• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.189-199
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• 2014

Currently, in the precast concrete construction, Precast Concrete (PC) and Cast-In-Place (CIP) concrete with different concrete strengths are frequently used. However, current design codes do not specifically provide shear design methods for PC-CIP hybrid members using dual concrete strengths. In the present study, simply supported composite beams with shear reinforcement were tested. The test variables were the area ratio of the two concretes, spacing of shear reinforcement, and shear span-to-depth ratio. The shear strengths of the test specimens were evaluated by current design codes on the basis of the test results. The results showed that the shear strength of the composite beams was affected by the concrete strength of the compressive zone and also proportional to the flexural rigidity of un-cracked sections. Furthermore, the contribution of shear reinforcements varied according to the concrete strength of the compressive zone.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.55-68
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• 2014

In this study, the beam-to column connections of concrete-encased-and-filled steel tube columns were tested under cyclic loading. Two specimens using steel beams and two specimens using precast concrete beams were tested. The dimension of the column cross section was $670mm{\pm}670mm$. The beam depths were 488mm and 588mm for the steel beams and 700mm for the precast concrete beams. The longitudinal bar ratios of the precast concrete beams were 1.1% and 1.5%. For the connections to the steel beams, continuity plates were used in the tube columns. For the connections to the PC beams, couplers were used for beam re-bar connections. The test results showed that except for a specimen, deformation capacities of the specimens were greater than 4% rotation angle, which is the requirement for the Special Moment Frame. Particularly, specimens using precast concrete beam showed excellent performances in the strength, deformation, and energy dissipation.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.399-409
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• 2015

Recently, the use of composite construction method using precast (PC) and cast-in-place (CIP) concrete is increased in modular construction. For PC members, pre-tensioning is used to improve efficiency of the structural performance. However, current design codes do not clearly define shear strength of prestressed PC-CIP composite members. In this study, 22 specimens were tested to evaluate shear strength of prestressed composite members with vertical shear reinforcement. The test variables were the area ratio of high-strength (60 MPa) to low-strength concrete (24 MPa), prestressing force of strands, shear span-to-depth ratio(a/d), and vertical shear reinforcement ratio. The test results showed the prestressing force did not completely restrain diagonal cracking of non-prestressed concrete in the web. Thus, the effect of prestress force was not insignificant in the effect for monolithic beams. The vertical shear strength and horizontal shear strength of the composite beams were compared with the strength predictions of KCI design method.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.253-260
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• 1998

An approximate method for the calculation of creep deflections of reinforced concrete beams under sustained service loads is proposed. The position of neutral axis and strain and stress distribution of fully cracked section after creep is determined from the requirements of strain compatibility and equilibruim of a section and then the long-term flexural rigidity of fully cracked section is determined based on the new neutral axis. The long-term flexural rigidity of uncracked section at the level of the reinforcenment. The approach of calculating long-term effective flexural rigidity and defections is similar to the current American Concrete Institue procedure for calculating effecitve moment of inertia and short-term deflections. The accuracy of the analysis is verified by comparison with several experimental mesurements of beam deflectons. The result is good between the theotetical values and mesured valus.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.37-43
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• 2007

Experiments for circular unreinforced concrete beams confined by carbon fiber tubes (CFT) made of carbon fiber sheets were performed. Selected test parameter was thickness of carbon fiber tube: 1.5mm (3 layers), 2.0mm (4 layers), 2.5mm (5 layers), and 3.0mm (6 layers). Based on the test results, an equation for estimating moment capacity of the circular beams confined by carbon fiber tubes was proposed. Comparison results showed good agreement up to 2.5mm (5 sheets) of the CFT thickness.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.185-192
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• 2011

A CFRP (Carbon Fiber-Reinforced Plastic) strengthening method being widely used to increase the load-carrying capacity of structures is very suitable for existing bridge structures. However, not only flexure and shear failures but also debonding failure might be additionally occured in reinforced concrete(RC) beams strengthened with the CFRP plates. The CFRP debonding failure would cause a brittle fracture of the beam. Therefore, health monitoring for the CFRP bonding condition is strongly required. In this study, a feasibility of the impedance-based damage detection method using PZT sensors was investigated through a series of experimental studies for realtime structural health monitoring(SHM) for the CFRP laminated concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.2
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• pp.76-82
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• 2006

The concrete shear strength of FRP Bar reinforced concrete beam according to the variation of flexural reinforcement ratio was investigated. A number of experimental result showed that the concrete shear strength was lower than that of RC beam, but it was increased according to the increasement of reinforcement ratio. Shear strength correction factors considering the kind and reinforcement ratio of FRP Bar was proposed using the proposed formula in the literature and regression analysis of the experimental result.

• Journal of Korean Society of Steel Construction
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• v.21 no.4
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• pp.421-432
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• 2009

In this study, push-out and static loading tests were conducted to evaluate the behavioral characteristics of composite beams with a perfobond rib shear connector. The shear capacity of the perfobond rib was found to be proportional to its concrete strength, which is in turn affected by the increase in the concrete end-bearing strength and concrete dowel action to resist the shear force. The relative slips of the push-out specimen, however, which was used to assess the ductility of the shear connector, increased to some extent, but it no longer increased when it reached the critical concrete strength because of the flexibility of the transverse rebar in the rib hole. The static-loading-test results revealed a crack on the concrete slab in the composite beam with a perfobond rib on the side of the rib hole and transverse rebar for the applied moment and shear force to the rib hole, depending on the static loading. The shear resistance characteristics of the perfobond rib shear connector were found to resist the shear force from the relative slip on the interface of the composite beam. Thus, the sectional effect of the shear connector to the composite beam with a perfobond rib should be considered when designing the composite beam because the behavior of the composite beam can change owing to the shear connector.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.665-673
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• 2008

The composite structures of steel and reinforced concrete, which have been widely used in large-scale concrete structures, werestudied to investigate the cause of unexpected cracks and to verify the composite actions between the two materials. Vertical stiffeners between flanges, studs and dowel bars, stirrups, and concrete strength were chosen as experimental variables in afour-point loading test. The results showed that the vertical stiffener prevented not only the local web buckling, but also bond failures between steel and concrete. It increased the flexural resistance (fracture loads) due to the composite action of two materials, compared withthose of any experimental variable. However, the composite behavior of steel reinforced concrete beam was not affected seriously by additional studs, dowel bars, stirrups, and concrete strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.53-56
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• 2008

Reinforced concrete rahmen structures has been required ductility as well as strength of beam-column joint in seismically hazard area. Some investigations have been presented for retrofitting and/or strengthening structural elements in structure. Strain-hardening cementitious composite(SHCC) has been expected excellent reinforcement performance in beam-column joint area. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic moudulus, have great effect on the fracture behavior of SHCC. The purpose of this experimental study is to evaluate structural performance of exterior reinforced concrete beam-column joint strengthened with SHCC under cyclic loading.