• 한국지반공학회논문집
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• 제21권7호
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• pp.21-29
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• 2005

본 논문에서는 압축성이 큰 지반 위에 시공되는 지오그리드 보강 계단형 블록식 보강토 옹벽의 거동 특성에 관한 내용을 다루었다. 대상옹벽으로는 2단으로 시공되는 높이 lOrn의 블록식 보강토 옹벽을 고려하였으며 압축성이 큰 지반위에 시공되는 경우를 고려하였다. 본 연구는 검증된 유한요소해석 모델을 사용하여 수행되었으며 기초지반의 침하가 옹벽의 변위 및 보강재 유발 인장력에 미치는 영향을 집중적으로 다루었다. 연구결과 시공중 발생하는 기초지반의 과다 침하는 옹벽의 변위 뿐 아니라 보강재 유발 인장력 또한 현저히 증가시켜 내·외적 안정성에 지대한 영향을 미치는 것으로 나타났다. 본 논문에서는 연구결과와 아울러 실무적 관점에서의 고려사항 을 기술하였다.

• Geomechanics and Engineering
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• 제6권2호
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• pp.173-194
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• 2014

Laboratory and field data showed that deep mixed (DM) columns accelerated the rate of consolidation of the soft foundations. Most analyses of consolidation of DM column-improved foundations so far have been based on the elastic theory. In reality, the DM columns may yield due to the stress concentration from the soft soil and its limited strength. The influence of column yielding on the degree of consolidation of the soft foundation improved by DM columns has not been well investigated. A three-dimensional mechanically and hydraulically-coupled numerical method was adopted in this study to investigate the degree of consolidation of the DM column foundation considering column yielding. A unit cell model was used, in which the soil was modeled as a linearly elastic material. For a comparison purpose, the DM column was modeled as an elastic or elastic-plastic material. This study examined the aspects of stress transfer, settlement, and degree of consolidation of the foundations without or with the consideration of the yielding of the DM column. A parametric study was conducted to investigate the influence of the column yielding on the stress concentration ratio, settlement, and average degree of consolidation of the DM column foundation. The stress concentration ratio increased and then decreased to reach a constant value with the increase of the column modulus and time. A simplified method was proposed to calculate the maximum stress concentration ratios under undrained and drained conditions considering the column yielding. The simplified method based on a composite foundation concept could conservatively estimate the consolidation settlement. An increase of the column modulus, area replacement ratio, and/or column permeability increased the rate of consolidation.

• International Journal of Industrial Entomology and Biomaterials
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• 제6권2호
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• pp.197-202
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• 2003

The hot climatic conditions prevailing particularly in summer are not conducive to rear these high yielding bivoltine hybrids throughout the year, In order to select efficiently the breeds with high temperature tolerance, it is very important to analyze critically the impact of high temperature on many silk yielding attributes of silkworm races. Keeping the above in view, the present study was undertaken to determine the effect of high temperature $(36 {\pm} 1^{\circ}C)$ and high humidity $(80 {\pm} 5% Relative Humidity)$ on the rearing performance of pure races, foundation crosses, single hybrids and double hybrids of bivoltine silkworm, Bombyx mori L. The robust bivoltine breeds, CSR18, CSR19, 8HT and 5HT, eight foundation crosses, eight single hybrids and eight double hybrids involving these breeds were chosen as materials in this study.

• Earthquakes and Structures
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• 제19권4호
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• pp.273-286
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• 2020

The pile group foundation is widely used for gravity pier of high-speed railway bridges in China. If a moderate or strong earthquake occurs, the pile-surrounding soil will exhibit obvious nonlinearity and significant pile group effect. In this study, an improved pushover analysis model for the pile group foundation with consideration of pile group effect is presented and validated by the quasi-static test. The improved model uses simplified springs to simulate the soil lateral resistance, side friction and tip resistance. PM (axial load-bending moment) plastic hinge model is introduced to simulate the impact of the axial force changing of pile group on their elastic-plastic characteristics. The pile group effect is considered in stress-stain relations of the lateral soil resistance with a reduction factor. The influence factors on nonlinear characteristics and plastic hinge distribution of the pile group foundation are discussed, including the pier height, longitudinal reinforcement ratio and stirrup ratio of the pile, and soil mechanical parameters. Furthermore, the displacement ductility factor, resistance increase factor and yielding stiffness ratio are provided to evaluate the seismic performance of soil-pile system. A case study for the pile group foundation of a railway simply supported beam bridge with a 32 m-span is conducted by numerical analysis. It is shown that the ultimate lateral force of pile group is not determined by the yielding force of the single one in these piles. Therefore, the pile group effect is essential for the seismic performance evaluation of the railway bridge with pile group foundation.

• Structural Engineering and Mechanics
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• 제40권6호
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• pp.763-782
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• 2011

Results from nonlinear time-history analyses of wall-frame structural models indicate that the condition of vulnerable foundations -for which uplifting and reaching the bearing capacity of the supporting soil can occur before yielding at the base of the shear walls- may not be necessarily detrimental to the drift response of buildings under strong ground motions. Analyses also show that a soil-foundation system can inherently have deformation capacity well in excess of the demand and thus act as a source of energy dissipation that protects the structural integrity of the shear walls.

• Geomechanics and Engineering
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• 제21권1호
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• pp.73-84
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• 2020

In the seismic design of bridges, formation of plastic hinges plays an important role in the dissipation of seismic energy. In the case of conventional fixed-base bridges, the plastic hinges are allowed to form in the superstructure alone. During seismic event, such bridges may be safe from collapse but the superstructure undergoes significant plastic deformations. As an alternative design approach, the plastic hinges are guided to form in the soil thereby utilizing the inevitable yielding of the soil. Rocking foundations work on this concept. The formation of plastic hinges in the soil reduces the load and displacement demands on the superstructure. This study aims at evaluating the seismic response of bridge pier supported on rocking shallow foundation. For this purpose, a BNWF model is implemented in OpenSees platform. The capability of the BNWF model to capture the SSI effects, nonlinear behavior and dynamic loading response are validated using the centrifuge and shake table test results. A comparative study is performed between the seismic response of the bridge pier supported on the rocking shallow foundation and conventional fixed-base foundation. Results of the study have established the beneficial effects of using the rocking shallow foundation for the seismic response analysis of the bridge piers.

• Steel and Composite Structures
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• 제35권2호
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• pp.279-294
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• 2020

Foundation of a building is damaged under service loads during construction. First visit shows that the foundation has been punched at the 6 column's foot region led to building rotation. Foundation shear punching occurring has made some stresses and deflections in construction. In this study, progressing of damage caused by foundation shear punching and inverse loading in order to resolve the building rotation has been evaluated in the foundation and frame of building by finite element modeling in ABAQUS software. The stress values of bars in punched regions of foundation has been deeply exceeded from steel yielding strength and experienced large displacement based on software's results. On the other hand, the values of created stresses in the frame are not too big to make serious damage. In the beams and columns of ground floor, some partial cracks has been occurred and in other floors, the values of stresses are in the elastic zone of materials. Finally, by inverse loading to the frame, the horizontal displacement of floors has been resolved and the values of stresses in frame has been significantly reduced.

• Geomechanics and Engineering
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• 제14권4호
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• pp.377-386
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• 2018

This paper focuses on the development of a new non-linear macro-element for the modelling of soil-foundation interaction. Material and geometrical nonlinearities (soil yielding and foundation uplift respectively) are taken into account in the present macro-element to examine the response of shallow foundations under monotonic and cyclic loads. Several applications of soil-foundation systems are studied. The results obtained from these applications are in very favourable agreement with those obtained through other numerical models in the literature.

• Korean Chemical Engineering Research
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• 제60권1호
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• pp.125-131
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• 2022

The microstructure of highly aggregated colloidal dispersions was investigated by probing the rheological behavior of magnetic suspensions. The dynamic moduli as functions of frequency and strain amplitude are shown to closely resemble that of colloidal gels indicating the formation of network structure. The two types of characteristic critical strain amplitudes, γ_c and γ_y, were characterized in terms of the changing microstructure. The amplitude of γ_c indicates the transition from linear to nonlinear viscoelasticity and depends only on particle volume fraction not magnetic interactions. The study of scaling behavior suggests that it is related to the breakage of interfloc, i.e., floc-floc structure. However, yielding strain, γ_y, was found to be independent of particle volume fraction as well as magnetic interaction. It relates to extensive deformation resulting in yielding behavior. The scaling of elastic constant, G_e, implies that this yielding behavior and hence γ_y is due to the breakage of long-range interfloc interactions. Also, the deformation of flocs due to increase strain was indicated from the investigation of the fractal nature.

• Earthquakes and Structures
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• 제8권3호
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• pp.591-617
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• 2015

Standards for seismic assessment and retrofitting of buildings provide deformation limit states for structural members and connections. However, in order to perform fully consistent performance-based seismic analyses of soil-structure systems; deformation limit states must also be available for foundations that are vulnerable to nonlinear actions. Because such limit states have never been established in the past, a laboratory testing program was conducted to study the rotational capacity of small-scale foundation models under combined axial load and moment. Fourteen displacement-controlled monotonic and cyclic tests were performed using a cohesionless soil contained in a $2.0{\times}2.0{\times}1.2m$ container box. It was found that the foundation models exhibited a stable hysteretic behavior for imposed rotations exceeding 0.06 rad and that the measured foundation moment capacity complied well with Meyerhof's equivalent width concept. Simplified code-based soil-structure analyses of an 8-story building under an array of strong ground motions were also conducted to preliminary evaluate the implication of finite rotational capacity of vulnerable foundations. It was found that for the same soil as that of the experimental program foundations would have a deformation capacity that far exceeds the imposed rotational demands under the lateral load resisting members so yielding of the soil may constitute a reliable source of energy dissipation for the system.