• Tunnel and Underground Space
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• v.6 no.2
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• pp.144-156
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• 1996

The deformation behaviors under uniaxial compressive cyclic loading were investigated for fresh rocks and freeze-thaw cycled samples. The Pocheon granite which is one of the most popular building stone in Korea was selected for tests. 0.5 Hz and 50% of dynamic strength were used as test conditions for frequency and fatigue span, respectively. For freezethaw procedure, sample were frozen for 3 hours under the temperature of -2$0^{\circ}C$ and then followed 3 hours thawing under the temperature of +2$0^{\circ}C$. Twenty seven samples were used as untreated and seventy three for freeze-thaw samples. No failure occurred up to 15000 cycles at the stress level of 60% of dynamic strength, indicating that the lowest strees level for fatigue failure may be around 60% of dynamic strength. Permanent strain and damping capacity curves show that there were three stages when rock behaves like under creep. Young's moduli were increased and Possion's ratios were decreased with the increase of the number of cycles. Possion's ratios varied more rapidly than Young's moduli did with the increase of the number of cycles. This may represent that most microcracks developed by fatigue stress are parallel to the axis of loading. The deformation behavior of freeze-thaw cycled samples were almost the same as that of untreated samples. However, the result of freeze-thaw cycled samples showed lower regression constant, indicating that the physical durability of rock is much lowered because of cyclic temperature variation.

• Structural Engineering and Mechanics
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• v.89 no.1
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• pp.23-31
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• 2024

Ratcheting is the cyclic buildup of inelastic strain on a structure resulting from a combination of primary and secondary cyclic stress. It can lead to excessive plastic deformation, incremental collapse, or fatigue. Ratcheting has been numerically investigated on a cantilever beam, considering the current study's primary and secondary bending loads. In addition, the effect of input frequency on the onset of ratcheting has been investigated. The non-linear dynamic elastic-plastic approach has been utilized. Analogous to Yamashita's bending-bending ratchet diagram, a non-dimensional ratchet diagram with a frequency effect is proposed. The result presents that the secondary stress values fall sequentially with the increase of primary stress values. Moreover, a displacement amplification factor graph is also established to explain the effect of frequency on ratchet occurrence conditions. In terms of frequency effect, it has been observed that the lower frequency (0.25 times the natural frequency) was more detrimental for ratchet occurrence conditions than the higher frequency (2 times the natural frequency) due to the effect of dynamic displacement. Finally, the effect of material modeling of ratcheting behavior on a beam is shown using different hardening coefficients of kinematic hardening material modeling.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.569-576
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• 2003

Based on the equivalent uniform stress concept Presented by Seed and Idriss, sinusoidal cyclic loads which simplified earthquake loads have been applied in evaluating the liquefaction resistance strength experimentally. However, the liquefaction resistance strength of soil based on the equivalent uniform stress concept can not exactly reflect the dynamic characteristics of the irregular earthquake motion. The liquefaction assessment method which was invented by using the equivalent uniform stress concept is suitable for the severe earthquake region such as Japan or USA, so the proper method to Korea is needed. In this study, estimation of the resistance to liquefaction was conducted by applying real earthquake loading to the cyclic triaxial test. From the test results, the characteristics of the fine sand under moderate earthquake were analyzed and compared with the results under strong earthquakes. Typically real earthquake loads used in this study are divided into two types - impact type and vibration type. Furthermore, results of the liquefaction resistance strength based on the equivalent uniform stress concept and tile concept using real earthquake loading were compared.

• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.559-572
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• 2014

This paper presents the results of an experimental investigation on the flexural behavior of doubly reinforced lightweight concrete (R.L.C.) beams tested under cyclic loading. A total of 20 beam specimens were tested. Test results are presented in terms of ductility index, the degradation of strength and stiffness, and energy dissipation. The flexural properties of R.L.C. beam were compared to those of normal concrete (R.C.) beams. Test results show that R.L.C. beam with low and medium concrete strength (20, 40MPa) performed displacement ductility similar to the R.C. beam. The ductility can be improved by enhancing the concrete strength or decreasing the tension reinforcement ratio. Using lightweight aggregate in concrete is advantageous to the dynamic stiffness of R.L.C. beam. Enhancement of concrete strength and increase of reinforcement ratio will lead to increase of the stiffness degradation of beam. The energy dissipation of R.L.C beam, similar to R.C. beam, increase with the increase of tension reinforcement ratio. The energy dissipation of unit load cycle for smaller tension reinforcement ratio is relatively less than that of beam with higher reinforcement ratio.

• Steel and Composite Structures
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• v.48 no.1
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• pp.103-111
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• 2023

The caving property of top coal is a key factor to the success of top coal caving mining. The influence law of cyclic loading and unloading of hydraulic support on top coal caving is of great significance to improve the recovery rate of top coal. The similar simulation methods were used to study the dynamic evolution of the top coal cracks under the multi-cycle action of the support, and the parameters of top coal cracks were analyzed quantitatively in this paper. The results show that the top coal cracks can be divided into horizontal cracks and vertical cracks under the cyclic loading and unloading of the support. With the increase of the times of the support cycles loading and unloading, the load on the support decreases, the fractal dimension of the cracks increases, the number and total length of the top coal cracks increases, and the top coal caving is getting better. With the increase of the times of multi-cycle loading and unloading, the fractal dimension, total crack length and crack rate of top coal show a trend of rapid increase first and then increase slowly. Both the total length of the top coal cracks and the crack rate basically show linear growth with the change of the fractal dimension. The top coal caving can be well improved and the coal resource recovery rate increased through the multi-cycle loading and unloading.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.239-246
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• 2000

It has been generally much fine contents in West Coast of Korea. When cyclic shear stress causing liquefaction was estimated as using cyclic triaxial tests in these grounds, it didn't appear linear relations between deviator stress and confining stress where σ'₃ was more than 150 kpa. Namely, due to no normalization of cyclic shear stress ratio, the errors of this is increased. Therefore, more confining stress is increased, more increment of deviator stress is decreased. So, using linear relations between tanø'/sub d/ of dynamic internal friction angle and CSR where σ'₃ was less than 150 kpa, liquefaction of these grounds was evaluated. Also, as doing detail evaluation which had carried response analysis of earthquake, this appeared good results which was well compatible with empirical methods using N-value of SPT. It was thought that these result evaluated vulnerable liquefaction area more correct than existing methods. Also, characteristics of liquefaction in West Coast grounds was compared with clean sands, with analysis of behavior of pore pressure ratio and axial strain affected by fine contents, as cyclic loading was applied.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.79-91
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• 2016

Geosynthetic-reinforced and Pile-supported (GRPS) embankment method is widely used to construct structures on soft ground due to restraining residual settlement and their rapid construction. However, effect of cyclic loading has not been established although some countries suggest design methods through many studies. In this paper, cyclic loading tests were conducted to analyze dynamic load transfer characteristics of pile-supported embankment reinforced with geosynthetics. A series of 3 case full scale model tests which were non-reinforced, one-layer-reinforced, two-layer reinforced with geosynthetics were performed on piled embankments. In these series of tests, the height of embankment and pile spacing were selected according to EBGEO (2010) standard in Germany. As a result of the vertical load parts on the pile and on the geosynthetic reinforcement measured separately, cyclic loads transferred by only arching effect decreased with strength geosynthetic-reinforced case. However, final loads on the pile showed no differences among the cases. These results conflict with previous studies that reinforcement with geosynthetics increases transfer load concentrated on piles. In addition, it is observed that the load transferred to pile decreases at the beginning of cycle number due to reduction of arching effected by cyclic loading. Based on these results, transferred mechanism for cyclic load on GRPS system has been presented.

• Structural Engineering and Mechanics
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• v.42 no.3
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• pp.383-407
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• 2012

A numerical approach to simulate the behaviour of timber shear walls under both static and dynamic loading is proposed. Because the behaviour of timber shear walls hinges on the behaviour of the nail connections, the force-displacement behaviour of sheathing-to-framing nail connections are first determined and then used to define the hysteretic properties of finite elements representing these connections. The model nails are subsequently implemented into model walls. The model walls are verified using experimental results for both monotonic and cyclic loading. It is demonstrated that the complex hysteretic behaviour of timber shear walls can be reasonably represented using model shear walls in which nonlinear material failure is concentrated only at the sheathing-to-framing nail connections.

• Geomechanics and Engineering
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• v.17 no.3
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• pp.253-259
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• 2019

Concrete-to-concrete bedding planes (CCBP) are observed from time to time due to the multistep hardening process of the concrete materials. In this paper, a series of direct/cyclic shear tests are performed on CCBP under static and dynamic normal load conditions to study the frictional behavior effect by the shear velocities, normal impact frequencies, horizontal shear frequencies, normal impact force amplitudes, horizontal shear displacement amplitudes and normal load levels. According to the experimental results, apparent friction coefficient k ($k=F_{Shear}/F_{Normal}$) shows different patterns under static and dynamic load conditions at the stable shear stage. k is nearly constant in direct shear tests under constant normal load conditions (DCNL), while it is cyclically changing with nearly constant peak value and valley value for the direct shear tests under dynamic normal load conditions (DDNL), where k increases with decreasing normal force and decreases with increasing normal force. Shear velocity has little influence on peak values of k for the DCNL tests, but increasing shear velocity leads to increasing valley values of k for DDNL tests. It is also found that, the valley values of k ascend with decreasing impact normal force amplitude in DDNL tests. The changing pattern of k for the cyclic shear tests under constant and dynamic normal load conditions (CCNL and CDNL tests) are similar, but the peak value of k is smaller in CDNL tests than that in CCNL tests. Normal load levels, shear displacement amplitudes, vertical impact frequencies, horizontal shear frequencies and normal impact force amplitudes have little influence on the changing pattern of k for the cyclic shear tests. The tests of this study provide useful data in understanding the frictional behavior of the CCBP under distinct loadings, and these findings are very important for analyzing the stability of the jointed geotechnical structures under complicated in situ stress conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.541-548
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• 2001

The interest in the dynamic properties of soils has increased strongly because of earthquake, heavy traffic, and foundations undergo high amplitude of vibrations. Most of soils in Korean peninsula are composed of granite soils, especially the decomposed mudstone soils are widely spread in Pohang areas, Kyong-buk province. Therefore, it Is very important to investigate the dynamic properties of these types of soils. The most important soil parameters under dynamic loadings are shear modulus and material dampings. Furthermore, few definitive data exist that can evaluate the behavior of unsaturated decomposed mudstone soils under dynamic loading conditions. The investigations described in this paper is designed to identify the shear modulus and damping ratio due to a surface tension for the unsaturated decomposed mudstone soils ulder low and high strain amplitude, For this purpose, the resonant column test and the cyclic triaxial test were performed. Test results and data have shown that the optimum degree of saturation under low and strain amplitude is 32 ∼ 37% which is higher than that of decomposed granite due to the amount of fine particles as well as the type and proportion of chief rock-forming minerals.