• Computers and Concrete
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• 제20권4호
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• pp.469-481
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• 2017

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

• 한국도로학회논문집
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• 제19권6호
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• pp.37-46
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• 2017

PURPOSES : A composite pavement utilizes both an asphalt surface and a concrete base. Typically, a concrete base layer provides structural capacity, while an asphalt surface layer provides smoothness and riding quality. This pavement type can be used in conjunction with rollercompacted concrete (RCC) pavement as a base layer due to its fast construction, economic efficiency, and structural performance. However, the service life and functionality of composite pavement may be reduced due to interfacial bond failure. Therefore, adequate interfacial bonding between the asphalt surface and the concrete base is essential to achieving monolithic behavior. The purpose of this study is to investigate the bond characteristics at the interface between asphalt (HMA; hot-mixed asphalt) and the RCC base. METHODS : This study was performed to determine the optimal type and application rate of tack coat material for RCC-base composite pavement. In addition, the core size effect, temperature condition, and bonding failure shape were analyzed to investigate the bonding characteristics at the interface between the RCC base and HMA surface. To evaluate the bond strength, a pull-off test was performed using different diameters of specimens such as 50 mm and 100 mm. Tack coat materials such as RSC-4 and BD-Coat were applied in amounts of 0.3, 0.5, 0.7, 0.9, and $1.1l/m^2$ to determine the optimal application rate. In order to evaluate the bond strength characteristics with temperature changes, a pull-off test was carried out at -15, 0, 20, and $40^{\circ}C$. In addition, the bond failure shapes were analyzed using an image analysis program after the pull-off tests were completed. RESULTS : The test results indicated that the optimal application rate of RSC-4 and BD-Coat were $0.8l/m^2$, $0.9l/m^2$, respectively. The core size effect was determined to be negligible because the bond strengths were similar in specimens with diameters of 50 mm and 100 mm. The bond strengths of RSC-4 and BD-Coat were found to decrease significantly when the temperature increased. As a result of the bonding failure shape in low-temperature conditions such as -15, 0, and $20^{\circ}C$, it was found that most of the debonding occurred at the interface between the tack coat and RCC surface. On the other hand, the interface between the HMA and tack coat was weaker than that between the tack coat and RCC at a high temperature of $40^{\circ}C$. CONCLUSIONS : This study suggested an optimal application rate of tack coat materials to apply to RCC-base composite pavement. The bond strengths at high temperatures were significantly lower than the required bond (tensile) strength of 0.4 MPa. It was known that the temperature was a critical factor affecting the bond strength at the interface of the RCC-base composite pavement.

• 대한토목학회논문집
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• 제29권5A호
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• pp.503-510
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• 2009

본 연구의 목적은 LMC로 덧씌우기 또는 보수 된 형태의 RC 보의 정적 거동 특성을 파악하는데 있다. 따라서, LMC로 덧씌우기 및 보수된 RC 보를 상대습도 60%, 온도 $20^{\circ}C$의 조건에서 양생을 실시하여 제작하였으며, 제작된 시험체를 4점 휨 실험을 수행하여 균열양상, 파괴거동 및 극한강도 등의 거동을 고찰하였다. 실험결과 전단철근이 보강된 보수형태의 RC보의 경우 100%이상의 내하력을 회복하여 보수 효과가 뛰어난 것을 알 수 있었고, LMC로 압축부에 덧씌우기 된 시험체의 경우 덧씌우기 두께가 증가함에 따라 내하력이 크게 증진되었다. 그러나, 전단철근이 보강되지 않은 보수형태의 시험체와 인장부 덧씌우기된 시험체는 부착계면 파괴양상을 보여주어 보수 및 보강 효과가 거의 없는 것으로 나타났다. 또한 부착계면의 거동특성을 파악하기 위하여 전단흐름 개념을 도입하여 LMC로 압축 덧씌우기된 시험체를 대상으로 하중증가에 따른 전단흐름량을 계산하여 부착계면 특성을 수치적으로 나타내었다.

• Smart Structures and Systems
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• 제17권2호
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• pp.297-311
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• 2016

Based on the distributed fiber optic sensing (DFOS) technique, plastic optical fibers (POFs) are attractive candidates to measure deformations of geotechnical structures because they can withstand large strains before rupture. Understanding the mechanical interaction between an embedded POF and the surrounding soil or rock is a necessary step towards establishing an effective POF-based sensing system for geotechnical monitoring. This paper describes a first attempt to evaluate the feasibility of POF-based soil deformation monitoring considering the POF-soil interfacial properties. A series of pullout tests were performed under various confining pressures (CPs) on a jacketed polymethyl methacrylate (PMMA) POF embedded in soil specimens. The test results were interpreted using a fiber-soil interaction model, and were compared with previous test data of silica optical fibers (SOFs). The results showed that the range of CP in this study did not induce plastic deformation of the POF; therefore, the POF-soil and the SOF-soil interfaces had similar behavior. CP was found to play an important role in controlling the fiber-soil interfacial bond and the fiber measurement range. Moreover, an expression was formulated to determine whether a POF would undergo plastic deformation when measuring soil deformation. The plasticity of POF may influence the reliability of measurements, especially for monitored geo-structures whose deformation would alternately increase and decrease. Taken together, these results indicate that in terms of the interfacial parameters studied here the POF is feasible for monitoring soil deformation as long as the plastic deformation issue is carefully addressed.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1275-1289
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• 1996

The plane elasticity problem of collinear cracks in a layered medium is investigated. The medium is modeled as bonded structure constituted from a surface layer and a semi-infinite substrate. Along the bond line between the two dissimilar homegeneous constituents, it is assumed that as interfacial zone having the functionally graded, nonhomogeneous elastic modulus exists. The layered medium contains three collinear cracks, one in each constituent material oriented perpendicular to the nominal interfaces. The stiffness matrix formulation is utilized and a set of homogeneous conditions relevant to the given problem is readily satisfied. The proposed mixed boundary value problem is then represented in the form of a system of integral equations with Cauchy-type singular kernels. The stress intensity factors are defined from the crack-tip stress fields possessing the standard square-root singular behavior. The resulting values of stress intensity factors mainly address the interactions among the cracks for various crack sizes and material combinations.

• 한국농공학회논문집
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• 제54권5호
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• pp.25-34
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• 2012

It has been well known that concrete structures exposed to acid and sulfate environments such as sewer etc. show significant decrease in their durability due to chemical attack. Such deleterious acid and sulfate attacks lead to expansion and cracking in concrete, and thus, eventually result in damage to cement mortar by forming expansive hydration products due to the reaction between cement hydration products and acid and sulfate ions. In this study, the effect of fly ash and blast furnace slag on the bond performances of structural synthetic fiber in latex modified cement mortar under sulfate environments. Fly ash and blast furnace slag contents ranging from 0 % to 20 % are used in the mix proportions. The latex modified cement mortar specimens were immersed in fresh water, 8 % sodium sulfate ($Na_2SO_4$) solutions for 28 and 50 days, respectively. Pullout tests are conducted to measure the bond performance of structural synthetic fiber from latex modified cement mortar after sulfate environments exposure. Test results are found that the incorporation of fly ash and blast furnace slag can effectively enhance the PVA fiber-latex modified cement mortar interfacial bond properties (bond behavior, bond strength and interface toughness) after sulfate environments exposure. The microstructural observation confirms the findings on the interface bond mechanism drawn from the fiber pullout test results under sulfate environments.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.669-672
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• 2006

Recently, large efforts have been made to develop and understand the behavior of Fiber Reinforced Concrete. As in the static loading cases, many researches have been done. However, a few studies have been conducted in cyclic behaviors of FRC. The main objective of the present work is to investigate the cyclic behavior of fiber reinforced concrete with theoretical method. First, cyclic constitutive relations which describe the crack bridging stress considering non-uniform interfacial bond degradation in short randomly oriented fiber reinforced matrix composites under uniaxial cyclic tension were considered. A cyclic degradation model of single fiber based on micromechanics also taken into consideration. As an example, fatigue analysis for ECC with PVA fiber was conducted using proposed equations. Results shows that proposed method can establish a basis for analyzing cyclic behavior of fiber reinforced composites.

• Structural Engineering and Mechanics
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• 제41권2호
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• pp.157-181
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• 2012

The paper presents a review of the application of the newly proposed mixed finite element model for seismic simulation of different types of composite frame structures. To evaluate the performance of the element, a comparison with displacement-based and force-based models is conducted. The study revealed that the mixed model is superior to the others in terms of both speed of convergence and numerical stability, and is therefore considered the most practical approach for modeling of composite structures. In this model, the element is derived using independent force and displacement shape functions. The nonlinear response of the frame element is based on the section discretization into fibers with uniaxial material models. The interfacial behavior is modeled using an inelastic interface element. Numerical examples to clarify the advantages of the model are presented for the following structural applications: anchored reinforcing bar problems, composite steel-concrete girders with deformable shear connectors, beam on elastic foundation elements, R/C girders strengthened with FRP sheets, R/C beam-columns with bond-slip, and prestressed concrete girders. These studies confirmed that the model represents a major advancement over existing elements in simulating the inelastic behavior of composite structures.

• ETRI Journal
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• 제31권6호
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• pp.660-666
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• 2009

We investigate the effects of interfacial dielectric layers (IDLs) on the electrical properties of top-gate In-Ga-Zn-oxide (IGZO) thin film transistors (TFTs) fabricated at low temperatures below $200^{\circ}C$, using a target composition of In:Ga:Zn = 2:1:2 (atomic ratio). Using four types of TFT structures combined with such dielectric materials as $Si_3N_4$ and $Al_2O_3$, the electrical properties are analyzed. After post-annealing at $200^{\circ}C$ for 1 hour in an $O_2$ ambient, the sub-threshold swing is improved in all TFT types, which indicates a reduction of the interfacial trap sites. During negative-bias stress tests on TFTs with a $Si_3N_4$ IDL, the degradation sources are closely related to unstable bond states, such as Si-based broken bonds and hydrogen-based bonds. From constant-current stress tests of $I_d$ = 3 ${\mu}A$, an IGZO-TFT with heat-treated $Si_3N_4$ IDL shows a good stability performance, which is attributed to the compensation effect of the original charge-injection and electron-trapping behavior.

• Advances in materials Research
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• 제11권2호
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• pp.91-109
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• 2022

This paper presents a closed-form higher-order analysis of interfacial shear stresses in RC continuous beams strengthened with bonded prestressed laminates. For retrofitting reinforced concrete continuous beams is to bond fiber reinforced prestressed composite plates to their tensile faces. An important failure mode of such plated beams is the debonding of the composite plates from the concrete due to high level of stress concentration in the adhesive at the ends of the composite plate. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the RC continuous beams strengthened with bonded prestressed laminates. The theoretical predictions are compared with other existing solutions. A parametric study has been conducted to investigate the sensitivity of interface behavior to parameters such as laminate stiffness and the thickness of the laminate where all were found to have a marked effect on the magnitude of maximum shear and normal stress in the composite member.