• Earthquakes and Structures
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• v.17 no.1
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• pp.115-129
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• 2019

The effectiveness of an innovative method for the earthquake-resistant rehabilitation of existing poorly detailed reinforced concrete (RC) structures is experimentally investigated herein. Eight column subassemblages were subjected to earthquake-type loading and their hysteretic behaviour was evaluated. Four of the specimens were identical and representative of columns found in RC structures designed in the 1950s-70s period for gravity load only. These original specimens were subjected to cyclic lateral deformations and developed brittle failure mechanisms. Three of the damaged specimens were subsequently retrofitted with innovative high-strength steel fiber-reinforced concrete (HSSFC) jackets. The main variables examined were the jacket width and the contribution of mesh steel reinforcement in the seismic performance of the enhanced columns. The influence of steel fiber volume fraction was also examined using test results of a previous work of Tsonos et al. (2017). The fourth earthquake damaged subassemblage was strengthened with a conventional RC jacket and was subjected to the same lateral displacement history as the other three retrofitted columns. The seismic behaviour of the subassemblages strengthened according to the proposed retrofit scheme was evaluated with respect to that of the original specimens and that of the column strengthened with the conventional RC jacket. Test results clearly demonstrated that the HSSFC jackets effectively prevented the development of shear failure mechanisms, while ensuring a ductile seismic response similar to that of the subassemblage retrofitted with the conventional RC jacket. Ultimately, an indisputable superiority in the overall seismic performance of the strengthened columns was achieved with respect to the original specimens.

• Journal of the Korean Society for Railway
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• v.20 no.1
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• pp.85-98
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• 2017

In general, under the repetitive dynamic load generated by rail cars running on the track, subgrade soil experiences changes of stress conditions such as deviatoric stress (${\sigma}_d$) and bulk stress (${\theta}$). Due to the repetitive change of deviatoric stress (${\sigma}_d$) with number of loadings, the resilient modulus ($M_R$) can be obtained by using the measured resilient strain (${\varepsilon}_r$) after a sufficient number of loadings. At present, no plausible and unified test method has been proposed to obtain the resilient modulus of railway track subgrade soil. In this study, a possible test method for obtaining the resilient modulus ($M_R$) of railway track subgrade soil is proposed; this test, by utilizing repetitive triaxial compression testing, can consider all the important parameters, such as the confining stress, deviatoric stress, and number of loadings. By adapting and using the proposed test method to obtain $M_R$, $M_R$ values for compacted track subgrade soil can be successfully determined using soil obtained in three field sites of railway track construction with changing water content range from OMC. In addition, shear modulus (G) ~ shear strain (${\gamma}$) relation data were also obtained using a mid-size RC test. A correlation analysis was performed using the obtained G and $M_R$ values while considering the strain levels and modes of strain direction.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.53-60
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• 2007

L/EPS, manufactured in the shape of block and used for civil engineering, is a lightweight material with an excellent resistance to compression, and provides a superb self-sufficient stability. EPS is a suitable material capable of resolving the problem of settlement and lateral flow if it is applied as the soil on soft ground. The Korean Standards (KS) has not yet proposed any testing method for use of EPS as an engineering banking material. Only its testing and quality ordinance as a heat insulation material has been standardized. The design criteria for EPS has been established and applied through the trial construction of KHC (Korea Highway Corporation) and quality test of manufacturer, but most studies on them have been confined to factory products. This study is focused on comparing and analyzing long-term durability by conducting cyclic load test, freezing and thawing test, absorption rate test and others. EPS used in the test was chosen from construction sites and factory products, focusing on the long-term durability of EPS depending on the passage of time. Unconfined compression test results indicated that the strength of collected samples was lower than factory products. While the triaxial compression test results indicated that the shear strength increased in proportion to the increase of confining pressure, and factory products had declining shear strength as the confining pressure rose.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.705-714
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• 2012

Precast reinforced concrete bridge columns with hollow rectangular section were tested under cyclic lateral load with constant axial force to investigate its seismic performance. After all the precast column segments were erected, longitudinal reinforcement was inserted in the sheath prefabricated in the segments, which were then mortar grouted. Main variables of the test series were column aspect ratio, longitudinal reinforcement ratio, amount of lateral reinforcement, and location of segment joints. The aspect ratios were 4.5 and 2.5, and the longitudinal steel ratios were 1.15% and 3.07%. The amount of lateral reinforcement were 95%, 55%, 50%, and 27% of the minimum amount for full ductility design requirements in the Korean Bridge Design Code. The locations of segment joints in plastic hinge region were 0.5 and 1.0 times of the section depth from the bottom column end. The test results of cracking and failure mode, axial-flexural strength, lateral load-displacement relationship, and displacement ductility are presented. Then, safety of the ductility demand based seismic design in the Korean Bridge Design Code is discussed. The column specimens showed larger ductility than expected, because buckling of longitudinal reinforcing bar was prevented due to confinement developed not only by transverse steel but also by sheath and infilling mortar.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.311-321
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• 2015

In this study, an experimental study to evaluate the seismic performance of beam-to-column connection for medium and low-rise building was conducted. Five connections using SHN490 steel were made with test variables such as flange welded or bolted, web welded or bolted. Specimen SHN-W-W is web welded and flange welded type. Specimen SHN-W-B is web welded and flange bolted type. Specimen SHN-B-W is web bolted and flange welded type. Specimen SHN-B-B is web bolted and flange bolted type. Specimen SHN-EP is a connection with the end plate to the beam ends. Cyclic loadings was applied at the tip of beam following KBC2009 load protocol. The load vs rotation curves for different connection are shown and final failure mode shapes are summarized. The connections are classified in terms of stiffness and strength as semi-rigid or rigid connection. Energy dissipation capacities for seismic performance evaluation were compared.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.147-157
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• 2018

The basis of capacity design has been explicitly or implicitly regulated in most bridge design specifications. It is to guarantee ductile failure of entire bridge system by preventing brittle failure of pier members and any other structural members until the columns provides fully enough plastic rotation capacity. Brittle shear is regarded as a mode of failure that should be avoided in reinforced concrete bridge pier design. To provide ductility behavior of column, the one of important factors is that flexural hinge of column must be detailed to ensure adequate and dependable shear strength and deformation capacity. Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with 4.5 aspect ratio. The test variables are longitudinal steel ratio, transverse steel ratio, and axial load ratio. Eight flexurally dominated columns were tested. In all specimens, initial flexural-shear cracks occurred at 1.5% drift ratio. The multiple flexural-shear crack width and length gradually increased until the final stage. The angles of the major inclined cracks measured from the vertical column axis ranged between 42 and 48 degrees. In particular, this study focused on assessing transverse reinforcement contribution to the column shear strength. Transverse reinforcement contribution measured during test. Each three components of transverse reinforcement contribution, axial force contribution and concrete contribution were investigated and compared. It was assessed that the concrete stresses of all specimen were larger than stress limit of Korea Bridge Design Specifications.

• Journal of the Korean GEO-environmental Society
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• v.19 no.10
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• pp.35-41
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• 2018

Dynamic interaction of the ground-foundation-structure must be considered for safety of earthquake resistant design for piles supported structures. The p-y curve, which is proposed in the static load and cyclic load cases, is used for the earthquake resistant design of piles. The p-y curve does not consider dynamic interaction of the ground-foundation-structure on dynamic load cases such as earthquake. Therefore, it is difficult to apply the p-y curve to earthquake resistant design. The dynamic p-y curve by considering dynamic interaction of the ground-foundation-structure has been studied, and researches had same conditions that pile caps were on the ground surface and superstructures were added on pile caps for the simple weight. However, group piles are normally embedded into the ground except for marine structures, so it seems that the embedding the pile cap influences on the dynamic p-y curve of group piles. In this study, the shaking table model test was conducted to confirm dynamic behavior of group piles by the embedded pile cap in the ground. The result showed that dynamic behavior was different between two cases by embedding the pile cap or not.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.3
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• pp.1-12
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• 2004

Due to the 1989 Loma Prieta, 1995 Hyogoken Nambu earthquakes, etc, a number of bridge columns  were collapsed in flexure-shear failures as a consequence of the premature termination of the column longitudinal reinforcement. Nevertheless, previous researches for the performance of bridge columns were concentrated on the flexural failure mode. It is well understood that the seismic behaviour of RC bridge piers was dependent on the performance of the plastic hinge of RC bridge piers, the ductility of which was desirable to be computed on the basis of the curvature. Experimental investigation was made to evaluate the variation of the curvature of the plastic hinge  region for the seismic performance of earthquake-damaged RC columns in flexure-shear failure mode. Seven test specimens in the aspect ratio of 2.5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading under a constant axial load, $P=0.1f_{ck}A_g$. Residual seismic capacity of damaged specimens was evaluated by analzying the moment-curvature hysteresis and the curvature ductility. Test results show that the biggest curvature was developed around 15cm above the footing, which induced the column failure. It was observed that RC bridge specimens with lap-spliced longitudinal steels appeared to fail at low curvature ductility but significant improvement was made in the curvature ductility of RC specimens with FRP straps wrapped around the plastic hinge region. Based on the experimental variation of the curvature of RC specimens, new equivalent length of the plastic hinge region was proposed by considering the lateral confinement in this study. The analytical and experimental relationship between the displacement and the curvature ductility were compared based on this proposal, which gave excellent result.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.467-476
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• 2016

For the connections between modular units in modular buildings, the bolted joints with connector plates are used commonly. The strength of structure is determined by the weakest part of structure and the connections may be weaker than the members being joined. Therefore, to check the safety of modular building, the structural performance of connections between modular units as well as that of beam-to-column connections should be evaluated. In this study, the behavior of module to module connection with straight and cross shaped connector plates is investigated by lateral cyclic tests according to KBC2009 0722.2.4 which shall be conducted by controlling the story drift angle in the width and the longitudinal direction respectively. All of test results generally show the stable ductile behavior up to 0.04rad drift levels and the tests in longitudinal direction show a superior energy dissipation per cycle in each of the load steps. However, the straight shaped connector plates have the degradation of stiffness with cyclic loading and the larger drift angle of column than the cross shaped connector plates.

• Magazine of the Korea Concrete Institute
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• v.4 no.1
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• pp.119-126
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• 1992

AC] 318-H9 Recommended that when the specified compressive strength of concrete in a column is greater than 1. 4 times that specified for a floor system, top surface of the colurrm concrete shall extend 2ftU;OOrrun) into the slab from the face of colUlml to avoid unexpected brittle failure. The purpose of this investigation is to suggest the basic information for the structural safety, The major variables are com preSSlve strength of concrete, shear confinement ratio, and loading types. The test results showed that the load capaCIty of speCImen subjected to monotOI1lC loading had more than that of specimen subjected to one way cyclic loading. The failure modes of specimens under cyclic loading were concentrated at 5-20cm apart region from beam-column joint face and ductility index are increased with increasing of shear confinement ratio. Keywords: ACI 318-89, High and Low Strength Concrete, Beam-Column Joint, Shear Confinement Ratio, Loading Type, Ductility Index, Extension Distance.