• Structural Engineering and Mechanics
• /
• v.84 no.5
• /
• pp.575-590
• /
• 2022

In this paper, bond-slip behavior of high strength concrete filled circular steel tube (HSCFCST) after elevated temperatures treatment was studied. 17 specimens were designed for push-out test. The influence was discussed as following parameters: (a) concrete strength, (b) constant temperature, and (c) bond length. The results showed that (1) after elevated temperatures treatment, the bond strength of the HSCFCST specimens increased first and then decreased with temperature rising; (2) the bond strength increased with the increase of concrete strength at room temperature, while the influence subsided after elevated temperatures treatment; (3) the strain of the circular steel tube was distributed exponentially along its length, the stress changed from exponential distribution to uniform distribution with the increase of load; (4) the bond damage process was postponed with the increase of constant temperature; and (5) the energy consumption capacity of the bonding interface increased with the rise of concrete strength and constant temperature. Moreover, computational formulas of ultimate and residual bond strength were obtained by regression, and the bond-slip constitutive models of HSCFCSTs after elevated temperatures was established.

• Smart Structures and Systems
• /
• v.20 no.2
• /
• pp.175-180
• /
• 2017

The load-carrying capacity and structural behavior of concrete-filled steel tube (CFST) structures is highly influenced by the grouting compactness in the steel tube. Due to the invisibility of the grout in the steel tube, monitoring of the grouting progress in such a structure is still a challenge. This paper develops an active sensing approach with combined piezoceramic-based smart aggregates (SA) and piezoceramic patches to monitor the grouting compactness of CFST bridge structure. A small-scale steel specimen was designed and fabricated to simulate CFST bridge structure in this research. Before casting, four SAs and two piezoceramic patches were installed in the pre-determined locations of the specimen. In the active sensing approach, selected SAs were utilized as actuators to generate designed stress waves, which were detected by other SAs or piezoceramic patch sensors. Since concrete functions as a wave conduit, the stress wave response can be only detected when the wave path between the actuator and the sensor is filled with concrete. For the sake of monitoring the grouting progress, the steel tube specimen was grouted in four stages, and each stage held three days for cement drying. Experimental results show that the received sensor signals in time domain clearly indicate the change of the signal amplitude before and after the wave path is filled with concrete. Further, a wavelet packet-based energy index matrix (WPEIM) was developed to compute signal energy of the received signals. The computed signal energies of the sensors shown in the WPEIM demonstrate the feasibility of the proposed method in the monitoring of the grouting progress.

• Journal of Korean Society of Steel Construction
• /
• v.22 no.3
• /
• pp.253-260
• /
• 2010

The purpose of this paper is to investigate the behavior of concrete-filled tube columns for footing connections. Eight specimens were tested to investigate such structural behavior according to the column base type. The specimens consisted of concrete-filled steel tube columns (or bare steel tube columns), reinforced concrete footings, and base plates (or stud connectors). The specimens were subjected to lateral cyclic load. The cyclic load was applied according to a predetermined strength sequence. The results of the experiment indicated that the flexural strength of the stud-connector- type column base is higher than that of the base-plate-type column base. The structural behavior of the concrete-filled tube column base was similar to that of the bare steel column base.

• Advances in concrete construction
• /
• v.13 no.2
• /
• pp.163-181
• /
• 2022

To study the mechanical properties of steel reinforced recycled concrete (SRRC) filled circular steel tube columns under eccentric compression loads, this study presents a finite element model which can simulate the eccentrically compressed columns using ABAQUS software. The analytical model was established by selecting the reasonable nonlinear analysis theory and the constitutive relationship of materials in the columns. The influences of design parameters on the eccentric compressive performance of columns were also considered in detail, such as the diameter-thickness ratio of circular steel tube, replacement percentage of recycled coarse aggregate (RCA), slenderness ratio, eccentricity, recycled aggregate concrete (RAC) strength and steel strength and so on. The deformation diagram, stress nephogram and load-displacement curves of the eccentrically compressed columns were obtained and compared with the test results of specimens. The results show that although there is a certain error between the calculation results and the test results, the error is small, which shows the rationality on the numerical model of eccentrically compressed columns. The failure of the columns is mainly due to the symmetrical bending of the columns towards the middle compression zone, which is a typical compression bending failure. The eccentric bearing capacity and deformation capacity of columns increase with the increase of the strength of steel tube and profile steel respectively. Compared with profile steel, the strength of steel tube has a greater influence on the eccentric compressive performance of columns. Improving the strength of RAC is beneficial to the eccentric bearing capacity of columns. In addition, the eccentric bearing capacity and deformation capacity of columns decrease with the increase of replacement percentage of RCA. The section form of profile steel has little influence on the eccentric compression performance of columns. On this basis, the calculation formulas on the nominal eccentric bearing capacity of columns were also put forward and the results calculated by the proposed formulas are in good agreement with the test values.

• Proceedings of the KSR Conference
• /
• 2002.05a
• /
• pp.183-188
• /
• 2002

In locations where the cost or concrete is relatively high, or in situations where the weight or concrete members is to be kept to a minimum, it may be economical to use hollow reinforced concrete vertical members. Hollow reinforced concrete columns with low axial load, moderate longitudinal steel percentage, and a reasonably thick wall were found to perform in a ductile manner at the flexural strength, similar to solid columns. However, hollow reinforced concrete columns with high axial load, high longitudinal steel percentage, and a thin wall were found to behave in a brittle manner at the flexural strength, since the neutral axis is forced to occur away from the inside face of the tube towards the section centroid and, as a result, crushing of concrete occurs near the unconfined inside face of the section. If, however, a steel tube is placed near the inside face of a circular hollow column, the column can be expected not to fail in a brittle manner by disintegration of the concrete in the compression zone. Design recommendation and example by moment-curvature analysis program for curvature ductility are presented. Theoretical moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted providing the stress-strain relation for the concrete and steel are known. In this paper, a unified stress-stain model for confined concrete by Mander is developed for members with circular sections.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.6 no.2
• /
• pp.32-39
• /
• 2015

So far, square concrete filled tubular(CFT) columns have been used in a limited width thickness ratio. The reason is that local buckling occurs in steel tube easily. Once the local buckling occurs, the confinement effect of steel tube on concrete disappears. In this study, we developed welded built-up square steel tube with reinforcement which are placed at the center of the tube width acts as an anchor. 3 specimens of slender welded built-up square CFT columns and 3 specimens of slender welded built-up square steel tube columns were manufactured with parameters of width(B) of steel tube, width thickness ratio(B/t). we conducted a experimental test on the 6 specimens under eccentric load, and evaluated the structural resistance and behavior of 6 specimens.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05a
• /
• pp.422-425
• /
• 2006

AISC-LRFD, ACI 318 and Korean design specifications for concrete filled circular steel tube columns do not consider the increasing of axial stiffness such as the elastic modulus and the yield strength due to the confinement effect. AISC-LRFD and ACI 318, however, shows different basic philosophy and equations for computing the elastic modulus and the strength of CFT columns. Through this experimental study, 9 circular CFT column specimens were made by varying thickness steel tube and concrete strength, the axial stiffness were compared. The comparison between the design specifications and the test results shows different values on the elastic modulus and yield strength of the CFT columns. Even though, yield strength of the CFT columns are very similar between AISC-LRFD and Korean design specifications.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.45-46
• /
• 2009

The main objective of this study is to suggest section design method of CFFT(Concrete Filled FRP Tube) structures which are considered of confined effect by FRP tube and using high strength concrete and PS strands for pier. It may be stated that the proposed method may be implemented as a rational and practical approach for CFFT section design.

• Proceedings of the KSR Conference
• /
• 2001.05a
• /
• pp.241-248
• /
• 2001

The ductility of circular hollow reinforced concrete columns with one layer of longitudinal and spiral reinforcement placed near the outside face of the section and the steel tube placed on the inside face of the section is investigated. Such hollow sections are confined through the wall thickness since the steel tube is placed. The results of analytical moment-curvature analyses for such hollow sections are compared with those for the circular section with the sane diameter. In this study, moment-curvature analyses are conducted with Mandel's confined concrete stress-strain relationship in which the effect of confinement is to increase the compression strength and ultimate strain of concrete. The moment-curvature analyses confirmed that the ductility is primarily influenced on the ultimate strain. The variables influenced on the ultimate strain is the ratio and yield strength of confining reinforcement and the compression strength for confined concrete. From this ultimate strain - the transverse reinforcement ratio relationship, the transverse reinforcement ratio for circular hollow reinforced columns with confinement is proposed. The proposed transverse reinforcement ratio is confirmed by experimental results.

• Journal of the Korean housing association
• /
• v.11 no.1
• /
• pp.171-181
• /
• 2000

The purpose of the resent research is to investigate the characteristics of sound insulation at the circular voided concrete slab in the multi-housing. In order to do this research, the method for field measurement of floor impact sound level was used following the Korea Standard F2810-1996. For the multi-housing, three kinds of circular voided concrete slabs are used to measure the characteristics of sound insulation.The results are as follows; 1.The main factor affecting the characteristics of sound insulation at the circular voided concrete slab in the multi-housing is sound-absorbing materials in the circular tube. 2. The main factor to effect the difference of sound pressure level is circular tube in the concrete slab. 3. The forms of circular tubes effect the characteristics of sound insulation at the circular tube. 4. Sound Pressure Level resulting from the piping direction of circular tubes in little different to octave band level.More study will be needed about the depth and distance of sound insulation materials, and the components of sound insulation materials for the multi-housing.