• International Journal of Railway
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• 제1권2호
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• pp.72-81
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• 2008

This paper introduces a new steel jacketing method for reinforced concrete columns with lap splice and evaluates its performance by a series of axial tests of concrete cylinders. At first, 45 concrete cylinders were fabricated with varying the design compressive strengths of 21, 27 and 35 MPa and, then, the part of them was jacketed with two-split-steel jackets under lateral confining pressure. The parameters in the first test were the steel jacket's thickness and the existence of adhesive between steel and concrete surface. In the second test, whole steel jackets were used to wrap cylinders with lateral pressure. Also, a double-layer jacket consisted of two steel plates was introduced; a cylinder was jacketed by two steel plates one after another. The effect of the new method was verified through comparing the results of the compressive tests for plain and jacketed cylinders. The steel jacket built following the new method showed good results of increasing the compressive strength and ductility of the jacketed cylinders with respect to the plain cylinders. The thicker steel jackets showed the more increased compressive strength, and the ductility at failure depended on the welding quality on steel jackets. The adhesive between steel and concrete surface reduced the confining effect of the steel jackets. The whole jacket showed more ductile behavior than the two-split jackets. The double-layered jackets were estimated to possess an equal performance to that of a single steel jacket having the same thickness of the double-layered jacket. Finally, the experimental results were compared with the constitutive model of steel-jacketed concrete; which showed a good agreement between the experimental results and the models.

• 한국전산구조공학회논문집
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• 제28권4호
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• pp.375-384
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• 2015

해상풍력발전의 건설이 여러 가지 환경 및 가설공법 등의 설치환경 등의 원인에 의하여 건설지점이 천해에서 심해로 이동하는 경향을 나타내고 있다. 이러한 경향 속에 해상풍력발전 지지구조물의 심해화에 따른 지지구조물에 대한 연구는 중요성이 더욱 증대될 것으로 판단된다. 본 연구에서는 기존의 Jacket 구조물에 대하여 Precast Concrete Block 및 Suction pile을 적용한 Jacket 구조물을 제안하고 이에 대하여 구조해석 및 안전성 평가를 실시하였다. 또한 제안된 구조물에 동조액체감쇠기를 적용하여 구조물 진동성능 향상을 도모하고자 하였다. 연구결과, 제안된 신형식 Jacket 구조물은 충분한 안전성을 가지고 있는 것으로 평가되었으며, 동조액체감쇠기를 적용하였을 경우, 약 5%의 진동저감 효과가 있는 것으로 검토되었다.

• 한국공간구조학회논문집
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• 제13권1호
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• pp.69-77
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• 2013

This study is the research appling the representative Displacement-Based Design which is the basic concept of Direct Displacement Based Design proposed by Chopra and Goel to original Reinforced Concrete moment frame and determining the thickness of retrofit Steel Jacket about the Maximum design ground acceleration, and developing the more improved Algorithm as well as program by the Retrofit Design method and Nonlinear analysis by the Performance design method before and after reinforcement appling the determined retrofit thickness. It also shows the result of the seismic performance improvement which is the ratio of seismic performance appreciation result yield displacement 19%, yield strength ratio 24%, displace ductility ratio the maximum 27% comparing Multi degree of freedom, column member of Reinforced Concrete with the performance improvement column member considering the thickness of the determined Steel Jacket. The developed Algorithm and program are easy to apply seismic design and application to the original Reinforced Concrete building, at the same time, it applicate to display well the design result of Target displacement performance level about nonlinear behavior.

• Earthquakes and Structures
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• 제15권3호
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• pp.275-283
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• 2018

Seismic strengthening is essential for existing bridge piers which are deficient to resist the earthquake. The concrete and CFRP jackets with a bottom-anchoring method are used to strengthen railway bridge piers with low reinforcement ratio. Quasi-static tests of scaled down model piers are performed to evaluate the seismic performance of the original and strengthened bridge pier. The fracture characteristics indicate that the vulnerable position of the railway bridge pier with low reinforcement ratio during earthquake is the pier-footing region and shows flexural failure mode. The force-displacement relationships show that the two strengthening techniques using CFRP and concrete jackets can both provide a significant improvement in load-carrying capacity for railway bridge piers with low reinforcement ratio. It is clear that the bottom-anchoring method by using planted steel bars can guarantee the CFRP and concrete jackets to work jointly with original concrete piers Furthermore, it can be found that the use of CFRP jacket offers advantages over concrete jacket in improving the energy dissipation capacity under lateral cyclic loading. Therefore, the seismic strengthening techniques by the use of CFRP and concrete jackets provide alternative choices for the large numbers of existing railway bridge piers with low reinforcement ratio in China.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.197-198
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• 2009

본 연구는 기존 철근콘크리트 구조물에 대하여 대표적인 변위-기반 설계법인 Chopra&Goel이 제안한 직접변위-기반 설계법의 기본개념을 적용하여 최대 설계지반 가속도에 대한 보강 Steel Jacket의 두께를 결정하고, 결정된 보강 두께를 적용하여 보강전 후 성능설계기법에 의한 비선형 해석 및 보강 설계법에 의한 보다 개선된 알고리즘 및 프로그램을 개발하는 것이다.

• Architectural research
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• 제17권1호
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• pp.41-48
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• 2015

Early investigations focused mainly on manipulating the confinement effect to develop a reinforced concrete column with lateral hoops. Based on this legacy model, Li's model incorporated the additional confinement effect of a steel jacket. However, recent experiments on plain concrete cylinders with steel jackets revealed relatively large discrepancies in the estimates of strength enhancement and the post-peak behavior. Here, we describe a modified constitutive law for confined concrete with an unbonded external steel jacket in terms of three regions for the loading stage. We used a two-phase heterogeneous concrete model to simulate the uniaxial compression test of a $150mm{\times}300mm$ concrete cylinder with three thicknesses of steel jackets: 1.0 mm, 1.5 mm, and 2.0 mm. The proposed constitutive model was verified by a series of finite element analyses using a finite element program. The damaged plasticity model and extended Drucker-Prager model were applied and compared in terms of the level of pressure sensitivity for confinement in 3D. The proposed model yielded results that were in close agreement with the experimental results.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.155-168
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• 2019

This paper presents the results of an experimental investigation on the compressive strength of small scale concentrically axially loaded fiber-reinforced polymer (FRP) confined plain concrete columns, with cylinder concrete strength 19 MPa. For columns with circular (150-mm diameter) and square (150-mm side) cross sections wrapped with glass- and carbon-FRP sheets (GFRP and CFRP, respectively) applied with dry lay-up the effect of different jacket schemes and different overlap configurations on the confined characteristics is investigated. Test results indicate that the most cost effective jacket configuration among those tested is for one layer of CFRP, for both types of sections. In square sections the location of the lap length, either in the corner or along the side, does not seem to affect the confined performance. Furthermore, in circular sections, the presence of an extra wrap with FRP fibers parallel to the column's axis enhances the concrete strength proportionally to the axial rigidity of the FRP jacket. The recorded strains and the distributions of lateral confining pressures are discussed. Existing design equations are used to assess the lateral confining stresses and the confined concrete strength making use of the measured hoop strains.

• 한국공간구조학회논문집
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• 제10권4호
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• pp.49-57
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• 2010

본 연구는 기존 철근콘크리트 구조물에 대하여 대표적인 변위-기반 설계법인 Chopra&Goel 이 제안한 직접변위-기반 설계법의 기본개념을 적용하여 최대 설계지반 가속도에 대한 보강 Steel Jacket의 두께를 결장하고, 결정된 보강 두께를 적용하여 보강전 후 성능설계기법에 의한 비선형 해석 및 보강설계법에 의한 보다 개선된 알고리즘 및 프로그램을 제시하였다. Steel Jacket 보강된 철근콘크리트 기둥에 대한 설계 변위 추정을 위해 Steel Jacket 보강된 철근콘크리트 부재의 비선형 층상화 세그멘트 해석 모델을 제시하고, 성능기반설계에 의한 성능개선설계를 위하여 목표성능변위 및 설계자전가속도 조건에 대해 직접 변위-기반 설계 방법 및 변위계 수법에 의한 내진성능개선 설계 방법을 제시하였다. 적용 예에서 본 방법은 기존 철근콘크리트 기둥과 비교하여 성능개선설계 결과 보강 전에 비해 변위 연성비 및 변위성능에서 크게 개선된 성능설계 결과를 제공해 주었다.

• Steel and Composite Structures
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• 제19권5호
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• pp.1077-1094
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• 2015

This paper presents an experimental study on the effectiveness of simultaneous application of carbon fiber-reinforced polymer (CFRP) and steel jacket in strengthening slender reinforced concrete (RC) column. The columns were 200 mm square cross section with lengths ranging from 1600 to 3000 mm. Ten columns were tested under axial load. The effects of the strengthening technique, slenderness ratio, cross-section area of steel angle and CFRP layer number were examined in terms of axial load-axial strain curve, CFRP strain, steel strip strain and steel angle strain. The experiments indicate that strengthening RC columns with combined CFRP and steel jacket is effective in enhancing the load capacity, ductility and energy dissipation capacity of RC column. Based on the existing models for RC columns strengthened with CFRP and with steel jacket, a design formula considering a slenderness reduction factor is proposed to predict the load capacity of the RC columns strengthened with combined CFRP and steel jacket. The predictions agree well with the experimental results.

• Computers and Concrete
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• 제6권2호
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• pp.95-108
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• 2009

In the current research, a displacement-based seismic design scheme to retrofit reinforced concrete columns using FRP composite materials has been proposed. An accurate prediction for the nonlinear flexural analysis of FRP jacketed concrete members has been presented under multiaxial constitutive laws of concrete and composite materials. Through modification of the displacement coefficient method (DCM) and the direct displacement-based design method (DDM) of reinforced concrete structures, two algorithms for a performance-based seismic retrofit design of reinforced concrete columns with a FRP jacket have been newly introduced. From applications to retrofit design it is known that two methods are easy to apply in retrofit design and the DCM procedure underestimates the target displacement to compare with the DDM procedure.