• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2000년도 사면안정 학술발표회
• /
• pp.213-220
• /
• 2000

Numerical modeling of cut slope has some limits in simulating the real slopes. In the case of 2D analysis of slope stability, it is assumed that slope is simply straight even when it is concave or convex in plan view. In this study, 3D analysis in curved shape slopes has been conducted for the comparison with 2D analysis in terms of failure mode and factor of safety. For this, 3D analysis by FLAC3D was compared with 2D analysis in plane strain condition and axi-symmetric model condition by FLAC. It was also observed how safety factors of slopes were affected by the variation of the tensile strength and cohesion, which are important variables to decide whether the slope fails or not. 2D analysis of concave slopes under plane strain condition showed much smaller safety factors by 16-40 % errors depending on the radius of curvature of slopes, compared to the more realistic values from 3D analysis. In case of convex slopes, the lower values by 7-10 % has been reported. 2D analysis of axi-symmetric model showed also smaller safety factors by 6-10 % and by 2-4 %, in case of concave and convex slopes, respectively. Such results are expected to contribute to the better understanding of failure process and could be applied for improved design of slopes.

• 한국지반환경공학회 논문집
• /
• 제4권3호
• /
• pp.27-40
• /
• 2003

본 연구에서는 프리텐션을 적용한 쏘일네일링 공법을 제시하고, 프리텐션 쏘일네일링 시스템에 대한 변위제어방식 현장인발시험을 총 9회 실시하여 프리텐션 쏘일네일링 구조체의 관련 설계변수인 쉬스관 길이 및 고정콘 유 무 등에 대한 영향에 대해 분석하였으며, 아울러 프리텐션 하중의 평가도 다루어 졌다. 또한 응력제어방식 현장인발시험을 총 3회 실시하여, 일반 쏘일네일 및 프리텐션 쏘일네일의 장 단기적인 인발-변형 특성 등을 비교 분석하였다. 계속해서, 프리텐션 쏘일네일링 시스템의 안정성 평가를 위해, 예상파괴면 및 최소안전율을 결정하기 위해 사면안정해석 등에 주로 적용되고 있는 전단강도감소기법을 이용한 수치해석적 접근방법의 제시 및 분석 등이 이루어졌다.

• 한국터널지하공간학회 논문집
• /
• 제13권2호
• /
• pp.115-131
• /
• 2011

최근 들어 방재 및 환경훼손 측면을 고려하여 병설터널의 시공 사례가 증가하고 있다. 병설터널의 굴착 시 필라(Pillar)부에 응력이 집중되어 터널의 안정성이 저하된다. 필라부의 거동에 대한 기존 연구들은 주로 수치해석과 실내 모형 실험을 통한 병설터널의 거동평가 및 지표침하 경향 분석 등에 국한되어 있어서, 필라부의 정량적 안정성 평가에는 한계가 있다. 따라서 본 연구에서는 병설터널의 필라폭이 터널의 안정성에 미치는 영향을 정량적으로 살펴보았다. 이를 위해 토피고가 다른 두 단면에 대해 전단강도 감소법을 이용한 수치해석적 방법으로 구한 터널 전체 안전율, Matsuda 등이 제안한 식을 이용하여 구한 필라부 국부안전율, 및 필라부의 강도/응력비를 산정하고 결과를 분석하였다. 합리적인 병설터널의 필라부 설계를 위해, 평균 강도/응력비, Matsuda 제안식에 의한 안전율, 수치해석적으로 구한 전체 안전율이 독립적으로 사용되기보다는 유기적으로 사용되어야 할 것으로 판단되었다.

• 한국지반공학회논문집
• /
• 제31권1호
• /
• pp.47-52
• /
• 2015

사면안정분야의 해석과 설계에는 한계평형법(LEM)과 전단강도 감소기법(SSR)이 주로 사용된다. 이 두 방법은 2차원과 3차원 해석을 모두 수행할 수 있지만 많은 연구자들에 의해 전단강도 감소기법이 해석 변수에 대해 더욱 민감하게 반응하고 합리적인 결과를 산출한다고 알려져있다. 그러나 전단강도 감소기법의 모델링의 복잡함과 해석시간의 증가 등의 이유로 현계평형법이 여전히 일반적으로 사용되고 있다. 본 연구에서는 FLAC 3D를 사용하여 전단강도 감소기법을 통한 돌출된 암반사면의 3차원 효과에 대해 연구하였다. 수치해석 변수는 사면의 경사, 높이, 지반강도, 사면의 돌출길이이며 연구 결과 사면의 안전율은 암반의 강도보다 사면의 형상에 더 영향을 받는 것으로 나타났다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 추계 학술발표회
• /
• pp.168-175
• /
• 2008

The method of reinforced earth walls has grown remarkably and the frequency of utilization has been increased on a national scale thereafter introduced in the middle 1980s in Korea. Furthermore the construction case of the extensive Geosynthetic-Reinforced Segmental Retaining Walls had been increased. Currently, the design criterion of FHWA and NCMA mainly used in Korea suggest determining the horizontal distance of the upper/lower retaining wall based on the study results of the internal stability and the external stability of Segmental Retaining Walls but in many cases are not suitable for the actual situation in Korea. Therefore, in this study reviewed the design criterion of Geosynthetic-Reinforced Segmental Retaining Walls, performed the internal and external stability in Paju, Gyeonggi-do based on the design criterion of FHWA and NCMA, suggested the modified design criterion of FHWA with analyzing the results, and performed the stability analysis for the internal and external stability and the compound failure. Moreover for the confirmation of the modified FHWA design standard, the suggestion and the analysis of the numerical analysis approaching method using shear strength reduction technique were performed and the design cases utilized the modified FHWA design standard based on the study analysis were introduced.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 추계 학술발표회
• /
• pp.1029-1037
• /
• 2008

The finite element analysis of transient water flow through unsaturated soils was used to investigate effects of hydraulic characteristics, initial relative degree of saturation, methods to consider boundary condition, and rainfall intensity and duration on water pressure in slopes. The finite element method with shear strength reduction technique was used to evaluate the stability of slopes under rainfall. The slope-related disasters in Korea usually occur between July and September during the typhoon and localized heavy rain. This means that the rainfall is the most important factor that leads to the slope-related disasters. The slope-related disasters can happen at very short time and lead to big damage. To forecast the change of the heave of the groundwater in slope the Seep/w program was used.

• 한국구조물진단유지관리공학회 논문집
• /
• 제13권6호통권58호
• /
• pp.183-191
• /
• 2009

본 연구에서는 지진시 nailed-soil 굴착벽체의 안전율과 거동특성에 대하여 제시하였다. 시간이력해석을 이용하여 정적하중과 지진하중을 받는 nailed-soil 굴착벽체 전면부의 수평변위, 축력, 전단력, 모멘트를 해석하였다. Dawson과 Roth가 제안한 전단강도 감소기법에 바탕을 둔 안전율을 지진시 nailed-soil 굴착벽체의 안전율 계산에 사용하였다. 제안된 방법에 의한 안전율을 기존의 연구에서 산정된 안전율과 비교하여 그 타당성을 확인하였다.

• Steel and Composite Structures
• /
• 제42권4호
• /
• pp.427-446
• /
• 2022

Cutouts in the beams or plates are often unavoidable due to inspection, maintenance, ventilation, structural aesthetics purpose, and sometimes to lighten the structures. Therefore, there will be a substantial reduction in the strength of the structure due to the introduction of the cutouts. However, these cutouts can be reinforced with the different patterns of ribs (stiffener) to enhance the strength of the structure. The present study highlights the influence of the elliptical cutout reinforced with a different pattern of ribs on the stability performance of such stiffened composite panels subjected to non-uniform edge loads by employing the Finite element (FE) technique. In the present formulation, a 9-noded heterosis element is used to model the skin, and a 3-noded isoparametric beam element is used to simulate the rib that is attached around a cutout in different patterns. The displacement compatibility condition is employed between the plate and stiffener, and arbitrary orientations are taken care by introducing respective transformation matrices. The effect of shear deformation and rotary inertia are incorporated in the formulation. A new mesh configuration is developed to house the attached ribs around an elliptical cutout with different patterns. Initially, a study is performed on the panels with different stiffener schemes for various ply orientations and for different stiffener depth to width ratios (d_s/b_s) to determine an optimal stiffener configuration. Further, various parametric studies are conducted on an obtained optimal stiffened panel to understand the effect of cutout size, cutout orientation, panel aspect ratio, and boundary conditions. Finally, from the analysis, it can be observed that the arrangement of the stiffener attached to a panel has a major impact on the buckling capacity of the stiffened panel. The stiffener's depth to width ratio also significantly influences the buckling characteristic.

• Structural Engineering and Mechanics
• /
• 제78권1호
• /
• pp.41-52
• /
• 2021

Inelastic static pushover analysis has been used in the academic-research widely for seismic analysis of structures. Nowadays, the variety pushover analysis methods have been developed, including Modal pushover, Adaptive pushover, and Cyclic pushover, in which some weaknesses of the conventional pushover method have been rectified. In the conventional pushover analysis method, the effects of cumulative growth of cracks are not considered on the reduction of strength and stiffness of RC members that occur during earthquake or cyclic loading. Therefore, the Cyclic Pushover Analysis Method (CPA) has been proposed. This method is a powerful technique for seismic evaluation of regular reinforced concrete buildings in which the first mode of them is dominant. Since the bridges have different structures than buildings, their results cannot necessarily be attributed to bridges, and more research is needed. In this study, a cyclic pushover analysis with four loading protocols (suggested by valid references) by the Opensees software was conducted for seismic evaluation of two regular reinforce concrete bridges. The modeling method was validated with the comparison of the analytical and experimental results under both cyclic and dynamic loading. The failure mode of the piers was considered in two-mode of flexural failure and also a flexural-shear failure. Along with the cyclic analysis, conventional analysis has been studied. Also, the nonlinear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. The time history of 20 far-field earthquake records was used to conduct IDA. After analysis, the base shear vs. displacement in the middle of the deck was drawn. The obtained results show that the cyclic pushover analysis method is able to evaluate an accurate seismic behavior of the reinforced concrete piers of the bridges. Based on the results, the cyclic pushover has proper convergence with IDA. Its accuracy was much higher than the conventional pushover, in which the bridge piers failed in flexural-shear mode. But, in the flexural failure mode, the results of each two pushover methods were close approximately. Besides, the cyclic pushover method with ACI loading protocol, and ATC-24 loading protocol, can provided more accurate results for evaluating the seismic investigation of the bridges, specially if the bridge piers are failed in flexural-shear failure mode.

• Structural Engineering and Mechanics
• /
• 제57권1호
• /
• pp.1-20
• /
• 2016

On the basis of the geological conditions of high and steep mountainous slope on which an exit portal of an express railway tunnel with a bridge-tunnel combination is to be built, the composite structure of the exit portal with a bridge abutment of the bridge-tunnel combination is presented and the stability of the slope on which the express railway portal is to be built is analyzed using three dimensional (3D) numerical simulation in the paper. Comparison of the practicability for the reinforcement of slope with in-situ bored piles and diaphragm walls are performed so as to enhance the stability of the high and steep slope. The safety factor of the slope due to rockmass excavation both inside the exit portal and beneath the bridge abutment of the bridge-tunnel combination has been also derived using strength reduction technique. The obtained results show that post tunnel portal is a preferred structure to fit high and steep slope, and the surrounding rock around the exit portal of the tunnel on the high and steep mountainous slope remains stable when rockmass is excavated both from the inside of the exit portal and underneath the bridge abutment after the slope is reinforced with both bored piles and diaphragm walls. The stability of the high and steep slope is principally dominated by the shear stress state of the rockmass at the toe of the slope; the procedure of excavating rockmass in the foundation pit of the bridge abutment does not obviously affect the slope stability. In-situ bored piles are more effective in controlling the deformation of the abutment foundation pit in comparison with diaphragm walls and are used as a preferred retaining structure to uphold the stability of slope in respect of the lesser time, easier procedure and lower cost in the construction of the exit portal with bridge-tunnel combination on the high and steep mountainous slope. The results obtained from the numerical analysis in the paper can be used to guide the structural design and construction of express railway tunnel portal with bridge-tunnel combination on high and abrupt mountainous slope under similar situations.