• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.747-756
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• 2008

The purpose of this paper is to investigate the effect of the important parameters on the transfer length during the dynamic flame cutting of tendon experimentally. The considered parameters were strand diameter, concrete cover thickness, stirrup, debonding strand and release method. Ten pretensioned concete beam specimens were cast and tested. Time history curves for the axial strain of tendon were measured by electrical resistance strain gauges mounted on the strands. Experimental results indicated that large dynamic shock effects occurred near cut-end during the sudden release. The prestressing forces are dependent on the parameters above considered. The ratio of residual prestressing forces of 12.7 mm strands is greater than 15.2 mm strands. Using debonding strand and gradual release are more efficient for applying prestressing forces.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1707-1721
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• 2014

Half-depth panels were developed with the merits of CIP (Cast In Place) decks and precast decks for constructability and fast construction. In this paper, details of half-depth panels with pre-tensioning were suggested. For evaluation of structural performance, five half-depth panel specimens were fabricated and static tests were conducted. The cross-sections of these specimens were composed of pre-tensioned half-depth panels and pre-tensioned two-span half-depth panels. Test parameters were the amount of the prestressing force and the longitudinal reinforcements. Static tests on simply-supported slabs showed that ultimate strength was 1.55 times greater than calculated nominal strength. The flexural strength was only 10 % increased and the influence on crack width control was negligible when the member of tendons was increased twice. For two-span continuous specimens, the ultimate strength increased 1.2 times and 1.38 times respectively as the reinforcement was additionally provided. The verified half-depth panels by this research can be effectively utilized for the fast replacement or construction of bridges.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.353-364
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• 2011

In a previous research performed by the authors, the allowable compressive stress coefficient (K) in pretensioned members with rectangular section at transfer was proposed based on strength design theory. In this study, a subsequent research of an enormous analysis was performed to determine the K factor for Tee and inverted Tee section members, considering the effect of section height (h), section type, amount of tendons ($A_{ps}$), and eccentricity ratio (e/h). Based on the analysis results, the allowable compressive stress coefficients (K) for Tee and inverted Tee section members at transfer were derived, which limit the maximum allowable stresses as 80% and 70% of the compressive strengths at the time of release for Tee section and inverted Tee section, respectively. And these were larger than the allowable stresses specified in domestic and other international codes. In order to verify the proposed equations, they were compared to the test results available in literature and other codes, which showed that the allowable stresses in domestic and international codes are unconservative for the cases with low eccentricity ratios while conservative for those with high eccentricity ratios. The proposed equations, however, estimate the allowable stresses of the Tee and inverted Tee section members reasonably close to test results.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.182-182
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• 2011

현재 국내에서 PSC 거더의 제작은 주로 포스트텐션방식을 사용하고 있다. 포스트텐션방식은 콘크리트 양생 후 긴장력을 도입하여 제작회전율이 높은 특성을 가지나 쉬스, 그라우팅, 정착장치 등이 요구되어 조립과정이 복잡하고 제작단가가 높다. 교량에 적용되는 PSC 거더를 포스트텐션방식 대신에 프리텐션방식으로 제작한다면 제작단가를 대폭 감소시킬 수 있을 것이나, 교량용 PSC 거더의 길이가 일반적으로 30~50m이므로 공장에서 제작하여 현장으로 운반하는 것은 운반비용의 상승 및 운반 가능한 크기의 제한을 받게 된다. 운반의 문제를 해결하기 위해서는 현장에서 PSC 거더를 제작하여야 하는데 현장에 긴장대를 고정식으로 설치하는 것은 제작단가의 상승으로 이어져 경제성을 잃게 된다. 따라서 현장에서 사용할 수 있도록 이동식 긴장대를 제작한다면 경제성을 갖춘 프리텐션방식의 PSC 거더 생산이 가능할 것이다. 50m급 이동식 긴장대에는 약 10MN에 이르는 매우 큰 긴장력이 가해져 이동식 긴장대가 콘크리트 양생전까지 이 긴장력을 저항하여야 한다. 본 논문에서는 유한요소 해석프로그램인 ABAQUS를 사용하여 50m급 PSC 거더를 생산할 수 있는 이동식 긴장대를 모델링하여 약 10MN에 이르는 긴장력이 가해질 때에 이동식 긴장대의 각 구성요소의 거동특성 및 하중에 대한 안전성 및 좌굴에 대한 안정성 확보 여부를 해석적으로 파악하고자 한다. 이동식 긴장대는 구성요소인 정착블럭(긴장BOX)과 중간연결블럭으로 나누어 모델링하였다. 정착블럭(긴장BOX)은 다수의 강판을 4절점 쉘요소(S4R)를 사용하여 직육면체의 BOX 형상에 내부를 보강한 단면으로 구성하였고, 중간연결블럭은 H형강 2개를 일체화한 긴장대 거더와 콘크리트 바닥판 블록이 볼트로 합성된 구조이며, H형강은 4절점 쉘요소(S4R), 바닥판블럭은 8절점솔리드요소(C3D8R)를 사용하였다. 긴장대거더와 바닥판블럭은 합성거동을 하도록 weld option을 사용하여 부분적으로 결합하였다. 정적해석결과 이동식 긴장대에 발생하는 응력은 도로교 설계기준에 SS400 강재의 허용응력 140MPa 보다 작으며 선형탄성좌굴 해석결과 가력하중의 2.22배 약 21MN의 하중이 가력되어야 전체좌굴이 발생하게 될 것으로 추정된다. 해석결과를 보아 50m급 PSC 거더를 생산할 수 있는 이동식 긴장대는 하중에 대한 안전성 및 좌굴에 대한 안정성을 확보하고 있는 것으로 판단된다.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.293-302
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• 2004

The transfer of prestress force in pretensioned prestressed concrete (PSC) members is of great concern because it affects directly the distribution of stress around the transfer zone. The design provision of current design code on the transfer length considers only the prestress intensity and the diameter of prestressing steels. However, other factors such as concrete compressive strength and concrete cover may affect greatly the transfer length. The purpose of the present paper is to explore the various factors that affect the transfer length in pretensioned PSC members. The bond stress-slip relation between prestressing steel and concrete was modeled first from experimental data and then this model was incorporated into the interface element. The interface element was used to perform the finite element analysis for pretensioned PSC members. The results indicate that the compressive strength and concrete cover are also very important parameters which affect the transfer length greatly. This means that the current design code, which considers only the effective prestress and diameter of prestressing steel, must be improved to take into account the other important variables of compressive strength and concrete cover. The present study allows more realistic analysis and design of pretensioned PSC members.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.4
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• pp.237-244
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• 2020

This study investigates the effect of the outrigger wall reinforced with post-tension on reducing differential column shortening. Since the outrigger wall is a concrete structure, the effect of its long-term behavior should be considered. The long-term behavior of the outrigger wall increases differential column shortening and decreases the shear force acting on the outrigger. When the stiffness of the outrigger becomes small, the effect of its long-term behavior increases. Furthermore, a method of reinforcing with post-tension to reduce differential column shortening is proposed. Following the analysis, it was confirmed that the post-tension method shows a significant reduction in the differential column shortening. This study shows that the effect of the outrigger wall reinforced with post-tension on reducing differential column shortening increases with the prestressing force of tendon.

• Magazine of the Korea Concrete Institute
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• v.6 no.6
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• pp.35-41
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• 1994

• Computational Structural Engineering
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• v.26 no.4
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• pp.52-58
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• 2013

• 지반과기술
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• v.9 no.2
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• pp.44-48
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• 2012

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.341-344
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• 2008

In this paper, the effect of flame cutting order of tendons on the concrete stress was investigated experimentally. For this, the three slab specimens with 14 tendons were cast and tested. During the detensioning, the longitudinal and transversal strain were measured. Test results showed that the measured strains of transversal stirrups were varied by the cutting order.