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Tension test considering the shape change of CFT Column-to-Beam Interior Diaphragm

CFT 기둥-보 내다이아프램의 형상변화를 고려한 인장실험

  • Kwak, Sung-Shin (Department of Architectural Engineering, Kyonggi University Graduate School) ;
  • Choi, Byong-Jeong (Department of Architectural Engineering, Kyonggi University Graduate School)
  • 곽성신 (경기대학교 일반대학원 건축공학과) ;
  • 최병정 (경기대학교 일반대학원 건축공학과)
  • Received : 2018.12.07
  • Accepted : 2019.02.01
  • Published : 2019.02.28

Abstract

The diaphragm used for CFT columns has a small amount of steel to be used, but has a disadvantage that welding is difficult and openings are required because the steel tube and four sides must be welded. The improved diaphragm to be examined in this study was cut into four corners by cutting the center hole for concrete filling. In the improved diaphragm, the width of the center hole is the same as that of the previous diaphragm, but the width of the diaphragm contacting the steel tube is reduced, thereby reducing the welding length by about 70% compared to the previous diaphragm. The in-plane strain of each specimen was analyzed when the same load was applied to the interior diaphragm through a simple tensile test. Using the general FEM program(ANSYS 19.2), the analysis was performed under the same conditions as the actual simple tensile test, and the load transfer between the improved diaphragm and the previous diaphragm was compared. When the width of the diaphragm is equal to or smaller than the flange width, stress is concentrated from the end of the diaphragm, and when the flange width is larger, stress is concentrated at the center.

콘크리트 충전강관(Concrete Filled Steel Tube, 이하 CFT) 기둥에 사용되는 내다이아프램은 사용 강재량은 적으나 강관과 네 면을 용접해야 하므로 용접이 까다롭고 개구부가 필요한 단점을 가지고 있다. 본 연구에서 살펴보고자하는 개선 다이아프램은 콘크리트 충전을 위한 중앙부 홀을 4등분하여 각 코너부위를 절삭했다. 개선 다이아프램은 중앙부 홀의 넓이는 기존 다이아프램과 동일하지만 강관과 접하는 다이아프램의 폭이 감소하여 용접 길이가 기존 다이아프램 대비 약 70%가 감소된다. 개선 다이아프램의 인장성능을 검토하기 위하여 콘크리트 타설 홀의 반지름인 R값을 설계 변수로 3개의 실험체를 제작하였다. 단순 인장 실험을 통하여 내다이아프램에 동일 하중을 받았을 때 각 실험체의 면내 변형률을 분석하였다. 범용유한요소해석 프로그램을(ANSYS 19.2)를 사용하여 실제 단순 인장 실험과 동일한 조건으로 해석을 수행하고 개선 다이아프램과 기존 다이아프램의 하중 전달을 비교하였다. 다이아프램의 폭이 플랜지 폭과 같거나 작을 때는 다이아프램의 단부에서 부터 응력이 집중되고 플랜지 폭이 더 클 때는 중앙부에서 응력이 집중되는 것을 확인하였다.

Keywords

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Fig. 1. Variable Factor(R, Radius) for experiment

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Fig. 2. Specimen details of improved diaphragm

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Fig. 4. Stress-Strain curve of steel

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Fig. 5. Diaphragm pressing force situation

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Fig. 6. Stress-Strain curve for Specimens

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Fig. 7. Stress-Strain curve difference of three types

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Fig. 8. Modeling of experiments using FEM

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Fig. 9. Mesh quality of modeling

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Fig. 10. Coordinates according to strain gauge position

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Fig. 11. Stress-Strain curve comparison of test and FEM

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Fig. 12. Stress transfer analysis in FEM

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Fig. 13. Experimental and analytical plastic deformation area

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Fig. 14. Specific point values in the stress-strain curves

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Fig. 3. Specimen details of previous diaphragm

Table 1. List of specimens

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Table 3. Material test results

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Table 4. Comparison of maximum strain at the same Pmax

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Table 5. Material properties

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Table 6. Maximum strain comparison of test and FEM

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Table 7. Results of stress distribution analysis according to Stress

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