• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.62-73
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• 2005

The objects of this research are to establish the criteria of peel occurrence considering the shape of bond terminus and to compare the strength properties of adhesive joint of different three type such as butt joint, T-shape, and single lap Joints. The criteria of peel occurrence at the bond terminus was suggested. Peel loads of three type adhesive joint (butt Joint, T-shape specimen, single lap joint) were determined from tensile tests. Principal stress distributions of these joints were determined from finite element method analysis. Then, peel occurrence was estimated with stress singularity factor$(K_{prin})$ when the terminus shape was square, with average principal stress when the terminus shape was rounded. The conclusions are summarized as follows; (1) In the non-filleted model(e.g., butt joint, T-shape specimen), principal stress shows singularity at the bond terminus, intensity of stress(principal stress) singularity $(K_{prin})$ can use as the criteria of peel occurrence at the bond terminus. (2) In the filleted model(e.g., single lap joint), principal stress has not affected singularity at the bond terminus. Average principal stress$(K_{av})$ can use as the criteria of peel occurrence at the bond terminus.

• Bulletin of the Korean Chemical Society
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• v.12 no.2
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• pp.182-188
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• 1991

The reactions of aniline with benzyl and phenacyl compounds are studied by the AM1 method. Two types of modeling were adopted: Cation-neutral, in which a proton is attached to the leaving group F and anion-neutral model, in which aniline was replaced by phenoxide with Cl as the leaving group. The cation-neutral model represented the reactvery well, reproducing the various solution-phase experimental results. In the benzyl system, the ${\pi}$-electrons of the two rings (X-ring in the nucleophile and Y-ring in the substrate) interact conjugatively in the transition state (TS) resulting in a bond contraction of the $C_{\alpha}-C_{Y1}$ bond (benzylic effect), whereas in the phenacyl system the ${\pi}$ electrons of the X-ring delocalizes more efficiently into the carbonyl group than into the Y-ring (resonance shunt effect) with a bond contraction of the $C_{\alpha}-C_{\beta}$ bond. The bond contraction in the benzylic effect was substantially greater than that in the resonance shunt effect. The TS was rather loose for benzyl while it was tighter for phenacyl system. Various bond length changes with substituents in the TS were, however, found to be irregular.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.99-107
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• 2022

Existing reinforced concrete building structures constructed before 1988 have seismically-deficient reinforcing details, which can lead to the premature failure of the columns and beam-column joints. The premature failure was resulted from the inadequate bonding performance between the reinforcing bars and surrounding concrete on the main structural elements. This paper aims to quantify the bond-slip effect on the dynamic responses of reinforced concrete frame models using finite element analyses. The bond-slip behavior was modeled using an one-dimensional slide line model in LS-DYNA. The bond-slip models were varied with the bonding conditions and failure modes, and implemented to the well-validated finite element models. The dynamic responses of the frame models with the several bonding conditions were compared to the validated models reproducing the actual behavior. It verifies that the bond-slip effects significantly affected the dynamic responses of the reinforced concrete building structures.

• Computers and Concrete
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• v.16 no.3
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• pp.449-466
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• 2015

This paper aims to study the local bond stress-slip behavior of reinforcing bars embedded in lightweight aggregate concrete (LWAC). The experimental variables of the local bond stress-slip tests include concrete strength (20, 40 and 60 MPa), deformed steel bar size (#4, #6 and #8) and coarse aggregate (normal weight aggregate, reservoir sludge lightweight aggregate and waterworks sludge lightweight aggregate). The test results show that the ultimate bond strength increased with the increase of concrete compressive strength. Moreover, the larger the rib height to the diameter ratio ($h/d_b$) of the deformed steel bars is, the greater the ultimate bond stress is. In addition, the suggestion value of the CEB-FIP Model Code to the LWAC specimen's ultimate bond stress is more conservative than that of the normal weight concrete.

• Computers and Concrete
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• v.23 no.3
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• pp.155-160
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• 2019

The use of recycled aggregate concrete for the purpose of environmental and resource conservation has gained increasing interest in construction engineering. Nevertheless, few studies have reported on the bonding performance of the bars in recycled aggregate concrete after exposed to high temperatures. In this paper, 72 pull-out specimens and 36 cubic specimens with different recycled coarse aggregate content (i.e., 0%, 50%,100%) were cast to evaluate the bond behavior between recycled aggregate concrete and steel bar after various temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$). The results show that the recycled aggregate concrete pull-out specimens exhibited similar bond stress-slip curves at both ambient and high temperature. The bond strength declined gradually with the increase of the temperature. On the basis of a regression analysis of the experimental data, a revised bond strength mode and peak slip ratios relationship model were proposed to predict the post-heating bond-slip behavior between recycled aggregate concrete and steel bar.

• Bulletin of the Korean Chemical Society
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• v.7 no.3
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• pp.186-190
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• 1986

Effects of substituents in the nucleophile(X), the substrate(Y) and the leaving group(Z) on the structure of $S_N2$ transition states have been analyzed by considering effects of four components, electrostatic($E_{es}$), exchange repulsion ($E_{ex}$), polarization($E)_{pl}$) and charge transfer($E_{ct}$) terms, of interaction between the reactants on the degree of bond making and bond breaking. Prediction of net effects of all substituents(X, Y and Z) on the degree of bond making were found to be clearcut whereas the effect of an electron withdrawing group on the substrate (Y = EWG) on the degree of bond breaking was complex; the substituent(Y = EWG) is normally carbon-leaving group($C^{\ast}$-L) bond tightening($E_{pl}$ dominance) but becomes $C^{\ast}$-L bond loosening when the bond is strongly antibonding ($E_{ct}$ dominance). Our model calculations on the reaction of $CH_2XNH_2$ with $YCH_2COOCH_2Z$ using energy decomposition scheme have confirmed that predictions based on our analysis are correct.

• Bulletin of the Korean Chemical Society
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• v.27 no.12
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• pp.2045-2050
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• 2006

The interstitial hydrogen bonding in NiTi solid and its effect on the metal-to-metal bond is investigated by means of the EH tight-binding method. Electronic structures of octahedral clusters $Ti_4Ni_2$ with and without hydrogen in their centers are also calculated using the cluster model. The metal d states that interact with H 1s are mainly metal-metal bonding. The metal-metal bond strength is diminished as the new metal-hydrogen bond is formed. The causes of this bond weakening are analyzed in detail.

• Communications for Statistical Applications and Methods
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• v.21 no.5
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• pp.445-459
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• 2014

This paper investigates the dependence structure of Korean financial markets (stock, foreign exchange (FX) rates and bond) using copula-GARCH and dynamic conditional correlation (DCC) models. We examine GJR-GARCH with skewed elliptical distributions and four copulas (Gaussian, Student's t, Clayton and Gumbel) to model dependence among returns, and then employ DCC model to describe system-wide correlation dynamics. We analyze the daily returns of KOSPI, FX (WON/USD) and KRX bond index (Gross Price Index) from $2^{nd}$ May 2006 to $30^{th}$ June 2014 with 2,063 observations. Empirical result shows that there is significant asymmetry and fat-tail of individual return, and strong tail-dependence among returns, especially between KOSPI and FX returns, during the 2008 Global Financial Crisis period. Focused only on recent 30 months, we find that the correlation between stock and bond markets shows dramatic increase, and system-wide correlation wanders around zero, which possibly indicates market tranquility from a systemic perspective.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.219-222
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• 2003

Substantial experimental and theoretical work exists on the bond characteristics of FRP-concrete adhesive joints. Experimental studies show that the bond strength cannot always increase with an increase in the bond length, and that the ultimate strength is strongly influenced by the concrete strength. To solve this feature, analytic solutions based on fracture mechanics are widely used, and the local shear stress-slip curve with a softening branch is known as more rational model. The analytic solution, however, cannot describe various shapes of model curve. In this study, numerical method using interface element is introduced to express various shapes of model curve. Characteristics of adhesive joint is investigated for the shapes of the model curve and their parameters. And the numerical solutions are compared with the test results of CFRP sheet adhesive joints.

• Computers and Concrete
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• v.19 no.4
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• pp.375-385
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• 2017

In the present paper experimental and numerical analysis of hook-ended steel fiber reinforced concrete is carried out. The experimental tests are performed on notched beams loaded in 3-point bending using fiber volume fractions up to 1.5%. The numerical analysis of fiber reinforced concrete beams is performed at meso scale. The concrete is discretized with 3D solid finite elements and microplane model is used as a constitutive law. The fibers are modelled by randomly generated 1D truss finite elements, which are connected with concrete matrix by discrete bond-slip relationship. It is demonstrated that the presented approach, which is based on the modelling of concrete matrix using microplane model, able to realistically replicate experimental results. In all investigated cases failure is due to the pull-out of fibers. It is shown that with increase of volume content of fibers the effective bond strength and slip capacity of fibers decreases.