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Behavior and Improvement of Construction Crack occurred on Anchorage of PSC-edge Girder Rahmen Bridge

PSC-Edge 거더 라멘교의 정착부에 발생한 시공 균열 거동과 개선

  • Ok, Jae-Ho (Department of Civil Engineering, University of Seoul) ;
  • Yhim, Sung-Soon (Department of Civil Engineering, University of Seoul)
  • 옥재호 (서울시립대학교 토목공학과) ;
  • 임성순 (서울시립대학교 토목공학과)
  • Received : 2019.02.12
  • Accepted : 2019.05.03
  • Published : 2019.05.31

Abstract

PSC-Edge Rahmen Bridge makes low thickness and long span by introducing prestressed force to the edge girder and reducing positive moment. In the bridge, diagonal tension cracks occurred in the direction of $45^{\circ}$ to outer side of the girder after the temporary bent supported on the lower part of the upper slab and the secondary strand is tensioned on the girder. Researches on stress distribution and burst crack behavior of pre-stress anchorage has been conducted, it is difficult to analyze an obvious cause due to difference between actual shape and boundary condition. This study performed 3D frame analysis with additional boundary condition of temporary bent, the maximum compression stress occurred in the girder and there was a limit to identify the cause. It performed 3D Solid analysis with LUSAS 16.1 and the maximum principal tensile stress occurred at the boundary between the girder and the slab. As analyzing required reinforcement quantity at obtuse angle of the girder with the maximum principal tensile stress and directional cosine, reinforcement quantity was insufficient. Additional bridges have increased reinforcement quantity and extended area and crack was not occurred. It is expected that cracks on the girder during construction could be controlled by applying the proposed method to PSC-Edge Rahmen Bridge.

PSC-Edge 거더 라멘교는 Edge 거더에 긴장력을 도입하고 정모멘트를 감소시켜 저형고와 장경간화가 가능한 교량이다. 본 교량은 가설벤트가 상부슬래브의 하부에 지지되고 Edge 거더부에 2차 강연선이 긴장된 후 거더 외측 면에 $45^{\circ}$방향의 사인장 균열이 발생하였다. 프리스트레스 정착부의 응력분포 및 파열균열의 양상에 관한 연구가 활발히 진행되었지만 기존 연구 결과는 본 구조물의 실제 형상과 경계조건이 상이하여 명백한 원인분석이 어려운 실정이다. 따라서 본 논문에서는 가설벤트의 경계조건을 추가로 고려된 3D Frame 해석을 수행하였으나 Edge 거더부에서 최대 압축응력이 발생하여 균열을 원인을 규명하기에는 한계가 있었다. 따라서 LUSAS 16.1을 사용한 3D Solid 해석을 수행하였으며 그 결과 Edge 거더의 하부와 상부슬래브의 경계부분에서 최대 주인장응력이 발생하였다. 최대 주인장응력과 방향여현을 사용하여 둔각부 Edge 거더 외측면의 소요 철근량을 분석한 결과 사용 철근량이 부족한 것으로 분석되었다. 따라서 추가 시공된 교량은 기존 교량보다 정착부의 철근량과 철근보강 범위를 확장시켰다. 그 결과 Edge 거더부의 균열은 더 이상 발생하지 않는 것으로 관찰되었다. 이와 유사한 PSC-Edge 거더 형식의 교량을 설계 및 시공할 때 본문에서 제안한 해석 및 보강방법을 적용하면 시공 중 발생하는 Edge 거더 외측면의 균열을 충분히 제어할 수 있을 것으로 기대된다.

Keywords

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Fig. 1. Construction Flowchart of PSC Edge Rahmen Bridge

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Fig. 2. Crack shape during PSC Edge part construction

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Fig. 3. Flow of stress in loaded anchorage zone(a) Principal tension stress and general zone(b) Principal compression stress and local zone

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Fig. 4. Analytical modeling considering support condition of temporary bent

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Fig. 5. Analysis result considered condition of temporary bent(a) Edge-Girder top stress(b) Edge-Girder bottom stress

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Fig. 6. 3D solid analysis modeling of PSC-Edge rahmen bridge (a) Obtuse angle part (b) Acute angle part

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Fig. 7. Figure of load weight by construction stage (a) Stage1 : self-weight of slab (b) Stage2 : prestress of slab (c) Stage3 : self weight of edge (d) Stage4 : prestress of edge

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Fig. 8. Contour of principal stress S1 in 3D-modeling (a) Obtuse angle part (b) Acute angle part

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Fig. 9. Direction vector of principal stress in 3D-modeling (a) 3D view (b) X-Y plan view

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Fig. 10. S1 and Node number in 3D solid analysis (a) S1 and Node number on obtuse angle part (b) S1 and Node number on acute angle part

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Fig. 11. Element division diagram and Drawing of PSC-Edge girder reinforcement (a) Element division diagram (b) Drawing of PSC-Edge girder reinforcement

Table 1. Check of rebar in obtuse angle part of PSC-Edge girder

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Table 2. Check of rebar in actual angle part of PSC-Edge girder

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