• Steel and Composite Structures
• /
• v.38 no.4
• /
• pp.431-445
• /
• 2021

This paper presents experiments and theoretical analysis on shear behavior of eight concrete-encased square concrete-filled steel tube (CECFST) specimens and three traditional reinforced concrete (RC) specimens. A total of 11 specimens with the test parameters including the shear span-to-depth ratio, steel tube size and studs arrangement were tested to explore the shear performance of CECFST specimens. The failure mode, shear capacity and displacement ductility were thoroughly evaluated. The test results indicated that all the test specimens failed in shear, and the CECFST specimens enhanced by the interior CFST core exhibited higher shear capacity and better ductility performance than that of the RC specimens. When the other parameters were the same, the larger steel tube size, the smaller shear span-to-depth ratio and the existence of studs could lead to the more satisfactory shear behavior. Then, based on the compatible truss-arch model, a set of formulas were developed to analytically predict the shear strength of the CECFST members by considering the compatibility of deformation between the truss part, arch part and the steel tube. Compared with the calculated results based on several current design specifications, the proposed formulas could get more accurate prediction.

• Steel and Composite Structures
• /
• v.47 no.6
• /
• pp.781-794
• /
• 2023

In order to directly apply seawater and sea sand in construction without desalination, a type of square concrete-filled steel tube (CFST) encased with prefabricated seawater sea-sand concrete filled Polyvinyl Chloride (PVC)/Glass Fiber Reinforced Polymer (GFRP) tube column was proposed. Twenty short columns were tested under uniaxial loads, and the test parameters included inner tube types, seawater sea-sand concrete replacement ratios, concrete strength, the wrapping area of Carbon Fiber Reinforced Polymer (CFRP) strips and the thickness of GFRP tube. The effects of the parameters on failure modes, loading capacity, ductility and strain responses were discussed. All the tested specimens failed with serious buckling of the steel tubes and fracture of the inner tubes. The specimens had good residual bearing capacity corresponding to 64% to 88.9% of the peak capacity. The inner GFRP tubes and PVC tubes wrapped by CFRP strips provided stronger confinement to the core concrete, and were good choices for the proposed columns. Moreover, an analytical model for the composite column with different inner tube types was proposed.

• Steel and Composite Structures
• /
• v.47 no.1
• /
• pp.121-134
• /
• 2023

This paper tested 11 concrete-encased concrete-filled steel tube (CFST) composite columns and one reinforced concrete column under combined axial compression and lateral loads. The primary parameters, including the loading system, axial compression ratio, volume stirrup ratio, diameter-to-thickness ratio of the steel tube, and stirrup form, were varied. The influence of the parameters on the failure mode, strength, ductility, energy dissipation, strength degradation, and damage evolution of the composite columns were revealed. Moreover, a two-parameter nonlinear seismic damage model for composite columns was established, which can reflect the degree and development process of the seismic damage. In addition, the relationships among the inter-story drift ratio, damage index and seismic performance level of composite columns were established to provide a theoretical basis for seismic performance design and damage assessments.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.4 s.50
• /
• pp.85-94
• /
• 2006

In the design of bridge piers in seismic area, the ductility requirement is the most important factor. In order to enhance the seismic performance of RC columns, it is necessary to make the ductility of columns larger by covering RC columns with steel tubes or confining RC columns by arranging transverse reinforcements such as hoop ties closely. Using core steel composite columns is useful as one of the reinforcing RC columns. In this paper, quasi-static tests on concrete encased composite columns with single core steel or multiple steel elements were performed to investigate the seismic performance of the composite columns. Eight concrete-encased composite specimens were fabricated. The cross-sections of these specimens are composed of concrete-encased H-shaped structural steel columns and a concrete-encased circular tube with partial in-filled concrete. Test parameters were the amount of the transverse reinforcements, type and number of encased steel member. Through the tests, it was evaluated the ductility of SRC composite specimens. It has become clear from the test results that encased steel elements makes the deformation capacity of the columns to be larger. The displacement ductility and lateral strength of specimen with concrete-encased circular tube were indicated the biggest value.

• Steel and Composite Structures
• /
• v.22 no.1
• /
• pp.63-77
• /
• 2016

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.5
• /
• pp.353-359
• /
• 2017

The purpose of this study is to evaluate the strength and behavior of the composite member in case of concrete filled steel tube embedded in concrete for application concrete filled steel tube to steel rib support in tunnel. A total of six beam specimens were prepared for steel tube in-filled with plain concrete and aerated concrete, and static bending tests were performed. As a result, the member of concrete steel tube embedded with plain concrete showed higher strength than those with aerated concrete. However, it was found that the flexural strength of member with reinforcing bar around the steel tube is more influenced by the amount of the reinforcing bar than the type of the filled concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.10a
• /
• pp.210-214
• /
• 1995

Research on concrete-filled steel columns has been conducted. It is also well known that the load and deformation capacity of concrete-filled steel columns are considerable larger than those of widely used reinforced concrete columns and steel encased concrete columns because the concrete core in the steel is confined laterally by the steel. But, most of these works focused on columns with strength enhancement by the confinement effect, so that no local buckling prevented by the concrete. columns because the concrete core in the steel is confined laterally by the steel. But, most of these works focused on columns with strength enhancement by the confinement effect, so that no local buckling prevented by the concrete. This paper, therefore, presents on the stress-strain relation of a concrete filled rectangular steel tube under axial compression. As the results, the axial load verse average axial strain relationship of concrete-filled rectangular steel columns were very stable. The small B/t ratios in concrete-filled rectangular steel columns aren't affected prevention of local buckling but strength enhancement by confinement effect.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2006.03a
• /
• pp.269-275
• /
• 2006

In the design of bridge piers in seismic area, the ductility requirement is one of the most important design criteria. In order to enhance the seismic performance of RC columns, it is necessary to make the ductility of columns larger by covering RC columns with steel tubes or confining RC columns by arranging transverse reinforcement such as hoop ties closely. Concrete encased composite columns can be utilized for bridge piers especially in seismic area. In this paper, finite element analyses are performed to study the nonlinear behavior of concrete encased composite columns with single core steel or multiple steel elements under static and quasi-static loads. The cross-sections of these specimens ate composed of concrete-encased H-shaped structural steel columns and a concrete-encased circular tube with partial in-filled concrete. Test parameters were the amount of the transverse reinforcement, encased steel member, and loading axis. Through the comparison between FE analyses and test results, adequate material models for confined concrete and unconfined concrete ate investigated. After getting the proper analysis models for composite columns, several parameters are considered to suggest design considerations on the details of composite piers.

• Journal of Korean Society of Steel Construction
• /
• v.26 no.1
• /
• pp.31-42
• /
• 2014

In this paper, concrete-filled steel tubular columns encased with precast reinforced concrete were studied. Four eccentrically loaded columns and a concentrically loaded column were tested to investigate the axial load-carrying capacity. The test parameters were the use of fiber reinforcement for cover concrete, eccentricity, column length, and lateral reinforcement. The maximum axial loads of the specimens agreed with the nominal strengths predicted by KBC 2009. However, in some specimens, the load carrying capacity quickly decreased after the peak strength due to spalling of the cover concrete.

• Journal of Korean Society of Steel Construction
• /
• v.27 no.1
• /
• pp.43-52
• /
• 2015

Constructions of buildings downtown are increasing as much as ever with a strong demand. Top-Down Method is suitable for its advantage in minimizing its disturbance to the neighborhood. Pre-founded when applied to CFT Column on-site welded is required for splicing. To complement the welded built-up square composite Column was developed. Top-down process will be pouring concrete in accordance with a step-by-step process. Thus, Pre-founded Column and cover concrete to determine the stress condition. Therefore, Concrete filled steel square tubular columns encased with precast concrete were studied. Five Centrally loaded Columns were tested to investigate the axial load carrying capacity. we analyzed the strength and behavior of CET Column by Loading conditions and concrete strength, thickness of cover concrete through structure experiments.