• 저자: 김현진, 황현종, 박홍근

• Abstract: For better structural performance and constructability, a concrete-encased steel column that uses a steel cage prefabricated with bolt connections was developed. The steel cage consists of longitudinal steel angles and transverse steel plates. As a fundamental verification of the proposed column, an eccentric-axial-load test was performed on eight composite column specimens. Test parameters included column type (i.e., conventional concrete-encased steel column versus proposed column), shape and spacing of transverse plate, and axial load eccentricity. The test results showed that, owing to the high flexural stiffness of the steel angles placed at the corners of the cross section, the axial strength and ductility of the proposed column were greater than those of the conventional composite column using a wide flange steel section at the center of the cross section, particularly in the large eccentricity of axial load. Z-section plates and closely spaced flat plates used for transverse reinforcement provided better lateral confinement to the concrete, thereby increasing the load-carrying capacity of the proposed columns. In general, existing design methods safely predicted the axial-flexural capacities of the specimens. Nonlinear numerical analysis was performed to verify test results. The numerical analysis results agreed with the test results in terms of yield stiffness, peak strength, and postpeak strength degradation.

• 저자: 김현진, 황현종, 박홍근, 김동관

• Abstract: For economical and fast construction, a prefabricated composite (PSRC) column that uses steel angles has been developed. In the existing PSRC columns, transverse bars are welded to the steel angles in a factory. In the present study, to further improve the constructability, transverse steel plates are used, and the plates are bolted to the steel angles. In addition, steel forms (for concrete casting) can be integrated with the steel angles, which significantly reduces the construction time. As a fundamental structural test, concentric axial loading was applied to the proposed PSRC columns, to verify their axial load-carrying capacity. The test results showed that the axial load-carrying capacity of the PSRC columns was comparable with that of the conventional concrete-encased steel (CES) columns. Z-section plates for transverse reinforcement provided good lateral confinement to the cover concrete as well as the core concrete. In contrast, the PSRC columns with transverse flat plates were vulnerable to bond failure of the cover concrete, which degraded their load-carrying capacity. The strengths of the test specimens were predicted by the current design method and nonlinear numerical analysis. The predictions agreed with the test results.

<DOWNLOAD>

• Numerical Investigation on Load-carrying Capacity of High-strength Concrete-encased Steel Angle Columns

• 저자: 김창수, 황현종

• Abstract: To investigate the load-carrying capacity of high-strength concrete-encased steel angle (CES-A) columns, in which corner steel angles are encased in concrete and transmit column loads directly, a numerical study was performed by using a proposed analysis model. The proposed model considered the strain compatibility, confinement effect, local buckling, and premature cover-spalling, and was verified against previous experimental study results. To investigate the effect of design parameters, a parametric study was conducted, and based on the parametric study results, a simple approach was also discussed to predict the residual strength (2nd peak load) after spalling of concrete cover at corners (1st peak load). The numerical investigations showed that when steel contribution and confinement efficiency are high, CES-A columns exhibit relatively large load-carrying capacity even after cover-spalling, due to the maintained strength of confined concrete and yielding of steel angles, and the proposed simple approach gave a good prediction for the residual strength.

<DOWNLOAD>

• 고강도 강재를 사용한 앵글매입형 합성기둥의 축방향 압축거동

• 저자: 엄태성, 김진원, 양종민

• Abstract: In this study, the compression behavior of encased composite columns with high-strength angle was experimentally investigated. Cold-formed angles of a yield strength 718 MPa were used as the longitudinal reinforcement of the composite columns. The axial compression tests of six column specimens with different reinforcement details were performed. Test results showed that the failure mode of the columns was local buckling of the angles and crushing failure of the confined concrete. The column performance such as the peak strength and post-peak strength degradation, were significantly affected by the classification of angle sections and details of lateral confinement. The test strengths were compared with the theoretical strengths computed in accordance with KBC 2016 and AISC 36016. In addition, effects of the composite action of high strength angles and normal strength concrete on the strength and ductility of the columns were investigated through nonlinear section analysis.

<DOWNLOAD>

• 볼트접합 앵글을 사용한 PSRC 합성기둥의 편심 압축실험

• 저자: 김현진, 황현종, 박홍근, 김동관, 양종민

• Abstract: In order to investigate the structural performance of a novel prefabricated-SRC column using bolt-connected steel angles(PSRC column), eccentric axial loading tests were performed for six PSRC column specimens and two conventional SRC column specimens. The test parameters were the spacing and sectional configurations of lateral reinforcement, and eccentricity ratio of axial load. The test results showed that, due to high axial-stiffness of the angles located at the corners of the cross section, the compressive load-carrying capacity and deformation capacity of the PSRC specimens were greater than those of the SRC specimens in the large eccentricity ratio of axial load. Closely spaced lateral steel plates and Z-shaped lateral steel plates improved lateral confinement, which increased the load-carrying capacity of the PSRC specimens. The combined flexural and axial load-carrying capacity of the specimens by tests and nonlinear numerical analysis were greater than the predictions by current design codes. The numerical analysis agreed well with the test results including the initial stiffness, peak strength, and post-peak strength degradation.

<DOWNLOAD>

• 볼트접합 앵글을 사용한 합성기둥의 중심축 압축실험

• 저자: 김현진, 황현종, 박홍근, 김동관, 양종민

• Abstract: The present study focused on the structural performance of newly developed prefabricated composite columns (PSRC composite column) using bolt-connected steel angles. Concentric axial loading tests were performed for four 2/3 scaled PSRC column specimens and two conventional SRC column specimens. The test parameters were the spacing and sectional configurations of lateral reinforcement, and width-to-thickness ratio of steel angles. The test results showed that the axial load-carrying capacity and deformation capacity of the PSRC column specimens were comparable to those of the conventional SRC column specimens. Closely spaced steel plates and Z-shaped steel plates for lateral reinforcement increased the deformation capacity of the PSRC column specimens. The load-carrying capacity was greater than the prediction by current design codes. Numerical analysis was performed for the specimens. The results agreed well with the test results in terms of initial stiffness, load-carrying capacity, except for strength degradation due to cover concrete spalling.

<DOWNLOAD>

• Concentric and Eccentric axial load test of bolt-connected prefabricated composite column

• 저자: 김현진, 황현종, 박홍근

• Abstract: Concentric and eccentric axial load tests on 2/3 scaled B-PSRC(Bolt-connected Prefabricated Steel Reinforced Concrete) and conventional SRC column specimens were performed. The experiment variables were the shape of vertical steel sections, the vertical spacing of transverse steel elements, the shape of transverse steel sections, the eccentric distance of axial load. Using concentric load test, The B-PSRC specimens showed similar degree of load-carrying capacity and deformation capacity compared to the conventional SRC specimens. Integrated section behaviors between concrete and steel angles were verified by eccentric load tests, showing well-fitted results with P-M interaction curves obtained from numerical section analysis.

<DOWNLOAD>

• 볼트조립을 적용한 PSRC 합성기둥의 부착성능 실험

• 저자: 김현진, 황현종, 박홍근, 이승환, 김동관

• Abstract: In this study, bond performance of prefabricated composite columns which are fabricated by bolt connection between steel angles and thin steel plates for lateral stiffening (B-PSRC composite column) was researched. To verify the bond performance, Flexural load tests were performed on 2/3 scaled B-PSRC specimens. From the test results, all the specimens showed flexural failure which is due to rupture of hole-section at the angle-bolt joints. Shear failure caused by bond slip between the angles and concrete was not found in any of specimens.

<DOWNLOAD>

• TSC 합성보 – PSRC 합성기둥 접합부에 대한 주기하중 실험 (Cyclic Loading Test for TSC Beam – PSRC Column Connections)

– 저자 : 황현종, 엄태성, 박홍근, 이창남, 김형섭

In the present study, details of the TSC beam-to-PSRC column connection for low and middle seismic zones were developed. For ease construction, the top and bottom flanges of the steel section of the TSC beam were discontinuous at the joint face on purpose, while the web passes through the joint. Thus, tensile resistance of the top and bottom flanges is not considered in the calculation of nominal strength of the connection. Cyclic loading tests on two interior connections and an exterior connection were performed to verify the seismic performance. The test parameter for two interior connections was the depth of the TSC beams: 600 and 700 mm including the slab depth. The test results showed that the nominal strength of the connections predicted by KBC 2009 correlated well with the test results. The connection specimens exhibited relatively good deformation and energy dissipation capacities, greater than the requirements for the ordinary and intermediate moment frames. Ultimately, the connection specimens were failed at the story drift ratios of 3.0 to 4.0 % due to local buckling and tensile fracture of the web of the TSC beam passing through the joint. By modifying the existing provisions of ASCE, the joint shear strength of the TSC beam-PSRC column connection was evaluated.

<DOWNLOAD>

• PSRC 합성기둥의 반복가력 실험 (Cyclic Loading Tests for Prefabricated Composite Columns Using Steel Angle and Reinforcing Bar)

– 저자 : 황현종, 엄태성, 박홍근, 이창남, 김형섭

PSRC composite column is a concrete encased steel angle column. In the PSRC composite column, the steel angles placed at the corner of the cross-section resists bending moment and compression load. In the present study, using the performance criteria in KBC 2009, cyclic lateral loading test was performed for PSRC columns to verify the seismic performance. The test parameters were the column type, the use of continuous hoop, and the use of studs for steel angle. 2/3 scale specimens of a conventional composite column and three PSRC columns were tested. The test results showed that the load-carrying capacity predicted by KBC 2009 correlated well with the test results. The specimens also exhibited good deformation and energy dissipation capacities. After concrete cover spalling under cyclic loading, the load-carrying capacity were decreased by buckling of longitudinal bars and steel angles. When continuous hoop was used, the deformability of the PSRC column was improved, preventing early buckling of the steel angles.