• Steel and Composite Structures
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• v.39 no.1
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• pp.21-33
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• 2021

This paper aims to improve the current state-of-the-art in long-term deflection prediction in steel-concrete composite beams. The efficiency of a time-dependent finite element model based on linear creep theory is verified with available experimental data. A parametric numerical study is then carried out, which focuses on the effects of concrete creep and/or shrinkage, ultimate shrinkage strain and reinforcing bars in the slab. The study shows that the long-term deformations in composite beams are dominated by concrete shrinkage and that a higher area of reinforcing bars leads to lower long-term deformations and steel stresses. The AISC model appears to overestimate the shrinkage-induced deflection. A modified ACI equation is proposed to quantify time-dependent deflections in composite beams. In particular, a modified reduction factor reflecting the influence of reinforcing bars and a coefficient reflecting the influence of ultimate shrinkage are introduced in the proposed equation. The long-term deflections predicted by this equation and the results of extensive numerical analyses are found to be in good agreement.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.29-34
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• 2007

This paper presents a novel photonic bandgap (PBG) structure for size reduction and linearity improvement in power amplifier. The proposed structure is a two-dimensional (2-D) periodic lattice patterned on a dielectric slab that does not require nonplanar fabrication process. Throughout the experi-mental results, this structure has more broad stopband and high suppression performance than conventional three cell PBG and distorted uniplanar compact-PBG (DUC-PBG). This new PBG structure can be applied with power amplifier for linearity improvement. The 3rd intermodulation distortion (IMD3) of the power amplifier using new PBG structure is -36.16 dBc for (code division multiple access) CDMA applications. Compared with power amplifier without the proposed PBG structure, improved IMD3 is -13.49 dBc.

• Geomechanics and Engineering
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• v.36 no.2
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• pp.167-181
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• 2024

The soil-structure relative stiffness is a key factor affecting the seismic response of underground structures. It is of great significance to study the soil-structure relative stiffness for the soil-structure interaction and the seismic disaster reduction of subway stations. In this paper, the dynamic shear modulus ratio and damping ratio of an inhomogeneous soft soil site under different buried depths which were obtained by a one-dimensional equivalent linearization site response analysis were used as the input parameters in a 2D finite element model. A visco-elasto-plastic constitutive model based on the Mohr-Coulomb shear failure criterion combined with stiffness degradation was used to describe the plastic behavior of soil. The damage plasticity model was used to simulate the plastic behavior of concrete. The horizontal and vertical relative stiffness ratios of soil and structure were defined to study the influence of relative stiffness on the seismic response of subway stations in inhomogeneous soft soil. It is found that the compression damage to the middle columns of a subway station with a higher relative stiffness ratio is more serious while the tensile damage is slighter under the same earthquake motion. The relative stiffness has a significant influence on ground surface deformation, ground acceleration, and station structure deformation. However, the effect of the relative stiffness on the deformation of the bottom slab of the subway station is small. The research results can provide a reference for seismic fortification of subway stations in the soft soil area.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.185-193
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• 2015

Ultra high performance concrete (UHPC) has been developed to overcome the low tensile strengths and brittleness of conventional concrete. Considering that UHPC, owing to its composition and the use of steel fibers, develops a compressive strength of 180 MPa as well as high stiffness, the top flange of the steel girder may be superfluous in the composite beam combining a slab made of UHPC and the steel girder. In such composite beam, the steel girder takes the form of an inverted-T shaped structure without top flange in which the studs needed for the composition of the steel girder with the UHPC slab are disposed in the web of the steel girder. This study investigates experimentally and analytically the flexural behavior of this new type of composite beam to propose details like stud spacing and slab thickness for further design recommendations. To that goal, eight composite beams with varying stud spacing and slab thickness were fabricated and tested. The test results indicated that stud spacing running from 100 mm to 2 to 3 times the slab thickness can be recommended. In view of the relative characteristic slip limit of Eurocode-4, the results showed that the composite beam developed ductile behavior. Moreover, except for the members with thin slab and large stud spacing, most of the specimens exhibited results different to those predicted by AASHTO LRFD and Eurocode-4 because of the high performance developed by UHPC.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.761-769
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• 2014

Ultra high performance concrete (UHPC) has been developed to overcome the low strengths and brittleness of conventional concrete. Considering that UHPC, owing to its composition and the use of steel fibers, develops a compressive strength of 180 MPa as well as high stiffness, the top flange of the steel girder may be superfluous in the composite beam combining a slab made of UHPC and the steel girder. In such composite beam, the steel girder takes the form of an inverted-T shaped structure without top flange in which the studs needed for the composition of the steel girder with the UHPC slab are disposed in the web of the steel girder. This study investigates experimentally and analytically the flexural behavior of this new type of composite beam to propose details like stud spacing and slab thickness for further design recommendations. To that goal, eight composite beams with varying stud spacing and slab thickness were fabricated and tested. The test results indicated that stud spacing running from 100 mm to 2 to 3 times the slab thickness can be recommended. In view of the relative characteristic slip limit of Eurocode-4, the results showed that the composite beam developed ductile behavior. Moreover, except for the members with thin slab and large stud spacing, most of the specimens exhibited results different to those predicted by AASHTO LRFD and Eurocode-4 because of the high performance developed by UHPC.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.5 s.39
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• pp.1-14
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• 2004

The seismic behavior of a 1/3-scale model of a two-story unreinforced masonry (URM) structure typically used in constructing low-rise residential buildings in Korea is studied through a shaking table test. The purposes of this study are to investigate seismic behavior and damage patterns of the URM structure that was not engineered against seismic loading and to provide its experimental test results. The test structure was symmetric about the transverse axis but asymmetric to some degrees about longitudinal axis and had a relatively strong diaphragm of concrete slab. The test structure was subjected to a series of differentlevels of earthquake shakings that were applied along the longitudinal direction. The measured dynamic response of the test structure was analyzed in terms of various global parameters (i.e., floor accelerations, base shear, floor displacements and storydrift, and torsional displacements) and correlated with the input table motion. Moreover, different levels of seismic performance were suggested for performance-based design approach. The results of the shaking table test revealed that the shear failure was dominant on a weak side of the 1stfloor while the upper part of the test model remained as a rigid body. Also, it was found that substantial strength and deformation capacity existed after cracking.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.1
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• pp.34-40
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• 2013

The 1st assessment(performance test) was applied to assure the floor impact sound performance for developing the dry double-floor with the change of rubber hardness of the upper panel's support and the ceiling structure of the sub-floor. Depends on the change of the rubber hardness in sub-structure, the heavy-weight sound impact value is improved up to 3 dB, and the light-weight sound impact value is moved up to 21 dB, comparing with the bare-slab. Also, the improved value for the floor impact sound conjugating with the sub-floor's ceiling was 5 dB. Based on this result, the 2nd assessment(performance test) was made the state that the rubber hardness of the sub-floor support was ranged between 50 and 70 for considering the stability of walking patients. In addition to this process, the assessment was carried out with a variety of ceiling structure applied to the dry double-floor structure with the air flow system on the sub-floor's ceiling. The result for the 2nd assessment proved that TYPEII-3 had the better sound reduction performance in the heavy-weight impact sound test than other types, and also for the light-weight impact sound TYPEII-3 had the 29 dB sound reduction performance overall. Henceforth, based on the result the research for the sound reduction performance from the floor impact sound shall be ongoing process as well as the development of a double-dry floor and a sound reduction ceiling to suitable on the field.

• Structural Engineering and Mechanics
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• v.33 no.2
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• pp.113-136
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• 2009

The seismic induced interaction between multistory structures with unequal story heights (inter-story pounding) is studied taking into account the local response of the exterior beam-column joints. Although several parameters that influence the structural pounding have been studied sofar, the role of the joints local inelastic behaviour has not been yet investigated in the literature as key parameter for the pounding problem. Moreover, the influence of the infill panels as an additional parameter for the local damage effect of the joints on the inter-story pounding phenomenon is examined. Thirty six interaction cases between a multistory frame structure and an adjacent shorter and stiffer structure are studied for two different seismic excitations. The results are focused: (a) on the local response of the critical external column of the multistory structure that suffers the hit from the slab of the adjacent shorter structure, and (b) on the local response of the exterior beam-column joints of the multistory structure. Results of this investigation demonstrate that the possible local inelastic response of the exterior joints may be in some cases beneficial for the seismic behaviour of the critical column that suffers the impact. However, in all the examined cases the developing demands for deformation of the exterior joints are substantially increased and severe damages can be observed due to the pounding effect. The presence of the masonry infill panels has also been proved as an important parameter for the response of the exterior beam-column joints and thus for the safety of the building. Nevertheless, in all the examined inter-story pounding cases the presence of the infills was not enough for the total amelioration of the excessive demands for shear and ductility of the column that suffers the impact.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.651-658
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• 2014

Notification 2013-611 of MOLIT has come into effect. It relates primarily to new standard impact source. In this study, an in-depth experimental analysis of the difference between a bang machine and an impact ball was performed via field testing of shear wall and flat plate structure at 51 sites. This paper focuses on the difference in single number quantities between a bang machine and an impact ball. At wall thicknesses of 180 and 210 mm in shear wall structure, the single number quantities exhibited differences of 3.1 and 4.5 dB, respectively, and at thicknesses exceeding 250 mm in flat plate structure, the difference was constant at 4.6 dB. With regard to flat plate structures, the single-index difference increased up to 11 dB as the thickness of the floor slab increased. In general, the highest level of contribution for the bang machine was 63 Hz, irrespective of thickness determining bandwidth. The highest level for the impact ball were 63 Hz and 125 Hz. In future research, when reviewing additional field performance measurement data, it will be necessary to consider a detailed examination instead of the current method of uniformly adding 3 dB for all thicknesses and types of structures.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.115-119
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• 2008

In this paper, the linearity of Doherty power amplifier has been improved by applying a new Photonic Bandgap(PBG) structure on the output of amplifier. The reposed spiral PBG structure is a two-dimensional(2-D) periodic lattice patterned on a dielectric slab that does not require nonplanar fabrication process. This structure has more broad stopband and high suppression performance than the conventional three cell PBG. Also, It has a sharp skirt property. We obtained the 3rd-order intermodulation distortion(IMD3) of -33dBc for CDMA applications with that of maintaining the constant power added efficiency(PAE), the IMD3 performance is improved as much as -8 dB compared with a Doherty power amplifier without PBG structure. Moreover, the physical length of PBG is shortened, therefore the whole amplifier circuit size is considerably reduced.