• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.98-104
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• 2018

Nondestructive strength Equations are commonly used to determine the strength of concrete. However, the application of the existing equations may include many errors because this method is proposed on the basis of limited experimental parameters while actual bridges have various parameters such as conditions of concrete mixtures, properties of concrete strength, etc. Also, the error among the existing equations causes the confusion when engineers select the proper estimation equation for the concerned bridge. In this study, a series of the field inspection and the test have been performed on 297 existing bridges, in order to evaluate the bridges, based on the test results of the in-depth inspection, and the estimated strengths by means of the nondestructive strength equations are analyzed and compared with results of the core specimen strengths. According to results of analyses, the nondestructive strength equation proposed by CNDT Committee of Architectural Institute of Japan had high relationship with core strength. However, the strengths predicted by this equation, are underestimated when concrete's strengths are over 30 MPa, otherwise, they are overestimated. Also in this paper, based on the relationship between the estimated nondestructive concrete strengths and the core specimen strengths the modified strength equation through simple correlation analysis is proposed.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.1-7
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• 2002

The purpose of this research is to obtain a practical expression for the estimation of compressive strength of concrete using non-destructive testing method such as rebound Schmidt hammer and ultrasonic pulse

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.2
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• pp.145-150
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• 2019

This paper proposes a model for the calculation of the ultimate torsional strength in normal-strength and high-strength concrete beams which include the concrete contribution strength and use a reasonable thickness of shear flow. The adequacy of the proposed model is evaluated by comparing the calculated torsional strength with the experimentally observed results from 104 test specimens reported in the literature. The results are also compared with the calculations of the KCI and the ACI building code equations, and those of other model which include the concrete contribution strength. The comparisons show that the ultimate torsional strengths calculated by the proposed equation and Rahal's equation are closer to the experimentally observed results than those calculated by the code equations.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.162-162
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• 2011

표면파 속도 측정은 근래 토목분야에서는 비파괴 지반조사기법으로 활용되고 있다. 최근에는 디지털 신호처리기술의 발달과 함께, 더욱 정확해진 자료분석 알고리즘을 통하여 표면파 탐사관련 기술이 향상되어 3차원의 공간연속적인 시험이 가능해졌다. 본 연구는 표면파의 분산 특성을 이용하여 콘크리트 구조물의 깊이별 강성평가를 하는 SASW(Spectral Analysis of Surface Waves)기법과 STFT(Short time Fourier Transform)과 HWT(Harmonic Wavelet Transform)를 이용한 주파수영역에서의 공진주파수를 통한 부재평가 기법인 IE(Impact Echo)기법을 이용하여 대상부재의 강도평가를 수행하기 위한 시제품 개발을 수행하였다. 시제품은 메인프레임과 2개의 센서로 이루어져 측정을 수행하며 측정장치와 DAQ장치 및 S/W로 구성되어 있다. 메인프레임의 진동특성영향을 제거하기 위하여 2개의 센서는 프레임과 띄움구조로 설계하였고 센싱하는 위치는 대상 재료의 밀착되어 계측할 수 있도록 설계하였다. 탄성파를 계측하여 대상 재료의 깊이별 측정된 표면파의 속도를 계측하며 개발된 시제품의 구조물별 적용성 평가를 위한 실험을 수행하였고 평균 표면파 속도를 통해 추정한 콘크리트 두께와 결함 및 강도 추정의 적용성을 평가하였다. 시제품을 이용해 시험콘크리트 표면파를 측정한 결과 SASW기법을 이용하여 깊이에 대한 위상속도 분포와 IE기법의 결과로 개발된 시제품의 합리적 적용성이 평가되었다. 그러나 재료의 강도추정에 있어서는 각각 알고리즘의 주파수분석 요소들에 의해 변동되는 경향을 보여 추후 많은 테스트를 통해 속도-강도 추정의 회귀곡선식을 S/W에 탑재시키고 다양한 방법으로 조합하는 알고리즘으로 신뢰성있는 강도추정을 위한 알고리즘을 개발하여야 한다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.303-306
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• 2011

본 논문은 콘크리트의 양생 강도 발현을 모니터링하기 위하여 매립형 압전 센서를 이용하여 콘크리트 내부의 임피던스 및 유도초음파 신호를 측정함으로써, 콘크리트의 양생 강도를 실시간 추정할 수 있는 기법을 개발하였다. 임피던스 및 유도초음파 신호는 구조물의 물성을 나타내며 특히 양생 기간 중 임피던스 및 유도초음파의 변화는 해당 콘크리트 구조물의 강도변화를 나타낼 수 있다. 이를 이용하여 매립형 압전 센서로부터 저비용의 셀프 센싱 기반 임피던스 및 유도초음파를 계측하여 콘크리트의 임피던스 공진 주파수 및 유도초음파의 전달 강도를 측정하고 측정된 신호를 통하여 콘크리트 양생 강도를 추정할 수 있게 된다. 제안된 기법의 적용가능성을 검증하기 위하여 설계 압축강도 30MPa의 콘크리트 슬라브 내부에 매립형 압전 센서를 매립하고 양생기간 동안 임피던스 및 유도초음파 신호를 측정, 비교 분석 하였다. 측정된 신호 및 압축강도를 통하여 임피던스 및 유도초음파 기반 강도 추정 모델을 도출하고 보다 높은 정확도를 얻기 위해 다중스케일 강도 추정 모델을 개발하였다. 결과적으로 본 연구를 통해 매립형 압전 센서를 이용하여 콘크리트의 양생 강도를 실시간 모니터링할 수 있음이 검증되었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.388-391
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• 2011

강우침식인자를 구하기 위해서는 개별 호우사상의 30분 최대 강우강도를 산정해야 한다. 이를 위해서는 연속된 분단위 강우자료가 필요하지만, 자료 획득이 제한되어 지점별로 보다 얻기 쉬운 시간 단위 강우량을 이용하여 30분 최대 강우강도를 추정하려는 노력이 있어왔다. 본 연구는 시강우량을 이용하여 개별 호우사상의 30분 최대 강우강도를 추정하기 위한 것으로서 대구 지점의 1960년~1999년 기간의 818개 호우사상을 이용하였다. 분류된 호우사상별 30분 최대 강우강도를 기상청으로부터 획득한 분단위 강우자료를 이용하여 산출한 뒤, 이를 참값으로 하여 60분 최대 강우강도와의 상관관계를 분석하였다. 그 결과 대구 지점의 60분 최대 강우강도로부터 30분 최대 강우강도를 추정할 수 있는 변환계수는 1.228로 나타났으며, 고정시간 1시간 최대 강우강도로부터 30분 최대 강우강도를 추정할 수 있는 변환계수는 1.3778로 나타났다.

• Magazine of the Korea Concrete Institute
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• v.6 no.6
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• pp.159-172
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• 1994

The relmund hammer test and ultrasonic pulse velocity test methods are commonly used to determine the in-situ compressive strength of concrete. One of the special feature of these methods is that they cannot give consistent and reliable results for variety of structures. In particular, very old existing structures have been generally received sreious environmental affectsand thus the strength prediction will be different from normal structures. The purpose of the present study is, therefore, to propose realistic equations to predict the in-situ strengths of actual old concrete structures. The rebound hammer and ultrasonic pulse velocity tests, carbonation depth measurments and core compressive strength measurements have been carried out for very old hydraulic and seacoast concrete structures spanning from one to about seventy years in age. From these test results, the strength-rebound number relations, the strength-pluse velocity relatinns and the strength-rebound number-pluse velocity relations have been obtained through multiple regression analysis. The present study indicates that the existing equations by nondestructive tests give quite different results from the present data. The proposed equations reasonably well predict the measured data for old concrete structures, especially for low strength concrete. The prediction equations proposed here can be efficiently used in determining the in-situ strength of old concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.25-34
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• 2015

Proposed equation is used many time in calculation of concrete compressive strength using the non-destructive testing at precision safety diagnosis. Most of proposed equation is suggested in abroad and have an error to estimate concrete compressive strength in the domestic. Therefor, proposed equation is low reliability to estimate concrete compressive and it has a significant effect in reliability of precision safety diagnosis. Nevertheless, It is possible to increase the reliability through a number of experiments from this problem that occurs in some localized part. This paper is proposed assessment formula of reliability related core compressive strength to increase the reliability. It is verified that reliability of proposed assessment formula is useful by probabilistic techniques. It is compared with each graphs of concrete compressive strength of proposed equation. It has been found that the present methods are very efficient.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.191-202
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• 1998

The maturity method in which the strength increase of cement concrete is expressed as a function of an intergral of the curing period and temperature of the concrete has often been applied to its strength prediction. For the purpose of the application of the maturity method to the compressive strength prediction for lightweight polymer mortars using an unsaturated polyester resin as a binder, the lightweight polymer mortars with various catalyst and accelerator contents, are prepared. tested for compressive strength, and the datum temperatures for the maturity equations are estimated. The maturity is calculated by using the maturity equations with the estimated datum temperature. The compressive strengths of the lighweight polymer mortars are predicted from the maturity-compressive strength relationships.

• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.655-661
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• 2020

In this study, the correlation between concrete core compressive strength and rebound hardness of urban railway underground structures was analyzed. The equations for the range of rebound hardness were derived and compared with the measured concrete core strengths for each range of rebound hardness to confirm the adequacy of the estimated compressive strength. As the result, the linear regression analysis results of the average compressive strength by the Gaussian probability density function (representative compressive strength estimation formula) and the estimation formula by the rebound hardness range were founded to match well within 3% of the experimental concrete core compressive strength test results. Therefore, the stochastic statistical analysis using the rebound hardness measurement results suggested in this study could be help to secure the confidence level of the correlation between the rebound hardness and the concrete compressive strength which are relatively large deviation according to the estimation equations.