• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.97-106
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• 2003

In this study, the effect of temperature and soil confining stress on geosyntheic stress-strain properties was quantified by performing the temperature dependent confined tension tests for four types of geosynthetic including woven geotextile, composite, geomembrane and geogrid specimen. Temperature instrumentation on the GRS-retaining wall constructed in Jaechon-shi area was also performed to examine the a seasonal temperature variation of geosynthetic reinforcements in the backfill. Based on the test results, a comparison was made between unconfined and confined moduli far each temperature to quantify the soil confinement and temperature effect on stress-strain properties. And it was also proposed that the simple expressions for the secant moduli of geosynthetics as a function of temperature and confining stress on geosynthetics. As a result of the FDM analysis of GRS-retaining wall, the method of considering the effect of temperature and confining stress on geosynthetic reinforcements when performing the FDM analysis of GRS-retaining wall was proposed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.729-732
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• 2003

The K-R design curve is an engineering method of linear-elastic fracture analysis under plane-stress loading conditions. By the way, linear-elastic fracture mechanics (LEFM) is valid only as long as nonlinear material deformation is confined to a small region surrounding the crack tip. Like general steels, it is virtually impossible to characterize the fracture behavior with LEFM, in many materials. Critical values of J contour integral or crack tip opening displacement (CTOD) give nearly size independent measures of fracture toughness, even for relatively large amounts of crack tip plasticity. Furthermore, the crack tip opening displacement is the only parameter that can be directly measured in the fracture test. On the other. the crack tip opening angle (CTOA) test is similar to CTOD experimentally. Moreover, the test is easier to measure the fracture toughness than other method. The shape of the CTOA curve depends on material fracture behavior and, on the opening configuration of the cracked structure. CTOA parameter describes crack tip conditions in elastic-plastic materials, and it can be used as a fracture criterion effectively. In this paper, CTOA test is performed for steel JS-SS400 hot-rolled thin plates under plane-stress loading conditions. Special experimental apparatuses are used to prevent specimens from buckling and to measure crack tip opening angle for thin compact tension (CT) specimens.

• Smart Structures and Systems
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• v.25 no.2
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• pp.241-254
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• 2020

Using confined shape memory alloy (SMA) bar or plate, this study proposes an innovative self-centering damper. The damper is essentially properly machined SMA core, i.e., bar or plate, that encased in buckling-restrained device. To prove the design concept, cyclic loading tests were carried out. According to the test results, the damper exhibited desired flag-shape hysteretic behaviors upon both tension and compression actions, although asymmetric behavior is noted. Based on the experimental data, the hysteretic parameters that interested by seismic applications, such as the strength, stiffness, equivalent damping ratio and recentering capacity, are quantified. Processed in the Matlab/Simulink environment, a preliminary evaluation of the seismic control effect for this damper was conducted. The proposed damper was placed at the first story of a multi-story frame and then the original and controlled structures were subjected to earthquake excitations. The numerical outcome indicated the damper is effective in controlling seismic deformation demands. Besides, a companion SMA damper which represents a popular type in previous studies is also introduced in the analysis to further reveal the seismic control characteristics of the newly proposed damper. In current case, it was found that although the current SMA damper shows asymmetric tension-compression behavior, it successfully contributes comparable seismic control effect as those having symmetrical cyclic behavior. Additionally, the proposed damper even shows better global performance in controlling acceleration demands. Thus, this paper reduces the concern of using SMA dampers with asymmetric cyclic behavior to a certain degree.

• Structural Engineering and Mechanics
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• v.70 no.1
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• pp.13-31
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• 2019

A nonlinear finite element model (FEM) using ATENA-3D software to simulate the axially compressive behavior of circular steel tube confined concrete (CSTCC) columns infilled with ultra high performance concrete (UHPC) was presented in this paper. Some modifications to the material type "CC3DNonlinCementitious2User" of UHPC without and with the incorporation of steel fibers (UHPFRC) in compression and tension were adopted in FEM. The predictions of utimate strength and axial load versus axial strain curves obtained from FEM were in a good agreement with the test results of eighteen tested columns. Based on the results of FEM, the load distribution on the steel tube and the concrete core was derived for each modeled column. Furthermore, the effect of bonding between the steel tube and the concrete core was clarified by the change of friction coefficient in the material type "CC3DInterface" in FEM. The numerical results revealed that the increase in the friction coefficient leads to a greater contribution from the steel tube, a decrease in the ultimate load and an increase in the magnitude of the loss of load capacity. By comparing the results of FEM with experimental results, the appropriate friction coefficient between the steel tube and the concrete core was defined as 0.3 to 0.6. In addition to the numerical evaluation, eighteen analytical models for confined concrete in the literature were used to predict the peak confined strength to assess their suitability. To cope with CSTCC stub and intermediate columns, the equations for estimating the lateral confining stress and the equations for considering the slenderness in the selected models were proposed. It was found that all selected models except for EC2 (2004) gave a very good prediction. Among them, the model of Bing et al. (2001) was the best predictor.

• Geotechnical Engineering
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• v.5 no.2
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• pp.57-77
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• 1989

This paper describes the design and construction aspects of time-dependent deformation test apparatus for slut.oiling rocks and presents the test results obtained using these apparatus. These tests are modified semi-confined swell test, swell test under uniaxial tension and swell test under biaxial stress. These apparatus measure the time.dependent deformations in three orthogonal directions of the test specimen under simplified field stress conditions. The test results obtained from these test apparatus for the last several years show that these apparatus have performed satisfactorily. The test results show that the time-dependent deformation behaviour of the Queenston shale is cross-anisotropic with higher swelling in the vertical direction (normal to bedding plane) than in horizontal direction (parallel to bedding plane) under free swell condition. The applied stress in one direction suppresses the swelling deformation in that direction as well as that in the orthogonal directions.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.2 s.17
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• pp.57-63
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• 2005

In case of general structures, it has been known that the strain amplitude band experienced by the base in a state of service load is less than 1% and most of the base show low, strain amplitude behavior less than 0.01%. In this study examining the influence affected to dynamic behavior in a condition of the low strain amplitude of unsaturated decomposed granite soils, the resonant column test, using some samples in Su-won area, has been performed for each degree of saturation resulted from different void ratios and confined stress. It is found out that the minimum value of the damping ratio occurred in roughly $17{\sim}18%$ according to void ratios regardless of confined pressure in the same manner with the case of the maximum shear elastic modulus; and it is estimated that for the influence of surface tension in the optimum degree of saturation, the damping ratio appears to be least.

• Steel and Composite Structures
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• v.16 no.6
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• Journal of Korean Society of Steel Construction
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• v.9 no.1 s.30
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• pp.121-128
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• 1997

It has been reported by the existing papers that the ultimate load capacity and energy absorption capacity of the CFST column are considerably higher than those resulting from a simple addition of the capacities of the concrete and the steel tube. It is normally believed that the confined effect for the infilled concrete due to the hoop tension of steel at the parameter of cross sections can remarkably improve the ductility and energy absorption capacities of the CFST columns. This paper provides the results of a study on the load-carrying capacities and energy absorption capacities of the CFST columns, a numerical analysis method, i. e. N-M interaction curves and Moment curvature relationships. The numerical approaches are verified by comparing with the existing test results and the circular and square steel tube sections are selected to clarify the amount of confinement effects to improve the ultimate deformable capacity(a ultimate strain value) of the infilled concrete. Then, an adequate value of the ultimate strain of the infilled concrete and an equation of the ultimate capacity of the CFST column are suggested.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6A
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• pp.861-872
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• 2008

Concrete-filled glass fiber reinforced polymer tubes are often used for marine structures with the benefit of good durability and high resistance against corrosion under severe chemical environment. Current research presents results of a comprehensive experimental investigation on the behavior of axially loaded circular concrete-filled glass fiber reinforced polymer tubes. This paper is intended to examine several aspects related to the usage of glass fiber fabrics and filament wound layers used for outer shell of piles subjected to axial compression. The objectives of the study are as follows: (1) to evaluate the effectiveness of filament winding angle of glass fiber layers (2) to evaluate the effect of number of GFRP layers on the ultimate load and ductility of confined concrete (3) to evaluate the effect of loading condition of specimens on the effectiveness of confinement and failure characteristics as well, and (4) to propose a analytical model which describes the stress-strain behavior of the confined concrete. Three different types of glass fiber layers were chosen; fabric layer, ${\pm}45^{\circ}$ filament winding layer, and ${\pm}85^{\circ}$ filament winding layer. They were put together or used independently in the fabrication of tubes. Specimens that have various L:D ratios and different diameters have also been tested. Totally 27 GFRP tube specimens to investigate the tension capacity, and 66 concrete-filled GFRP tube specimens for compression test were prepared and tested. The behavior of the specimens in the axial and transverse directions, failure types were investigated. Analytical model and parameters were suggested to describe the stress-strain behavior of concrete under confinement.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.441-450
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• 2010

This is a preliminary study on the development of precast beam-column joints for dry construction methodology. Precast beam column joints with thru-connectors (BCJ_TC) using high strength bars or PS strands were developed and their seismic performance including strength degradation, stiffness degradation and energy dissipation capacity was experimentally evaluated. Test results showed that compressive failures at the end blocks of PC beam members occurred dominantly while PC columns including panel zones were free from any damage. However, the connections confined with CFRP at the end block showed much improved seismic performance than that of the unconfined connections. Connections with neoprene pad fillers between beam and column interfaces were better than the other connections in all the seismic performances except initial stiffness. To improve the seismic performances of BCJ_TC, compressive strength of the concrete at the end block need to be increased to compensate for the additional compressive stresses due to unbonded connectors and deformation of connectors should be controlled respectively.