• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.325-333
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• 2010

In this study, new moment-resisting precast concrete beam-column joint made up of hybrid steel concrete was developed and tested. This beam-column joint is proposed for use in moderate seismic regions. It has square hollow tubular section in concrete column and connecting plate in precast U-beam. The steel elements in column and beam members were connected using bolt. Furthermore, in order to prevent the premature failure of concrete in hybrid steel-concrete connection, ECC(engineered cementitious composite) was used. An experimental study was carried out investigating the joint behavior subjected to reversed cyclic loading and constant axial compressive load. Two precast beam-column joint specimens and monolithic reinforced concrete joint specimen were tested. The variables for interior joints were cast-in-situ concrete area and transverse reinforcement within the joint. Tests were carried out under displacement controlled reverse cyclic load with a constant axial load. Joint performance is evaluated on the basis of connection strength, stiffness, energy dissipation, and displacement capacity. The test results showed that significant differences in structural behavior between the two types of connection because of different bonding characteristics between steel and concrete; steel and ECC. The proposed joint detail can induce to move the plastic hinge out of the ECC and steel plate. And proposed precast connection showed better performance than the monolithic connection by providing sufficient moment-resisting behavior suitable for applications in moderate seismic regions.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.381-388
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• 2010

In this study, characteristics of the seismic response of the non-earthquake resistant reinforced concrete (RC) frame were identified. The test building is designed to withstand only gravity loads and not in compliance with modern seismic codes. Smooth bars were utilized for the reinforcement. Members are provided with minimal amount of stirrups to withstand low levels of shear forces and the core concrete is virtually not confined. Columns are slender and more flexible than beams, and beam-column connections were built without stirrups. Through the modeling of an example RC frame, the feasibility of the fiber elementbased 3D nonlinear analysis method was investigated. Since the torsion is governed by the fundamental mode shape of the structure under dynamic loading, pushover analysis cannot predict torsional response accurately. Hence, dynamic response history analysis is a more appropriate analysis method to estimate the response of an asymmetric building. The latter method was shown to be accurate in representing global responses by the comparison of the analytical and experimental results. Analytical models without rigid links provided a good estimation of reduced stiffness and strength of the test structure due to bond-slip, by forming plastic hinges closer to the column ends. However, the absence of a proper model to represent the bond-slip poased the limitations on the current inelastic analysis schemes for the seismic analysis of buildings especially for those with round steel reinforcements. Thus, development of the appropriate bond-slip model is in need to achieve more accurate analysis.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.734-741
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• 2002

An experimental study was carried out for beam-column joints composed of RC column and RS beams. The purpose of this study is to examine the inelastic seismic behavior for the RC-RS connection. Two interior and one exterior beam-column assemblies with variable moment ratios were tested. Experimental results showed that strength and deformability except stiffness were satisfactory. It is considered that the lack of stiffness was due to the slipping of steel beam from RS beam. The behavioral characteristics of the RC-RS connection were evaluated according to the quideline suggested by Hawkins et al. Nominal strength at 5 ％ joint distortion was not satisfactory, but all the other requirements, such as strength preserving capability, energy dissipation, and initial stiffness and strength ratios after peak load were satisfactory compared with the guideline. Thus it was concluded that the RC-RS connections can maintain ductility with excellent energy-dissipating capacity if being provided with appropriate reinforced structural system such as RC core wall for the initial lateral stiffness.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.77-89
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• 2020

Submerged floating tunnel (SFT) is a type of tunnel that allows tunnel segments to float underwater by buoyancy, and is being actively studied in recent years. When the submerged floating tunnel is connected to the ground, the tunnel and the bored tunnel inside the ground must be connected. There is risk that the stress will be concentrated at the connection between the two tunnels due to the different constraints and behavior of the two tunnels. Therefore, special design and construction methods should be applied to ensure the stability around the connection. However, previous studies on the stability at the connection site have not been sufficiently carried out, so study on the basic stage of the stability at connection site are necessary. In this study, numerical analysis simulating the connection between submerged floating tunnel and the bored tunnel confirmed that the shear strain concentration occurred in the ground around the connection, and it was analyzed that the structural factors can be handled during construction to have effects on the stability of the ground around the connection. Numerical results show that the risks from disproportionate displacements in the two tunnels can be mitigated through the construction of grouting material and joint design. Although the results from this study are qualitative results, it is expected that it will contribute to the determination of structural factors and risk areas that should be considered in the design of connections between the submerged floating tunnel and bored tunnel in the future studies.

• Journal of Korean Society of Steel Construction
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• v.22 no.2
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• pp.129-137
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• 2010

In this study, a five-story steel frame was designed in accordance with KBC2005 to evaluate the effect of the beam-column connection on the structural behavior. The connections were designed as a fully rigid connection and as a semirigid connection. A fiber model was utilized to describe the moment-curvature relationship of the steel beam and column, and a three-parameter power model was adopted for the moment-rotation angle of the semirigid connection. To evaluate the effects of higher modes on structural behavior, the structure was subjected to a KBC2005-equivalent lateral load and lateral loads considering higher modes. The structure was idealized as a separate 2D frame and as a connected 2D frame. The pushover analysis of 2D frames for the lateral load yielded the top displacement-base shear force, design coefficients such as overstrength factor, ductility ratio, and response modification coefficient, demanded ductility ratio for the semirigid connection,and distribution of plastic hinges. The sample structure showed a greater response modification coefficient than KBC2005, the higher modes were found to have few effects on the coefficient, and the lateral load of KBC2005 was found to be conservative. The TSD connection was estimated to secure economy and safety in the sample structure.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.271-280
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• 2010

This study was programmed to fabricate a beam-to-column connection that is limited to a steel-welded moment connection with full-scale members, using SN steel. A cyclic seismic test was conducted of the nine specimens that were fabricated by choosing the test variable for the weld access hole geometry, connection design method, and RBS. From the test results, failure modes, the moment-drift behavior, and the strain distribution were provided. From the specimen material properties, the beam's nominal plastic flexural capacity and classified qualified connection as a special moment flame were calculated. By analyzing the skeleton part and the baushinger part, a range of strength-raising effects, and deformation ratios were provided, with which the seismic performance of the specimens were evaluated. The test results showed that the specimens eliminated their weld access holes that demonstrated higher seismic performance than the specimens' existing weld access holes, and that the WUF-W connection that was reinforced by the supplemental fillet weld around the shear tap that was fastened by five bolts demonstrated superior seismic performance.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.503-514
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• 2011

In this research, the seismic connection details for two concrete-filled U-shape steel beam-to-H columns were proposed and cyclically tested under a full-scale cruciform configuration. The key connecting components included the U-shape steel section (450 and 550 mm deep for specimens A and B, respectively), a concrete floor slab with a ribbed deck (165 mm deep for both specimens), welded couplers and rebars for negative moment transfer, and shear studs for full composite action and strengthening plates. Considering the unique constructional nature of the proposed connection, the critical limit states, such as the weld fracture, anchorage failure of the welded coupler, local buckling, concrete crushing, and rebar buckling, were carefully addressed in the specimen design. The test results showed that the connection details and design methods proposed in this study can well control the critical limit states mentioned above. Especially, the proposed connection according to the strengthening strategy successfully pushed the plastic hinge to the tip of the strengthened zone, as intended in the design, and was very effective in protecting the more vulnerable beam-to-column welded joint. The maximum story drift capacities of 6.0 and 6.8% radians were achieved in specimens A and B, respectively, thus far exceeding the minimumlimit of 4% radians required of special moment frames. Low-cycle fatigue fracture across the beam bottom flange at a 6% drift level was the final failure mode of specimen A. Specimen B failed through the fracture of the top splice plate of the bolted splice at a very high drift ratio of 8.0% radian.