• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.5-15
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• 2014

Abandoned mine deposits are exposed to various physico-chemical geo-environmental hazards and disasters, such as acid mine drainage, water contamination, erosion, and landslides. This paper presents the ring shear characteristics of waste materials. The ring shear box with a rotatable O-ring was used in this study. Three tests were performed: (i) Shear stress-time relationship for given normal stress and shear speed, (ii) shear stress as a function of shear speed, and (iii) shear stress as a function of normal stress. For a given normal stress (50 kPa) and speed (0.1 mm/sec), the materials tested exhibit a strain softening behavior, regardless of drainage condition. The peak and residual shear stresses were determined for each normal stress and shear speed. The shear stress was measured when shear speed is equal to 0.01, 0.1, 1, 10, 50, 100 mm/sec or when normal stress is equal to 20, 40, 60, 80, 100, 150 kPa. From the test results, we found that the shear stress increases with increasing shear speed. The shear stress also increases with increasing normal stress. However, different types of shearing mode were observed in drained and undrained conditions. Under drained condition, particle crushing was observed from the shearing zone to the bottom of lower ring. Under undrained condition, particle crushing was observed only at the shearing zone, which has approximately 1 cm thick. It means that a significant high shear speed under undrained condition can result in increased landslide hazard.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.3
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• pp.226-233
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• 1994

The present paper considers the method to estimate the bottom friction driven by waves and current on rough turbulent flow. Parameter adjusting technique is suggested for the computation of bed shear stress driven by uni-directional flow. and the value of parameter is determined by comparing the computational results against Bijker's laboratory data. For the computation of combined flow bottom shear stress, two methods are presented; one is the modified Bijker approach (BYO Model) and the other is the modified Fredsoe approach (FY Model). both of which are refined by the present writer. Both models are again refined in two aspects, and tested against the Bijker's laboratory data.

• Structural Engineering and Mechanics
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• v.65 no.3
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• pp.303-314
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• 2018

Shear walls are a typical member under a complex stress state and have complicated mechanical properties and failure modes. The separated-elements model Genetic Evolutionary Structural Optimization (GESO), which is a combination of an elastic-plastic stress method and an optimization method, has been introduced in the literature for designing such members. Although the separated-elements model GESO method is well recognized due to its stability, feasibility, and economy, its adequacy has not been experimentally verified. This paper seeks to validate the adequacy of the separated-elements model GESO method against experimental data and demonstrate its feasibility and advantages over the traditional elastic stress method. Two types of reinforced concrete shear wall specimens, which had the location of an opening in the middle bottom and the center region, respectively, were utilized for this study. For each type, two specimens were designed using the separated-elements model GESO method and elastic stress method, respectively. All specimens were subjected to a constant vertical load and an incremental lateral load until failure. Test results indicated that the ultimate bearing capacity, failure modes, and main crack types of the shear walls designed using the two methods were similar, but the ductility indexes including the stiffness degradation, deformability, reinforcement yielding, and crack development of the specimens designed using the separated-elements model GESO method were superior to those using the elastic stress method. Additionally, the shear walls designed using the separated-elements model GESO method, had a reinforcement layout which could closely resist the actual critical stress, and thus a reduced amount of steel bars were required for such shear walls.

• Journal of Ocean Engineering and Technology
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• v.22 no.4
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• pp.51-58
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• 2008

The objective of this study was to investigate the mechanical characteristics of fiber-reinforced lightweight soil using waste fishing net or monofilament for recycling both dredged soils and bottom ash. Reinforced lightweight soil consists of dredged soil, cement, air foam, and bottom ash. Waste fishing net or monoiament was added the mixture in order to increase the shear strength of the lightweight soil. Test specimens were fabricated with various mixing conditions, including waste fishing net content and monofilament content. Several series of unconfined compression tests and direct shear tests were carried out. From the experimental results, it was found that the unconfined compressive strength, as well as the stress-strain behavior of reinforced lightweight soil was strongly influenced by mixing conditions. In this study, the maximum increase in shear strength was obtained with either a 0.5% content of monofilament or 0.25% waste fishing net. The unconfined compressive strength of reinforced lightweight soil with monofilament was greater than that of reinforced lightweight soil with waste fishing net.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.4
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• pp.224-232
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• 2004

Sedimentation changes related with bottom shear stress attenuation at JangHang channel in the Keum River Estuary, where several huge coastal constructions including an estuarine dam have been conducted for last 2 decades, were evaluated for 7 cases to figure out passage hindrance through the channel by a hydrodynamic model using hind-casting technique from 1988 to 2000 at every 2 years interval. Due to the construction of Keum River Estuary Dam, the maximum bottom shear stress rapidly lessened to $0.2-0.6N/m^2$ compared to$1-2N/m^2$ in natural status. Especially it marks below the critical shear stress of $0.4N/m^2$ resulting in severe siltation in the channel just after the closing of dam gates in 1994. It is concluded that the dam may block the tidal energy propagation to upstream and directly results in sedimentation environment in front of dam site. It is also revealed that at least 20% of passage hindrance of small fishing boats through the channel could be counted due to sedimentation by analysis of predicted mean spring tides.

• Journal of Korean Society on Water Environment
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• v.25 no.1
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• pp.48-57
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• 2009

A two-dimensional (2D), laterally-averaged hydrodynamic and water quality model, CE-QUAL-W2 was applied to evaluate the performance on simulating the effect of flushing from Daecheong Reservoir on the downstream water quality variations during the flushing events held on November, 2003 and March, 2008. The hydraulic and water quality simulation results were compared with field measurement data, as well as a one-dimensional (1D), unsteady model (KORIV1) that revealed limited capability in the previous study due to missing the resuspension process of river bottom sediments. The results showed that although the 2D model made satisfactory performance in reproducing the temporal variations of dissolved matters including phosphate, ammonia and nitrate, it revealed poor performance in simulating the increase of biological oxygen demand and suspended sediment (SS) concentrations during the passage of the flushing flow. The reason of the error was that the resuspension process of the 2D model is only the function of shear stress induced by wind. In reality, however, as shown by significant correlation between bottom shear stress ($\tau$) and observed SS concentration, the resuspension process can be significantly influenced by current velocity in the riverine system, especially during flushing event. The results indicate that the resuspension of river bottom materials should be incorporated into the water quality modeling processes if $\tau$ is greater than a critical shear stress (${\tau}_c$) for better simulation of flushing effect.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.1
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• pp.18-26
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• 1998

In order to find out hydrodynamic changes due to huge complex constructions in the Keum River Estuary, two-dimensional finite element model is applied. Model results show that gate closing of the estuary dam yields tide amplifications at Kunsan Inner Port to 17 cm and 6 cm of M$_2$ and S$_2$, while 5 cm and 3 cm of amplification at Kunsan Outer Port. Tidal currents in the main channel due to stepwise flow-guide dikes construction have been simulated and show that dynamic equilibrium bottom shear stress is 0.4 N/m$\^$2/ on this Keum River Estuary. Sedimentation rates R have correlation with maximum bottom shear stress (equation omitted), R=-0.37-0.40 ln $\tau$.

• Coupled systems mechanics
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• v.12 no.4
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• pp.391-407
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• 2023

This paper presents a static study of a rectangular functional graded material (FGM) plate, simply supported on its four edges, adopting a refined higher order theory that looks for, only,four unknowns,without taking into account any corrective factor of the deformation energy with the satisfaction of the zero shear stress conditions on the upper and lower faces of the plate. We will have determined the contribution of these stresses in the transverse deflection of the plate, as well as their effects on the axial stress within the interfaces between the layers(to avoid any problem of imperfections such as delamination) and on the top and bottom edges of the plate in order to take into account the fatigue phenomenon when choosing the distribution law of the properties used during the design of the plate. A numerical statement, in percentage, of the contribution of the shear effect is made in order to show the reliability of the adopted theory. We will also have demonstrated the need to add the shear effect when the aspect ratio is small or large. Code routines are programmed to obtain numerical results illustrating the validity of the model proposed in the theory compared to those available in the literature.

• Steel and Composite Structures
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• v.14 no.1
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• pp.85-104
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• 2013

The present work deals with the thermomechanical bending response of functionally graded plates resting on Winkler-Pasternak elastic foundations. Theoretical formulations are based on a recently developed refined trigonometric shear deformation theory (RTSDT). The theory accounts for trigonometric distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. Unlike the conventional trigonometric shear deformation theory, the present refined trigonometric shear deformation theory contains only four unknowns as against five in case of other shear deformation theories. The material properties of the functionally graded plates are assumed to vary continuously through the thickness, according to a simple power law distribution of the volume fraction of the constituents. The elastic foundation is modelled as two-parameter Pasternak foundation. The results of the shear deformation theories are compared together. Numerical examples cover the effects of the gradient index, plate aspect ratio, side-to-thickness ratio and elastic foundation parameters on the thermomechanical behavior of functionally graded plates. It can be concluded that the proposed theory is accurate and efficient in predicting the thermomechanical bending response of functionally graded plates.

• Structural Engineering and Mechanics
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• v.44 no.2
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• pp.197-217
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• 2012

Detailed analysis of internal forces of exterior beam-column joints of RC frames under seismic action is reported in this paper. A formula is derived for calculating the average joint shear from the column shears, and a formula is proposed to estimate torque in eccentric joints induced by seismic action. Average joint shear stress and strain are defined consistently for exterior joints, which can be used to establish joint shear constitutive relationship. Numerical results of shear, bending moment and torque in joints induced by seismic action are presented for a pair of concentric and eccentric exterior connections extracted from a seismically designed RC frame, and two sections located at the levels of beam bottom and top reinforcement, respectively, are identified as the critical joint sections for evaluating seismic joint behavior. A simplified analysis of the effects of joint shear and torque on the flexural strengths of the critical joint sections is made for the two connections extracted from the frame, and the results indicate that joint shear and torque induced by a strong earthquake may lead to "joint-hinging" mechanism of seismically designed RC frames.