• Geomechanics and Engineering
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• v.13 no.3
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• pp.489-504
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• 2017

The localized shear and the slip lines are easily observed in elastic-brittle-plastic rock. After yielding, the strength of the brittle rock suddenly drops from the peak value to the residual value, and there are slip lines which divide the macro rock into numbers of elements. There are slippages of elements along the slip lines and the displacement field in the plastic region is discontinuous. With some restraints, the discontinuities can be described by the combination of two smooth functions, one is for the meaning of averaging the original function, and the other is for characterizing the breaks of the original function. The slip lines around the circular opening in the plastic region of an isotropic H-B rock which subjected to a hydrostatic in situ stress can be described by the logarithmic spirals. After failure, the deformation mechanism of the plastic region is mainly attributed to the slippage, and a slippage parameter is introduced. A new analytical solution is presented for the plane strain analysis of displacements around circular openings. The displacements obtained by using the new solution are found to be well coincide with the exact solutions from the published sources.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.20-27
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• 2021

The present study presents a nonlinear finite element analysis (FEA) approach using the general program of Abaqus to evaluate the seismic response of unreinforced masonry walls strengthened with the steel bar truss system developed in the previous investigation. For finite element models of masonry walls, the concrete damaged plasticity (CDP) and meso-scale methods were considered on the basis of the stress-strain relationships under compression and tension and shear friction-slip relationship of masonry prisms proposed by Yang et al. in order to formulate the interface characteristics between brick elements and mortars. The predictions obtained from the FEA approach were compared with test results under different design parameters; as a result, a good agreement could be observed with respect to the crack propagation, failure mode, rocking strength, peak strength, and lateral load-displacement relationship of masonry walls. Thus, it can be stated that the proposed FEA approach shows a good potential for designing the seismic strengthening of masonry walls.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.3
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• pp.103-110
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• 2021

A shake table test is conducted for the three-story reinforced concrete building structure using 0.28 g, 0.5 g, 0.75 g, and 1.0 g of seismic input motions based on the Gyeongju earthquake. Computational efforts are made in parallel to explore the mechanical details in the structure. For engineering practice, the elastic modulus of concrete and rebar in the dynamic analysis is reduced to 38% and 50%, respectively, to calibrate the structure's natural frequencies. The engineering approach to the reduced modulus of elasticity is believed to be due to the inability to specify the flexibility of the actual boundary conditions. This aspect may lead to disadvantages of nonlinear dynamic analysis that can distort local stress and strain relationships. The initial elastic modulus can be applied directly without the so-called engineering adjustment with infinite element models with spring and spring-dashpot boundary conditions. This has the advantage of imposing the system flexibility of the structure on the sub-boundary conditions of springs and damping devices to control its sensitivity in a serial arrangement. This can reflect the flexibility of realistic boundary conditions and the effects of system damping (such as the gap between a concrete footing and shake table, loosening of steel anchors, etc.) in scalar quantities. However, these spring and dashpot coefficients can only be coordinated based on experimental results, making it challenging to select the coefficients in-prior to perform an experimental test.

• Journal of the Korean Geosynthetics Society
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• v.18 no.2
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• pp.11-21
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• 2019

This paper describes the applicability of FEA(Finite Element Analysis) to the simulation of pile pullout behavior under various soil conditions (relative density and fines content), in order to evaluate reasonably the pullout resistance of pile. That is, the results of previous research (You et al., 2018) were analyzed by FEA under the same conditions. The FEA results showed that axisymmetric analysis using virtual ground was able to evaluate the skin friction of the pile. Also, axisymmetric analysis, which can apply the shear resistance characteristics of the pile-soil interface in various soil conditions, could be used as an analytical method that can simulate a reasonable pile pullout behavior. Therefore, the analytical model proposed in this study was able to simulate appropriately the pullout behavior based on the stress-strain relationship of the pile-soil interface.

• Structural Engineering and Mechanics
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• v.72 no.3
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• pp.355-366
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• 2019

Self-centering wall (SCW) is a resilient and sustainable structural system which incorporates unbonded posttensioning (PT) tendons to provide self-centering (SC) capacity along with supplementary dissipators to dissipate seismic energy. Hysteretic energy dissipators are usually placed at two sides of SCWs to facilitate ease of postearthquake examination and convenient replacement. To achieve a good prediction for the skeleton curve of the wall, this paper firstly developed an analytical investigation on lateral load responses of self-centering walls with distributed vertical dampers (VD-SCWs) using the concept of elastic theory. A simplified method for the calculation of limit state points is developed and validated by experimental results and can be used in the design of the system. Based on the analytical results, parametric analysis is conducted to investigate the influence of damper and tendon parameters on the performance of VD-SCWs. The results show that the proposed approach has a better prediction accuracy with less computational effects than the Perez method. As compared with previous experimental results, the proposed method achieves up to 60.1% additional accuracy at the effective linear limit (DLL) of SCWs. The base shear at point DLL is increased by 62.5% when the damper force is increased from 0kN to 80kN. The wall stiffness after point ELL is reduced by 69.5% when the tendon stiffness is reduced by 75.0%. The roof deformation at point LLP is reduced by 74.1% when the initial tendon stress is increased from $0.45f_{pu}$ to $0.65f_{pu}$.

• Computers and Concrete
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• v.24 no.2
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• pp.103-115
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• 2019

In this study, the strength and stiffness (EI) of wood-concrete composite beams for bridges with T-shaped cross section were evaluated. Two types of connectors were used: connectors bonded with epoxy adhesive and connectors attached to the wood just by pre-drilling (without adhesive). The connectors consisted of common steel bars with a diameter of 12.5 mm. Initially, the strength and stiffness (EI) of the beams were analyzed by bending tests with the load applied at the third point of the beam. Subsequently, the composite beams were evaluated by numerical simulation using ANSYS software with focus on the connection system. To make the composite beams, Eucalyptus citriodora wood and medium strength concrete were used. The slip modulus K and the ultimate strength values of each type of connector were obtained by direct shear tests performed on composite specimens. The results showed that the connector glued with epoxy adhesive resulted in better strength and stiffness (EI) for the composite beams when compared to the connector fixed by pre-drilling. The differences observed were up to 10%. The strength and stiffness (EI) values obtained analytically by $M{\ddot{o}}hler^{\prime}$ model were lower than the values obtained experimentally from the bending tests, and the differences were up to 25%. The numerical simulations allowed, with reasonable approximation, the evaluation of stress distributions in the composite beams tested experimentally.

• Journal of the Korean GEO-environmental Society
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• v.20 no.3
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• pp.39-46
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• 2019

The liquefaction is a phenomenon that the effective stress becomes zero due to the rapidly accumulated excess pore water pressure when a strong load acts on the ground for a short period of time, such as an earthquake or pile driving, resulting in the loss of the shear strength of the ground. Since the Geongju and Pohang earthquake, liquefaction brought increasing domestic attention. This liquefaction can be assessed mainly through the semi-empirical procedures proposed by Seed and Idriss (1982) and the liquefaction risk based on the penetration resistance obtained from borehole DB and SPT. However, the geotechnical information data obtained by the in-situ tests or boring information fundamentally have an issue of the representative of the target area. Therefore, this study sought to construct a ground information database by classifying and reviewing the ground information required for liquefaction assessment, and tried to solve the representative problem of the soil layer that is subject to liquefaction evaluation by performing spatial interpolation using GIS.

• International journal of steel structures
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• v.18 no.4
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• pp.1440-1463
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• 2018

The Wagner coefficient is a key parameter used to describe the inelastic lateral-torsional buckling (LTB) behaviour of the I-beam, since even for a doubly-symmetric I-section with residual stress, it becomes a monosymmetric I-section due to the characteristics of the non-symmetrical distribution of plastic regions. However, so far no theoretical derivation on the energy equation and Wagner's coefficient have been presented due to the limitation of Vlasov's buckling theory. In order to simplify the nonlinear analysis and calculation, this paper presents a simplified mechanical model and an analytical solution for doubly-symmetric I-beams under pure bending, in which residual stresses and yielding are taken into account. According to the plate-beam theory proposed by the lead author, the energy equation for the inelastic LTB of an I-beam is derived in detail, using only the Euler-Bernoulli beam model and the Kirchhoff-plate model. In this derivation, the concept of the instantaneous shear centre is used and its position can be determined naturally by the condition that the coefficient of the cross-term in the strain energy should be zero; formulae for both the critical moment and the corresponding critical beam length are proposed based upon the analytical buckling equation. An analytical formula of the Wagner coefficient is obtained and the validity of Wagner hypothesis is reconfirmed. Finally, the accuracy of the analytical solution is verified by a FEM solution based upon a bi-modulus model of I-beams. It is found that the critical moments given by the analytical solution almost is identical to those given by Trahair's formulae, and hence the analytical solution can be used as a benchmark to verify the results obtained by other numerical algorithms for inelastic LTB behaviour.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.366-372
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• 2021

Cadherin-Catenin complex is thought to play an essential role in the transmission of force at adherens junction. Due to the lack of proper tools to visualize and detect mechanical force signals, the underlying mechanism by which the cadherin-catenin complex regulates force transmission at intercellular junctions remains elusive. In this study, we visualize cadherin-mediated force transmission using an engineered α-Catenin sensor based on fluorescence resonance energy transfer. Our results reveal that α-catenin is a key force transducer in cadherin-mediated mechanotransduction at cell-cell junctions. Thus, our finding will provide important insights for studying the effects of chemical and physical signals on cell-cell communication and the relationship between physiological and pathological phenomena.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1119-1126
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• 2021

Spacer grid with mixing vane had been widely used in nuclear reactor core. One of the main feather of spacer grid with mixing vane was that strong swirl flow was formed after the spacer grid. The swirl flow not only changed the bubble generation in the near wall field, but also affected the bubble behaviors in the center region of the subchannel. The interaction between bubble and the swirl flow was one of the basic phenomena for the two phase flow modeling in fuel assembly. To obatin better understanding on the bubble behaviors in swirl flow, full three dimension numerical simulations were conducted in the present paper. The swirl flow was assumed in the cylindral calculation domain. The bubble interface was captured by Volume Of Fluid (VOF) method. The properties of saturated water and steam at different pressure were applied in the simulation. The bubble trajectory, motion, shape and force were obtained based on the bubble parameters captured by VOF. The simulation cases in the present study included single bubble with different size, at different angular velocity conditions and at different pressure conditions. The results indicated that bubble migrated to the center in swirl flow with spiral motion type. The lateral migration was mainly related to shear stress magnitude and bubble size. The bubble moved toward the center with high velocity when the swirl magnitude was high. The largest bubble had the highest lateral migration velocity in the present study range. The effect of pressure was small when bubble size was the same. The prelimenery simulation result would be beneficial for better understanding complex two phase flow phenomena in fuel assembly with spacer grid.