• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.579-589
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• 2003

Most beam-to-column connections are symmetrically reinforced because of the reverse action caused by earthquakes. However, in weak-earthquake regions like Korea, asymmetrically reinforced connections could be used. In particular, the connections between concrete-filled tube (CFT) column and H-shape beam could be applied using a simplified lower diaphragm. The tensile capacity or Combined Cross Diaphragm for upper reinforcing was tested using a simple tension test. Four types for lower reinforcing combined Cross, none, horizontal T-bar, and vertical plate were tested using the ANSI/AISC SSPEC 2002 loading program. Horizontal T-bar and stud bolts in vertical flat, bar transmit tensile stress from the beam's bottom flange to filled concrete. All test specimens satisfied 0.01 radian inelastic rotational requirement in ordinary moment frame of AISC seismic provision. According to the results of the parametric studies simplified lower diaphragms demonstrated outstanding strength, stiffness, and plastic deformation capacity which could lead to more sufficient seismic performance in the field.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.431-439
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• 2014

Concrete filled tubular columns are widely used because the mutual reaction between the concrete and the tube improves strength and ductility of the columns. In an attempt to secure efficient use of members, built-up square columns featuring large width-thickness ratio and the use of thin steel plates are suggested in this study. In order to evaluate the structural characteristics and seismic performance of the column-to-beam connections of the new shape columns, cyclic load test of T-shaped column-to-beam connections was conducted with variables of diaphragms and concrete-filling. Moment-rotational angle relationship, dissipated energy and failure behavior were compared to evaluate stress transfer mechanism of the new shape built-up square column-to-beam connections associated with the variables.

• Steel and Composite Structures
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• v.43 no.3
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• pp.327-340
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• 2022

A vast amount of experimental and analytical research has been conducted related to the seismic behavior and performance of concrete filled steel tubular (CFT) columns. This research has resulted in a wealth of information on the component behavior. However, analytical and experimental data for structural systems with CFT columns is limited, and the well-known behavior of steel or concrete structures is assumed valid for designing these systems. This paper presents the development of an analytical model for nonlinear analysis of composite moment resisting frame (CFT-MRF) systems with CFT columns and steel wide-flange (WF) beams under seismic loading. The model integrates component models for steel WF beams, CFT columns, connections between CFT columns and WF beams, and CFT panel zones. These component models account for nonlinear behavior due to steel yielding and local buckling in the beams and columns, concrete cracking and crushing in the columns, and yielding of panel zones and connections. Component tests were used to validate the component models. The model for a CFT-MRF considers second order geometric effects from the gravity load bearing system using a lean-on column. The experimental results from the testing of a four-story CFT-MRF test structure are used as a benchmark to validate the modeling procedure. An analytical model of the test structure was created using the modeling procedure and imposed-displacement analyses were used to reproduce the tests with the analytical model of the test structure. Good agreement was found at the global and local level. The model reproduced reasonably well the story shear-story drift response as well as the column, beam and connection moment-rotation response, but overpredicted the inelastic deformation of the panel zone.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.4024-4030
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• 2010

Axial load tests and cyclic load tests for FRP reinforced rectangular CFT columns were carried out The main parameters were width-thickness ratio of a steel tubeand FRP layer numbers for the axial load tests and were concrete strength and FRP layer numbers for cyclic load tests. The maximum strength and ductility capacity were compared between the current CFT columns and the FRP reinforced CFT columns. Finally, the axial design formulas were presented for the FRP reinforced CFT columns.

• International Journal of High-Rise Buildings
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• v.5 no.3
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• pp.213-220
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• 2016

The "China Zun" tower in Beijing will rise to 528 meters in height and will be the tallest building in Beijing once built. Inspired by an ancient Chinese vessel, the "Zun", the plan dimensions reduce gradually from the bottom of the tower to the waist and then expand again as it rises to form an aesthetically beautiful and unique geometry. To satisfy the structural requirement for seismic and wind resistance, the structure is a dual system composed of a perimeter mega structure made of composite mega columns, mega braces, and belt trusses, and a reinforced-concrete core with steel plate-embedded walls. Advanced parametric design technology is applied to find the most efficient outer-perimeter structure system. The seismic design basically follows a mixed empirical and performance-based methodology that was verified by a shaking table test and other specimen lab tests. The tower is now half-way through its construction.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.300-307
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• 2005

Steel Reinforced Concrete (SRC) composite column has several advantage such as excellent durability, rapid construction, reduction of column section. Due to these aspect, applications of SRC columns to bridge piers are continuously increasing. For the design of relatively large SRC columns for bridge piers, it is necessary to check the current design provisions which were based on small section having higher steel ratio. In this study, seven concrete encased composite columns were fabricated and static tests were performed. Embedded steel members were a H-shape rolled beam and a partially filled steel tube. Based on the test results, the ultimate strength according to section details and local behavior were estimated. For the analysis of inelastic behavior of the SRC column, the cracked section stiffness of the columns was evaluated and compared with calculations. The stiffness of the cracked section showed that 25% of the initial value and this stiffness reduction occurred at 85% of the ultimate load in the experiments.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.747-754
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• 2017

The Concrete-Filled Tube (CFT) system was developed for its excellent structural performance, such as its good stiffness, stress and ductility, which is derived from the mechanical advantages of its composite structure. However, it is known that the flat type of reinforcing plates need stiffeners placed at a certain distance from each other to avoid buckling failure, which increases the cost accordingly. This paper investigates the contribution of the rib elements placed inside the steel tube for the purpose of increasing the bond strength between the steel and concrete and fire performance with no additional protection. The test results also demonstrate the effectiveness of the corrugated rib's shape against fire. The results of this study showed that the buckling prevention and fire resistance performance criteria were satisfied by the application of the inner surface attachment rib, due to the resulting increase in the strength of the CFT column. Therefore, it is considered that the CFT method using the corrugated rib structure reinforcement developed through this study satisfies the structural and fire resistance performance criteria without the need for a refractory coating. Future studies will be needed to make the process efficient and economical for factory production.

• Structural Engineering and Mechanics
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• v.50 no.4
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• pp.501-524
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• 2014

This paper presents a type of composite box girder with corrugated webs and concrete filled steel tube slab to overcome cracking on the web and reduce self-weight. Utilizing corrugated steel web improves the efficiency of prestressing introduced into the top and bottom slabs due to the accordion effect. In order to understand the loading capacity of such new composite structure, experimental and numerical analyses were conducted. A full-scale model was loaded monotonically to investigate the deflection, strain distribution, loading capacity and stiffness during the whole process. The experimental results show that test specimen has enough loading capacity and ductility. Based on experimental works, a finite element (FE) model was established. The load-displacement curves and stress distribution predicted by FE model agree well with that obtained from experiments, which demonstrates the accuracy of proposed FE model. Moreover, simplified theoretical analysis was conducted depending on the assumptions which were confirmed by the experimental and numerical results. The simplified analysis results are identical with the tested and numerical results, which indicate that simplified analytical model can be used to predict the loading capacity of such composite girder accurately. All the findings of present study may provide reference for the application of such structure in bridge construction.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.299-310
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• 2015

CFT(Concrete-Filled Tube) structures have problems at processing cause closed section and concrete filling problems. In this study, a CFT structure that uses different types of diaphragms in its upper and lower connections to improve the concrete filling was tested and analyzed via the FEM program. Implementation of variable analysis of EP-T type to find out the reason that effect on the resistance force of the connection. As a result, through experiments and analysis investigated the structural characteristics of circular CFT beam-to-column connection.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.443-450
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• 2012

In this study, This study investigates the axial load behavior of concrete-filled steel columns using seismic rectangular steel tube with the width-to-thickness and slenderness ratio. Due to cold-roll forming and cold-press forming of steel tube, the flat part and the corner part of the rectangular steel tubes are changed in the material properties compared to SN-steel plate. It was showed the tendency to increase yield strength, tensile strength and upper limit of yield ratio This phenomenon affects the nonlinear behavior after local buckling of the steel tube. Therefore, the coupon test was performed by the processing of rectangular steel tube, in order to assess forming performance. And a total of 6 CFT-columns were tested under monotonic loading condition. Main parameters were the width-thickness ratio and the slenderness ratio.