• Korean Journal of Materials Research
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• v.2 no.3
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• pp.172-179
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• 1992

$Al_2O_3/ZrO_2$ composites were fabricated by pressureless sintering from commercial powders and/or nano composite powder of $Al_2O_3/ZrO_2$. The Properties of the composites such as density, strength, hardness and fracture toughness were evaluated. Microstructures and fracture surfaces ware also examined. The flexural strength remains unchanged(~640 MPa) as long as the content of commercial powders is not extreamly high, and depends on microstructures of the composites. Fracture toughness(4.3-5.3 $Mpa{\cdot}m^{1/2}$) increases with increasing content of commercial powders. Fractography shows that failure-initiating sources are 1)surface flaws resulting from machining damage, 2)crack-shaped voids formed due to $ZrO_2$ agglomeration, and 3)surface separation caused by inhomogeneous blending and by sinterability difference between nato composite powder and commercial powders of $Al_2O_3/ZrO_2$. Failure mode of the composites was mainly transgranular.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.859-862
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• 2008

The objective of this study offer the equation of the development length for GFRP reinforcement. Pullout test carried out to propose the development length for GFRP reinforcement. Test variables included embedment length (L=15, 30 and 45d$_b$ ), pure cover thickness(C=0.5, 1.0, 1.5, and 2.0d$_b$ ), diameter of reforcement(D10, D13 and D16), and three types, (domestic : K2KR, K3KR, foreign : AsUS) of GFRP reinforcement. The method of test were introduced pure pullout and tests lasted until the GFRP reinforcements were reached final failure. Based on the results through the pullout test, the bond characteristics and average bond stress for GFRP reinforcement were investigated. The equation of development length was proposed based on the regression analysis selected specimens having splitting failure. The equation gained from this study compared with the design equation provided by ACI committee 440.1R-06. The results through this study are capable of the flexural member design with GFRP reinforcement having lab spliced.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.323-334
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• 2003

For performance-based design using nonlinear static analysis, it is required to predict the inelastic behavior of structural members accurately. In the present study, a nonlinear numerical analysis was peformed to develop the method describing the moment-curvature relationship of structural wall with boundary confinement. Through the numerical analysis, variations of behavioral characteristics and failure mechanism with the arrangement of vertical reinforcement and the length of boundary confinement were studied. According to the analysis, the maximum moment-carrying capacity of structural walls with adequately confined boundary elements is developed at the moment the unconfined concrete reaches the ultimate compressive strain. Walls with flexural re-bars concentrated on the boundaries fails in a brittle manner. As vortical re-bars in the web increases, the brittle failure is prevented and a ductile failure occurs. Based on the findings, moment-curvature curves for walls with a variety of re-bar arrangement were developed. According to the proposed relationships, deformability of the structural walls wth boundary confinement increases as the compressive strength of the confined concrete increases compared to the applied compressive force.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.4
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• pp.141-148
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• 2008

In the recent construction industry, Carbon Fiber Reinforced Polymers(CFRPs) have been highly considered as innovative strengthening materials for civil structures due to their superior material properties. This paper is to offer design data and strengthening efficiency of reinforced concrete beams strengthened with CFRP Plate. Static tests were carried out to evaluate failure modes and strengthening capacity. Displacements and strains of steel and CFRP plates were obtained and analyzed through a series of fatigue tests. Also, Those evaluated the energy dissipation. Results of the tests showed increase in strengthening ratios caused debonding failure at the end of beams. For the beams wrapped with CFRP sheets around the end of the plates, debonding failure mode that was induced from flexural cracks was indicated. Through the fatigue tests, it was observed that displacements, strains of steel and CFRP plates converged into certain values. It is also proved that the beams strengthened with CFRP plates are able to resist fatigue loading under serviceability.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.221-227
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• 2001

Both strength and stiffness of RC structures strengthened by a steel plate greatly increase and however, their ductility might not be sufficient because premature failures usually occur at the adhesive-concrete interface. In this study, Mohr-Coulomb criterion was adopted to examine the bonding failure mechanism, and the diagonal shear bonding test, the direct shear bonding test, and the flexural test on RC beams strengthened by a steel plate were carried out to measure the bonding properties. It is found from the experimental and numerical results that the cohesive strengths of epoxy-concrete interfaces are ranging from 50 kgf/㎠ to 70 kgf/㎠ when the friction angle is 45°. Bonding failure loads can be predicted by applying the bonding properties to the structural analysis of RC beams strengthened by steel plate. By considering them in the design of strengthened beams, the premature failure would be effectively prevented.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.59-68
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• 2010

In the present study, the deformation capacity of slender shear walls with thin web subject to inelastic deformation after flexural yielding was studied. Web-crushing and rebar-fracture were considered as the governing failure mechanisms of walls. To address the effect of the longitudinal elongation on web-crushing and rebar-fracture, the longitudinal elongation was predicted by using truss model analysis. The failure criteria by web-crushing and rebar-fracture were defined as a function of the longitudinal elongation. The proposed method was applied to 17 shear wall specimens with boundary columns, and the prediction results were compared with the test results. The results showed that proposed method predicted the maximum deformations and failure modes of the wall specimens with reasonable precision.

• Computers and Concrete
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• v.16 no.3
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• pp.357-380
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• 2015

In this study, a simple indeterminate strut-tie model which reflects complicated characteristics of the ultimate structural behavior of continuous reinforced concrete deep beams was proposed. In addition, the load distribution ratio, defined as the fraction of applied load transferred by a vertical tie of truss load transfer mechanism, was proposed to help structural designers perform the analysis and design of continuous reinforced concrete deep beams by using the strut-tie model approaches of current design codes. In the determination of the load distribution ratio, a concept of balanced shear reinforcement ratio requiring a simultaneous failure of inclined concrete strut and vertical steel tie was introduced to ensure the ductile shear failure of reinforced concrete deep beams, and the primary design variables including the shear span-to-effective depth ratio, flexural reinforcement ratio, and compressive strength of concrete were reflected upon. To verify the appropriateness of the present study, the ultimate strength of 58 continuous reinforced concrete deep beams tested to shear failure was evaluated by the ACI 318M-11's strut-tie model approach associated with the presented indeterminate strut-tie model and load distribution ratio. The ultimate strength of the continuous deep beams was also estimated by the experimental shear equations, conventional design codes that were based on experimental and theoretical shear strength models, and current strut-tie model design codes. The validity of the proposed strut-tie model and load distribution ratio was examined through the comparison of the strength analysis results classified according to the primary design variables. The present study associated with the indeterminate strut-tie model and load distribution ratio evaluated the ultimate strength of the continuous deep beams fairly well compared with those by other approaches. In addition, the present approach reflected the effects of the primary design variables on the ultimate strength of the continuous deep beams consistently and reasonably. The present study may provide an opportunity to help structural designers conduct the rational and practical strut-tie model design of continuous deep beams.

• Structural Engineering and Mechanics
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• v.76 no.4
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• pp.465-477
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• 2020

This paper presents an investigation on the dynamic behavior of SRC columns with built-in cross-shaped steels under impact load. Seven 1/2 scaled SRC specimens were subjected to low-speed impact by a gravity drop hammer test system. Three main parameters, including the lateral impact height, the axial compression ratios and the stirrup spacing, were considered in the response analysis of the specimens. The failure mode, deformation, the absorbed energy of columns, as well as impact loads are discussed. The results are mainly characterized by bending-shear failure, meanwhile specimens can maintain an acceptable integrity. More than 33% of the input impact energy is dissipated, which demonstrates its excellent impact resistance. As the impact height increases, the flexural cracks and shear cracks observed on the surface of specimens were denser and wider. The recorded time-history of impact force and mid-span displacement confirmed the three stages of relative movement between the hammer and the column. Additionally, the displacements had a notable delay compared to the rapid changes observed in the measured impact load. The deflection of the mid-span did not exceed 5.90mm while the impact load reached peak value. The impact resistance of the specimen can be improved by proper design for stirrup ratios and increasing the axial load. However, the cracking and spalling of the concrete cover at the impact point was obvious with the increasing in stiffness.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.143-153
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• 2021

The corroded pier that has corrosion of the tranverse steel, main steel and lapsplice directly affects the seismic performance. The corrosion of the tranvese and main steel directly reduce the shear strength and bendig strength. If steel corrosion occurs in lap splice, the flexural strength and flexibility of existing corroded pier that are not seismic design are significantly reduced. In addition, as the axial force acting on the pier increase the shear strength. Considering these effects. In this stuydy, we cosidered steel corrosion, lap splice and axial force, for a reasonable evaluation of seismic-performance. It is confirmed that flexular failure occurs at pies where shear failure is expected to occur due to corrosion of reinforcement. These failure modes and their reason are analyzed, and necessary considerations are presented for seismic reinforcement.

• Earthquakes and Structures
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• v.21 no.6
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• pp.613-625
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• 2021

Non-seismically designed eccentric reinforced concrete beam-column joints were extensively used in existing reinforced concrete frame buildings, which were found to be vulnerable to seismic action in many incidences. To provide a fundamental understanding of the seismic performance and failure mechanism of the joints, three 2/3-scale exterior beam-column joints with non-seismically designed details were cast and tested under reversed cyclic loads simulating earthquake excitation. In this investigation, particular emphasis was given on the effects of the eccentricity between the centerlines of the beam and the column. It is shown that the eccentricity had significant effects on the damage characteristics, shear strength, and displacement ductility of the specimens. In addition, shear deformation and the strain of joint hoops were found to concentrate on the eccentric face of the joint. The results demonstrated that the specimen with an eccentricity of 1/4 column width failed in a brittle manner with premature joint shear failure, while the other specimens with less or no eccentricity failed in a ductile manner with joint shear failure after beam flexural yielding. Test results are compared with those predicted by three seismic design codes and two non-seismic design codes. In general, the codes do not accurately predict the shear strength of the eccentric joints with non-seismic details.