• Geomechanics and Engineering
• /
• v.34 no.3
• /
• pp.303-316
• /
• 2023

With the development and utilization of urban underground space, the artificial ground freezing technology has been widely used in the construction of underground engineering in soft soil areas. The mechanical properties of soft clay changed greatly after freezing and thawing, which affected the seismic performance of underground structures. In this paper, a series of triaxial tests were carried out to study the dynamic response of the freezing-thawing clay under the seismic load considering different dynamic stress amplitudes and different confining pressures. The reduction factor of dynamic shear stress was determined to correct the amplitude of the seismic load. The deformation development mode, the stress-strain relationship and the energy dissipation behavior of the soft clay under the seismic load were analyzed. An empirical model for predicting accumulative plastic strain was proposed and validated considering the loading times, the confining pressures and the dynamic stress amplitudes. The relevant research results can provide a theoretical reference to the seismic design of underground structures in soft clay areas.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.7
• /
• pp.7-16
• /
• 2010

Stress history increases the residual horizontal stress of granular soil and, consequently, the penetration resistance. This study analyzes the effect of stress history on the cone resistance ($q_c$), horizontal stress index ($K_D$) and dilatometer modulus ($E_D$) of CPT and DMT from calibration chamber specimen in OC as well as NC state. Test results show that the normalized cone resistance by mean effective stress correlates well with the relative density and the state parameter, whereas the normalized cone resistance by vertical effective stress is a little affected by stress history. The influence of stress history is more reflected on $K_D$ than $E_D$ and $q_c$. The $K_D/K_0$, in which the effect of stress history on $K_D$ is compensated by the at-rest coefficient of earth pressure, $K_0$, is related to relative density, state parameter and the normalized cone resistance by mean effective stress. It is also observed that the normalized dilatometer modulus by mean effective stress ($E_D/{\sigma}_m'$) shows a unique correlation with the state parameter, regardless of stress history.

• Journal of Korean Academy of Fundamentals of Nursing
• /
• v.23 no.4
• /
• pp.419-429
• /
• 2016

Purpose: The purpose of this study was to examine the effects of a intensive clinical training program for nursing practice on the clinical competence, state anxiety, clinical practice stress in nursing students who were beginning their first clinical practice. Methods: This practice has been processed as a 'Pre-Post design with a non-equivalent control group'. The participants were 177 students in a college of nursing. The students were divided into two groups: 89 students in the experimental group and 88 students in the control group. Results: The experimental group showed significant improvement in their clinical competence scores compared to the control group. The difference between the two groups was also significant. State anxiety in the experimental group significantly decreased compared to the control group. However, scores for stress during practice were not significantly different. Conclusion: The findings in this research reveal that the program, 'Close clinical practice training for nursing students' practice entry, contributes to improving students' overall ability and performance, and reduces anxiety of nursing students as they start their first clinical practice. These findings can be utilized in helping nursing students improve the quality of their performance.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.2
• /
• pp.188-197
• /
• 1986

With respect to structural carbon steel(SM 22C), it was studied how the overstress or the understress has effects on fatigue inside crack propagation curve of a two level stress. Obtained results are summarized as follows. (1) The overstress or the understress, at a slip band occurrence stage, does not change the inside crack propagation curve because the crack closure and opening phenomena do not happen. (2) The overstress, at a crack propagation stage, does not change the inside crack propagation curve because the crack closure of overstress in compressive state is nearly same that of base stress in compressive state. (3) The understress, at a crack propagation stage, give rise to an acceleration of crack growth because the crack closure of understree in compressive state is more open than that of base stress in compressive state and the phenomenon is the essential increase of the actual applied stress of the specimen.

• Journal of the Korean Society of Industry Convergence
• /
• v.7 no.2
• /
• pp.181-186
• /
• 2004

This study presents a optimization of structure, in which constraints contain the conditions of stress and serviceability, while the sequential linear programming method (SLP) is used as a rational approach. The optimum design results contained on the limit state constraints are compared with those obtained by the only stress and ministry of construction enacted standard plans. A simple slab bridge is analysed numerically for illustration of the structural optimization. It may be asserted that serviceability constraints is very important to a structure design.

• Geomechanics and Engineering
• /
• v.10 no.3
• /
• pp.325-334
• /
• 2016

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.

• Transactions of Materials Processing
• /
• v.19 no.7
• /
• pp.405-410
• /
• 2010

Double layered tube that has been used for transportation and oil piping system is occasionally exposed to elevated temperature. The change in stress state at elevated temperature is important for the safe design of double layered tube. In this study, the variation of stress state for hydroformed double layered tube of which inner tube is stainless steel and outer tube is mild steel has been analytically analyzed. To characterize the thermal stress at elevated temperature, analytical model to provide thermal stresses between outer tube and inner tube was developed by using theories of elasticity and Lame equation. The feasibility of analytical model is verified by finite element analysis using ANSYS $CLASSIC^{TM}$, commercially available code. The variation of thermal stress at various thickness combination of inner and outer tube has also been investigated by proposed analytical model.

• Structural Engineering and Mechanics
• /
• v.7 no.2
• /
• pp.225-240
• /
• 1999

This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.

• Journal of Mechanical Science and Technology
• /
• v.17 no.2
• /
• pp.254-268
• /
• 2003

The explicit formulation of the J-integral and the M-integral is constructed in terms of the stress intensity factor and the higher order stress coefficients for Mode II cracks under small or large scale yielding. Furthermore, the stress intensity factor and the higher order stress coefficients as well are computed with the aid of the two-state J- and the M-integral, which is found to be accurate and efficient. It is found that the contribution from the higher order singularities to the J-integral is closely related to the configuration of the plastic zone.

• Journal of Preventive Medicine and Public Health
• /
• v.29 no.3 s.54
• /
• pp.609-616
• /
• 1996

This study was conducted to evaluate the degree of stress state and the risk factors related to in 967 white collar workers and 275 blue collar workers by using Psycosocial Well-being Index. The results obtained were as follows : 1. In the white collar workers and blue collar workers, young age, low education and low income groups had high scores of stress, while in white collar workers, female had high scores of stress but in blue collar workers, male had high scores of stress. 2. According to psychosocial well-being index, mild stress sto were 73.9% and 53.1%, high risk stress state were 8.9% and 44.4%, and healthy state were 17.2% and 2.6% in white collar and blue collar workers respectively. 3. The total stress score was highly associated with the factors of depression, social performance and self-confidence, general well-being and vitality, and sleeping disturbance and anxiety in order. 4. In reliability test of stress factors, Cronbach's $\alpha$ coefficients of depression, social performance and self-confidence, general well-being and vitality, and sleeping disturbance and anxiety were 0.89, 0.81, 0.79, and 0.74 respectively. In conclusion, it suggested that age, sex, marital status, income, education, sleeping time, smoking and exercise habit were associated with stress score, all of the above factors should considered to occupational health.