• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1476-1483
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• 2005

This paper presents the results of small scale model tests on the behavior of propped wall and ground movements during deep excavation. Small scale model tests were performed in order to investigate the effects of various influencing factors on the deep excavation, such as stiffness of ground and unsupported span length. The results of model tests indicated that the wall behavior is significantly influenced not only by the stiffness of ground but by the over-excavation, and that the wall behavior can be reduced by decreasing the unsupported span length and increasing the stiffness of ground.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.397-404
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• 2001

Sand pile is one of the widely used ground improvement methods. Sand pile improved ground will have composite ground effects, even though the primary purpose is the accelerated consolidation. However, the consolidation of sand pile improved ground as a composite ground is substantially under developed. This study investigate the effect of composite ground for relatively low volume displacement sand piles. Plate bearing tests and earth pressure cell measurements are performed. It turned out that the contribution of sand pile as a load bearing mechanism is not substantial. However the bearing capacity of the surrounding clayey soil is increased by sixty percent, and it cause the stiffness change during consolidation. Therefore it is expected that, the effect of increased stiffness of sand pile improved ground is influenced by change of ground stiffness.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1187-1193
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• 2006

Traditionally, the continuum-based topology optimization methods employing the SIMP technique have been used to design compliant mechanisms. Although they have been successful, the optimized mechanisms by the methods are usually difficult to manufacture because of their geometrical complexities. The objective of this study is to develop a topology optimization method that can produce easy-to-fabricate mechanism structure. The proposed method is a ground beam method where beam connectivity is controlled by the beam joint stiffness. In this approach, beam joint stiffness determines the mechanism configuration. Because b the ground structure beams have uniform thicknesses varying only discretely, the resulting mechanism topologies become easily manufacturable.

• Computational Structural Engineering : An International Journal
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• v.2 no.1
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• pp.33-42
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• 2002

A computationally efficient stiffness design method for building structures is proposed in which dynamic soil-structure interaction based on the wave-propagation theory is taken into account. A sway-rocking shear building model with appropriate ground impedances derived from the cone models due to Meek and Wolf (1994) is used as a simplified design model. Two representative models, i.e. a structure on a homogeneous half-space ground and a structure on a soil layer on rigid rock, are considered. Super-structure stiffness satisfying a desired stiffness performance condition are determined via an inverse problem formulation for a prescribed ground-surface response spectrum. It is shown through a simple yet reasonably accurate model that the ground conditions, e.g. homogeneous half-space or soil layer on rigid rock (frequency-dependence of impedance functions), ground properties (shear wave velocity), depth of surface ground, have extensive influence on the super-structure design.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.688-693
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• 2007

Most frame structures cannot be manufactured in a single-piece form. Ideally, when a structure is built up by assembling multi pieces, assembly at the joints should be rigidly performed enough to have almost full stiffness, which is difficult for practical reasons such as manufacturing cost and time. In this research, we aim to develop a manufacturability-oriented compliance-minimizing topology optimization using a ground beam model incorporating additional zero-length elastic joint elements. In the present formulation, design variables control the stiffness of zero-length elastic joints, not the stiffness of beams. Because joint stiffness values at the converged state can be utilized to select candidate assembly locations and their strengths, the technique is extremely useful to design multi-piece frame structures. An optimal layout is also extracted based on the stiffness values.

• Geomechanics and Engineering
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• v.33 no.1
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• pp.101-112
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• 2023

When a submerged floating tunnel is connected to the ground, there is a risk of stress concentration at the shore connection owing to the displacement imbalance caused by low confinement pressures in water and high confinement pressures in the ground. Here, the effects of the boundary condition and stiffness of the joints installed at the shore connection on the behaviors of a submerged floating tunnel and its shore connection were analyzed using a numerical method. The analysis results obtained with fixed and ground boundaries were similar due to the high stiffness of the ground boundary. However, the stability of the shore connection was found to be improved with the ground boundary as a small displacement was allowed at the boundary. The effect of the joint stiffness was evaluated by investigating the dynamic behavior of the submerged floating tunnel, the magnitude of the load acting on the bored tunnel, and the stress distribution at the shore connection. A lower joint stiffness was found to correspond to more effective relief of the stress concentration at the shore connection. However, it was confirmed that joints with low stiffness also increase the submerged floating tunnel displacement and decrease the frequency of the dynamic behavior, causing a risk of increased resonance when wave loads with low frequency are applied. Therefore, it is necessary to derive the optimal joint stiffness that can achieve both stress concentration relief and resonance prevention during the design of shore connections to secure their dynamic stability.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.303-314
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• 2010

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 49 kinds of the laboratory model tests were conducted. And the result the study suggested $\beta_s$, the stiffness coefficient to evaluate the stiffness effect of reinforcement materials. Then, it was also found that the stiffness coefficient, $\beta_s$ as the testing constant would be appropriate as high as 1.0, 1.1 and 1.5 for geotextile, geogrid and steel bar, respectively. And It was evaluated that the stiffness effect affecting reinforcement improvement effect would be reduced as the thickness of embeded depth increases and that RFe, the stiffness effect reduction coefficient would have positive correlation with H/B. Finally, it was confirmed that the bearing capacity gained from the method to calculate bearing capacity, which was suggested in the study, would almost correctly estimate the capacity, demonstrating the appropriateness of the proposed bearing capacity calculation method.

• Structural Engineering and Mechanics
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• v.54 no.1
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• pp.19-33
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• 2015

Open ground storey (OGS) buildings are characterized by the sudden reduction of stiffness in the ground storey with respect to the upper infilled storeys. During earthquakes, this vertical irregularity may result in accumulated damage in the ground storey members of OGS buildings without much damage in the upper storeys. Hence, the structural design of OGS buildings needs special attention. The present study suggests a modification of existing displacement-based design (DBD) procedure by proposing a new lateral load distribution. The increased demands of ground storey members of OGS buildings are estimated based on non-linear time history analysis results of four sets of bare and OGS frames having four to ten storey heights. The relationship between the increased demand and the relative stiffness of ground storey (with respect to upper storeys) is taken as the criterion for developing the expression for the design lateral load. It is also observed that under far-field earthquakes, there is a decrease in the ground storey drift of OGS frames as the height of the frame increases, whereas there is no such reduction when these frames are subjected to near-field earthquakes.

• Geomechanics and Engineering
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• v.19 no.4
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• pp.315-327
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• 2019

Deep excavations for development of subway systems in metropolitan regions surrounded by adjacent buildings is an important geotechnical problem, especialy in Tabriz city, where is mostly composed of young alluvial soils and weak marly layers. This study analyzes the wall displacement and ground surface settlement due to deep excavation in the Tabriz marls using two dimensional finite element method. The excavation of the station L2-S17 was selected as a case study for the modelling. The excavation is supported by the concrete diaphragm wall and one row of steel struts. The analyses investigate the effects of wall stiffness and excavation width on the excavation-induced deformations. The geotechnical parameters were selected based on the results of field and laboratory tests. The results indicate that the wall deflection and ground surface settlement increase with increasing excavation depth and width. The change in maximum wall deflection and ground settlement with considerable increase in wall stiffness is marginal, however the lower wall stiffness produces the larger wall and ground displacements. The maximum wall deflections induced by the excavation with a width of 8.2 m are 102.3, 69.4 and 44.3 mm, respectively for flexible, medium and stiff walls. The ratio of maximum ground settlement to maximum lateral wall deflection approaches to 1 with increasing wall stiffness. It was found that the wall stiffness affects the settlement influence zone. An increase in the wall stiffness results in a decrease in the settlements, an extension in the settlement influence zones and occurrence of the maximum settlements at a larger distance from the wall. The maximum of settlement for the excavation with a width of 14.7 m occurred at 6.1, 9.1 and 24.2 m away from the wall, respectively, for flexible, medium and stiff walls.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.2
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• pp.95-103
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• 2022

In order to evaluate the earthquake safety of equipment in structures, it is essential to analyze the In-Structure Response Spectrum (ISRS). The ISRS has a peak value at the frequency corresponding to the structural vibration mode, but the frequency and amplitude at the peak can vary because of many uncertain parameters. There are several seismic design criteria for ISRS peak-broadening for fixed base structures. However, there are no suggested criteria for constructing the design ISRS of seismically isolated structures. The ISRS of isolated structures may change due to the major uncertainty parameter of the isolator, which is the shear stiffness of the isolator and the several uncertainty parameters caused by the nonlinear behavior of isolators. This study evaluated the effects on the ISRS due to the initial stiffness of the bi-linear curve of isolators and the variation of effective stiffness by the input ground motion intensity and intense motion duration. Analyzing a simplified structural model for isolated base structure confirmed that the ISRS at the frequency of structural mode was amplified and shifted. It was found that the uncertainty of the initial stiffness of isolators significantly affects the shape of ISRS. The variation caused by the intensity and duration of input ground motions was also evaluated. These results suggested several considerations for generating ISRS for seismically isolated structures.