• Geomechanics and Engineering
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• 제27권5호
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• pp.465-479
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• 2021

One of the important causes of building and infrastructure failure, such as bridges on pile foundations, is the placement of the piles in liquefiable soil that can become unstable under seismic loads. Therefore, the overarching aim of this study is to investigate the seismic behavior of a soil-pile system in liquefiable soil using three-dimensional numerical FEM analysis, including soil-pile interaction. Effective parameters on concrete pile response, involving the pile diameter, pile length, soil type, and base acceleration, were considered in the framework of finite element non-linear dynamic analysis. The constitutive model of soil was considered as elasto-plastic kinematic-isotropic hardening. First, the finite element model was verified by comparing the variations on the pile response with the measured data from the centrifuge tests, and there was a strong agreement between the numerical and experimental results. Totally 64 non-linear time-history analyses were conducted, and the responses were investigated in terms of the lateral displacement of the pile, the effect of the base acceleration in the pile behavior, the bending moment distribution in the pile body, and the pore pressure. The numerical analysis results demonstrated that the relationship between the pile lateral displacement and the maximum base acceleration is non-linear. Furthermore, increasing the pile diameter results in an increase in the passive pressure of the soil. Also, piles with small and big diameters are subjected to yielding under bending and shear states, respectively. It is concluded that an effective stress-based ground response analysis should be conducted when there is a liquefaction condition in order to determine the maximum bending moment and shear force generated within the pile.

• 대한치과보철학회지
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• 제45권2호
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• pp.216-227
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• 2007

Statement of problem: For the long-term success of removable partial dentures, the bonding between metal framework and denture base resin is one of the important factors. To improve bonding between those, macro-mechanical retentive form that is included metal framework design has been generally used. However it has been known that sealing at the interface between metal framework and denture base resin is very weak, because this method uses mechanical bonding. Purpose: Many studies has been made to find a simple method which induces chemical bond, now various bonding system is applied to clinic. In this experiment, shear bond strengths of heat-cured denture base resin to the surface-treated Co-Cr alloy were measured before and after thermocycling. Chemically treated groups with Alloy $Primer^{TM}$, Super-Bond $C&B^{TM}$, and tribochemically treated group with $Rocatec^{TM}$ system were compared to the beadtreated control group. The data were analyzed with two-way ANOVA. Result: 1. Shear bond strength of bead-treated group is highest, and Alloy $Primer^{TM}$ treated group, Super-Bond $C&B^{TM}$ treated group, RocatecTM system treated group were followed. Statistically significant differences were found in each treated group(p<0.05). 2. Surface treatment and thermocycling affected shear bond strength(p<0.05), however there was no interaction between two factors(p>0.05). 3. Shear bond strengths of bead-treated group and Alloy $Primer^{TM}$ treated group showed no statistically significant difference before and after thermocycling(p>0.05), and those of Super-Bond $C&B^{TM}$ treated group and $Rocatec^{TM}$ system treated group showed statistically significant difference after thermocycling(p<0.05).

• 대한환경공학회지
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• 제33권3호
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• pp.191-195
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• 2011

본 연구의 목적은 낮은 전단흐름조건에서 편모 운동성이 박테리아의 거동 특성에 미치는 영향을 파악하는데 있다. 대다수의 미생물은 편모를 이용하여 수용액 내에서 운동할 수 있는 능력을 가지고 있으며, 이러한 운동성은 수계나 수처리 시스템에서 미생물의 거동에 있어서 중요한 역할을 한다. 그러나 현재까지 병원성 미생물의 이동 현상과 관련된 연구에서 편모에 의한 운동성은 거의 고려되지 않고 있는 실정이다. 본 연구에서는 미세유체장치를 이용하여 전단흐름이 낮은 조건에서 E. coli의 거동 특성을 파악하고자 하였다. 실험을 통하여 유속이 작은 경우에 E. coli는 포물선의 형태의 궤적들을 그리며 이동하는 것을 알 수 있었으며, 벽면 근처에서는 상류로 헤엄쳐 올라간다는 것을 파악하였다. 또한 유속과 종횡비(aspect ratio)에 따른 궤적의 변화를 분석하였는데, 유속이 작을수록 포물선 형태의 궤적을 그리게 되며, 길이가 짧을수록 보다 작은 회전 반경을 그리며 운동하는 것을 관찰할 수 있었다.

• Wind and Structures
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• 제23권2호
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• pp.109-125
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• 2016

Flow interference is investigated between two tripped cylinders of identical diameter D at stagger angle ${\alpha}=0^{\circ}{\sim}180^{\circ}$ and gap spacing ratio $P^*$ (= P/D) = 0.1 ~ 5, where ${\alpha}$ is the angle between the freestream velocity and the line connecting the cylinder centers, and P is the gap width between the cylinders. Two tripwires, each of diameter 0.1D, were attached on each cylinder at azimuthal angle ${\beta}={\pm}30^{\circ}$, respectively. Time-mean drag coefficient ($C_D$) and fluctuating drag ($C_{Df}$) and lift ($C_{Lf}$) coefficients on the two tripped cylinders were measured and compared with those on plain cylinders. We also conducted surface pressure measurements to assimilate the fluid dynamics around the cylinders. $C_D$, $C_{Df}$ and $C_{Lf}$ all for the plain cylinders are strong function of ${\alpha}$ and $P^*$ due to strong mutual interference between the cylinders, connected to six interactions (Alam and Meyer 2011), namely boundary layer and cylinder, shear-layer/wake and cylinder, shear layer and shear layer, vortex and cylinder, vortex and shear layer, and vortex and vortex interactions. $C_D$, $C_{Df}$ and $C_{Lf}$ are very large for vortex and cylinder, vortex and shear layer, and vortex and vortex interactions, i.e., the interactions where vortex is involved. On the other hand, the interference as well as the strong interactions involving vortices is suppressed for the tripped cylinders, resulting in insignificant variations in $C_D$, $C_{Df}$ and $C_{Lf}$ with ${\alpha}$ and $P^*$. In most of the (${\alpha}$, $P^*$ ) region, the suppressions in $C_D$, $C_{Df}$ and $C_{Lf}$ are about 58%, 65% and 85%, respectively, with maximum suppressions 60%, 80% and 90%.

• Advances in concrete construction
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• 제8권4호
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• pp.285-294
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• 2019

In the present paper, the fiber theory has been employed to model the reinforced concrete (RC) deep beams (DBs) considering the reinforcing steel bar-concrete interaction. To simulate numerically the behavior of materials, the uniaxial materials' constitutive laws have been employed for reinforcements and concrete and the bond stress-slip between the reinforcing steel bars and surrounding concrete are taken into account. Because of the high sensitivity of DBs to shear deformations, the Timoshenko beam theory has been applied. The shear stress-strain (S-SS) relationship has been defined by the modified compression field theory (MCFT) model. By modeling about 300 RC panels and employing a produced numerical database, a study has been carried out to show the sensitivity of the MCFT model. This is performed based on the multiple linear regression (MLR) models. The results of this research also illustrate how different parameters such as characteristic compressive strength of concrete, yield strength of reinforcements and the percentages of reinforcements in different directions get involved in the shear behavior of RC panels without applying complex theories. Based on the results obtained from the analysis of the MCFT S-SS model, a relatively simplified numerical S-SS model has been proposed. Application of the proposed S-SS model in modeling and analyzing the considered samples indicates that there is a good agreement between the simulated and the experimental test results. The comparison between the proposed S-SS model and the MCFT model indicates that in addition to the advantage of better accuracy, the main advantage of the proposed method is simplicity in application.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.671-682
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• 2004

본 연구는 부분 전단연결을 가지는 강-콘크리트 합성보의 처짐에 미치는 전단슬립의 영향을 조사하는 것이다. 현재 각국의 설계규준에서는 합성보의 처짐 계산시 전단연결재의 강도와 관련되어 있지만, 본 연구에서는 하중조건에 상관없는 전단연결재의 강성에 기반을 둔 정확한 해를 유도하였다. 우선, 평형조건, 곡률의 적합조건에 기반을 둔 3가지 하중조건에서의 합성보의 등가강성을 유도하고, 이로부터 하중조건에 상관없이 슬립의 영향을 적용할 수 있는 간편한 제안식을 유도하였다. 이러한 제안식의 타당성을 검증하기 위해서 현재 AISC에서 사용하고 있는 합성보의 유효강성 및 Nie가 제안한 식과 비교하였다. 일반적으로 사용되는 보의 경우, 전단슬립의 영향은 스팬이 짧을 경우, AISC에 비해서 최대 18%까지의 강성의 감소를 나타냄을 알 수 있었다. 완전합성보의 경우, AISC의 제안 값이 본 연구의 결과 보다 크게 나타났는데, 이는 안전측이 되지 못함을 알 수 있었으며, 불완전 합성보의 경우, AISC 제안식이 본 연구보다 강성을 과소 평가하는 결과를 나타내었다.

• Structural Engineering and Mechanics
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• 제40권1호
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• pp.65-84
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• 2011

In this paper a simple mathematical model for approximate static analysis of combined system of framed tube, shear core and two outrigger-belt truss structures subjected to lateral loads is presented. In the proposed methodology, framed tube is modeled as a cantilevered beam with a box section and interaction between shear core and outrigger-belt truss system with framed tube is modeled using torsional springs placed at location of outrigger-belt truss; these torsional springs act in a direction opposite to rotation generated by lateral loads. The effect of shear lag on axial deformation in flange is quadratic and in web it is a cubic function of geometry. Here the total energy of the combined system is minimized with respect to lateral deflection and rotation in plane section. Solution of the resulting equilibrium equations yields the unknown coefficients of shear lag along with the stress and displacement distributions. The results of a numerical example, 50 storey building subjected to three different types of lateral loading obtained from SAP2000 are compared to those of the proposed method and the differences are found to be reasonable. The proposed method can be used during the preliminary design stages of a tall building and can provide a better understanding of the effects of various parameters on the overall structural behavior.

• 한국구조물진단유지관리공학회 논문집
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• 제22권6호
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• pp.30-36
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• 2018

기존 콘크리트 구조물의 노후화 또는 지진과 같은 외부 하중에 의하여 구조물의 구조 성능이 저하되기 때문에, 기존 건물의 보수 및 보강 연구는 중요하다. 외부부착 탄소섬유 보강 공법과 같은 효율적인 보수 공법을 사용하면 경제적으로 콘크리트 구조물의 구조 성능을 높일 수 있다. 따라서 외부부착 탄소섬유를 사용한 콘크리트 부재의 실험 연구는 많이 진행되었다. 특히, 콘크리트 보를 사용한 전단 보강에 관한 연구는 탄소섬유의 양, 부착 각도, 스트립의 폭, 그리고 재료간의 상호작용에 관한 것이었다. 하지만 선행된 연구에 비하여 탄소섬유의 이 방향 레이아웃에 관한 다양한 변수 연구는 부족한 상황이다. 따라서 이 연구에서는 이 방향 레이아웃 외부부착 탄소섬유 공법을 사용하여 콘크리트 보의 전단보강 효과를 검증하였다. 이 방향 레이아웃의 보강 효과는 스터럽과의 전단 기여도, 실험체의 전단 거동과 보강 시점에 따른 최대 내력의 비교를 통하여 이루어졌다.

• Earthquakes and Structures
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• 제24권5호
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• pp.345-352
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• 2023

This paper studied the effect of soil-structure interaction (SSI) on the seismic response and retrofit of a reinforced concrete structure with a soft-first story for different soil types. A 5-story structure built on a 30m deep homogeneous soil mass was considered as a case study structure, and steel column jacketing and steel bracing were chosen as seismic retrofit methods. Seismic responses of a fixed-base and a flexible base structure subjected to seven scaled earthquake records were obtained using the software OpenSees to investigate the effect of soil on seismic response and retrofit. The nonlinearBeamColumn elements with the fiber sections were used to simulate the nonlinear behavior of the beams and columns. Soil properties were defined based on shear wave velocity according to categorized site classes defined in ASCE-7. The finite element model of the soil was made using isoparametric four-noded quadrilateral elements and the nonlinear dynamic responses of the combined system of soil and structure were calculated in the OpenSees. The analysis results indicate that the soil-structure interaction plays an important role in the seismic performance and retrofit of a structure with a soft-first story. It was observed that column steel jacketing was effective in the retrofit of the model structure on a fixed base, whereas stronger retrofit measures such as steel bracing were needed when soil-structure interaction was considered.

• Steel and Composite Structures
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• 제27권1호
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• pp.123-133
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• 2018

Steel-concrete-steel (SCS) sandwich composite structure with corrugated-strip connectors (CSC) has the potential to be used in buildings and offshore structures. In this structure, CSCs are used to bond steel face plates and concrete. To overcome executive problems, in the proposed system by the authors, shear connectors are one end welded as double skin composites. Hence, this system double skin with corrugated-strip connectors (DSCS) is named. In this paper, finite element model (FEM) of push-out test was presented for the basic component of DSCS. ABAQUS/Explicit solver in ABAQUS was used due to the geometrical complexity of the model, especially in the interaction of the shear connectors with concrete. In order that the explicit analysis has a quasi-static behavior with a proper approximation, the kinetic energy (ALLKE) did not exceed 5% to 10% of the internal energy (ALLIE) using mass-scaling. The FE analysis (FEA) was validated against those from the push-out tests in the previous work of the authors published in this journal. By comparing load-slip curves and failure modes, FEMs with suitable analysis speed were consistent with test results.