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Treatment of Headed Rebars

fib Task Group 4.5 „Bond Models“ – 8 th Meeting, November 4, 2005, Stuttgart, Germany –. Treatment of Headed Rebars. Investigations by Hofmann. Improvement of the CC – method for single bolts at the edge. CC - method. New equation.

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Treatment of Headed Rebars

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  1. fib Task Group 4.5 „Bond Models“ – 8th Meeting, November 4, 2005, Stuttgart, Germany – Treatment of Headed Rebars

  2. Investigations by Hofmann Improvement of the CC – method for single bolts at the edge CC - method New equation Influence of edge distance is taken into account more accurately Influence of the slope of the head is taken into account Equation is based on tests and theoretical considerations Calculation of the average blow out failure load of single anchors at the edge:

  3. ? Influence of a ribbed bar Basic concept: Nu,m = Nu,cb+Nu,v ? Nu,v according to the modified CC - method Nu,cb Average resistance of ribbed headed bars:

  4. Investigations by Hofmann Head displacement versus steel stress 0,25 mm 0,20 mm Head displacement sk 0,15 mm dH = 3ds 435 N/mm² Steel stress ssteel Behaviour of the head (Furche): s1s s1h d a ssteel sk

  5. Investigations by Hofmann bond 6 5 4 3 Bond slip curves 2 1 Slip Behaviour of bond (Hofmann): s2 [N/mm²] = shead s1 [N/mm²] s2 [N/mm²] = shead s1 [N/mm²] Bond slip curves Bond slip curves 6 6 5 4 3 2 1 6 6 5 4 3 2 1 lb lb Nu,m sk,cb Nu,cb (According to Furche)

  6. Investigations by Hofmann Nu,cb Calculations for:8 mm < ds < 32 mm1.5 < ds / dk < 3 5 ds < lb < 20 ds Nu,cb+ Nu,v sH [N/mm²] sk,cb s1 8 mm < ds < 32 mm 5 ds < lb < 20 ds 5 bw Min. fb,m[N/mm²] fb,m = 3.0 N/mm² for suk < 5 bw for suk > 5 bw fb,m = 1.5 N/mm² sH [N/mm²]

  7. Investigations by Hofmann Behaviour of bond: Mean bond strength of straight bars: Mean bond strength of headed bars:

  8. Investigations by Hofmann Improvement of the CC – method: Calculation of the average resistance in non - cracked concrete in case of blow out failure (6) (7) (8) (1) (2) (3) (4) (5) (6)

  9. Investigations by Hofmann

  10. Investigations by Hofmann Introduction: Reduction of the development length with headed bars forces are transmitted into the concrete by bond and mechanical interlock Failure mechanism ? Local failure Behaviour of mechanical interlock ? Behaviour of bond Tensile force

  11. Investigations by Hofmann Minimum Maximum Arverage 1.25 (2) (3) (1) (1) (3) (3) (2) Factor considering confining reinforcement: No effect Small effect Numerical simulation with confining reinforcement 10 cm No effect As As As (1)

  12. Investigations by Hofmann Necessary development length for headed reinforcing bars with n: number of staggered t- headed bars Simplification Without special reinforcement With special reinforcement

  13. Investigations by Appl (Splices with Headed Rebars)

  14. Investigations by Appl (Splices with Headed Rebars)

  15. Investigations by Appl (Splices with Headed Rebars)

  16. Investigations by Appl (Splices with Headed Rebars)

  17. Investigations by Appl (Splices with Headed Rebars)

  18. Investigations by Schmid Unconfined Confined

  19. Investigations by Schmid

  20. Investigations by Schmid More research necessary

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