• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.601-604
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• 1999

The objective of this study is to investigate the flexural behavior of reinforced concrete columns confined by lateral ties. This test was carried on the twelve reinforced concrete columns, 200$\times$200$\times$800mm size. objected to flexure and constant axial loads. The main variables are concrete strength, the configuration of lateral ties and the amount of lateral ties. Test results indicated that steel configuration plays an important role in column behavior, and a proper configuration of lateral ties can be more ductile than the reduce of the space of lateral ties. By this experiment, the ductility of high-strength concrete columns designed on A.C.I Code is not adequate, and are concluded that the design of high-strength concrete column is executed by more lateral ties under high axial loads.

• Structural Monitoring and Maintenance
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• v.1 no.3
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• pp.323-338
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• 2014

In this study a new innovative method of earthquake-resistant strengthening of reinforced concrete structures is presented for the first time. Strengthening according to this new method consists of the construction of steel fiber ultra-high-strength concrete jackets without conventional reinforcement which is usually applied in the construction of conventional reinforced concrete jackets. An innovative solution is proposed also for the first time that ensures a satisfactory seismic performance of existing reinforced concrete structures, strengthened by using composite materials. The weak point of the use of such materials in repairing and strengthening of old R/C structures is the area of beam-column joints. According to the proposed solution, the joints can be strengthened with a steel fiber ultra-high-strength concrete jacket, while strengthening of columns can be achieved by using CFRPs. The experimental results showed that the performance of the subassemblage strengthened with the proposed mixed solution was much better than that of the subassemblage retrofitted completely with CFRPs.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.77-85
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• 2001

Concrete filled steel tubular (CFT) columns are becoming popular in structural applications. The increased popularity comes from their excellent structural properties such as high strength, high ductility, and large energy absorption capacity. However, the disadvantage feature of CFT column is the difficulty in predicting its time dependant characteristic (i.e., creep and shrinkage) of inner concrete. The time dependent behavior of CFT column can cause serious serviceability problems. Therefore, it is necessary to investigate the long term behavior of CFT column. This paper presents analytical and experimental studies on long-term behavior of CFT-column under a central axial loading. Two loading cases are considered in the research; (1) the load applied only at the inner core concrete of CFT-column and (2) the load applied simultaneously on both concrete and steel tube. Analysis method using the bond strength model is proposed and conclusions on long-term properties of CFT-column can be derived from the results.

• Steel and Composite Structures
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• v.34 no.6
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• pp.803-818
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• 2020

Semi-rigid connections with blind bolts could solve the difficulty that traditional high strength bolts were unavailable to splice a steel/composite beam to a closed section column. However, insufficient investigations have focused on the performance of semi-rigid connection to square concrete filled double-skin steel tubular (CFDST) columns. In this paper, a component model was developed to evaluate the mechanical behavior of semi-rigid composite connections to CFDST columns considering the stiffness and strength of column face in compression and column web in shear which were determined by the load transfer mechanism and superstition method. Then, experimental investigations on blind bolted composite joints to square CFDST columns were conducted to validate the accuracy of the component model. Dominant failure modes of the connections were analyzed and this type of joint behaved semi-rigid manner. More importantly, strain responses of CFDST column web and tubes verified that stiffness and strength of column face in compression and column web in shear significantly affected the connection mechanical behavior owing to the hollow part of the cross-section for CFDST column. The experimental and analytical results showed that the CFDST column to steel-concrete composite beam semi-rigid joints could be employed for the assembled structures in high intensity seismic regions.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.159-160
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• 2009

The application of 40MPa high strength concrete was accepted as a goal for improving durability and reducing column's section in concrete bridge piers. As a result of applying 40MPa high strength concrete, it could be achieved that column diameter and coping height were reduced into 0.6m, 0.4m, respectively. And crack by heat evolution of hydration did not generate, because of a careful quality and curing control of high strength concrete.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.707-714
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• 2014

CFT (Concrete-Filled Tube) is a type of steel column comprised of steel tube and concrete. Steel tube holds concrete and the concrete inside tube takes charge of compressive load. This study presents structural performance of the CFT column which has 73~100 MPa high strength concrete inside. Fluidity, mechanical compression, pump pressure test in flexible pipe were conducted for understanding properties of the high strength concrete. Material properties were achieved by various experimental tests, such as slump, slump flow, air content, U-box, O-Lot, L-flow. In addition, mock-up tests were conducted to monitor concrete filling, hydration heat, compressive strength. From construction sites in Sang-am dong and University of Seo-kang, long-term behaviors could be effectively predicted in terms of ACI 209 material model considering elastic deformation, shrinkage and creep.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.457-460
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• 2008

This study evaluated fire resistance performance for polypropylene/steel fiber reinforced high strength concrete column. Full-size columns were constructed and tested with or without fibers using ISO-834 fire curve. As the result of test, non-fiber high strength concrete column specimen occurred serious spalling and indicated rapidly internal temperature increase. Specimen with polypropylene fiber occurred not spalling. Specimen with hybrid fiber occurred not spalling as well as does not propagated temperature propagation. Therefore, hybrid fiber reinforced column specimen indicated a good fire resistance performance than other cases.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.430-433
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• 2006

The reinforced concrete column confined by square steel tubes(RCST) is a reinforced column (RC) confined by thin steel tubes which cover over the full length of the column but terminates 15mm from the column's ends. The steel tube is in uniaxial tension stress state and won't buckle when the column sustains axial load. This will highly increase the bearing capacity and ductility of the columns. The hysteretic behavior of four square RCST columns and one square RC column were experimentally studied under constant axial load and lateral cyclic load. The wide-to-thickness (D/t) ratio of RCST columns employed in this research is 75. The main variables of the experiment were axial load ratio and compressive strength of the concrete. Based on the findings in this research, RCST columns exhibits high lateral strength, ductility, and energy dissipation ability.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.149-160
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• 1999

This paper is a part of a research aimed at the verification of basic design rules of high-strength concrete columns. A total of 32 column specimens were tested to investigate structural behavior and strength of eccentrically loaded reinforced concrete tied columns. Main variables included in this test program were concrete compressive strength. steel amount, eccentricity, and slenderness ratio. The concrete compressive strength varied from 356 kg/$cm^2$ to 951 kg/$cm^2$ and the longitudinal steel ratios were between 1.13 % and 5.51 %. Test results of column sectional strength are compared with the results of analyses by ACI rectangular stress block, trapezoidal stress block, and modified rectangular stress block. Axial force-moment-curvature analysis is also performed for predicting axial load-moment strength and compared with the test results. The ACI rectangular stress block provides over-estimated column strengths for the lightly reinforced high strength column specimens. The calculated strengths by moment-curvature analyses are highly affected by $k_3$ values of the concrete stress-strain curve. Observed failure mode. concrete ultimate strain, and stress block parameters are discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.577-578
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• 2009

For cases where the column concrete strength exceeds 1.4 times the slab concrete strength, the KCI Code requires that either: puddled high-strength concrete(HSC) be used in the slab, or the use of vertical dowels and spirals through the joint, or the use of an effective concrete strength in the joint. This paper studies on the third strategy. A prediction model of the effective concrete strength for interior columns was proposed using an analogy of brick and mortar in brick masonry. The proposed prediction model is verified by comparison with experimental results and various design equations.