• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.60-66
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• 2006

Three differing sandstones, two synthetic and one field sample, have been tested ultrasonically under a range of confining pressures and pore pressures representative of in-situ reservoir pressures. These sandstones include: a synthetic sandstone with calcite intergranular cement produced using the CSIRO Calcite In-situ Precipitation Process (CIPS); a synthetic sandstone with silica intergranular cement; and a core sample from the Otway Basin Waarre Formation, Boggy Creek 1 well, from the target lithology for a trial $CO_2$ pilot project. Initial testing was carried on the cores at "room-dried" conditions, with confining pressures up to 65 MPa in steps of 5 MPa. All cores were then flooded with $CO_2$, initially in the gas phase at 6 MPa, $22^{\circ}C$, then with liquid-phase $CO_2$ at a temperature of $22^{\circ}C$ and pressures from 7 MPa to 17 MPa in steps of 5 MPa. Confining pressures varied from 10 MPa to 65 MPa. Ultrasonic waveforms for both P- and S-waves were recorded at each effective pressure increment. Velocity versus effective pressure responses were calculated from the experimental data for both P- and S-waves. Attenuations $(1/Q_p)$ were calculated from the waveform data using spectral ratio methods. Theoretical calculations of velocity as a function of effective pressure for each sandstone were made using the $CO_2$ pressure-density and $CO_2$ bulk modulus-pressure phase diagrams and Gassmann effective medium theory. Flooding the cores with gaseous phase $CO_2$ produced negligible change in velocity-effective stress relationships compared to the dry state (air saturated). Flooding with liquid-phase $CO_2$ at various pore pressures lowered velocities by approximately 8% on average compared to the air-saturated state. Attenuations increased with liquid-phase $CO_2$ flooding compared to the air-saturated case. Experimental data agreed with the Gassmann calculations at high effective pressures. The "critical" effective pressure, at which agreement with theory occurred, varied with sandstone type. Discrepancies are thought to be due to differing micro-crack populations in the microstructure of each sandstone type. The agreement with theory at high effective pressures is significant and gives some confidence in predicting seismic behaviour under field conditions when $CO_2$ is injected.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.5
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• pp.53-58
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• 2002

A recent development, a concrete-filled steel(CFS) pier is an alternative to a reinforced concrete bridge pier in an urban area, because of its fast construction and excellent ductility against earthquakes. The capacity of CFS piers has not been used to a practical design, because there is no guide of a seismic design for CFS piers. Therefore, the guide of a seismic design value is derived from tests of CFS piers in order to apply it to a practical seismic design. Steel piers and concrete-filled steel piers are tested with constant axial load using quasi-static cyclic lateral load to check ductile capacity and using the real Kobe ground motion of pseudo-dynamic test to verify seismic performance. The results prove that CFS piers have more satisfactory ductility and strength than steel piers and relatively large hysteretic damping in dynamic behaviors. The seismic performance of steel and CFS piers is quantified on the basis of the test results. These results are evaluated through comparison of both the response modification factor method by elastic response spectrum and the performance-based design method by capacity spectrum and demand spectrum using effective viscous damping. The response modification factor of CFS piers is presented to apply in seismic design on a basis of this evaluation for a seismic performance.

• Journal of the Korean Geotechnical Society
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• v.34 no.2
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• pp.55-63
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• 2018

In order to support the load of the train with enough stiffness, a study on an effective method for the characterization of the stiffness of the compacted subgrade is required. In this study, the crosshole-type dynamic cone penetrometer (CDCP) is used for the stiffness characterization of the subgrade along the depth. For the application of the CDCP test, three points of compacted subgrades are selected as the study sites. For the study sites, CDCP test, in-situ density test, and light falling weight deflectometer (LFWD) test are conducted. As the results of CDCP tests, shear wave velocity profiles are obtained by using the travel times and the travel distances of the shear waves along the depth. In addition, maximum shear modulus ($G_{max}$) profiles are estimated by using the density of the subgrades and the shear wave velocity profiles. The averaged maximum shear moduli at each testing point are highly correlated with the dynamic deflection moduli ($E_{vd}$) determined by LFWD tests. Therefore, a reliable stiffness characterization of the subgrade can be conducted by using CDCP tests. In addition, because CDCP characterizes the stiffness of the subgrade along the depth rather than a representative value, CDCP test may be effectively used for the stiffness characterization of the subgrade.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.16-24
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• 2009

In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.141-144
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• 2008

Deflection in terms of serviceability of reinforced concrete structures is considered as one of significant factor. Domestic concrete specification offers a procedure to evaluate deflection using effective moment of inertia at cracked section, which has been known as Branson's equation in ACI. Branson's equation was derived from statistical analysis of maximum deflection of flexural members, but is somewhat weak in no reflection of bond characteristics between reinforced bars and concrete, such as tension stiffening effect. Therefore, present code creates difference from actual deflection. In this study, experiments about deflection of RC beams was completed to compare domestic standard and Eurocode 2, which calculates deflection considering tension stiffening effect. Four RC beams were built and tested, and initial modulus of elasticity and tensile strength of concrete used in the test was calculated by each design standard.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.519-525
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• 2009

In this study a cohesive zone model was used to simulate the delamination phenomena which occurs by a successive crack initiation and propagation in composite laminates. The cohesive zone model was incorporated to the classical finite element method via cohesive element formulation and then implemented into the user-subroutine UEL of a commercial finite element program Abaqus. To validate the formulation and implementation of the cohesive element the finite element results were compared with the experimental data of double cantilever beam and end notched flexure tests. The numerical results well agree with the experimental load-displacement curves. Also the effect of the elastic stiffness and the size of the cohesive element on the global load-displacement curves were studied numerically. To minimize the mesh-dependency of the crack propagation path and eliminate the zig-zag patterns in the load-displacement curve, cohesive elements should be refined at the crack-tip.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.820-830
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• 1989

The tire inflation and contact problem has been solved by a finite element method. The finite element formulation is derived from the equilibrium equations by the principle of virtual work in the form of an updated Lagrangian formulation for incremental analysis. Then, a contact formulation is added to the finite element formulation to calculate stress state of tire in contact with flat rigid road under the load due to the self-weight of a vehicle. In the finite element analysis, equations of effective material properties are introduced to analyze a plane strain model of the shell-like tire by considering the bending effect of reinforced steel cords. The proposed equations of effective material properties produced stress concentration around the edge of belt layers, which does not appear when other well-known equations of material properties are adopted. The result from the above algorithm demonstrates the validity of the formulation and the proposed equations for the effective elastic constants. The result fully interprets the cause of separation between belt layers by showing the stress concentration.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.469-475
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• 2010

In this study, the interfacial bond strength of a squeeze infiltrated $Al_{18}B_{4}O_{33}$/AS52 Mg composite was investigated by using a finite element method. Three types of Mg composites with volume fractions of 15, 25 and 35% were fabricated. Three-dimensional models of the composite were developed by using a unit cell model in order to determine the effective elastic modulus of the metal matrix composite and the interfacial bond strength between the whisker and magnesium matrix. After modeling, numerical results were compared with the experimental tensile test results of $Al_{18}B_{4}O_{33}$/AS52 Mg composites. The results showed that the effective modulus of the composite strongly depended on the interfacial strength between the matrix and reinforcement. Based on the numerical and experimental findings, it was found that the strong interfacial bond was achieved by the interfacial reaction product of 30 nm thick MgO, which led to an improvement in the mechanical properties of the $Al_{18}B_{4}O_{33}$/AS52 Mg composites.