter than that of a sound pipe bend predicted from the design fatigue curve, and it clearly decreased with decreasing axial length of the wall-thinning defect.

• The Journal of Advanced Prosthodontics
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• v.13 no.3
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• pp.152-159
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• 2021

Purpose. The aim of this study was to investigate to what extent cyclic load affects the screwless implant-abutment connection for Morse taper dental implants. Materials and Methods. 16 implants (SICvantage max) and 16 abutments (Swiss Cross) were used. The screwless implant-abutment connection was subjected to 10,000 cycles of axial loading with a maximum force of 120 N. For the pull-off testing, before and after the same cyclic loading, the required force for disconnecting the remaining 6 implant-abutment connections was measured. The surface of 10 abutments was examined using a scanning electron microscope 120× before and after loading. Results. The pull-off test showed a significant decrease in the vertical force required to pull the abutment from the implant with mean 229.39 N ± 18.23 before loading, and 204.30 N ± 13.51 after loading (P<.01). Apart from the appearance of polished surface areas and slight signs of wear, no visible damages were found on the abutments. Conclusion. The deformation on the polished abutment surface might represent the result of micro movements within the implant-abutment connection during loading. Although there was a decrease of the pull-off force values after cyclic loading, this might not have a notable effect on the clinical performance.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.205-220
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• 1997

The objective of this study is to investigate the structural behavior of concrete-filled steel tubular column-H beam connections with exterior stiffeners. As a preliminary test, simple tensile test on the column to H-beam flange connections stiffened were conducted The paramaters of tensile test are the thickness(T=9, 12, 15m) and the width(W=50, 75, 100, 150mm) of exterior stiffeners. The simple tensile test were conducted to 7 kinds of specimens. Estimating the load, displacement, and strain from each kind, results of simple tensile test were compared with results of second test. On the basis of simple tensile test, test on the column to H-km connections stiffened with the sames under monotonic and cyclic load were conducted. Specimens of 5 for the second experiment were made. In analysis, comparing each strengthes and stiffnesses we estimated deformation capacity. Comparing and estimating each yielding strength ratios and maxium-strength ratios on the basis of yield line theory, new strength formula of beam-to-column connections was suggested.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.243-249
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• 2001

In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The inelastic deformation of the reactor baffle cylinder can occur due to the moving temperature distribution along the axial direction as the hot free surface moves up and down under the cyclic heat-up and cool-down of reactor operations. The ratchet deformations were measured with the laser displacement sensor and LVDTs after cooling the structural specimen which experiences thermal load up to $550^{\circ}$ and the temperature differences of about $500^{\circ}C$. During structural thermal ratchet test, the temperature distribution of the test cylinder along the axial direction was measured from 28 channels of thermocouples and the temperatures were used for the ratchet analysis. The thermal ratchet deformation analysis was performed with the NONSTA code whose constitutive model is nonlinear combined kinematic and isotropic hardening model and the test results were compared with those of the analysis. Thermal ratchet test was carried out with respect to 9 cycles of thermal loading and the maximum residual displacements were measured to be 1.8mm. It was shown that thermal ratchet load can cause a progressive deformation to the reactor structure. The analysis results with the combined hardening model were in reasonable agreement with those of the tests.

• Journal of Korean Association for Spatial Structures
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• v.16 no.3
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• pp.99-106
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• 2016

The proposed hybrid damper installs at a coupling beam and consists of a high-damping rubber (HDR) and steel pin. The proposed hybrid damper adopted a pin-lock system acts as a viscoelastic damper under wind load (small displacement) while it behaves as a hysteretic damper under earthquake load (large displacement). In this paper, the pin-lock mechanism and structural performance of the proposed hybrid damper is evaluated through experiment. Experiments were carried out with the variables which displacement, loading frequency and steel pin quantities were used. Test results showed that the pin-lock mechanism and the performance of the hybrid damper under a large displacement were verified. Also equivalent damping ratios of HDR were increasing at a small displacement as displacement amplitudes were increasing. However HDR did not depend on frequency.