• Steel and Composite Structures
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• v.8 no.4
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• pp.265-280
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• 2008

An investigation on the combined effect of foundation type, foundation flexibility, axial load and PR (semi-rigid) connections on the natural frequencies of steel frames is presented. These effects were investigated using a suitable modified FE program for cases where the foundation flexibility, foundation connectivity, and semi-rigid connections could be treated as equivalent linear springs. The effect of axial load on the natural frequency of a structure was found to be significant for slender structures subjected to high axial loads. In general, if columns of medium slenderness are designed without consideration of axial load effects, the frequency of the structure will be overestimated. Studies on the 3-story Los Angeles PR SAC frame indicate that the assumption of rigid connections at beam-column and column-base interfaces, as well as the assumption of a rigid foundation, can lead to significant errors if simplified design procedures are used. These errors in an equivalent static analysis are expected to lead to even more serious problems when considering the effect of higher modes under a non-linear dynamic analysis.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.407-414
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• 1999

Sand drain as a vertical drainage is widely used in soft ground improvement. Recently, sand, the principal source of sand drain, is running out. A laboratory model test was carried out to utilize gravel as a substitute for sand. Though which the characteristics of gravel are compared to those of sand for engineering purpose. According to the test, the settlement was found to be smaller in gravel drain than in sand drain. The increase in bearing capacity by gravel rile explains the result. The clogging effect was not found in gravel column. As a result, it is assumed that gravel is relatively acceptable as a drainage material. Gravel material seems better than sand material in bearing capacity and it is found that bearing capacity is larger when gravel is used as compaction pile than as drain from in-situ test on bearing capacity. Increase of bearing capacity with gravel pile means an effect of composite ground by stiffness of gravel material. It can lie supposed to use gravel pile instead of sand pile in view of consolidation effect and bearing capacity.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.147-156
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• 2012

In recent years, many high-rise buildings have been constructed in irregular structural system with inclined columns, which may have effect on the structural behavior of beam-column joints. Since the external load leads to shear and flexural forces on the inclined columns in different way from those on the conventional vertical columns, failure mode, resistant strength, and ductility capacity of the inclined column-beam joints may be different than those of the perpendicular beam-column joints. In this study, six RC inclined beam-column joint specimens were tested. The main parameter of the specimens was the angle between axes of the column and beam (90, 67.5, and 45 degree). Test results indicated that the structural behavior of conventional perpendicular beam-column joint was different to that of the inclined beam-column joints, due to different loading conditions between inclined and perpendicular beam-column joints. Both upper and lower columns of perpendicular beam-column joints were subjected to compressive force, while the upper and lower columns of the inclined beam-column joints were subjected to tensile and compressive forces, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.5
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• pp.194-202
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• 2006

In the present study, stiffness prediction methodologies for flat-plate structures were evaluated in comparison with the experimental results on the full-scale slab-column connections of flat-plate structures. The methodologies are as follows: the methodology proposed by Jacob S. Grossman and the methodology proposed by Choi & Song. The former does not predict the stiffness change of the slab-column connection due to the change in the column section shape and the latter overestimates the stiffness when edge length of the column section in the loading direction is long. In the present study, the equation to calculate the effective width of slabs was modified to reflect the effect of the change in the column section shape.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.3
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• pp.153-158
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• 2020

In this study, a numerical approach for evaluating the resisting capacity of a partial concrete-filled steel tube (CFST) column is introduced. By strengthening the plastic hinge part of a traditional reinforced concrete column with a steel tube, a partial CFST shows a similar bending moment capacity as that of a full CFST column but with reduced material cost. To conduct an elaborate numerical analysis of a partial CFST column, an improved bond-slip model is applied to a finite element (FE) model at the interface between the steel tube and in-filled concrete. This numerical model is verified through the results of a double curvature bending-compression test. A parametric study with the proposed numerical model is used to obtain the load moment interaction diagrams for evaluating the resisting capacity based on various dimensions. Finally, the required strengthening length is estimated for each degree of thickness of the steel tube, and the failure mechanism of the partial CFST column based on the dimensions of the steel tube are identified.

• Journal of Korean Association for Spatial Structures
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• v.6 no.1 s.19
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• pp.55-63
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• 2006

Concrete-filled steel columns consist of circular, square or rectangular hollow sections filled concrete. Much research has studied for the behavior of concrete-filled steel structures. The advantages from structural point of view are the triaxial confinement of the concrete within the section, and the fire resistance of the column which largely depends on the residual capacity of the concrete core. The axial capacity of a concrete-filled rectangular or circular section is enhanced by the confining effect of the steel section on the concrete which depends in the magnitude on the shape of the section and the length of the column. Buckling tends to reduce the benefit of confinement on the squash load as the column slenderness increases. In circular sections it is possible to develop the cylinder strength of the concrete. When compare with reinforced concrete columns, the concrete-filled composite column possesses much better strength and ductility in shear and generally in flexure also. Many researches are being conducted about concrete filled steel column to get these advantages in building design. In this paper it is provided to the basic experimental study of compression behavior of the circular and rectangular tubular steel pipe filled with concrete.

• Steel and Composite Structures
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• v.35 no.1
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• pp.13-27
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• 2020

To investigate the stress-strain relation of PVC-FRP Confined Concrete (PFCC) column with RC ring beam joint subjected to eccentric compression, the experiment of 13 joint specimens, which were designed with principle of "strong joint and weak column", were presented. Several variable parameters, such as reinforcement ratio, width and height of ring beam, FRP strips spacing and eccentricity, were considered. The specimens were eventually damaged by the crushing of concrete, the fracture of PVC tube and several FRP strips. With the FRP strips spacing or eccentricity increased, the ultimate carrying capacity of specimens declined. The strain of FRP strips and axial strain of PVC tube decreased as FRP strips spacing decreased. The decrease of eccentricity would slow down the development of strain of FRP strips and axial strain of PVC tube. The slope of stress-strain curve of PFCC column decreased as FRP strips spacing or eccentricity increased. The ultimate strain of PFCC column reduced as FRP strips spacing increased, while the effect of eccentricity on the ultimate strain of PFCC was not distinct. Considering the influence of eccentricity on the stress-strain relation, a modified stress-strain model for conveniently predicting the weak PFCC column and strong RC ring beam joint under eccentric compression was proposed and it was in good agreement with the experimental data.

• Structural Engineering and Mechanics
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• v.61 no.4
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• pp.527-538
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• 2017

The evaluation of the loss-of-support conditions of frictional beam-to-column connections using simplified numerical models describing the transverse response of a portal-like structure is presented in this paper considering the effects of the seismic-hazard disaggregation. Real earthquake time histories selected from European Strong-motion Database (ESD) are used to show the effects of the seismic-hazard disaggregation on the beam loss-of-support conditions. Seismic events are classified according to different values of magnitudes, epicentral distances and soil conditions (stiff or soft soil) highlighting the importance of considering the characteristics of the seismic input in the assessment of the loss-of-support conditions of frictional beam-to-column connections. A rigid and an elastic model of a frame of a precast industrial building (2-DoF portal-like model) are presented and adopted to find the minimum required friction coefficient to avoid sliding. Then, the mean value of the minimum required friction coefficient with an epicentral distance bin of 10 km is calculated and fitted with a linear function depending on the logarithm of the epicentral distance. A complete parametric analysis varying the horizontal and vertical period of vibration of the structure is performed. Results show that the loss-of-support condition is strongly influenced by magnitude, epicentral distance and soil conditions determining the frequency content of the earthquake time histories and the correlation between the maxima of the horizontal and vertical components. Moreover, as expected, dynamic characteristics of the structure have also a strong influence. Finally, the effect of the column nonlinear behavior (i.e. formation of plastic hinges at the base) is analyzed showing that the connection and the column are a series system where the maximum force is limited by the element having the minimum strength. Two different longitudinal reinforcement ratios are analyzed demonstrating that the column strength variation changes the system response.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.101-109
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• 2018

Modular structural systems have been used increasingly for low- and mid-rise structures such as school and apartment buildings. Studies have recently been conducted on the application of the modular structural system to high-rise buildings. To provide sufficient resistances and economical construction for the high-rise modular structural system, a composite unit modular structure was proposed. In this study, the strength of the non-symmetric composite column for the proposed composite unit modular structure was investigated through a series of tests. The experimental study focused on the effect of the slenderness of the column, eccentricity, and through bars on the strength of such a column. Design equations for the non-symmetric column for a modular unit structure were also proposed. From the results, it was found that the proposed design equations provide reasonable strength prediction of the non-symmetric composite column for the modular unit structure.

• International journal of steel structures
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• v.18 no.4
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• pp.1153-1166
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• 2018

This paper was concerned with the nonlinear analysis on the overall stability of H-type honeycombed composite column with rectangular concrete-filled steel tube flanges (STHCC). The nonlinear analysis was performed using ABAQUS, a commercially available finite element (FE) program. Nonlinear buckling analysis was carried out by inducing the first buckling mode shape of the hinged column to the model as the initial imperfection with imperfection amplitude value of L/1000 and importing the simplified constitutive model of steel and nonlinear constitutive model of concrete considering hoop effect. Close agreement was shown between the experimental results of 17 concrete-filled steel tube (CFST) specimens and 4 I-beams with top flanges of rectangular concrete-filled steel tube (CFSFB) specimens conducted by former researchers and the predicted results, verifying the correctness of the method of FE analysis. Then, the FE models of 30 STHCC columns were established to investigate the influences of the concrete strength grade, the nominal slenderness ratio, the hoop coefficient and the flange width on the nonlinear stability capacity of SHTCC column. It was found that the hoop coefficient and the nominal slenderness ratio affected the nonlinear stability capacity more significantly. Based on the results of parameter analysis, a formula was proposed to predict the nonlinear stability capacity of STHCC column which laid the foundation of the application of STHCC column in practical engineering.