• Advances in concrete construction
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• v.12 no.6
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• pp.517-525
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• 2021

More underground structures are increasingly being constructed such as box culverts for electric power transmission, and the life extension of these structures is very important. It is well known that the steel embedded in concrete is usually invulnerable to corrosion because the high alkalinity of the pore solution in concrete generates a thin protective oxide layer on the surface of the steel. Recent observations in the field and experimental evidence have shown that even steel in concrete can be corroded through the carbonation reaction of cover concrete. Carbonation-induced corrosion in concrete may often occur in a high carbon dioxide environment. In this study, the risk of carbonation of underground box culverts in Korea was evaluated by measuring the car¬bonation rate and concrete cover depth in the field. Then, the carbonation-free service life for the cover depth of the steel was calcu¬lated with in situ information and Monte Carlo simulation. Additionally, an accelerated carbonation test for a cracked beam specimen was performed, and the effect of a crack on the service life of a box culvert was numerically investigated with Monte Carlo simulation based on experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.317-325
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• 2020

The development of a technique that can monitor the cracks, which is one of the typical types of damage, is necessary to secure the structural safety of elastically restrained cantilever-type beams with a tip mass that is used widely in infrastructure. Impedance techniques have been actively researched to detect cracks, and the cracks were estimated mainly by experimentally investigating the relationship between the crack and impedance signal. This study examined the correlation between the change in the impedance signals due to the crack, and the natural frequency obtained analytically. After updating the analysis model for the intact beam, the impedance signal was measured while gradually inflicting cracks in the cantilever-type beam, and the damage index was obtained. The results were compared with the natural frequencies calculated from the updated analysis model to investigate the correlation. A close correlation was observed between the experimentally obtained impedance damage index, and the analytically calculated natural frequency. Using this correlation, the structural characteristics could be evaluated more accurately from the damage estimation results, and the behavior of the structure could be predicted effectively using the analysis model.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.511-517
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• 2010

The purpose of this study is to investigate the shear behavior of prestressed concrete deep beams and to provide the data for development of improved design criteria. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. Hence, in this study, the computer program, named RCAHEST (reinforced concrete analysis in higher evaluation system technology), was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. A bonded or unbonded tendon element based on the finite element method, that can represent the interaction between tendon and concrete of prestressed concrete member, is used. The proposed numerical method for the shear behavior of prestressed concrete deep beams is verified by comparing the analytical results with test data by others.

• 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 the Korea Concrete Institute
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• v.14 no.6
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• pp.1010-1021
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• 2002

The current ACI design code does not take into account the contribution of concrete for the torsional moment of reinforced concrete(RC) beams subjected to pure torsion. This code is not capable of evaluating the inter-effects between concrete and torsional reinforcement on the torsional resistance of the RC beams. Some test results indicated that the current ACI code was not successful in predicting the observed torsional moment of the RC beams with reasonable accuracy. The research reported in this paper provides an evaluation equation to predict the torsional moment of the RC beams subjected to pure torsion. The proposed equation is derived from the equilibrium as well as compatibility equations of the truss model for the cracked RC beams. Comparisons between the observed and calculated torsional moments of the 66 tested beams, showed reasonable agreement.

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.145-155
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• 1995

The purpose of this paper is to present an analysis method which can exactly analyze load-deflection relationships. crack propagations and stresses and strains of steel reinforccnlent and concrete in hehaviors of elastic, mclastic and ultlmate ranges of reinforced concretc beams under monotonically increasing loads. For these purposes, the material nonlinearities are taken into account by comprising the tension. compression and shear models of cracked concrete and a model for reinforcement in the concrete. Smeared crack model is used as a modeling of concrete. The steel reinforcement is assumed to be in an uniaxial stress state and modeled srncaretl layers of eqivalent thickness and line elernents for correct positiori arid behavior. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzed and compared with those from other researchers. As a results, this method shown in 3.5-15(%) error is correct.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.30-40
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• 2014

The demand of underground structure such as box culvert for electric power transmission is increasing more and more, and the service life extension of these structures is very important. Recent observations in field and experimental evidences show that even steel in concrete can be corroded by carbonation reaction of cover concrete. Carbonation-induced corrosion in concrete may often occur in a high carbon dioxide environment. In this study, the risk of carbonation of box culverts in our nation was evaluated by measuring the carbonation rate and concrete cover depth in field. Then, the service life due to carbonation at the cover depth was calculated by in situ information and the Monte Carlo simulation in a probabilistic way. Additionally, the accelerated carbonation test for the cracked beam specimen was executed and the crack effect owing to the carbonation process on the service life of box culvert was numerically investigated via Monte Carlo simulation based on the experimental results.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.2
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• pp.19-26
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• 2020

Flexible displays have been evolved into curved, foldable, and rollable as the degree of bending increases. Due to the presence of brittle electrodes (e.g. indium-tin oxide (ITO)) that easily cracked and delaminated under severe bending deformation, lowering mechanical stress of the electrodes has been critical issue. Because of this, mechanical stress of brittle electrode in flexible displays has been analyzed mostly in terms of bending radius. On the other hand, in order to make rollable display, various mechanical components such as roller and spring are needed to roll-up or extend the screen for the rollable display apparatus. By these mechanical components, brittle electrode in the rollable display is subjected to the excessive tensile stress due to the retracting force as well as the bending stress by the roller. In this study, mechanical deformation of rollable OLED display was modeled considering boundary conditions of the apparatus. An analytical modeling based on the classical beam theory was introduced in order to investigate the mechanical behavior of the rollable display. In addition, finite element analysis (FEA) was used to analyze the effect of mechanical components in the apparatus on the brittle electrode. Furthermore, a strategy for improving the mechanical reliability of the rollable display was suggested through controlling the stiffness of adhesives in the display panel.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.731-740
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• 2011

Provisions for the redistribution of negative moments in KCI 2007 and ACI 318-08 use a method for continuous flexural members subjected to uniformly-distributed gravity load. Moment redistributions and plastic rotations in beams of reinforced concrete moment frames subjected to lateral load differ from those in continuous flexural members due to gravity load. In the present study, a quantitative relationship between the moment redistribution and plastic rotation is established for beams subjected to both lateral and gravity loads. Based on the relationship, a design method for the redistribution of negative moments is proposed based on a plastic rotation capacity. The percentage change in negative moments in the beam was defined as a function of the tensile strain of re-bars at the section of maximum negative moment, which is determined by a section analysis at an ultimate state using KCI 2007 and ACI 318-08. Span, reinforcement ratio, cracked section stiffness, and strain-hardening behavior substantially affected the moment redistribution. Design guidelines and examples for the redistribution of the factored negative moments determined by elastic theory for beams under lateral load are presented.

• Structural Engineering and Mechanics
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• v.53 no.2
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.