• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
• /
• pp.455-456
• /
• 2010

본 연구는 5000세대 이상 대규모 아파트 현장에서 사용되는 현장 타설 콘크리트의 효율적인 품질관리를 위해 동일 배합규격에 대하여 35개 레미콘 공장별 B/P TEST를 실시하여 굳지않은 특성 및 경화 특성을 검토한 것이다.

• 콘크리트학회논문집
• /
• 제26권1호
• /
• pp.35-46
• /
• 2014

중량 PC기둥의 양중부하를 저감하고 접합부 구조일체성을 개선하기 위하여, 두 가지 형태의 현장타설 콘크리트 채움 중공 PC기둥(HPC1, HPC2)을 개발하였다. 중공의 PC단면을 구현하기 위해, HPC1은 조립철근망이 설치된 선제작 PC패널 한 쌍을 활용하였으며, HPC2는 특별한 띠철근을 활용하였다. 심부콘크리트 타설시 측압을 측정하였으며, 내진성능을 평가하기 위하여 실물크기의 HPC1, HPC2 기둥과 비교용 RC 기둥에 대하여 일정축력하 주기횡하중실험을 수행하였다. 실험 결과 HPC 실험체는 초기강성, 최대강도, 변위연성도 등 구조성능면에서 RC 실험체와 유사한 거동을 보였으며, 다만 단면을 관통하는 내부띠철근이 없는 HPC2의 경우에는 주철근의 좌굴이 발생한 이후 에너지소산능력이 다소 떨어졌다. 하지만 세 실험체 모두 ACI 374에서 요구하는 에너지소산능력을 만족하였다.

• 콘크리트학회지
• /
• 제16권2호
• /
• pp.57-61
• /
• 2004

• Geomechanics and Engineering
• /
• 제5권2호
• /
• pp.119-142
• /
• 2013

Pile load tests using Osterberg cells (O-cell) were conducted on cast-in-place concrete piles founded in oil sand fill and in situ oil sand at an industrial plant site in Fort McMurray, Alberta, Canada. Interpreted pile test results show that very high pile shaft resistance (with the Bjerrum-Burland or Beta coefficient of 2.5-4.5) against oil sand could be mobilized at small relative displacements of 2-3% of shaft diameter. Finite element simulations based on linear elastic and elasto-plastic models for oil sand materials were used to analyze the pile load test measurements. Two constitutive models yield comparable top-down load versus pile head displacement curves, but very different behaviour in mobilization of pile shaft and end bearing resistances. The elasto-plastic model produces more consistent matching in both pile shaft and end bearing resistances whereas the linear elastic under- and over-predicts the shaft and end bearing resistances, respectively. The mobilization of high shaft resistance in oil sand under pile load is attributed to the very dense and interlocked structure of oil sand which results in high matrix stiffness, high friction angle, and high shear dilation.

• Structural Engineering and Mechanics
• /
• 제58권1호
• /
• pp.39-58
• /
• 2016

Since the publication of ACI 318-02, the concrete capacity design (CCD) method has been used to determine the resistance of unreinforced concrete anchors. The regulation of steel-reinforced anchors was proposed in ACI 318-08. Until ACI 318-08, the shear resistance of concrete breakout for an unreinforced anchor during an earthquake was reduced to 75% of the static shear strength, but this reduction has been eliminated since ACI 318-11. In addition, the resistance of a hairpin-reinforced anchor was calculated using only the strength of the steel, and a regulation on the dynamic strength was not given for reinforced anchors. In this study, shaking table tests were performed to evaluate the dynamic shear strength of unreinforced and hairpin-reinforced cast-in-place (CIP) anchors during earthquakes. The anchors used in this study were 30 mm in diameter, with edge distances of 150 mm and embedment depths of 240 mm. The diameter of the hairpin steel was 10 mm. Shaking table tests were carried out on two specimens using the artificial earthquake, based on the United States Nuclear Regulatory Commission (US NRC)'s Regulatory Guide 1.60, and the Northridge earthquake. The experimental results were compared to the current ACI 318 and ETAG 001 design codes.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2005년도 동계학술발표대회 논문집
• /
• pp.148-154
• /
• 2005

Ground-source (Geothermal) heat pump (GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump (ASHP) systems. However, GSHP systems are not widespread in Japan because of their expensive boring costs. The authors have developed a GSHP system that employs the cast-in-place concrete pile foundations of a building as heat exchangers in order to reduce the initial boring cost. In this system, eight U-tubes are arranged around the surface of a cast-in-place concrete pile foundation. The heat exchange capability of this system, subterranean temperature changes and heat pump performance were investigated in a foil-scale experiment. As a result, the average values for heat rejection were 186${\sim}$201 W/m (for pile, 25 W/m per Pair of tubes) while cooling. The average COP of this system was 4.6 while cooling; rendering this system more effective in energy saving terms than the typical ASHP systems. The initial cost of construction per unit for heat extraction and rejection is ${\yen}$72/W for this system, whereas it is f300/W for existing standard borehole systems.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.225-230
• /
• 2001

Cast-in-place foamed concrete is a high porous material placed as base the layer of mortar screeds in the panel heating system, so the quality of mortar is affected by it. Therefore, this study is aims to investigate how the absorption characteristics of foamed concrete influences on mortar screeds according to the foamed ratio-62%, 67% and 72%- and the surface treatments of foamed concrete-water and acrylic emulsion primer spray, etc. The result of this study shows that water-spray in the surface of foamed concrete has a good effects to reduce mortar cracking.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 1998년도 추계학술대회 논문집
• /
• pp.54-60
• /
• 1998

PSC box bridges by MSS construction method in high-speed railway may not be cast in place at one step. Web and bottom flange(U member) in the cross section are cast in place at first, then top flange will be cast in place later with some time lag. In this section, stress distributions of U member and top flange are different with those in generally complete cast in place cross section. In the composite section composed of two different aged members, the redistribution of stresses takes place. This results from time-dependent strain characteristics of concrete and the effects of forces applied at the various stages. For comparison in the present paper, two models, one with the composite cross section and the other with generally complete cast in place cross section, are analyzed. The longitudinal stress differences of two models on considering construction stages are compared. As the analysis results show the considerable differences in the stresses of cross section between two models, the composition of cross section is considered for rational design of PSC box girder bridge.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
• /
• pp.209-216
• /
• 2004

Numerical analysis is carried out to identify the appropriateness of the design codes that is available for the tensile design of fastening system at Nuclear Power Plant (NPP) in this study. This study is intended for the cast-in-place anchor that is widely used for the fastening of equipment in Korean NPPs. The microplane model and the elastic-perfectly plastic model are employed for the quasi-brittle material like concrete and for the ductile material like anchor bolt as constitutive model for numerical analysis and smeared crack model is employed for the crack and damage phenomena. The developed numerical model is verified on a basis of the various test data of cast-in-place anchor. The appropriateness of both ACI 349 Code and CCD approach of CEB-FIP Code is evaluated for the tensile design of cast-in-place anchor and it is proved that both design codes give a conservative results compared with real tensile capacity of cast-in-place anchor.

• Advances in concrete construction
• /
• 제6권6호
• /
• pp.645-658
• /
• 2018

Despite being one of the most abundantly used construction materials because of its exceptional properties, concrete is susceptible to deterioration and damage due to various factors particularly corrosion, improper loading, poor workmanship and design discrepancies, and as a result concrete structures require retrofitting and strengthening. In recent times, Fiber Reinforced Polymer (FRP) composites have substituted the conventional techniques of retrofitting and strengthening of damaged concrete. Most of the research studies related to concrete strengthening using FRP have been performed on undamaged test specimens. This contribution presents the results of an experimental study in which concrete specimens were damaged by mechanical loading and elevated temperature in laboratory prior to application of Carbon Fiber Reinforced Polymer (CFRP) sheets for strengthening. The test specimens prepared using concrete of target compressive strength of 28 MPa at 28 days were subjected to compressive and splitting tensile testing up to failure and the intact pieces of the failed specimens were collected for the purpose of repair. In order to induce damage as a result of elevated temperature, the concrete cylinders were subjected to $400^{\circ}C$ and $800^{\circ}C$ temperature for two hours duration. Concrete cylinders damaged under compressive and split tensile loads were re-cast using concrete and rich cement-sand mortar, respectively and then strengthened using CFRP wrap. Concrete cylinders damaged due to elevated temperature were also strengthened using CFRP wrap. Re-cast and strengthened concrete cylinders were tested in compression and splitting tension. The obtained results revealed that re-casting of specimens damaged by mechanical loadings using concrete & mortar, and then strengthened by single layer CFRP wrap exhibited strength even higher than their original values. In case of specimens damaged by elevated temperature, the results indicated that concrete strength is significantly dropped and strengthening using CFRP wrap made it possible to not only recover the lost strength but also resulted in concrete strength greater than the original value.