• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.1
• /
• pp.131-139
• /
• 2012

The lateral reinforcements of concrete such as hoops and spiral bars are known to confine concrete to compensate the strength loss due to fire by reducing explosive spalling and improving the capacity of ductility. In this context, a study was conducted to investigate the residual mechanical properties of confined and unconfined concrete($f_{ck}$=60MPa) after a single thermal cycle at 300, 600, $800^{\circ}C$. The main parameters required to establish the stress-strain relationship are the peak stress, the elastic modulus, and the strain at peak stress. The knowledge of the residual mechanical properties of concrete is necessary whenever the thermally damaged structure is required to bear a significant share of the loads, even after a severe thermal accident. Based on the results obtained in this study, the residual stress of confined concrete under thermal damage is higher according to the level of confinement and the larger strain made it to have better ductility. The decreasing ratio of elastic modulus from the relationship of stress and strain was also smaller than that of unconfined concrete.

• Journal of the Korea Concrete Institute
• /
• v.24 no.6
• /
• pp.705-714
• /
• 2012

Precast reinforced concrete bridge columns with hollow rectangular section were tested under cyclic lateral load with constant axial force to investigate its seismic performance. After all the precast column segments were erected, longitudinal reinforcement was inserted in the sheath prefabricated in the segments, which were then mortar grouted. Main variables of the test series were column aspect ratio, longitudinal reinforcement ratio, amount of lateral reinforcement, and location of segment joints. The aspect ratios were 4.5 and 2.5, and the longitudinal steel ratios were 1.15% and 3.07%. The amount of lateral reinforcement were 95%, 55%, 50%, and 27% of the minimum amount for full ductility design requirements in the Korean Bridge Design Code. The locations of segment joints in plastic hinge region were 0.5 and 1.0 times of the section depth from the bottom column end. The test results of cracking and failure mode, axial-flexural strength, lateral load-displacement relationship, and displacement ductility are presented. Then, safety of the ductility demand based seismic design in the Korean Bridge Design Code is discussed. The column specimens showed larger ductility than expected, because buckling of longitudinal reinforcing bar was prevented due to confinement developed not only by transverse steel but also by sheath and infilling mortar.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.4
• /
• pp.311-318
• /
• 2018

When reinforced concrete structures are exposed to fire, their mechanical properties such as compressive strength, elasticity coefficient and rebar yield strength, are degraded. Therefore, the structure's damage assessment is essential in determining whether to dismantle or augment the structure after a fire. In this study, the confinement effect of lateral reinforcement of RC column according to the numbers of fire exposure face and stirrup was verified by fire resistant test with the heating temperatures of $400^{\circ}C$, $600^{\circ}C$ and $800^{\circ}C$. The test results showed that the peak stress decreases and peak strain increases as the temperature is getting higher, also transverse ties are helpful in improving the compressive resistance of concrete subjected to high temperature. Based on the results of this study, the residual stress of confined concrete under thermal damage is higher at the condition of more lateral reinforcement ratio and less fire exposure faces. The decreasing ratio of elastic modulus of more confined and less exposure faces from the relationship of load and displacement was also smaller than that of opposite conditions.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.9 no.1 s.41
• /
• pp.17-24
• /
• 2005

Response of reinforced concrete (RC) column-bent piers subjected to bidirectional seismic loadings was experimentally investigated. RC column-bent piers represent one of the most popular shapes of piers used in Korea highway bridges. Four column-bent piers were constructed in 400 mm diameter and 2,000 mm height. Each pier has two circular supporting columns. These piers were tested under bidirectional lateral load reversals with an axial load of $0.1f_{ck}A_g$. The test parameters included : different transverse reinforcement contents and lap-spliced longitudinal reinforcing steels. Test results indicate that the lap splice of longitudinal reinforcing steels have significantly influenced on hysteretic response of column-bent piers similar to previous test results for single columns with corresponding test parameters. Column capacity was changed with the level of transverse confinement. From the comparison of test result for single column under unidirectional loading, the damage of single column was concentrated on lower plastic hinge region but the damage of column-bent piers was scattered to upper and lower plastic hinge region.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.3
• /
• pp.249-260
• /
• 2017

In order to investigate the structural performance of a novel prefabricated-SRC column using bolt-connected steel angles(PSRC column), eccentric axial loading tests were performed for six PSRC column specimens and two conventional SRC column specimens. The test parameters were the spacing and sectional configurations of lateral reinforcement, and eccentricity ratio of axial load. The test results showed that, due to high axial-stiffness of the angles located at the corners of the cross section, the compressive load-carrying capacity and deformation capacity of the PSRC specimens were greater than those of the SRC specimens in the large eccentricity ratio of axial load. Closely spaced lateral steel plates and Z-shaped lateral steel plates improved lateral confinement, which increased the load-carrying capacity of the PSRC specimens. The combined flexural and axial load-carrying capacity of the specimens by tests and nonlinear numerical analysis were greater than the predictions by current design codes. The numerical analysis agreed well with the test results including the initial stiffness, peak strength, and post-peak strength degradation.

• Journal of the Korea Concrete Institute
• /
• v.16 no.1 s.79
• /
• pp.61-69
• /
• 2004

The bridge piers under service suffered a brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or ductility. The earthquake induced lateral force results in tension which causes bond-slip failure at the lap-spliced region in circular bridge piers. In this case, such a brittle failure can be controlled by the seismic retrofit using FRP laminated circular tube. The retrofitted piers using FRP laminated circular tube showed significant improvement in seismic performance due to FRP's confinement effect. This paper presents the analytical results on the seismic strengthening effect of circular bridge piers with poor lap-splice details and strengthened with FRP laminated circular tube. FRP's confinement effect is predicted by the classical elasticity solution for the laminated circular tube manufactured with several layers. The FRP laminated circular tube induces the flexural failure instead of a bond-slip failure of the circular reinforced concrete piers under seismic induced lateral forces. To investigate the correctness and effectiveness of analytical solution derived in this study, the analytical results were compared with the experimental data and it was confirmed that the results were correlated well each other, The effects on the confinement of FRP laminated circular tube, such as the number of layers, the fiber orientations, and the mechanical properties, were investigated. From the parametric study, it was found that the number of layers, the fiber orientations, and the major Young's modulus (E11) of the FRP laminated circular tube were the dominant parameters affecting the confinement of reinforced concrete circular bridge piers.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10a
• /
• pp.589-596
• /
• 1998

Experimental studies are investigated for RC column retrofitting under cyclic load. Design considerations are jacketing of steel plate of carbon fiber with epoxy bonding, use of unbonded plate, additional concrete grouting, ratio of additional longitudinal steel reinforcement and longitudinal configuration of additional ties. Investigated results are 1) jacketing and additional reinforcements are effective for strengthening, 2) use of additional grouting is less effective with respect to increased section. Future studies are needed to evaluate the requirements about additional reinforcements for member stress level, 3) bond between original and additional grout concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.05a
• /
• pp.145-150
• /
• 2001

With the increase in the use of High-Strength Concrete(HSC) despite the its weakness like brittle characteristic, it is important to improve the performance of HSC columns, nowadays. Therefore, it is common to use higher strength steel in HSC for the purpose of ductility and strength improvement. This experimental study was set up to investigate the inelastic behavior of HSC(700kg/$cm^{2}$) columns subjected to combined axial and repeated lateral loads. Effects of key variables such as the volumetric ratio of transverse reinforcement, tie configuration and tie yield strength are studied in this research program. Test results indicate that inelastic response of HSC columns improve with proper confinement of core concrete. Increasing the amount of transverse reiuorement results in increased ductility.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.965-970
• /
• 2001

The object of this research is to evaluate the seismic performance of existing RC bridge piers that were constructed before the adoption of the seismic design provision of Korea Bridge Design Specification in 1992. In this research, adopted test parameters were limited ductile design or non-seismic design, aspect ratio, confinement steel type, loading pattern, lap-spliced ratio for longitudinal reinforcement. This study has been performed to verify the effect of test parameter by quasi-static test. Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as lateral force-displacement hysteretic curve, envelope curve etc. It has been observed that seismic performance of lap-spliced test specimen, non-seismically designed specimens, was significantly reduced.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.21 no.1
• /
• pp.49-57
• /
• 2017

In order to avoid collapse of bridges in earthquakes bridge piers are generally designed to attain sufficient ductility. This full-ductility design method has merits for securing the seismic safety readily against strong earthquakes but, it has weakness of high cost design because of excessive safety margin. Recently, in many countries with high seismic technologies, the seismic design concept tends to shift from the collapse prevention design to the performance-based one which requires different performance (damage) levels according to the structural importance. In order to establish this performance-based design method the displacement ductility of confined concrete members should be evaluated quantitatively. And the stress-strain model of confined concrete is indispensible in evaluating displacement ductility. In this study, 6 test groups with different lateral reinforcement ratios were prepared. 10 same specimens with circular section for each group were tested to obtain more reliable test results. The characteristic values necessary for composing the stress-strain model were obtained from experiments. Based on these characteristic values the new stress-strain model modifying the Hoshikuma's one has been proposed.