• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.59-66
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• 2004

Sand compaction pile (SCP)-improved ground is composite soil which consists of the SCP and the surrounding soft soil. When a surcharge load is applied to composite ground, time-dependent behaviors occur in the composite soil due to consolidation according to radial flow toward the SCP. In addition, stress transfer also takes place between the SCP and the soft soil. This paper presents the numerical results of cylindrical composite ground that was conducted to investigate smear effect on consolidation behaviors of SCP-improved ground. The results showed that the smeared zone of soft clay had a significant effect on effective stress-pore water pressure response, stress transfer mechanism and stress concentration ratio of composite ground. Amount of stress transfer between the clay and the SCP was maximum in depth of z/H=0.25, and decreased with depth. Stress concentration ratio of composite ground was not constant, but depended on consolidation process. It was also found that the value of stress concentration ratio in soft clay with smeared zone was larger than that in soft clay without smeared zone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.425-436
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• 2014

Although the strut-tie model approaches of current design codes are regarded as the valuable methods for designs of structural concretes with D-regions, the approaches have to be improved because of the uncertainties in terms of the concepts and provisions for designs of 3-dimensional structural concretes. To improve the uncertainties, a new strut-tie model approach is proposed in this study. In the proposed approach, the concepts of employing a 3-dimensional grid element allowing load transfers in all directions at a node to construct a strut-tie model, a numerical analysis approach to determine the effective strengths of concrete struts and nodal zones by reflecting the effects of reinforcing bars and 3-dimensional stress state, and maximum areas of struts and ties to examine their load carrying capacities are integrated into the strut-tie model approaches of current design codes.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.99-108
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• 2002

The nonlinear-brittle-plastic model derived from experiments as well as elastic and elasto-plastic models was applied to the analysis of the rock damaged zone around a highly stressed circular tunnel. The depths of stress redistribution and disturbed zone as well as the characteristic behaviors predicted from each numerical model were compared, As the magnitudes and stress differences of in situ stresses increased, influences of stress redistribution and stress disturbance on un(tiled region of rock mass also intensified. As a result, larger stress redistribution and disturbed zone as well as greater deviatoric stress and displacement were obtained by the nonlinear-brittle-plastic model rather than other conventional models such as elasto-plastic and elastic models. from such results, it was concluded that as the magnitudes and stress differences of in situ stresses increased, larger rock damaged zone might be predicted by the nonlinear-brittle-plastic model. Therefore, it is thought that the damage analysis may be indispensable far highly stressed tunnels.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5A
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• pp.841-848
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• 2006

There is a complex variation of stress in PSC anchorage zones and box girder diaphragms because of large concentrated load by prestress. According to the AASHTO LFRD design code, three-dimensional effects due to concentrated jacking loads shall be investigated using three-dimensional analysis procedures or may be approximated by considering separate submodels for two or more planes. In this case, the interaction of the submodels should be considered, and the model loads and results should be consistent. However, box girder diaphragms are 3-dimensional disturbed region which requires a fully three-dimensional model, and two-dimensional models are not satisfactory to model the flow of forces in diaphragms. In this study, the strengths of the prestressed box girder diaphragms are predicted using the 3-dimensional grid strut-tie model approach, which were tested to failure in University of Texas. According to the analysis results, the 3-dimensional strut-tie model approach can be possibly applied to the analysis and design of PSC box girder anchorage zones as a reasonable computer-aided approach with satisfied accuracy.

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.115-123
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• 2024

Stress is an invisible physical quantity, necessitating the use of earth pressure cells for its measurement within theground. Traditional strain-gauge type earth pressure cells, due to their rigidity, can distribute stress within the ground and subsequently affect the accuracy of earth pressure measurements. In contrast, force sensing resistors are thin and flexible, enabling the minimization of stress disturbance when measuring stress within the ground. This study developed a system that utilizes force sensing resistors to measure ground stress. It involved constructing a soil chamber for calibrating the force sensing resistors, assessing the variability of measurements from resistors embedded in sand ground, and verifying the attachment of pucks to the sensing area of the resistors.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.411-419
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• 2006

In this study, a new approach employing 3-dimensional strut-tie models for analysis and design of 3-dimensional structural concrete with disturbed regions that are not properly occupied by current design codes is proposed. In addition, a computer graphics program for the practical application of the approach is developed. The approach adopts a grid strut-tie model to exclude the subjectivity in the selection of strut-tie model and evaluates the effective strength of concrete strut by considering the 3-dimensional failure criteria of concrete and the deviation angles between the struts and compressive principal stress trajectories. To verify the appropriateness of the approach, nine pile caps tested to failure are analyzed and a bridge pier is designed. The analysis and design results are compared with those obtained by several different methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.115-130
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• 2013

The sectional methods of current design codes have been broadly used for the design of various kinds of reinforced concrete pile caps. Lately, the strut-tie model approach of current design codes also became one of the attracting methods for pile caps. However, since the sectional methods and the strut-tie model approach of current design codes have been established by considering the behaviors of structural concrete without D-regions and two-dimensional concrete structures with D-regions, respectively, it is inappropriate to apply the methods to the pile caps dominated by 3-dimensional structural behavior with disturbed stress regions. In this study, the refined 3-dimensional strut-tie models, which consider the strength characteristics of 3-dimensional concrete struts and nodal zones and the load-carrying capacity of concrete ties in tension regions, are proposed for the rational analysis and design of pile caps. To examine the validity of the proposed models and to verify the necessity of appropriate constituent elements for describing 3-dimensional structural behavior and load-transfer mechanism of pile caps, the ultimate strength of 78 reinforced concrete pile caps tested to failure was examined by the proposed models along with the sectional and strut-tie model methods of current design codes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.621-637
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• 2006

Although the approaches implementing strut-tie models are the valuable tools for designing discontinuity regions of structural concrete, the approaches of the current design codes have to be improved for the design of structural concrete subjected to complex loading and geometrical conditions because of the uncertainties in the selection of strut-tie model, in the use of an indeterminate strut-tie model, and in the effective strengths of struts and nodal zones. To improve the uncertainties, a grid struttie model approach is proposed in this study. The proposed approach, allowing to perform a consistent and effective design of structural concrete, employs an initial grid strut-tie model in which various load combinations can be considered. In addition, the approach performs an automatic selection of an optimal strut-tie model by evaluating the capacities of struts and ties using a simple optimization algorithm. The validity and effectiveness of the proposed approach is verified by conducting the analysis of the four reinforced concrete deep beams tested to failure and the design of shearwalls with two openings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.531-539
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• 2017

The strut-tie model approach has been recognized as an efficient methodology for the design of all types of concrete members with D-regions, and the approach has been accepted in design codes globally. However, the design of concrete members with the approach requires many iterative numerical structural analyses, numerous graphical calculations, enormous times and efforts, and designer's subjective decisions in terms of the development of appropriate strut-tie model, determination of required areas of struts and ties, and verification of strength conditions of struts and nodal zones. In this study, a computer graphics program, that enables the design of concrete members efficiently and professionally by overcoming the forementioned limitations of the strut-tie model approach, is developed. In the computer graphics program, the numerical programs that are essential in the strut-tie model analysis and design of concrete members including finite element analysis programs for the plane truss and solid problems with all kinds of boundary conditions, a program for automatic determination of effective strengths of struts and nodal zones, and a program for graphical verification of developed strut-tie model's appropriateness by displaying various geometrical shapes of struts and nodal zones, are loaded. Great efficiency and convenience during the application of the strut-tie model approach may be provided by the various graphics environment-based functions of the proposed program.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.3
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• pp.227-235
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• 2004

Tunneling in rock mass produces two types of damages in the vicinity of a tunnel: structural and constructional damages. Structural damage represents the damage induced by the unbalance of geostatic stress caused by the tunneling, and constructional damage is the damage produced during the construction. In this study, formulations of tangential and radial stresses in the elastic and plastic zones near a tunnel, and the calculation of radius of plastic zone surrounding a tunnel are introduced by modifying the Hoek-Brown criterion of 2002 edition, which has capability of considering in situ rock mass characteristics and construction damage. From the parametric study, influences of rock mass quality, uniaxial compressive strength of intact rock, and the dimension of the tunnel on the plastic zone are investigated. The accuracy of the proposed approach is evaluated by comparing with results from the previous study.