• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.446-449
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• 2006

Several experimental investigations have been carried out to study the behavior of reinforced concrete columns with short lap splices. However, very few analytical models have been developed for the analysis of such columns subjected to earthquakes. As nonlinear analysis procedures become more common in practice (such as those outlined in the Guidelines for Seismic Rehabilitation of Buildings published by the Federal Emergency Management Agency in the United States), the need for an accurate and reliable representation of the nonlinear response of strength degrading systems becomes more important. In this study, an analytical model for estimating the complete response of reinforced concrete columns with short lap splices is presented. The model is based on local bond stress-slip relationships and is validated against independent experimental data from cyclic loading tests on reinforced concrete columns with typical construction details of the 1960s. In this paper a simple equation for calculating the bar stress at splice failure is presented. Use of the proposed equation resulted in excellent agreement between the measured and calculated strength at splice failure.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1069-1072
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• 2008

As embedded reinforcing suffer from corrosion process, the bond strength and stiffness are reduced, and the structure proceed, eventually, to the deterioration of the concrete, shortening the service life of concrete structures rapidly. In order to deal with these problems, a multitude of researches have been carried out up to this date to evaluate the bond characteristics of RC members, i.e. by artificially inducing rapid corrosion of the reinforcing bar. These artificial corrosion methods, however, could not represent the real condition, resulting in the possibility of overestimation for the RC members in real situation. Accordingly, the purpose of this paper is to investigate the difference in the bond characteristics for RC members corroded by different corrosion methods (artificial rapid method, natural method). For the case of natural corrosion, the brittle failure was observedeven for the case of the area ofcorrosion of 50%. And, the bond strength decreased by about 10% or more for the caseofspecimens with the area of corrosion of 80% or above. Especially, the deterioration of concrete starts at the state of low corrosion level for the case of natural corrosion. Thus, the safety of RC members must be assessed and evaluated more carefully for the naturally corroded members than for the RC concrete members corroded rapidly by artificial method.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.233-240
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• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcement and the ratio of shear rebar. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. It is expected that this model can be applied to displacement-based design methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.719-727
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• 2008

The tensile and bond performance of GFRP rebar are different from those of conventional steel reinforcement. It requires some studies on concrete members reinforced with GFRP reinforcing bars to apply it to concrete structures. GFRP has some advantages such as high specific strength, low weight, non-corrosive nature, and disadvantage of larger deflection due to the lower modulus of elasticity than that of steel. Bridge deck is a preferred structure to apply FRP rebars due to the increase of flexural capacity by arching action. This paper focuses on the behavior of concrete bridge deck reinforced with newly developed GFRP rebars. A total of three real size bridge deck specimens were made and tested. Main variables are the type of reinforcing bar and reinforcement ratio. Static test was performed with the load of DB-24 level until failure. Test results were compared and analyzed with ultimate load, deflection behavior, crack pattern and width.

• Computers and Concrete
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• v.3 no.1
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• pp.65-77
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• 2006

This study reports the details of the finite element analysis of eleven shear critical partially prestressed concrete T-beams having steel fibers over partial or full depth. Prestressed concrete T-beams having a shear span to depth ratio of 2.65 and 1.59 and failing in the shear have been analyzed using 'ANSYS'. The 'ANSYS' model accounts for the nonlinear phenomenon, such as, bond-slip of longitudinal reinforcements, post-cracking tensile stiffness of the concrete, stress transfer across the cracked blocks of the concrete and load sustenance through the bridging of steel fibers at crack interface. The concrete is modeled using 'SOLID65'-eight-node brick element, which is capable of simulating the cracking and crushing behavior of brittle materials. The reinforcements such as deformed bars, prestressing wires and steel fibers have been modeled discretely using 'LINK8' - 3D spar element. The slip between the reinforcement (rebar, fibers) and the concrete has been modeled using a 'COMBIN39'-non-linear spring element connecting the nodes of the 'LINK8' element representing the reinforcement and nodes of the 'SOLID65' elements representing the concrete. The 'ANSYS' model correctly predicted the diagonal tension failure and shear compression failure of prestressed concrete beams observed in the experiment. The capability of the model to capture the critical crack regions, loads and deflections for various types of shear failures in prestressed concrete beam has been illustrated.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.828-833
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• 2003

In this paper, a study on fracture characteristics of chemically prestressed mortar with addition of expansive additives was carried out. Uni-axial tension tests with reinforced mortar specimen restrained by embedded reinforcing bar and three point bending tests with notched steel fiber reinforced beams were carried out to verify the characteristics of the cracking behavior, the tension stiffening effect due to bond between rebar and mortar, and fracture characteristic. Tension stiffening curve for the chemically prestressed mortar was obtained from uni-axial tension test. And increased fracture energy due to the chemical prestress was also obtained from bending test and tension softening curve for chemically prestressed mortar was also obtained.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.579-584
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• 1998

The purpose of this study is to evaluate the flexural strengthening effects of RC beams reinforced with carbon fiber sheets (CFS) in variable of strengthening amount and anchorage length of CFS. This study can be summarized as follows. The CFS shares the tensile stress such as rebar during loading test. Also, as the strengthening amount of CFS is increased, the maximum flexural strength of RC beams reinforced with CFS is increased. Therefore, it is confirmed that the CFS's strengthening method is very effective to improve the flexural strength of RC beams. The maximum flexural strength of RC beams with CFS is determined by bond failure between CFS and concrete surface. So, the evaluation of CFS's strengthening effect can be calculated using the tensile stress of CFS which is peeling. When the anchorage length of CFS. But, in case of same anchorage length of CFS, when the strengthening amount of CFA is increased, the ductility is decreased. Therefore, it is considered that the anchorage of CFS in the end zone is necessary.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.569-577
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• 2021

CFRP(Carbon Fiber Reinforced Plastic) can maintain the same strength even if the diameter is reduced by about one - third, and the weight is about one - twentieth of that of the deformed reinforcing bars that have been used in the construction industry. In particular, it is resistant to corrosion, which is the weakest part of reinf orcing bars, and there is no concern that it will deteriorate over time, It is light and durable, so transportation costs are low and it is convenient for high-rise buildings. This paper experimentally clarifies the adhesive properties of CFRP and clarifies its behavior. That is, bond strength test was conducted with the directness of CFRP and the strength of concrete as experimental variables, and the bond mechanism was clarified experimentally. Furthermore, based on the experimental results, we constructed the bond stress-slip-strain relationship of CFRP compared to the existing deformed reinforcing bars.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.187-194
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• 2013

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.275-283
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• 2012

Steel Plate for Rebar Connection was recently developed to splice rebars in delayed slab-wall joints in high-rise building, slurry wall-slab joints, temporary openings, etc. It consists of several couplers and a thin steel plate with shear key. Cyclic loading tests on slab-wall joints were conducted to verify structural behavior of the joints having Steel Plate for Rebar Connection. For comparison, joints with Rebend Connection and without splices were also tested. The joints with Steel Plate for Rebar Connection showed typical flexural behavior in the sequence of tension re-bar yielding, sufficient flexural deformation, crushing of compression concrete, and compression rebar buckling. However, the joints with Rebend Connection had more bond cracks in slabs faces and spalling in side cover-concrete, even though elastic behavior of the joints was similar to that of the joints with Steel Plate for Re-bar Connection. Consequently, the joints with Rebend Connection had less strengths and deformation capacities than the joints with Steel Plate for Re-bar Connection. In addition, stiffness of the joints with Rebend Connection degraded more rapidly than the other joints as cyclic loads were applied. This may be caused by low elastic modulus of re-straightened rebars and restraightening of kinked bar. For two types of diameters (13mm and 16mm) and two types of grades (SD300 and SD400) of rebars, the joints with Steel Plate for Rebar Connection had higher strength than nominal strength calculated from actual material properties. On the contrary, strengths of the joints with Rebend Connection decreased as bar diameter increased and as grade becames higher. Therefore, Rebend Connection should be used with caution in design and construction.