• Steel and Composite Structures
• /
• v.20 no.3
• /
• pp.599-621
• /
• 2016

In order to study the working mechanism of rectangular steel-concrete composite columns subjected to compression-bending load and further determine the seismic performance index, a bottom strengthened rectangular steel reinforced concrete (SRC) column with concealed steel plates and a bottom strengthened rectangular concrete filled steel tube (CFST) columns were proposed. Six column models with different configurations were tested under horizontal low cyclic loading. Based on the experiments, the load-bearing capacity, stiffness and degradation process, ductility, hysteretic energy dissipation capacity, and failure characteristics of the models were analyzed. The load-bearing capacity calculation formulas for a normal section and an oblique section of bottom strengthened rectangular steel-concrete composite columns were pesented and a finite element (FE) numerical simulation of the classical specimens was performed. The study shows that the load-bearing capacity, ductility, and seismic energy dissipation capacity of the bottom strengthened rectangular steel-concrete composite columns are significantly improved compared to the conventional rectangular steel-concrete composite columns and the results obtained from the calculation and the FE numerical simulation are in good agreement with those from the experiments. The rectangular steel-concrete composite column with bottom strengthened shows better seismic behavior and higher energy dissipation capacity under suitable constructional requirements and it can be applied to the structure design of high-rise buildings.

• Steel and Composite Structures
• /
• v.38 no.6
• /
• pp.739-749
• /
• 2021

This paper introduces an improved design equation to evaluate the resisting capacity of circular reinforced concrete (RC) columns partially strengthened with outer steel tube. When RC column members are required to be strengthened according to the change in the loadings considered and/or the deterioration progress in columns, wrapping up RC column with steel circular tube, which takes the form of concrete filled steel tube (CFST), has been popularly considered because of its structural advantage induced from the confinement effect. However, the relatively high construction cost of steel tube is restricting its use to the required region, while deriving the shape of a partial CFST column. To evaluate the resisting capacity of a partial CFST column, numerical analyses need to be performed, and a numerical model proposed in the previous study for the numerical analysis of full CFST columns is used to conduct parametric studies for the introduction of a design equation. The bond-slip effect developed along the interface between the in-filled concrete and the exterior steel tube is taken into consideration and the validity of the numerical model has been established through correlation studies between experimental data and numerical results for partial CFST circular columns. Moreover, parametric studies make it possible to introduce a design equation for determining the optimum length of outer steel tube which produces partial CFST circular columns.

• Steel and Composite Structures
• /
• v.43 no.6
• /
• pp.773-784
• /
• 2022

This paper aims to investigate the axial compressive behavior of reinforced concrete (RC) columns strengthened with self-compacting and micro-expanding (SM) concrete-filled steel tubes (SM-CFSTs). Nine specimens were tested in total under the local axial compression. The test parameters included steel tube thickness, filling concrete strength, filling concrete type and initial axial preloading. The test results demonstrated that the initial stiffness, ultimate bearing capacity and ductility of original RC columns were improved after being strengthened by SM-CFSTs. The ultimate bearing capacity of the SM-CFST strengthened RC columns was significantly enhanced with the increase of steel tube thickness. The initial stiffness and ultimate bearing capacity of the SM-CFST strengthened RC columns were slightly enhanced with the increase of filling concrete strength. However, the effect of filling concrete type and initial axial preloading of the SM-CFST strengthened RC columns were negligible. Three equations for predicting the ultimate bearing capacity of the SM-CFST strengthened RC columns were compared, and the modified equation based on Chinese code (GB 50936-2014) was more precise.

• Journal of Korean Association for Spatial Structures
• /
• v.22 no.4
• /
• pp.89-98
• /
• 2022

The recent earthquake in Korea caused a lot of damage to reinforced concrete (RC) columns with non-seismic details. The nonlinear analysis enables predicting the hysteresis behavior of RC columns under earthquakes, but the analytical model used for the columns must be accurate and practical. This paper studied the nonlinear analysis models built into a commercial structural analysis program for the existing RC columns. The load-displacement relationships, maximum strength, initial stiffness, and energy dissipation predicted by the three analysis models were compared and analyzed. The results were similar to those tested in the order of the fiber, Pivot, and Takeda models, whereas the fiber model took the most time to build. For columns subjected to axial load, the Pivot model could predict the behavior at a similar level to that of the fiber model. Based on the above, it is expected that the Pivot model can be applied most practically for existing RC columns.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.521-524
• /
• 1999

Twelve column specimens were tested in compression, six were slab-column specimens and six were isolated column specimens. The slab column specimens were first tested to punching shear failure before the columns of the specimens were loaded axially. The effects of confinement from the surrounding slab on the axial capacity of the columns was investigated. Other parameters investigated were the placement of fiber-reinforced concrete in the slab and the concentration of flexural reinforcement in the column vicinity.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.505-508
• /
• 1999

To evaluate the strength of square reinforced concrete shot columns, thirty specimens were manufactured and tested under monotonically increasing concentric compression. The test parameters included the volumetric ratio of transverse reinforcement($\rho$h = 0.49~2.65), and concrete compressive strength (234, 437, 704 kgf/$\textrm{cm}^2$). Test results are shown that : (1) Behavior of high -strength concrete column is improved by providing increased volumetric ratio; and (2) ACI, Eq. is not proper to evaluate HSC short column strength.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.247-252
• /
• 2000

The practical computer program COL3 was developed through this study to design of arbitrarily shaped reinforced concrete slender columns subjected to combined compression and biaxial bending. The program COL3 has been developed for user-friendly environment using spreadsheets. Several examples including for analysis of geometrically complex column sections subjected biaxial bending are introduced in this paper.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.405-408
• /
• 2003

In a slender column under sustained eccentric compression, the deformations caused by creep and shrinkage can lead to an increase in the loads on the structure and a reduction in strength. This study presents a methodlogy and improved computer program for the analysis of time-dependent long column in considering slender effects and nonlinear behaviors. In this result, when slenderness ratio is greater than 80, we know that magnified moment methods may be not applied in long columns.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.973-978
• /
• 2003

This paper describes the experimental study on seismic strengthening effect of circular bridge columns with poor lap-splice details using FRP(Fiber Reinforced Plastic) wrapping, The as-built column suffered brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or any ductility, The strengthening columns using FRP wrapping showed significant improvement in seismic performance due to FRP's confinement effect.

• Structural Engineering and Mechanics
• /
• v.27 no.4
• /
• pp.393-408
• /
• 2007

This paper presents the findings of an experimental study to evaluate retrofit methods which address particular weaknesses that are often found in reinforced concrete structures, especially older structures, namely the lack of the required flexural and shear reinforcement within the columns and the lack of the required shear reinforcement within the joints. Thus, the use of a high-strength fiber jacket for cases of post-earthquake and pre-earthquake retrofitting of columns and beam-column joints was investigated experimentally. In this paper, the effectiveness of the two jacket styles was also compared.