• Structural Engineering and Mechanics
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• 제53권6호
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• pp.1253-1269
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• 2015

The present paper investigates the post heating behavior of concrete beams reinforced with fiber reinforced polymer (FRP) bars, namely carbon fiber reinforced polymer (CFRP) bars and glass fiber reinforced polymer (GFRP) bars. Thirty rectangular concrete beams were prepared and cured for 28 days. Then, beams were either subjected (in duplicates) to elevated temperatures in the range (100 to $500^{\circ}C$) or left at room temperature before tested under four point loading for flexural response. Experimental results showed that beams, reinforced with CFRP and GFRP bars and subjected to temperatures below $300^{\circ}C$, showed better mechanical performance than that of corresponding ones with conventional reinforcing steel bars. The results also revealed that ultimate load capacity and stiffness pertaining to beams with FRP reinforcement decreased, yet their ultimate deflection and toughness increased with higher temperatures. All beams reinforced with FRP materials, except those post-heated to $500^{\circ}C$, failed by concrete crushing followed by tension failure of FRP bars.

• Advances in concrete construction
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• 제6권5호
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• pp.485-507
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• 2018

Concrete-Filled Steel Tube (CFST) columns are an increasingly popular means to support great compressive loads in buildings. The residual strength capacity of CFST stub columns may be utilized to assess the potential damage caused by fire and calculate the structural fire protection for least post-fire repair. Ten specimens under room conditions and 10 specimens under fire exposure to the Eurocode smouldering slow-growth fire were tested to examine the effects of diameter to thickness D/t ratio and reinforcing bars on residual strength capacity, ductility and stiffness of CFST stub columns. On the other hand, in sixteen among the twenty specimens, three or six reinforcing bars were welded inside the steel tube. The longitudinal strains in the steel tube and load-displacement relationships were recorded throughout the subsequent compressive tests. Corresponding values of residual strength capacity calculated using AISC 360-10 and EC4 standards are presented for comparison purposes with the experimental results of this study. The test results showed that after exposure to $750^{\circ}C$, the residual strength capacity increased for all specimens, while the ductility and stiffness were slightly decreased. The comparison results showed that the predicted residual strength using EC4 were close to those obtained experimentally in this research.

• Steel and Composite Structures
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• 제39권1호
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• pp.21-33
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• 2021

This paper aims to improve the current state-of-the-art in long-term deflection prediction in steel-concrete composite beams. The efficiency of a time-dependent finite element model based on linear creep theory is verified with available experimental data. A parametric numerical study is then carried out, which focuses on the effects of concrete creep and/or shrinkage, ultimate shrinkage strain and reinforcing bars in the slab. The study shows that the long-term deformations in composite beams are dominated by concrete shrinkage and that a higher area of reinforcing bars leads to lower long-term deformations and steel stresses. The AISC model appears to overestimate the shrinkage-induced deflection. A modified ACI equation is proposed to quantify time-dependent deflections in composite beams. In particular, a modified reduction factor reflecting the influence of reinforcing bars and a coefficient reflecting the influence of ultimate shrinkage are introduced in the proposed equation. The long-term deflections predicted by this equation and the results of extensive numerical analyses are found to be in good agreement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.438-441
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• 2004

This paper presents the results of the experimental study on the performances of reinforced concrete beams rehabilitated by external unbonded high tension steel-bar. Design variables for the experiment in this study includes the position of anchorage zone of the high tension steel bar, the anchorage length of the reinforcing steel bar and the types of the shear strengthening measures. 5 specimens were tested with one point monotonically increased loads and structural performances such as strength capacities, ductility capacities and failure modes were analysed. It is found that the structural performance of the rehabilitated beams are strongly depended on the location of anchorage zone of the high tension steel-bars. In the case that anchorage zone is located near the critical shear zone, it is observed that the rehabilitated beam is failed in brittle failure mode and the additional shear strengthening is necessitated. But if anchorage zone is properly located or additional shear strengthening device is provided properly, it is also observed that the strength capacity of the rehabilitated beams could be increased more than $200\%$ by the proposed method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1412-1416
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• 2003

Induction Heaters are commonly used in heating steel strip product, because it can rapidly and efficiently heat steel strip/bar. In this study, a inductive heating model is developed and the predictions are compared with measured temperatures. The temperatures are measured from POSCO thin-slab rolling facility (so called Minimill). Induction heater is installed between reduction unit and holding furnace This induction heater raise the temperature of steel bars from $930^{\circ}C$ to about $1100^{\circ}C$ which gives the required temperature for finishing mill process after holding period at holding furnace. Unlike other simple equation models, this model allows us to predict temperature profiles of sections of steel bars.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.231-234
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• 2005

Steel braced frames retrofit method has been broadly used due to their effectiveness in both light weight and construction periods. However, steel braced frames retrofit method has difficulties in application on the inner frames of buildings to be retrofitted consequently, there have been demands for the braced frames retrofit method that can be broadly and easily applicable to both inner and outer frames of the buildings. The objective of this study is to develop and evaluate the seismic retrofit method applicable to the inner frame also by dividing the reinforcing frames into three unit. From the cyclic test of specimens, the test results dearly showed that steel brace using HPFRCCs and steel bars ensure the better cyclic compressive performance than the normal braced members.

• 한국공간구조학회논문집
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• 제17권3호
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• pp.99-105
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• 2017

The SLIM AU composite beam consists of U-shaped steel plate, A-shaped steel cap and infilled concrete. The bottom steel plate acts as tension bars, and the top steel cap takes roles of shear connector and compression bars in the conventional reinforced concrete section. In this paper the shear strength of this composite beam with closed steel section has been evaluated through the concentrated loading shear experiments. Test results under the symmetrical and asymmetrical loading conditions were compared with the predicted values based on the KBC 2016. The composite beam showed the greater shear strength capacities than those of the theoretical evaluation.

• 콘크리트학회논문집
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• 제11권3호
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• pp.193-203
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• 1999

The corrosion of steel reinforcements in concrete is of great concern in recent years. This study is focused on the corrosion behavior of steel bars induced by internal chlorides in concrete at early ages. The main objective of this study is to determine the chloride thresholds causing depassivation and active corrosion of steel reinforcement in concrete. To examine the threshold concentration of chloride ion, the half-cell potential, chemical composition of expressed pore solutions of concrete and the rate of corosion area of the specimens were measured. Major variables include the added amount of chlorides in concrete, types of binders, and water-to-binder ration. From the present comprehensive experimental results, the factors influencing chloride-induced corrosion are investigated, and the chloride thresholds causing active corrosion of steel bars are proposed. The present study will enable to specify the realistic chloride limit in concrete which can be used in the future technical specification.

• KCI Concrete Journal
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• 제12권1호
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• pp.139-144
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• 2000

Ground Penetrating Radar (GPR) with 1 GHz antenna has been used to locate a steel bar embedded inside laboratory-prepared mortar specimens. Four mortar specimens are made with the dimensions of 100 cm (length) x 100 cm (width) x 14 cm (depth). One specimen had no bars and the other three specimens had a Dl9 steel bar at 4, 6. and 8 cm depth. As a part of the experimental work, the dielectric constants of mortar specimens are measured during curing. As the curing time increased. the dielectric constant decreased with decreasing moisture content inside the specimen. The steel bar embedded inside mortar specimens has been successfully identified in all three cases. The results using signal processing scheme developed in this study significantly improved the output of a commercially available radar system.

• 한국강구조학회 논문집
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• 제19권3호
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• pp.259-270
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• 2007

본 논문은 고장력 인장봉에 의해 보강된 RC보의 휨거동을 평가하기 위한 해석적 방법을 제시하고 있다. 본 연구에 대한 선행 실험결과를 이용하였다. 실험 논문에서는 외부 강봉 보강의 이점에 대해서 소개하고 있다. 휨거동을 평가하기 위해 본 논문은 해석적 방법으로 단순누가산정의 방법을 제시하고 있다. 이 방법은 기본적으로 고장력 인장봉에 의해 보강된 RC보가 받는 전체하중은 강봉이 없는 RC보가 받는 하중과 강봉 자체가 받는 하중의 합과 같다고 가정한 것이다. 추가로 강봉에 의해 발생하는 축력과 강봉에 주어진 프리스트레스트에 대하여 고려를 하였다. 실험 결과와 이론해석의 결과값을 비교하여 단순누가산정 방법은 고장력 인장봉에 의해 보강된 RC보의 비선형 휨거동을 예측함에 있어서 비교적 정확한 상관관계를 보여주고 있다.