• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.97-107
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• 2020

In this study, finite element analysis was carried out through the finite element analysis program (ANSYS) to investigate the fire resistance of composite columns in fire. Transient heat transfer analysis and static structural analysis were performed according to ASTM E 119 heating curve and axial force ratio 0.7, 0.6, 0.5 by applying stress-strain curves according to temperature, and loading heating experiments were carried out under the same conditions. In addition, the nominal compressive strength of the composite column according to the heating time according to the standard(Eurocode 4) was calculated and expressed as the axial force ratio and compared with the analytical and experimental values. Through the analysis, As a result of finite element analysis, the fire resistance time was 180 minutes and similar value to the experimental value was obtained, whereas the fire resistance time 150 minutes and 60 minutes were derived from the axial force ratios 0.6 and 0.7. In addition, it was confirmed that the fire resistance time according to the axial force ratio calculated according to the reference equation (Eurocode 4) was lower than the actual experimental value. However, it was confirmed that the standard(Eurocode 4) was higher than the experimental value at the axial force ratio of 0.7. Accordingly, it is possible to confirm the fire resistance characteristics(time-axial force ratio relationship) of the SRC column at high axial force, and to use the experimental and anaylsis data of the SRC column as the data for verification based on Eurocode.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.327-335
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• 2011

This study has two objectives: (1) to evaluate the degradation characteristics of symmetric unbraced steel frames by using analytical approach, and (2) to suggest equation which can approximately estimate the effect of degradation during the schematic design stage. For the analytical approach, the refined plastic hinge method with an arc length algorithm was adopted. The subject of analysis was one story one-bay, multistory one-bay, and multistory three-bay unbraced steel frames. The main parameters of the analytical approach include the stiffness ratio of column to beam and the axial force ratio. The study led to the following conclusions. The normalized stiffness of degradations is affected by both stiffness ratio of column to beam and the axial load ratio; however, the major influence on degradations is the axial force ratio. The equation, which can approximately estimate the effect of degradation, was suggested together with the research results.

• Fire Science and Engineering
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• v.27 no.6
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• pp.26-31
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• 2013

This study, to evaluate the technology of the fire resistance design of Reinforced Concrete columns based on fire resistance performance design, was suppose to use as basic data for performance design through a measure of temperature and deformation using heat transfer analysis and Heat-load test of the Reinforced Concrete columns as parameter is the axial load ratio. In accordance with axial load without eccentricity, the load ratio of 0.30, 0.35, 0.40 and 0.47 were imposed on columns. As a result of this study, 0.40 or more of axial load ratio can be ensured that the fire resistance performance was considered satisfactory.

• Fire Science and Engineering
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• v.24 no.6
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• pp.104-111
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• 2010

The strength of steel in a concrete filled steel tube (CFT) is reduced in a fire, but the concrete filled structurally ensures the fire resistance due to its high thermal capacity. This research analyzed the fire resistance performance due to the variances of concrete strength filled inside of steel tube and the load ratios, which can influence on the fire resistance of CFT. As $280{\times}280{\times}6$ CFT columns with the concrete strengths of 24 MPa and 40 MPa and the axial load ratios of 0.9, 0.6, and 0.2 in accordance with KS F 2257-1 and 7 were heated with loading to examine the fire resistance performance, the fire resistance used to 24 MPa concrete showed 27, 113, and 180 minutes according to the axial load ratios, 0.9, 0.6, and 0.2 respectively. In case of 40 MPa concrete, the fire resistance were turned out to be 19 and 28 minutes for the axial load ratios, 0.9 and 0.6 respectively. The results of fire resistance with 40 MPa concrete showed the much lower fire resistance performance than those of 24 MPa concrete. In case of 40 MPa, the fire resistance performance was not increased significantly according to the axial load ratio than that of 24 MPa. The main reason why the higher concrete strength showed lower fire resistance than that of lower guessed the internal stress had the concrete strength weak.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.251-259
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• 2003

In this paper, an analytical approach hwas been conductsed to clarify the relationships between the axial force and the deformation capacity of steel- encased reinforced- concrete beam-columns. The analytical model was defined as a cantilever. Several parameters influencing the inelastic performance of the beam-columns were selected, as follows: including encased steel area ratios, and sectional shapes of the encased steel, material strengths, and shear-span- to-depth ratios. The Analytical results of the analysis showed that the axial force had to have a maximum limit to ensure the stable behavior of a steel- encased reinforced- concrete beam-column when it was subjected to both axial and repeated lateral loading under a constant rotation angle amplitude. The maximum axial force of the beam-column to be resisted under cyclic lateral loading was defined as the stable-limit axial force to ensure the required rotation angle amplitude. The Analytical results of the analysis indicate that the stable-limit axial load ratio increases as the steel strength increases or as the compressive strength of the concrete decreases. The stable-limit axial load ratio decreases as the encased steel ' s sectional area increases in the case of a 1-shaped sections and it is almost not influenced by the steel sectional area in the case of a cross-shaped section.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.209-219
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• 2000

Concrete Filled steel Tube(CFT) Column has an excellent structural capacities in accordance with an interaction effect between the steel tube and concrete. Recently, CFT structure has been focussed on a structural system for a high-rise buildings. The purpose of this study is to evaluate a strength and deformation capacity of CFT square columns subjected to constant axial and cyclic lateral load. The test parameters are diameters to thickness ratio of steel tube, axial load ratios, concrete strengths, load applying types and whether or not filled concrete. Total sixteen specimens are fabricated to clarify the energy absorbtion capacity of CFT columns. Experimental results are summarized for maximum strength, initial stiffness and deformation capacity.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.453-461
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• 2014

In this study, the stub columns of built-up H-section and square hollow section subjected to eccentrical loads are tested to evaluate the applicability of the structural members with 800MPa high-strength steel (HSA800) on current design specification. Analytical studies of FE model are conducted to validate the test results and then the verified FE models are used for extensive parametric studies for checking up the applicability of current design code. The parameters are width-to-thickness ratios and axial load ratios. From P-M correlations on parameter models, all stub columns with non-compact sections exceed the current design requirements about axial force and flexural strength ratios are sufficiently secured as the axial load ratios are decreased. The built-up hollow sections with slender section model do not satisfy the current design specification about axial force.

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.207-217
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• 2003

The Concrete Filled Steel Tube (M) Column has excellent structural capacities that are in accordance with the interaction effect between the steel tube and concrete. CFT structure has been focussed on a struc tural system for high-rise buildings. The purpose of this study is to evaluate the strength and deformation capacities of CFT columns that are subject to constant axial and cyclic lateral load. The test parameters are diameters to the thickness ratio of the steel tube, axial load ratios, and the shapes of the tube. Total eighteen specimens were fabricated to clarify the energy absorption capacity of the CFT columns. Experimental results were summarized for their ultimate strengths and deformation capacities.

• Land and Housing Review
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• v.7 no.1
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• pp.31-41
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• 2016

In this paper, we propose experimental results, which target the major variables that influence the structural performance of a wall, as well as the resulting seismic and hysteretic behavior. Results also provide the basis for the application of performance based design by identifying the nonlinear hysteretic behavior of the wall with boundary element details recently proposed in previous study by Chun et al(2011). From the experimental results, the crack and fracture patterns of a specimen, which adopt the proposed boundary element details, showed similar tendencies regardless of whether axial force or high performance steel bars is applied. Furthermore, results show that the maximum strength of the specimen can be predicted accurately based on the design equation proposed by the standard. In addition, with a higher axial force, there is a tendency that both the initial load and maximum strength increase as deformation capacity reduces, requiring consideration of the reduced deformation capacity due to a high axial force. For walls under such high axial forces, using high performance steel bars is a very effective manner of enhancing deformation capacity. Therefore, reinforcing the plastic hinge region with boundary elements using high performance steel bars is preferable.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.49-58
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• 2013

Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with constant axial load. Test specimens were designed with 4.5 aspect ratio. The selected test variables are longitudinal steel ratio, transverse steel ratio, yielding strength of longitudinal steel and axial load ratio. The test results of columns with different longitudinal steel ratio, transverse steel ratio and axial load ratio showed different seismic performance such as equivalent damping ratio, residual displacement and effective stiffness. It was found that the column with low strength of longitudinal steel showed significantly reduced seismic performance, especially for equivalent damping ratio and residual displacement. The regulation of flexural over-strength is adopted by Korea Bridge Design Specifications (Limited state design, 2012). The test results are compared with nominal strength, result of nonlinear moment-curvature analysis and the design specifications such as AASHTO LRFD and Korea Bridge Design Specifications (Limited state design).