• International Journal of High-Rise Buildings
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• v.1 no.4
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• pp.311-332
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• 2012

Earthquake response of mid-rise to high-rise buildings provided with friction dampers is investigated. The steel buildings are modelled as shear-type structures and the investigation involved modelling of the structures of varying heights ranging from five storeys to twenty storeys, in steps of five storeys, subjected to real earthquake ground motions. Three basic types of structures considered in the study are: moment resisting frame (MRF), braced frame (BF), and friction damper frame (FDF). Mathematical modelling of the friction dampers involved simulation of the two distinct phases namely, the stick phase and the slip phase. Dynamic time history analyses are carried out to study the variation of the top floor acceleration, top floor displacement, storey shear, and base-shear. Further, energy plots are obtained to investigate the energy dissipation by the friction dampers. It is seen that substantial earthquake response reduction is achieved with the provision of the friction dampers in the mid-rise and high-rise buildings. The provision of the friction dampers always reduces the base-shear. It is also seen from the fast Fourier transform (FFT) of the top floor acceleration that there is substantial reduction in the peak response; however, the higher frequency content in the response has increased. For the structures considered, the top floor displacements are lesser in the FDF than in the MRF; however, the top floor displacements are marginally larger in the FDF than in the BF.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.705-712
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• 2000

In this study, the dispersion stability of CeO2 based complex oxide was studied, and density, porosity, and microstructure of green body were investigated using colloid surface chemistry to manufacture the Gd2O3 doped CeO2 solid electrolyte in an aqueous system. To prepare the stable slurry for slip casting, the dispersion stability was examined as a function of pH using ESA(electrokinetic sonic anplitude) analysis. The dynamic mobility of particles was enhanced with anionic and cationic dispersant were added the amount of 0.5wt% respectively, but pH value in slurries didn't move to below 6.0 because of the influence of dopants. This phenomenon also appeared in the CeO2-Y2O3 and CeO2-Sm2O3 systems, so it could be inferred that rare earth dopants such as Gd2O3, Sm2O3 and Y2O3 not only have the similar motion with changing pH in an aqueous system but also can be dissolved in the range of pH 6.0∼6.5. In CeO2-Gd2O3 system, when the anionic dispersant was added the amount of 0.5wt% and pH value in slurries was fixed at 9.5, the green body density was 4.07g/㎤, and the relative density of sintered body was 95.2%. It could be inferred from XRD analysis that Gd3+ substituted into Ce4+ site because there was no free Gd2O3 peak.

• 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.

• Earthquakes and Structures
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• v.20 no.3
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• pp.325-335
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• 2021

The majority of Turkey's geography is at risk of earthquakes. Within the borders of Turkey, including the two major active faults contain the North-Eastern and Eastern Anatolia, earthquake, threatening the safety of life and property. On January 24, 2020, an earthquake of magnitude 6.8 occurred at 8:55 p.m. local time. According to the data obtained from the stations in the region, peak ground acceleration in the east-west direction was measured as 0.292 g from the 2308 coded station in Sivrice. It is thought that the earthquake with a magnitude of Mw 6.8 was developed on the Sivrice-Puturge segment of the Eastern Anatolian Fault, which is a left lateral strike slip fault, and the tear developed in an area of 50-55 km. Aftershocks ranging from 0.8 to 5.1 Mw occurred following the main shock on the Eastern Anatolian Fault. The earthquake caused severe structural damages in Elazığ and neighboring provinces. As a result of the field investigations carried out in this study, significant damage levels were observed in the buildings since it did not meet the criteria in the earthquake codes. Within the study's scope, the structural damage cases in reinforced concrete and masonry structures were investigated. Many structural deficiencies and mistakes such as non-ductile details, poor concrete quality, short columns, strong beams-weak columns mechanism, large and heavy overhangs, masonry building damages and inadequate reinforcement arrangements were observed. Requirements of seismic codes are discussed and compared with observed earthquake damage.

• Steel and Composite Structures
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• v.42 no.2
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• pp.277-288
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• 2022

A novel flat steel plate-concrete-corrugated steel plate (FS-C-CS) sandwich panel was proposed for resisting impact load. The failure mode, impact force and displacement response of the FS-C-CS panel under impact loading were studied via drop-weight impact tests. The combined global flexure and local indentation deformation mode of the FS-C-CS panel was observed, and three stages of impact process were identified. Moreover, the effects of corrugated plate height and steel plate thickness on the impact responses of the FS-C-CS panels were quantitatively analysed, and the impact resistant performance of the FS-C-CS panel was found to be generally improved on increasing corrugated plate height and thickness in terms of smaller deformation as well as larger impact force and post-peak mean force. The Finite Element (FE) model of the FS-C-CS panel under impact loading was established to predict its dynamic response and further reveal its failure mode and impact energy dissipation mechanism. The numerical results indicated that the concrete core and corrugated steel plate dissipated the majority of impact energy. In addition, employing end plates and high strength bolts as shear connectors could prevent the slip between steel plates and concrete core and assure the full composite action of the FS-C-CS panel.

• Steel and Composite Structures
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• v.43 no.2
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• pp.139-152
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• 2022

Steel-reinforced concrete (SRC) L-shaped column is the vertical load-bearing member with high spatial adaptability. The seismic behavior of SRC L-shaped column is complex because of their irregular cross sections. In this study, the hysteretic performance of six steel truss reinforced concrete L-shaped columns specimens under the combined loading of compression, bending, shear, and torsion was tested. There were two parameters, i.e., the moment ratio of torsion to bending (γ) and the aspect ratio (column length-to-depth ratio (φ)). The failure process, torsion-displacement hysteresis curves, and bending-displacement hysteresis curves of specimens were obtained, and the failure patterns, hysteresis curves, rigidity degradation, ductility, and energy dissipation were analyzed. The experimental research indicates that the failure mode of the specimen changes from bending failure to bending-shear failure and finally bending-torsion failure with the increase of γ. The torsion-displacement hysteresis curves were pinched in the middle, formed a slip platform, and the phenomenon of "load drop" occurred after the peak load. The bending-displacement hysteresis curves were plump, which shows that the bending capacity of the specimen is better than torsion capacity. The results show that the steel truss reinforced concrete L-shaped columns have good collapse resistance, and the ultimate interstory drift ratio more than that of the Chinese Code of Seismic Design of Building (GB50011-2014), which is sufficient. The average value of displacement ductility coefficient is larger than rotation angle ductility coefficient, indicating that the specimen has a better bending deformation resistance. The specimen that has a more regular section with a small φ has better potential to bear bending moment and torsion evenly and consume more energy under a combined action.

• Journal of the Korean earth science society
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• v.38 no.7
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• pp.561-569
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• 2017

Fault plane solutions of the Iksan earthquake ($M_L=3.85$) and two aftershocks were obtained using the FOCMEC (FOCal MEChanism determination) program. The main event showed the characteristic of strike slip faulting with reverse component. It has the fault planes with NE-SW or NW-SE direction. This is similar to the fault characteristics of earthquake pattern in the inland area of the Korean Peninsula. In order to detect micro-earthquake events, continuous seismic waveform data of the thirteen seismic stations within a radius of 100km from epicenter were analyzed by PQLII program (PASSCAL, 2017) for the period from December 15, 2015 to January 22, 2016. The epicenters of nineteen micro-events were newly determined by Hypoinverse-2000 program. They are not concentrated along some lineaments or fault lines. The intensity of the Iksan earthquake was obtained by estimating the telephone inquiries, the degree of ground shaking or damage all around the southern peninsula. The instrumental intensity was also obtained using PGA (Peak Ground Acceleration) records. As a result, the maximum MM intensity was estimated to be V near the epicenter.

• Geomechanics and Engineering
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• v.24 no.3
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• pp.215-226
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• 2021

To study the evolution mechanism of cracks in rocks with multiple defects, rock-like samples with multiple defects, such as strip-shaped through-going cracks and cavity groups, are used, and the crack propagation law and changes in AE (acoustic emission) and strain of cavity groups under different inclination angles are studied. According to the test results, an increase in the cavity group inclination angle can facilitate the initial damage degree of the rock and weaken the crack initiation stress; the initial crack initiation direction is approximately 90°, and the extension angle is approximately 75~90° from the strip-shaped through-going cracks; thus, the relationship between crack development and cavity group initiation strengthens. The specific performance is as follows: when the initiation angle is 30°, the cracks between the cavities in the cavity group develop relatively independently along the parallel direction of the external load; when the angle is 75°, the cracks between the cavities in the cavity group can interpenetrate, and slip can occur along the inclination of the cavity group under the action of the shear mechanism rupture. With the increase in the inclination angle of the cavity group, the AE energy fluctuation frequency at the peak stress increases, and the stress drop is obvious. The larger the cavity group inclination angle is, the more obvious the energy accumulation and the more severe the rock damage; when the cavity group angle is 30° or 75°, the peak strain of the local area below the strip-shaped through-going fracture plane is approximately three times that when the cavity group angle is 45° and 60°, indicating that cracks are easily generated in the local area monitored by the strain gauge at this angle, and the further development of the cracks weakens the strength of the rock, thereby increasing the probability of major engineering quality damage. The research results will have important reference value for hazard prevention in underground engineering projects through rock with natural and artificial defects, including tunnels and air-raid shelters.

• Korean Journal of Environment and Ecology
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• v.10 no.2
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• pp.211-239
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• 1997

The flora of Oesorak in the Soraksan National Park including Chombongsan(Mountain) and Kwanmobong(Peak) were surveyed from February to August, 1996. These areas have very rich and diverse flora;620 taxa with 89 families, 321 genera, 526 species, 2 subspecies, 89 varieties and 3 forms in the Oesorak, 404 taxa with 251 genera, 350 species, 1 subspecies, 51 varieties and 2 forms in the Chombongsan(Mountain), 286 taxa with 206 genera, 233 species, 1 subspecies, 50 varieties and 2 forms in Kwanmobong(peak). The Oesorak had very distinct floristic characteristics such as the wild habitats of Asarum maculatum(Aristolochiaceae) and Ilex macropoda(Aquifoliaceae). In the phyorgeographical point of view, the six species such as Sapium japonicum (Euphorbiaceae), Euphorbia joldini(Euphorbiaceae), Ilex macropoda (Aquifoliaceae), Styrax japonica (Styracaceae), Carex sideros ticta (Cyperaceae) and Asarum maculatum (Aristolochiaceae) were naturalized into this region, while the 17 taxa such as Abies neprolepis(Pinaceae), Pinus pumila(Pinaceae), Thuja koraiensis(Cupressaceae), Allium senescens(Liliaceae), Lilium distichum(Liliaceae), Saxifraga punctata(Saxfragaceae), Rosa marretii(Rosaceae), Bupleurum euphorbioides(Umbelliferae), Androsace cortusaefolia (Primulaceae), Peducularis mandshurica(Scrophulariaceae) and Leontopodium coreanum (Compositae) were distrivuted to this region. The colonizing weedy species such as Ixris repens (Compositae) were distributed to this region. The colonizing weedy species losa(Labiatae) and Rosa rugosa(Rosaceae) were naturalized into ca. 900m at sea level mainly due to the sand soil from the seashore. Mountain roadbed is susceptible than other areas to the slippery road problems, due largely to snow and rain, particularly during winter. Sand soils from seashore are utilized to minimize this slip in traffic operation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.31-31
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• 2010

The growth of the high-quality GaN epilayers is of significant technological importance because of their commercializedoptoelectronic applications as high-brightness light-emitting diodes (LEDs) and laser diodes (LDs) in the visible and ultraviolet spectral range. The GaN-based heterostructural epilayers have the polar c-axis of the hexagonal structure perpendicular to the interfaces of the active layers. The Ga and N atoms in the c-GaN are alternatively stacked along the polar [0001] crystallographic direction, which leads to spontaneous polarization. In addition, in the InGaN/GaN MQWs, the stress applied along the same axis contributes topiezoelectric polarization, and thus the total polarization is determined as the sum of spontaneous and piezoelectric polarizations. The total polarization in the c-GaN heterolayers, which can generate internal fields and spatial separation of the electron and hole wave functions and consequently a decrease of efficiency and peak shift. One of the possible solutions to eliminate these undesirable effects is to grow GaN-based epilayers in nonpolar orientations. The polarization effects in the GaN are eliminated by growing the films along the nonpolar [$11\bar{2}0$] ($\alpha$-GaN) or [$1\bar{1}00$] (m-GaN) orientation. Although the use of the nonpolar epilayers in wurtzite structure clearly removes the polarization matters, however, it induces another problem related to the formation of a high density of planar defects. The large lattice mismatch between sapphiresubstrates and GaN layers leads to a high density of defects (dislocations and stacking faults). The dominant defects observed in the GaN epilayers with wurtzite structure are one-dimensional (1D) dislocations and two-dimensional (2D) stacking faults. In particular, the 1D threading dislocations in the c-GaN are generated from the film/substrate interface due to their large lattice and thermal coefficient mismatch. However, because the c-GaN epilayers were grown along the normal direction to the basal slip planes, the generation of basal stacking faults (BSFs) is localized on the c-plane and the generated BSFs did not propagate into the surface during the growth. Thus, the primary defects in the c-GaN epilayers are 1D threading dislocations. Occasionally, the particular planar defects such as prismatic stacking faults (PSFs) and inversion domain boundaries are observed. However, since the basal slip planes in the $\alpha$-GaN are parallel to the growth direction unlike c-GaN, the BSFs with lower formation energy can be easily formed along the growth direction, where the BSFs propagate straightly into the surface. Consequently, the lattice mismatch between film and substrate in $\alpha$-GaN epilayers is mainly relaxed through the formation of BSFs. These 2D planar defects are placed along only one direction in the cross-sectional view. Thus, the nonpolar $\alpha$-GaN films have different atomic arrangements along the two orthogonal directions ($[0001]_{GaN}$ and $[\bar{1}100]_{GaN}$ axes) on the $\alpha$-plane, which are expected to induce anisotropic biaxial strain. In this study, the anisotropic strain relaxation behaviors in the nonpolar $\alpha$-GaN epilayers grown on ($1\bar{1}02$) r-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVO) were investigated, and the formation mechanism of the abnormal zigzag shape PSFs was discussed using high-resolution transmission electron microscope (HRTEM).