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Gee-Joo Ha Young-Joo Ha Hyun-Wook KangAbstractIn this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (CFRP sheet, AFRP sheet, embedded CFRP rod) in existing reinforced concrete structure. Therefore it was constructed and tested seven specimens retrofitting the beam-column joint regions using suchretrofitting materials.Specimens, designed by retrofitting the beam-column joint regions of existing reinforced concrete structure, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and confinement of retrofitting materials during testing.Specimens LBCJ-CRUS, designed by the retrofitting of CFRP Rod and CFRP Sheet in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.54 times and its energy dissipation capacity by 2.36 times in comparison with standard specimen LBCJ for a displacement ductility of 4 and 7. And Specimens LBCJ-CS, LBCJ-AF series were increased its energy dissipation capacity each by 2.04~2.34, 1.63~3.02 times in comparison with standard specimen LBCJ for a displacement ductility of 7.Keywords : Embedded CFRP rod, CFRP sheet, AFRP sheet, Beam-column joint, Seismic performance, Retrofitting, Improvement

Gee-Joo Ha Young-Joo HaAbstractIn this study, experimental research was carried out to evaluate the structural performance of the reinforced concrete beam usinghybrid retrofitting with two materials (groove and embedding FRP rod, CFRP sheet) in existing reinforced concrete buildings. Seven reinforced concrete beams, retrofitted groove and embedding FRP rod (NER series) and groove and embedding FRP rod with CFRP sheet (NERL series), and standard specimen (NBS) were constructed and tested under monotonic loading. Design parameters of test specimens are the amount of groove and embedding FRP rod and lapping CFRP sheet.Test results showed that the maximum load carrying capacity of specimens with groove and embedding FRP rod and groove andembedding FRP rod with CFRP sheet (NERL series) were increased the by 12~46% and 22~77% respectively in comparison with the standard specimen NBS. Test specimens NER series were failed with the adhesion slip and concrete cover separation. And test specimens NERL series were failed with the adhesion slip due to the confining effect of lapping CFRP sheet.Keywords : R/C beam, Groove and embedding FRP rod, CFRP sheet, Structural performance, Hybrid retrofitting

In this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (embedded CFRP rod and CFRP sheet) in existing reinforced concrete building. Therefore it was constructed and tested six specimens retrofitting the beam-column joint regions using such retrofitting materials. Specimens, designed by retrofitting the beam-column joint regions of existing reinforced concrete building, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and confinement of retrofitting materials during testing. Specimens RBCJ-SRC2, designed by the retrofitting of CFRP Rod and CFRP Sheet in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.97 times and its energy dissipation capacity by 2.08 times in comparison with standard specimen RBCJ for a displacement ductility of 4 and 7. Also, specimens RBCJ-SRC2 were increased its maximum load carrying capacity by 1.09~1.11 times in comparison with specimen RBCJ-SR series. And Specimens RBCJ-CS, RBCJ-SR series, RBCJ-SRC2 were increased its energy dissipation capacity by 1.10~2.30 times in comparison with standard specimen RBCJ for a displacement ductility of 5, 6.

In this study, eleven reinforced concrete beams, ground granulated blast furnace slag, replacing recycled coarse aggregate (BRS series) and recycled coarse aggregate with steel fiber (BSRS series), and standard specimen (BSS) were constructed and tested under monotonic loading. Experimental programs were carried out to improve and evaluate the shear performance of such test specimens, such as the load-displacement, the failure mode and the maximum load carrying capacity. All the specimens were modeled in 1/2 scale-down size. Test results showed that test specimens (BSRS Series) was increased the compressive strength by 9%, the maximum load carrying capacity by 1~6% and the ductility capacity by 1.02~1.13 times in comparison with the standard specimen (BSS). And the specimens (BSRS Series) showed enough ductile behavior and stable flexural failure.

In this study, experimental research was carried out to evaluate the constructability and seismic performance of high strength R/C exterior beam-column joints regions, with or without the shear reinforcement, using high ductile fiber-reinforced mortar. Five specimens of retrofitted the exterior beam-column joint regions using high ductile fiber-reinforced mortar are constructed and tested for their retrofit performances. Specimens designed by retrofitting the exterior beam-column joint regions (BCJNSP series) of existing reinforced concrete building showed a stable mode of failure and an increased its maximum load-carrying capacity by 1.09~2.03 times in comparison with specimen of BCJNS due to the effect of enhancing dispersion of crack control at the time of initial loading and bridging of fiber from retrofitting new high ductile materials during testing. Specimens of BCJNSP series attained its maximum load carrying capacity by 0.92~0.96 times and increased its energy dissipation capacity by 1.62 times when compared to standard specimen of BCJC with a displacement ductility of 4.

In this study, it was developed eco-friendly inorganic binding material concrete using ground granulated blast furnace slag and alkali activator (water glass, sodium hydroxides). Eight reinforced concrete beam using inoganic binding material concrete were constructed and tested under monotonic loading. The major variables were mixture ratio of alkali activator, type of admixture and admixture. Experimental programs were carried out to improve and evaluate the flexural performance of such test specimens, such as the load-displacement, the failure mode, the maximum load carrying capacity, and ductility capacity. All the specimens were modeled in scale-down size. The eco-friendly concrete using inorganic binding material encouraged alkali activation reaction was rapidly hardening speed and showed possibility as a high strength concrete. Also, the RC beams using new materials showed similar behavior and failed similarly with RC beam used portland cement. It is thought that eco-friendly inorganic binding material concrete can be used with construction material and product as a basic research to replace cement concrete. If there is application to structures in PC member as well as production of 2nd concrete product, it could be improved the productivity and reduction of construction duration etc.

In this study, experimental research was carried out to evaluate and improve the seismic performance of high strength R/C interior beam-column joints regions using advanced reinforcing detailings and high ductile fiber-reinforced mortar. Five specimens of retrofitted the beam-column joint regions using advanced reinforcing detailings and high ductile fiber-reinforced mortar were constructed and tested for their retrofitring performances. Specimens designed by retrofitting the interior beam-column joint regions (IJIR series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity. Specimens of IJIR series, designed by the retrofitting of advanced reinforcing detailings and high ductile fiber-reinforced mortar in reinforecd beam-column joint regions increased its maximum load carrying capacity by 114.2~123.5% and its energy dissipation capacity by 1.55~1.85 times in comparison with the standard specimen of SIJC with a displacement ductility of 5.

In this study, experimental research was carried out to evaluate and improve the constructability and seismic performance of high strength R/C interior beam-column joints regions, with or without the shear reinforcement, using high ductile fiber-reinforced mortar. Six specimens of retrofitted the beam-column joint regions using high ductile fiber-reinforced mortar are constructed and tested for their retrofit performances. Specimens designed by retrofitting the interior beam-column joint regions (IJNS series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity due to the enhancement of crack dispersion by fiber bridging from using new high ductile materials for retrofitting. Specimens of IJNS series, designed by the retrofitting of high ductile fiber-reinforced mortar in beam-column joint regions increased its maximum load carrying capacity by 96~102.8% and its energy dissipation capacity by 0.99~1.11 folds when compared to standard specimen of SIJC with a displacement ductility of 5.

In this study, experimental research was carried out to evaluate the structural performance of the reinforced concrete beam using strengthening materials (embedded FRP rod, metal fittings) in existing reinforced concrete buildings. Seven reinforced concrete beams comprised of retrofitted embedded FRP rod (BCR series), embedded FRP rod with metal fittings (BCR-AC series), and standard specimen (BSS) were constructed and tested under monotonic loading. Design parameters of test specimens were amount of embedded FRP rod and metal fittings. The test results showed that the maximum load carrying capacity of specimens with embedded FRP rod (BCR series) and embedded FRP rod with metal fittings (BCR-AC series) increased by 21~55% and 21~63%, respectively, in comparison with the standard specimen BSS. BCR series test specimens failed by the adhesion slip and concrete cover separation. BCR-AC series test specimens failed by the adhesion slip due to the confining effect of metal fittings.

Recently, as structures in Korea and other countries become much taller, larger, and more specialized, concrete used for constructions of these structures is required to have high performance characteristics. Especially, seismic performance of concrete must be improved to resist cyclic loading from earthquakes. Consequently, this study was performed to focus on developing optimal mixtures of high ductile fiber reinforced mortar with high ductility and durability, which have good serviceability, stability and reliability performances. Eventually, this material is expected to improve seismic performance of concrete structures such as load carrying capacity, ductility capacity, and energy dissipation capacity when applied to critical regions of flat plate slab-column joint. Ultimately, this research is intended to develop a material for basic designs and practical constructions of reinforced concrete structures. Test results showed that the maximum load carrying capacity, the ductility capacity, and the energy dissipation capacity of the test specimens titled RCFPP series were increased by 15%~34%, by 33%~37%, and by 2.14 times, respectively, compared to those of the standard specimen titled SRCFP.

In this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (steel plate, carbon fiber sheet, and embedded carbon fiber rod) in existing reinforced concrete buildings. Six specimens of retrofitted beam-column joints are constructed using various retrofitting materials and tested for their retrofit performances. Specimens designed by retrofitting the beam-column joint regions (LBCJ series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity due to the effect of crack control at the time of initial loading and confinement from retrofitting materials during testing. Specimens of LBCJ series, designed by the retrofitting of FRP in reinforecd beam-column joint regions increased its maximum load carrying capacity by 26~50% and its energy dissipation capacity by 13.0~14.4% when compared to standard specimen of LBCJC with a displacement ductility of 4.

Prepackaged ECCs are rheologically designed by determining the amount of admixtures such that they are suitable for self-consolidating and shotcreting processes. Rheology is controlled such that it can be directly applicable to construction in the field, using prepackaged products with all powdered ingredients. To control the rheological properties of the composites, which have different fluid properties that facilitate two types of processing (i.e., self-consolidating and shotcreting processes), the viscosity change of the cement paste suspensions over time was initially investigated. The proper dosage of the admixtures in the cement paste was then determined. The two most appropriate mixture proportions were then selected by conducting self-consolidating and shotcreting tests. A series of self-consolidating and shotcreting tests demonstrated excellent self-consolidation properties and sprayability of the prepackaged ECC. Subsequent direct tensile tests also revealed hardened properties of prepackaged ECC comparable to those of normally cast ECC.

This study aims to make improvements to the standard estimation process used to estimate reasonable costs for construction work, and to suggest a work crew based estimation using a new cost estimation model. In addition, work crew shift combination and construction process were systematically organized in order to improve the estimation technique and the construction capability of the cement liquid waterproofing work for apartment buildings. In addition, in terms of manpower and productivity, analyses were performed on the cement liquid waterproofing work for apartment buildings with net areas between and , and the results were then compared with those calculated using the conventional work-crew based estimation method. Through this study, when the results of this study and those calculated by the conventional method were compared, for apartments with the net area of , the differences between specialists were shown to be 1.91 times to 2.13 times on average, while they were 8.82 times to 9.52 times between normal workers on average. For apartments with the net area of , the differences betweenspecialists were shownto be 1.89 times to 2.07 times on average, and 8.57 times to 9.38 times on average between normal workers.

An efficient design concept for earthquake loads, which is called performance based design, has been standard design in USA, Europe and Japan since those countries experienced severe earthquake damage at end of 90`s. For general design, struttie model well predicts the strength of the disturbed region, however, it does not provide ductility information at the failure. Therefore, simple tools which are able to predict both the strength and the ductility of RC structures are in demand. 2D lattice model is introduced in this study as an analysis tool for the RC structures subject to earthquake. Experimental correlation studies indicate the 2D lattice model quite well predict the strength as well as the ductility of RC structures.

In general, conventional sheeting H-pile is often used as a temporary member installed upon construction of outer retaining wall at basement floor. In CBW (composite basement wall), R/C basement wall is combined with H-Pile and resists lateral soil pressure together. This paper presents an experimental results of push out shear test of CBW with stud coupler as shear connectors to combine H-Pile with R/C wall six specimens with different diameter of FT (form tie) and arrangement of shear connectors were tested to evaluate the shear capacity of the composite wall. Test results showed that shear strength increased with diameter of FT. The shear strength of shear connector in CBW could be suitably predicted by using the previous equations codified in the codes. Best correlation, especially, was found when the calculation result by the formula in AISC 360-05 was compared to test one.

A number of studies have suggested that the use of high ductile and high shear materials, such as Engineered Cementitious Composites (ECC) and High Performance Fiber Reinforced Cementitious Composites (HPFRCC), significantly enhances the shear capacity of structural elements, even with/without shear reinforcements. The present study emphasizes the development of a nonlinear model of shear behaviour of a HPFRCC panel for application to the seismic retrofit of reinforced concrete buildings. To model the shear behaviour of HPFRCC panels, the original Modified Compression Field Theory (MCFT) for conventional reinforced concrete panels has been newly revised for reinforced HPFRCC panels, and is referred to here as the HPFRCC-MCFT model. A series of experiments was conducted to assess the shear behaviour of HPFRCC panels subjected to pure shear, and the proposed shear model has been verified through an experiment involving panel elements under pure shear. The proposed shear model of a HPFRCC panel has been applied to the prediction of seismic retrofitted reinforced concrete buildings with in-filled HPFRCC panels. In retrofitted structures, the in-filled HPFRCC element is regarded as a shear spring element of a low-rise shear wall ignoring the flexural response, and reinforced concrete elements for beam or beam-column member are modelled by a finite plastic hinge zone model. An experimental study of reinforced concrete frames with in-filled HPFRCC panels was also carried out and the analysis model was verified with correlation studies of experimental results.

An experimental program to apply a new retrofit technology using high performance carbon fiber reinforced polymer (CFRP) bars with a trapezoidal cross section to reinforce concrete beams has been investigated. The proposed method has two important advantages in the retrofit of concrete beams: the failure mode of the beam is controlled by flexural failures before reaching local failures and the retrofitting process in the construction field is simple and easy to apply in aged reinforced concrete beams or beam–column members. The new methodology has been proposed based on a system where geometrically modulated CFRP trapezoidal bars are embedded into grooved concrete with additional assistance from externally applied U-type metal fittings. The proposed retrofit method is validated by comparing it with the experimental results of conventionally strengthened beams and showing that the proposed method gives good improvement in ductility and load-carrying capacities of concrete beams. When compared with conventional retrofit methods using steel plates or FRP sheets, the proposed method is effective in preventing local failures before reaching the flexural failure of retrofitted beams, due to the superior composite action between the concrete and embedded CFRP trapezoidal bars.

In the current research, the scheme of displacement-based seismic design for seismic retrofit of concrete structures using FRP composite materials has been proposed. An algorithm of the nonlinear flexural analysis of FRP composite concrete members has been presented under multiaxial constitutive laws of concrete and composite materials. An algorithm for performance-based seismic retrofit design of reinforced concrete columns with FRP jacket has been newly introduced to modify the displacement coefficient method used in reinforced concrete structures. From applications of retrofit design, the method are easy to apply in the practice of retrofit design and give practical prediction of nonlinear seismic performance evaluation of retrofitted structures.

An engineered cementitious composite (ECC) produced with ground granulated blast furnace slag was developed for the purpose of achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, single fiber pullout tests and matrix fracture tests were performed, followed by micromechanical analyses to properly select the range of mixture proportion. Subsequent direct tensile tests were employed to assess the strain-hardening behavior of the composite, which exhibited high ductility and strength with the addition of slag. High ductility is most likely due to enhanced workability and fiber dispersion performance which is attributed to the oxidized grain surface of slag, as verified by fiber dispersion tests. These results suggest that, within the limited slag dosage employed in the present study, the contribution of slag to fiber dispersion outweighs the side-effect of decreased potential for saturated multiple cracking, including a slight increase in matrix fracture toughness and fiber/matrix bond strength.

This paper presents both experimental and analytical studies for the development of an ECC(Engineered Cementitious Composites) using ground granulated blast furnace slag(slag). This material has been focused on achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, micromechanics was adopted to properly select optimized range of the composition based on steady-state cracking theory and experimental studies on matrix, and interfacial properties. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties of the fiber in a matrix and the fracture toughness of mortar matrix. The addition of the slag resulted in slight increases in the frictional bond strength and the fracture toughness. Subsequent direct tensile tests demonstrate that the fiber reinforced mortar exhibited high ductile uniaxial tension behavior with a maximum strain capacity of 3.6%. Both ductility and tensile strength( MPa) of the composite produced with slag were measured to be significantly higher than those of the composite without slag. The slag particles contribute to improving matrix strength and fiber dispersion, which is incorporated with enhanced workability attributed to the oxidized grain surface. This result suggests that, within the limited slag dosage employed in the present study, the contribution of slag particles to the workability overwhelms the side-effect of decreased potential of saturated multiple cracking.

Under severe earthquake conditions, the lack of strength and ductility in reinforced concrete beam–column joints with non-seismic details raises serious concerns for overall structural safety. In this study, experimental research was carried out in order to try and improve the seismic strength and performance of reinforced concrete exterior beam–column joints by applying embedded carbon fiber-reinforced polymer (CFRP) bars combined with CFRP sheets. CFRP bars have a flat-typed hexagonal cross-section. Specimens of reinforced concrete exterior beam–column joints were manufactured based on a newly developed strengthening method by applying embedded CFRP hexagonal bars combined with externally bonded CFRP sheets, and tested for comparison with the specimen of a conventional reinforced concrete exterior beam–column joint. The newly developed design approach could minimize damage and improve the overall structural performances of beam–column joints under cyclic load reversals.

With the increasing use of high-rise reinforced concrete structures, high-strength materials, smaller member sections and larger reinforcing bars should be employed. Therefore, the stress resistance capacity of a joint is also required to be increased over other parts of a structure. The application of high-strength concrete has progressively increased in many structures, and it has now been used in many parts of the world. Previous research1–3 has shown that the behaviour of a reinforced high-strength concrete structure subjected to monotonic or earthquake-type loading is significantly different from that of a reinforced normal-concrete structure. It tends to be brittle when overloaded to failure, and to show a more sudden appearance of microcracking. Lack of ductility in concrete members raises serious concerns for structural safety. The behaviour of reinforced high-strength concrete members and joints must be accurately assessed before high-strength concrete can be used with confidence in reinforced concrete frame structures. The objective of this experimental research was to study the behaviour of reinforced high-strength concrete beam–column joints, and to develop a new approach for the design of such joints in high-rise reinforced concrete buildings.