• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2003.03a
• /
• pp.385-392
• /
• 2003

Experimental investigation was conducted into the flexure/shear-critical behavior of earthquake-damaged reinforced concrete columns with lap splicing of longitudinal reinforcement in the plastic hinge region. Six test specimens in the aspect ratio of 2.5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under a constant axial load, P = 0.1 $f_{ck}$ $A_{g}$. Residual seismic performance of damaged columns was evaluated and compared to that of the corresponding original columns. Test results show that RC bridge piers with lap-spliced longitudinal steels in the plastic hinge region appeared to fail at low ductility. This was due to the debonding of the lap splice, which resulted from insufficient development of the longitudinal steels. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region indicated significant improvement both in flexural strength and displacement ductility.y.

• Structural Engineering and Mechanics
• /
• v.72 no.2
• /
• pp.155-168
• /
• 2019

This paper presents the results of an experimental investigation on the compressive strength of small scale concentrically axially loaded fiber-reinforced polymer (FRP) confined plain concrete columns, with cylinder concrete strength 19 MPa. For columns with circular (150-mm diameter) and square (150-mm side) cross sections wrapped with glass- and carbon-FRP sheets (GFRP and CFRP, respectively) applied with dry lay-up the effect of different jacket schemes and different overlap configurations on the confined characteristics is investigated. Test results indicate that the most cost effective jacket configuration among those tested is for one layer of CFRP, for both types of sections. In square sections the location of the lap length, either in the corner or along the side, does not seem to affect the confined performance. Furthermore, in circular sections, the presence of an extra wrap with FRP fibers parallel to the column's axis enhances the concrete strength proportionally to the axial rigidity of the FRP jacket. The recorded strains and the distributions of lateral confining pressures are discussed. Existing design equations are used to assess the lateral confining stresses and the confined concrete strength making use of the measured hoop strains.

• Structural Engineering and Mechanics
• /
• v.18 no.2
• /
• pp.151-166
• /
• 2004

The interaction between concrete core expansion and deformation of perimeter ties has been known to have a significant effect on the effective confinement of rectangular reinforced concrete (RC) tied columns. This interaction produces passive confining pressure to the concrete core. Most existing models for determining the response of RC tied columns do not directly account for the influence of flexural stiffness of the ties and the variation of confining stress along the column height. This study presents a procedure for determining the confined compressive strength of RC square columns confined by rectilinear ties with various tie configurations considering directly the influence of flexural flexibility of the ties and the variation of confining stress along the vertical direction. The concept of area compatibility is employed to ensure compatibility of the concrete core and steel hoop in a global sense. The proposed procedure yields satisfactory predictions of confined strengths compared with experimental results, and the influence of tie flexibility, tie configuration and degree of confinement can be well captured.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.4 no.4
• /
• pp.147-154
• /
• 1984

A numerical procedure based on the finite element method for the analysis of reinforced concrete beam-columns under uniaxial bending is presented. Material nonlinearities such as the cracking and crushing of concrete and the yielding of reinforcing steel as well as the geometric nonlinearity which is an important factor affecting the behavior of beam-columns are considered in the analysis. This method traces the behavior of reinforced concrete beam-columns up to failure by solving incremental equilibrium equations, Numerical examples are presented to demonstrate the validity and usefulness of the present method.

• Fire Science and Engineering
• /
• v.27 no.6
• /
• pp.26-31
• /
• 2013

This study, to evaluate the technology of the fire resistance design of Reinforced Concrete columns based on fire resistance performance design, was suppose to use as basic data for performance design through a measure of temperature and deformation using heat transfer analysis and Heat-load test of the Reinforced Concrete columns as parameter is the axial load ratio. In accordance with axial load without eccentricity, the load ratio of 0.30, 0.35, 0.40 and 0.47 were imposed on columns. As a result of this study, 0.40 or more of axial load ratio can be ensured that the fire resistance performance was considered satisfactory.

• Structural Engineering and Mechanics
• /
• v.47 no.6
• /
• pp.741-756
• /
• 2013

Distributed-Steel Bar Reinforced Concrete (DSBRC) columns, a new and innovative construction technique for composite steel and concrete material which can alleviate the difficulty in the arrangement of the stirrup in the column, were studied experimentally and analytically in this paper. In addition, an ordinary steel Reinforced Concrete (SRC) column was also tested for comparison purpose. The specimens were subjected to quasi-static load reversals to model the earthquake effect. The experimental results including the hysteresis curve, resistance recession, skeleton curves and ductility ratio of columns were obtained, which showed well resistant-seismic behavior for DSBRC column. Meanwhile a numerical three-dimensional nonlinear finite-element (FE) analysis on its mechanical behavior was also carried out. The numerically analyzed results were then compared to the experimental results for validation. The parametric studies and investigation about the effects of several critical factors on the seismic behavior of the DSBRC column were also conducted, which include axial compression ratios, steel ratio, concrete strength and yield strength of steel bar.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.12 no.3
• /
• pp.29-36
• /
• 2008

The TR-CFT(Transversely Reinforced Concrete Filled Steel Tube) column is proposed to control or at least delay the state of local buckling at the critical section by wrapping the CFT columns with a carbon fiber sheet. In this study, an equation to determine the flexural strength of TR-CFT is proposed. The ACI-318 code, in which the contribution of the confining effect in the concrete filled steel tube is not appropriately accounted for, may be conservative. Therefore, flexural strength design equations for CFT columns and TR-CFT columns are proposed based on the concrete strain-stress curve, which contributes to the confining effect. Finally, the predicted results for the CFT and TR-CFT columns are shown to be in good agreement with actual test results.

• Structural Engineering and Mechanics
• /
• v.61 no.1
• /
• pp.1-13
• /
• 2017

The effectiveness of the repair scheme for the damaged captive-columns with CFRPs (Carbon Fiber Reinforced Polymer) was investigated in terms of response quantities such as strength, ductility, dissipated energy and stiffness degradation. Two 1/3 scale, one-story one-bay RC (Reinforced Concrete) frames were designed to represent the substandard RC buildings in Turkish building stock. The first one, which is the reference specimen, is the bare frame without infill wall. Partial infill wall with opening was constructed between the columns of the second frame and this caused captive column defect. Severe damage was observed with the concentration of shear cracks in the second specimen columns. Then, the damaged members were repaired by CFRP wrapping and retested. For the three test series, similar reversed cyclic lateral displacement under combined effect of axial load was applied to the top of the columns. Overall response of the bare frame was dominated by flexural cracks. Brittle type of shear failure in the column top ends was observed in the specimen with partial infill wall. It was observed that former capacity of damaged members of the second frame was recovered by the applied repair scheme. Moreover, ultimate displacement capacity of the damaged frame was improved considerably by CFRP wrapping.

• Structural Engineering and Mechanics
• /
• v.17 no.1
• /
• pp.99-112
• /
• 2004

It is known that lap splices in the longitudinal reinforcement of reinforced concrete (RC) bridge columns are not desirable for seismic performance, but it is sometimes unavoidable. Lap splices were practically located in the potential plastic hinge region of most bridge columns that were constructed before the 1992 seismic design provisions of the Korea Bridge Design Specification. The objective of this research is to evaluate the seismic performance of reinforced concrete (RC) bridge piers with lap splicing of longitudinal reinforcement in the plastic hinge region, to develop an enhancement scheme for their seismic capacity by retrofitting with glassfiber sheets, and to assess a damage of bridge columns subjected to seismic loadings for the development of rational seismic design provisions in low or moderate seismicity region. Nine (9) test specimens with an aspect ratio of 4 were made with three confinement ratios and three types of lap splice. Quasi-static tests were conducted in a displacement-controlled way under three different axial loads. A significant reduction of displacement ductility was observed for test columns with lap splices of longitudinal reinforcements, whose displacement ductility could be greatly improved by externally wrapping with glassfiber sheets in the plastic hinge region. A damage of the limited ductile specimen was assessed to be relatively small.

• Advances in concrete construction
• /
• v.5 no.5
• /
• pp.539-561
• /
• 2017

In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium -level, high -level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.