• Advances in concrete construction
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• v.10 no.1
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• pp.49-59
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• 2020

Precast concrete elements in accelerated bridge construction (ABC) extends from superstructure to substructure, precast pile foundation has proven a benefit for regions with fragile ecological environment and adverse geological condition. There is still a lack of knowledge of the seismic behavior and performance of the precast pile foundation. In this study, a 1/8 scaled model of precast pile foundation with elevated cap is fabricated for quasi-static test. The failure mechanism and responses of the precast pile-soil interaction system are analyzed. It is shown that damage occurs primarily in precast pile-soil interaction system and the bridge pier keeps elastic state because of its relatively large cross-section designed for railways. The vulnerable part of the precast pile with elevated cap is located at the embedded section, but no plastic hinge forms along the pile depth under cyclic loading. Hysteretic curves show no significant strength degradation but obvious stiffness degradation throughout the loading process. The energy dissipation capacity of the precast pile-soil interaction system is discussed by using index of the equivalent viscous damping ratio. It can be found that the energy dissipation capacity decreases with the increase of loading displacement due to the unyielding pile reinforcements and potential pile uplift. It is expected to promote the use of precast pile foundation in accelerated bridge construction (ABC) of railways designed in seismic regions.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.329-345
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• 2017

This paper devoted to study dynamic interaction between crack and inclusion or void by developing the eXtended Finite Element Methods (XFEM). A novel XFEM approximation is presented for these structures containing multi discontinuities (void, inclusion, and crack). The level set methods are used so that elements that include a crack segment, the boundary of a void, or the boundary of an inclusion are not required to conform to discontinuous edges. The investigation covers the effects of a single circular or elliptical void / stiff inclusion, and multi stiff inclusions on the crack propagation path under dynamic loads. Both the void and the inclusion have a significant effect on the dynamic crack propagation path. The crack initially curves towards into the void, then, the crack moves round the void and propagates away the void. If a large void lies in front of crack tip, the crack may propagate into the void. If an enough small void lies in front of crack tip, the void may have a slight or no influence on the crack propagation path. For a stiff inclusion, the crack initially propagates away the inclusion, then, after the crack moves round the inclusion, it starts to propagate along its original path. As ${\delta}$ (the ratio of the elastic modulus of the inclusion to that of the matrix) increases, a larger curvature of the crack path deflection can be observed. However, as ${\delta}$ increases from 2 to 10, the curvature has an evident increase. By comparison, the curvature has a slight increase, as ${\delta}$ increases from 10 to 1000.

• Geotechnical Engineering
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• v.9 no.1
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• pp.7-20
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• 1993

The first Korean earthquake resistant design code was enacted in 1988. In the code, the soil factor which takes into account both the soil amplification factor and the soil -structare interaction effect is divided into three groups : soil factor, 5 : 1.0, 1.2 and 1.5. In order to assist in choosing the soil factors appropriately in the earthquake resistant design, the local site effects on the based shear force induced by earthquakes are considered in depth for typical soil conditions in Korea. The depth of the alluvial and/or weathered zone is usually not deep and the fresh rock is found at depth shallower than 20 meters, and even at about 10 meters around Seoul. One dimensional wave propagation theory and the elastic half space method are used to obtain the soil -structure interaction effect as well as the soil amplification effect. The kinematic interaction effect due to scattering of waves by pile foundation is also considered. Finally, the soil factor is recommended for each soil condition from loose state to dense, and also from shallow soil depth to deep, so that the designer can choose the factor with-out difficulty.

• Structural Engineering and Mechanics
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• v.13 no.6
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• pp.615-638
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• 2002

This paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.1
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• pp.37-45
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• 1990

An analytical procedure is proposed for the seismic analysis of a soil-structure interaction system with besemat uplift, including the effects of concurrent vertical seismic ground motion, nonlinear distribution of bearing soil pressure under the basemat, and 3-dimensional behavior of the system. The soil-structure interaction system is assumed to have rectangular-shaped basemat on elastic half-space. Nonlinearity of soil spring constants and soil damping coefficients induced by the base mat uplift is modeled by considering not only the reduction of contact area between soil and structure but also the effects of rigid body rotational motion of the superstructure, and the shift in the point of action of the resultant reaction on the basemat. Throught various parametric studies. it has been confirmed that the seismic responses of the superstructure reduce notably while response at the basemat increases considerably. The results also show that the effects of concurrent vertical ground motion. nonlinear soil pressure distribution under basemat, and 3-dimensional behavior of the system shall be included in uplift analysis in order to obtain the correct structural responses.

• Structural Engineering and Mechanics
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• v.61 no.3
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• pp.407-417
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• 2017

RC shear walls are considered one of the main lateral resisting members in buildings. In recent years, FRP has been widely utilized in order to strengthen and retrofit concrete structures. A number of experimental studies used CFRP sheets as an external bracing system for retrofitting of RC shear walls. It has been found that the common mode of failure is the debonding of the CFRP-concrete adhesive material. In this study, behavior of RC shear wall was investigated with three different micro models. The analysis included 2D model using plane stress element, 3D model using shell element and 3D model using solid element. To allow for the debonding mode of failure, the adhesive layer was modeled using cohesive surface-to-surface interaction model at 3D analysis model and node-to-node interaction method using Cartesian elastic-plastic connector element at 2D analysis model. The FE model results are validated comparing the experimental results in the literature. It is shown that the proposed FE model can predict the modes of failure due to debonding of CFRP and behavior of CFRP strengthened RC shear wall reasonably well. Additionally, using 2D plane stress model, many parameters on the behavior of the cohesive surfaces are investigated such as fracture energy, interfacial shear stress, partial bonding, proposed CFRP anchor location and using different bracing of CFRP strips. Using two anchors near end of each diagonal CFRP strips delay the end debonding and increase the ductility for RC shear walls.

• Journal of the Korean Geotechnical Society
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• v.34 no.7
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• pp.29-38
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• 2018

Three-dimensional continuum modeling of dynamic soil-pile-structure interaction embedded in a liquefiable sand was carried out. Finn model which can model liquefaction behavior using effective stress method was adopted to simulate development of pore water pressure according to shear deformation of soil directly in real time. Finn model was incorporated into Non-linear elastic, Mohr-Coulomb plastic model. Calibration of proposed modeling method was performed by comparing the results with those of the centrifuge tests performed by Wilson (1998). Excess pore pressure ratio, pile bending moment, pile head displacement-time history according to depth calculated by numerical analysis agreed reasonably well with the test results. Validation of the proposed modeling method was later performed using another test case, and good agreement between the computed and measured values was observed.

• Elastomers and Composites
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• v.20 no.1
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• pp.25-39
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• 1985

Elastomer-filler interaction in terms of characterization of filler effects was studied using natural rubber(NR) loaded with kaolin fillers modified with sodium polyphosphate and poly(maleic anhydride), respectively. Kaolins modified with sodium polyphosphate or poly(maleic anhydride) show adhering characteristics by Kraus plot. Reinforcement activity according to Cunneen-Russell method is given by those fillers, in which sodium polyphosphate-treated kaolin presents more favorable results than that treated with poly(maleic anhydride) with respect to adhesion constant, reinforcement extent, elastic constant, and crosslink density. When applied to Blanchard's linkage reinforcement theory, NR vulcanizates loaded with kaolin modified with sodium polyphosphate meet the requirements for both approximate linkage reinforcement(${\psi}'$) of 1.02 to 4.94 and accurate linkage reinforcement($\psi$) of 1.00 to 1.18, representing the values of effective wetting($C_{\psi}$) for 0.001 to 0.029 and intrinsic linkage reinforcement(${\psi}_0$) for 1.015 to 1.124, respectively, whille negligible linkage reinforcement is shown by NR vulcanizates loaded with kaolin treated with poly(maleic anhydride). Dynamic storage modulus(G') given by surface modified kaolins presents more favorable crosslink density rates of $2.260{\times}10^{-5}\;mole/cm^3-min$. for sodium polyphosphate treated kaolin and $1.305{\times}10^{-5}\;mole/cm^3-min$. for poly(maleic anhydride) treated kaolin, respectively, compared to untreated kaolin showing the rate of $1.033{\times}10^{-5}\;mole/cm^3-min$.

• International journal of steel structures
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• v.18 no.5
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• pp.1617-1630
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• 2018

The crucial differences between conventional rail with split-type connectors and continuous welded rails are axial stress in the longitudinal direction and stability, as well as other issues generated under the influence of loading effects. Longitudinal stresses generated in continuously welded rails on railway bridges are strongly influenced by the nonlinear behavior of the supporting system comprising sleepers and ballasts. Thus, the track structure interaction cannot be neglected. The rail-support system mentioned above has properties of non-uniform material distribution and uncertainty of construction quality. The linear elastic hypothesis therefore cannot correctly evaluate the stress distribution within the rails. The aim of this study is to apply the nonlinear finite element method using the nonlinear coupling interface between the track and structural model and to illustrate the welded rail behavior under the loading effect and uncertain factors of the ballast. Numerical results of nonlinear finite analysis with a three-dimensional solid and frame element model are presented for a typical track-bridge system. A composite plate girder, modeled by solid and shell elements, is also analyzed to consider the behavior of the welded rail. The analysis result showed buckling under the independent calculations of load cases, including 'temperature change', 'bending of the supporting structure', and 'braking' of the railway vehicle. A parametric study of the load combination method and the loading sequence is also included in this analysis.

• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.499-507
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• 2003

As the load is increased on the steel-concrete composite structure, its interface begins to show nonlinear behavior due to the reduction of interaction, micro-crack, slip and separation, and it causes slip-softening, Therefore, it is essential to consider the partial-interaction analysis technique. Until now, however, full-interaction or, in some instances, the linear-elastic model, which are insufficient to simulate accurate behavior, are assumed in the analysis of composite structure since the analysis method and nonlinear model for interface are very difficult and complicated. Therefore, the design of composite structure is followed by the experimental method which is inefficient-because a number of tests have to be carried out according to the design environments. In this study, we carried out the nonlinear analysis according to various interface nonlinear models by interaction magnitude, and analyzed more accurate structural behavior and performance by maximum tangential traction and slip-softening at the interface. As a result of this study. we were able to prove that the nonlinear model of interface more exactly represents behavior after yielding, such as ultimate load: that initial tangential stiffness of interface has a significant effect on the yielding load of structural members or part: and that the maximum tangential traction and slip-softening mainly effects structural yielding and ultimate load. Therefore, the structural performance of composite structure is highly dependent on the steel-concrete interface or interaction, which may result in initial tangential stiffness, maximum tangential traction and slip-softening in nonlinear model.