• Geophysics and Geophysical Exploration
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• v.15 no.2
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• pp.92-101
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• 2012

Three-dimensional finite-difference simulation in a small-scale half-sphere basin with planar free-surface is performed for an arbitrary shear-dislocation point source. A new scheme to deal with free-surface boundary condition is presented. Then basin parameters are examined to understand main characteristics on ground-motion response in the basin. To analyze the frequency content of ground motion in the basin, spectral amplitudes are compared with each other for four sites inside and outside the basin. Also particle motions for those sites are examined to find which kind of wave plays a dominant role in ground-motion response. The results show that seismic energy is concentrated on a marginal area of the basin far from the source. This focusing effect is mainly due to constructive interference of the direct Swave with basin-edge induced surface waves. Also, ground-motion amplification over the deepest part of the basin is relatively lower than that above shallow basin edge. In the small-scale basin with relatively simple bedrock interface, therefore, the ground-motion amplification may be more related to the source azimuth or direction of the incident waves into the basin rather than depth of it.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.153-163
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• 2005

This paper presents two case studies for tunnelling in Bangkok: a subway tunnel site and a flood diversion tunnel site. The first case study is related to ground displacement response for dual tunnel Bangkok MRT subway. The MRT subway project of Bangkok city consists of dual tunnels about 20 km long with 18 subway stations. The tunnels are seated in the firm first stiff silty clay layer between 15-22 m in depth below ground surface. The behavior of ground deformation response based on instrumentation is presented. The back analysis based on plain strain FEM analysis is also presented and agrees with field performance. The shear strain of FEM analysis is in the range of 0.1-1% and in accordance with the results of self boring pressuremeter tests. Meanwhile, the second case study is related to the EPB tunnelling bored underneath through underground obstruction. The Premprachakorn flood diversion tunnel is the shortcut tunnel to divert the flood water in rainy season into the Choapraya river. The tunnel was bored by means of EPB shield tunnelling in very stiff silty clay layer at about 20-24 m in depth. During flood diversion tunnel bored underneath the existing Bangkok main water supply tunnel and pile foundation of the bridge, instrumentation was monitored and compared with predicted FEM analysis. The prevention risk potential by means of predicting damage assessment is also presented and discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.419-427
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• 2006

In this paper, an experimental real-time hybrid method, which implements the earthquake response control of a building structure with a TLD(Tuned Liquid Damper) by using only a TLD as an experimental part, is proposed and is experimentally verified through a shaking table test. In the proposed methodology, the whole building structure with a TLD is divided into the upper TLD and the lower structural parts as experimental and numerical substructures, respectively. The control force acting between their interface is measured with a shear-type load-cell which is mounted on the shaking table. The shaking table vibrates the upper experimental TLD with the response calculated from the numerical substructure, which is subjected to the excitations of the measured interface control force at its top story and an earthquake input at its base. The experimental results show that the conventional method, in which both a TLD and a building structure model are physically manufactured and are tested, can be replaced by the proposed methodology with a simple experimental installation and a good accuracy for evaluating the control performance of a TLD.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.335-344
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• 2019

Micropiles are widely used for foundation underpinning to enhance bearing capacity and reduce settlement of existing foundation. In this study, the main objective is to evaluate underpinning performance of a newly developed micropile called waveform micropile for foundation underpinning during vertical extension. Finite element method (FEM) was used to evaluate the underpinning performance of waveform micropile in terms of load-settlement response of underpinned foundation and load sharing behavior. For comparison, underpinning effects of three conventional micropiles with different lengths were also discussed in this study. Numerical results of load-settlement response for single pile demonstrated that bearing capacity and axial stiffness of waveform micropiles were higher than those of conventional micropiles because of the effect of shear keys of waveform micropiles. When additional loads 20 %, which is according to design loads of the vertical extension, were applied to the underpinned foundation, load sharing capacity of waveform micropile was 40 % higher than conventional micropile at the same size. The waveform micropile also showed better underpinning performance than the conventional micropile of length 1~1.5 times of waveform micropile.

• Structural Engineering and Mechanics
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• v.90 no.6
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• pp.551-568
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• 2024

The present study deals with static and dynamic behaviors including forced vibrations of an elastic rectangular nano plate on the two-parameter foundation. Firstly, the rectangular plate is assumed to be subjected to uniformly distributed and eccentrically applied concentrated loads. The governing equations of the problem are derived by considering the dynamic response of the plate, employing a series of the Chebyshev polynomials for the displacement function and applying the Galerkin method. Then, effects of the non-essential boundary conditions of the plate, i.e., the boundary conditions related to the shearing forces, the bending moments and the corner forces, are included in the governing equation of motion to compensate for the non-satisfied boundary conditions and increase the accuracy of the Galerkin method. The approximate numerical solution is accomplished using an iterative process due to the non-linearity of the unilateral property of the two-parameter foundation. The plate under static concentrated load is investigated in detail numerically by considering a wide range of parameters of the plate and the foundation stiffnesses. Numerical treatment of the problem in the time domain is carried out by assuming a stepwise variation of the concentrated load and the linear acceleration procedure is employed in the solution of the system of governing differential equations derived from the equation of motion. Time variations of the contact region and those of the displacements of the plate are presented in the figures for various numbers of the two-parameter of the foundation, as well as the classical and nano parameters of the plate particularly focusing on the non-linearity of the problem due to the plate lift-off from the unilateral foundation. The effects of classical and nonlocal parameters and loading are investigated in detail. Definition of the separation between the plate and the two-parameter foundation is presented and applied to the given problem. The effect of the lift-off on the static and dynamic behavior of the rectangular plate is studied in detail by considering various loading conditions. The numerical study shows that the effect of nonlocal parameters on the behavior of the plate becomes significant, when nonlinearity becomes more profound, due to the lift-off of the plate. It is seen that the size effects are significant in static and dynamic analysis of nano-scaled rectangular plates and need to be included in the mechanical analyses. Furthermore, the corner displacement of the plate is affected more significantly from the lift-off, whereas it is less marked in the time variation of the middle displacement of the plate. Several numerical examples are presented to examine the sensibility of various parameters associated with nonlocal parameters of the plate and foundation. Both stiffening and softening nonlocal parameters behavior of the plate are identified in the numerical solutions which show that increasing the foundation stiffness decreases the extent of the contact region, whereas the stiffness of the shear layer increases the contact region and reduces the foundation settlement considerably.

• Steel and Composite Structures
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• v.50 no.6
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• pp.705-720
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• 2024

Analyzing the collapse behavior of thin-walled steel structures holds significant importance in ensuring their safety and longevity. Geometric imperfections present on the surface of metal materials can diminish both the durability and mechanical integrity of steel shells. These imperfections, encompassing local geometric irregularities and deformations such as holes, cavities, notches, and cracks localized in specific regions of the shell surface, play a pivotal role in the assessment. They can induce stress concentration within the structure, thereby influencing its susceptibility to buckling. The intricate relationship between the buckling behavior of these structures and such imperfections is multifaceted, contingent upon a variety of factors. The buckling analysis of thin-walled steel shell structures, similar to other steel structures, commonly involves the determination of crucial material properties, including elastic modulus, shear modulus, tensile strength, and fracture toughness. An established method involves the emulation of distributed geometric imperfections, utilizing real test specimen data as a basis. This approach allows for the accurate representation and assessment of the diversity and distribution of imperfections encountered in real-world scenarios. Utilizing defect data obtained from actual test samples enhances the model's realism and applicability. The sizes and configurations of these defects are employed as inputs in the modeling process, aiding in the prediction of structural behavior. It's worth noting that there is a dearth of experimental studies addressing the influence of geometric defects on the buckling behavior of cylindrical steel shells. In this particular study, samples featuring geometric imperfections were subjected to experimental buckling tests. These same samples were also modeled using Finite Element Analysis (FEM), with results corroborating the experimental findings. Furthermore, the initial geometrical imperfections were measured using digital image correlation (DIC) techniques. In this way, the response of the test specimens can be estimated accurately by applying the initial imperfections to FE models. After validation of the test results with FEA, a numerical parametric study was conducted to develop more generalized design recommendations for the stainless-steel shell structures with the initial geometric imperfection. While the load-carrying capacity of samples with perfect surfaces was up to 140 kN, the load-carrying capacity of samples with 4 mm defects was around 130 kN. Likewise, while the load carrying capacity of samples with 10 mm defects was around 125 kN, the load carrying capacity of samples with 14 mm defects was measured around 120 kN.

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.97-107
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• 2003

To obtain a more accurate response from larninated composite structures, the effect of transverse shear deformation, transverse normal strain/stress, and nonlinear variation of in-plane displacements vis-$\\grave{a}$-vis the thickness coordinate should be considered in the analysis. The improved higher-order theory was used to determine the critical buckling load and natural frequencies of laminated composite structures. Solutions of simply supported laminated composite plates and sandwiches were obtained in closed form using Navier's technique, with the results compared with calculated results using the first order and other higher-order theories. Numerical results were presented for fiber-reinforced laminates, which show the effects of ply orientation, number of layers, side-toithickness ratio, and aspects ratio.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.2
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• pp.79-89
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• 1997

The objective of this paper is to investigate the mechanical characteristics of the laminated rubber bearings (LRBs) for the seismic isolation. The evaluations of the proposed equations of the LRB horizontal stiffness are carried out and these equations are extended to the visco-elastic problems to investigate the damping amplifications of LRBs. The stability evaluation of LRBs is also performed. For investigation of the dynamic characteristics of LRBs, the horizontal stiffness equations of the LRBs considering the P-delta effects are applied to the modeling of a seismically isolated structure and the earthquake response time history analyses are carried out. From this research, the proposed simple equation of the horizontal stiffness of LRB is so useful for the design loads and easily extended to the visco-elastic problems. Through the stability evaluation of LRB, the increasing ratio of the total rubber thickness of the LRB severely decrecises the bucking load than the increasing ratio of unit rubber thickness. From the comparison of the dynamic shear deflection of LRB, the analysis results are in good agreement with those of the experiments.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.81-92
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• 2013

The objective of conventional seismic design is to ensure an acceptable safety level while avoiding catastrophic failures of structures and loss of life. Over the last many years, a large amount of research has been devoted into developing effective earthquake resistant systems in order to raise the seismic performance level of structures. The purpose of this study is to propose a new damping system, which realize not only increasing seismic performance but also easy repairing after an earthquake. The proposed damping system is slit in the bottom of wall with damping devices installed in the slit horizontally aiming to dissipate energy during earthquakes. Cyclic loading tests were conducted to investigate hysteretic behavior and energy dissipation capacity. Test results show that the proposed systems exhibit a stable hysteretic response and the energy dissipation in this system is concentrated on the damping devices.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.309-316
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• 2015

A state-based peridynamic model is able to describe a general constitutive model from the standard continuum theory. The response of a material at a point is dependent on the deformation of all bonds connected to the point within the nonlocal horizon region. Therefore, the state-based peridynamic model permits both the volume and shear changes of the material which is promising to reproduce the complicated dynamic brittle fracture phenomena, such as crack branching, secondary cracks, cascade cracks, crack coalescence, etc. In this paper, the two-dimensional state-based peridynamic model for a linear elastic plane stress solid is employed. The damage model incorporates the energy release rate and the peridynamic energy potential. For brittle glass materials, the impact of the crack-parallel compressive stress waves on the crack branching pattern is investigated. The peridynamic solution for this problem captures the main features, observed experimentally, of dynamic crack propagation and branching. Cascade cracks under strong tensile loading and secondary cracks are also well reproduced with the state-based peridynamic simulations.