• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.521-529
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• 2002

A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.335-344
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• 2004

A general composite section of precast and cast-in-place concrete with prestressed and nonprestressed reinforcements was analyzed to calculate residual stresses and loss of prestressing force caused by internal constraints of concrete long-term deformation. From the analytical results, equations to design additional prestressing force and to evaluate resistant moment of the composite section were proposed. The equations shows that the additional prestressing force can be over-estimated if the loss rate of the first prestressing force is over-estimated from the lumped sum of a design code. The analytical procedure with the proposed equations has been applied to a composite section using the AASHTO Type 5 girder. The loss rates of the additional prestressing force appling to the precast concrete girder was less than those appling to the composite girder. However, the resistant moment of the additional prestressing force on the composite girder was much larger than that on the precast concrete girder. The additional prestressing force appling to the composite section was very effective for strengthening of the prestressed concrete composite girder.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.429-438
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• 2013

An object oriented numerical analysis program of axial-flexural elements and the step-by-step method (SSM) has been developed to analyze concrete long-term behaviors of structures constrained internally and externally. The results of the numerical analysis for simple and continuous prestressed (PS) concrete box and composite girders, pre-cast slab of continuous steel composite girder, and simple preflex composite girder show that the adjusting coefficient decreases by increasing constraint. The loss rates of pre-tension force were not sensitive but those of pre-compression force were increased rapidly by decreasing adjusting coefficient. This indicates that the design based on the loss rate of pre-tension can over-estimate the pre-compression force in a concrete section constrained internally and externally. The adjusting coefficients which satisfy results of the numerical analysis are 0.35~0.95, and it can be used as an index of constraint of concrete long-term deformation. The adjusting coefficient 0.5 of Bridge Design Specifications can under-estimate residual stress of PS concrete slab, and the coefficient 0.7 or 0.8 of LRFD Bridge Designing Specifications can under-estimate the loss rates of continuous PS concrete girders. The adjusting coefficient of hybrid structures should be less then 0.4.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.377-384
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• 2011

Although concrete is considered as fire proof materials, high strength concrete shows severe material and structural damages when exposed to fire. To understand such damages in high strength concrete structures, the effects of various design parameters and fire condition on the thermal behaviors of high strength concrete structures are investigated in this study. In order to achieve this goal, fire tests are performed on high strength concrete columns with different fire conditions and design parameters including cross sectional area, cover thickness, and reinforcement alignment. To investigate thermal behaviors, temperature distributions and amount of spalling are measured. In overall, the columns show rapidly increasing inner temperatures between 30~60 mins of the fire tests due to spalling. In detail, the higher temperature distributions are observed from the columns with the larger cross section and less cover thickness. Moreover, among the columns with same reinforcing ratio, larger number of reinforcements with the smaller diameter causes the higher temperature distribution. The findings from the experimental study allow not only understanding of thermal behaviors of high strength concrete columns under fire, but also guidance in revising fire safety design.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.260-261
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• 2002

파장 다중화(WDM) 방식의 광통신시스템에서 그림 1(a),(b)에 나타낸 바와 같이 한 쌍의 입출력 포트의 신호 방향을 바꾸는 광 가감기(Optical Add Drop Multiplexer)용의 2$\times$2 광 스위치가 사용된다 특히 멤스형 광 스위치는 삽입손실, 누화, 편광 및 파장 의존 손실 등이 낮아 많은 연구가 이루어지고 있다.(1-3) 광 스위치의 삽입손실을 낮추기 위해, 렌즈나 굴절률 맞춤액을 사용하는데, 광섬유를 정렬, 혹은 패키징할 때 렌즈나 맞춤액의 취급이 어렵다는 문제점이 있다. (중략)

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.484-492
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• 2023

The structural behaviour of concrete beam was examined by the three points bending test after the completion of the electrochemical chloride extraction (ECE), rather than bond strength mostly measured in previous studies. It was found that the flexural rigidity of concrete was lowered by the ECE, but the strength was enhanced in terms of the maximum load.The flexural rigidity, in the linear elastic range, was reduced by the loss of effective cross-section area. In fact, the inertia moment was substantially subjected to 70 % loss of the cross-section by the tensile strain at the condition of the failure. However, a lower rate of the inertia moment reduction was achieved by the ECE, implying the higher resistance to the cracking, but the higher risk of deformation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.38-44
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• 2007

Using the mathematical model suggested by Bennet et al.(1992), the reflection and transmission coefficients by a circular pile breakwater has been investigated in the framework of potential theory. Flow separation due to sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of exact energy loss coefficient is critical to enhance the reliability of mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code. The energy loss coefficient can be obtained from the pressure difference between upstream and downstream. Energy loss coefficient is the function of porosity and the relation equation between them is suggested throughout the curve fitting processing. To validated the suggested relation, comparison between the analytical results and the experimental results is made for four different porosities with good agreement.

• Korean Journal of Optics and Photonics
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• v.6 no.2
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• pp.148-155
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• 1995

The low loss single-mode $Al_{0.042}Ga_{0.958}As/GaAs/Al_{0.042}Ga_{0.958}As$ strip-loaded waveguides had been designed using an effective index method and fabricated using a MOCVD technique and chemical wet etching method. The propagation loss and facet reflectivity were measured by the Fabry-Perot resonance method and sequential cleaving experiment at $1.31{\mu}m$ wavelength. As a result, the propagation loss is as low as 0.62 dB/cm and the facet refiectivity(R) equals to 0.299 for straight waveguides with width $ w=4.1{\mu}m$..

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.78-83
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• 2010

This paper discusses the surface roughness of corroded reinforcement rebar in reinforced concrete structures focusing on the quantitative measurement technique for rebar corrosion. Reinforcement rebar was corroded using accelerated corrosion induced method and corrosion rates were 0%, 1%, 2%, 3%, 5%, and 10% of mass losses. Using 3-dimensional scanner each surface profile of reinforcement rebar was established, and surface roughness was measured. Through tests and analyses of corroded reinforcement rebar, the following topics were particularly discussed: measurement of surface roughness, relationship between area and surface roughness, relationship between surface roughness and bond performance. As a result, surface roughness of corroded rebar was found to be very effective to bond strength until 2% of corrosion rate. It was also discussed how to relate surface roughness of corroded rebar to bond strength of reinforced concrete structures.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.795-802
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• 2007

Recently, various strengthening methods using carbon fiber sheets (CFS) have been developed for the rehabilitation of structures and applied to the concrete member. However, still research need arises in order to verify the structural capacity of RC member which experienced bond loss between concrete and CFS after strengthening. This is because previous research has focused on the development of design process and evaluation of structural capacity only for retrofit. The appearance of this loss may be initiated at just after retrofit construction. And it will be more serious when the layer number of CFS increases. In order to minimize above mistake in retrofit design using CFS, more exact evaluation process to predict the bond loss of CFS is required. The objective of this research is to study the variation of flexural structural capacity of beam which has experienced bond loss after strengthening using CFS. Experimental and analytical study are performed and evaluation of the previous formula is conducted. Test result showed that the significant strength deterioration was not found until the bond loss of 20%. Overall structural behavior of the beams can be predicted by nonlinear sectional analysis.