University of Stuttgart Institute of Construction Materials (IWB) 1/21 Treatment of Headed Rebars fib Task Group 4.5 „Bond Models“ – 8 th Meeting, November 4, 2005, Stuttgart, Germany –

University of Stuttgart Institute of Construction Materials (IWB) 2/21 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: Improvement of the CC – method for single bolts at the edge Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 3/21 Influence of a ribbed bar Basic concept: N u,cb N u,v N u,m = N u,cb + N u,v ? ? according to the modified CC - method Average resistance of ribbed headed bars:

University of Stuttgart Institute of Construction Materials (IWB) 4/21 Behaviour of the head (Furche): sksk d a Head displacement s k Steel stress  steel 0,25 mm 0,20 mm 0,15 mm 435 N/mm² Head displacement versus steel stress d H = 3d s s 1h s 1s  steel Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 5/21 Bond slip curves  1 [N/mm²]  2 [N/mm²] =  head lblb Behaviour of bond (Hofmann): Slip bond Bond slip curves  1 [N/mm²]  2 [N/mm²] =  head lblb 6 N u,cb N u,m s k,cb (According to Furche) Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 6/21 8 mm < d s < 32 mm 5 d s < l b < 20 d s  H [N/mm²] s k,cb s1s1 N u,cb  H [N/mm²] N u,cb + N u,v 5  w f b,m = 1.5 N/mm² f b,m = 3.0 N/mm² for  uk < 5  w for  uk > 5  w Min. f b,m [N/mm²] Calculations for: 8 mm < d s < 32 mm 1.5 < d s / d k < 3 5 d s < l b < 20 d s Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 7/21 Mean bond strength of straight bars: Behaviour of bond: Mean bond strength of headed bars: Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 8/21 Improvement of the CC – method: Calculation of the average resistance in non - cracked concrete in case of blow out failure (1) (2) (3) (4) (5) (6) (7) (8) Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 9/21

University of Stuttgart Institute of Construction Materials (IWB) 10/21 Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 11/21 Introduction: Reduction of the development length with headed bars Local failure Tensile force Failure mechanism forces are transmitted into the concrete by bond and mechanical interlock Behaviour of mechanical interlock Behaviour of bond ? ? Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 12/21 Investigations by Hofmann Factor considering confining reinforcement: (2) (3) (1) AsAs 1.25 (1) (3) (2) Minimum Maximum Arverage No effect Small effect 10 cm Numerical simulation with confining reinforcement AsAs AsAs

University of Stuttgart Institute of Construction Materials (IWB) 13/21 Simplification Without special reinforcement With special reinforcement Necessary development length for headed reinforcing bars with n: number of staggered t- headed bars Investigations by Hofmann

University of Stuttgart Institute of Construction Materials (IWB) 14/21 Investigations by Appl (Splices with Headed Rebars)

University of Stuttgart Institute of Construction Materials (IWB) 15/21 Investigations by Appl (Splices with Headed Rebars)

University of Stuttgart Institute of Construction Materials (IWB) 16/21 Investigations by Appl (Splices with Headed Rebars)

University of Stuttgart Institute of Construction Materials (IWB) 17/21 Investigations by Appl (Splices with Headed Rebars)

University of Stuttgart Institute of Construction Materials (IWB) 18/21 Investigations by Appl (Splices with Headed Rebars)

University of Stuttgart Institute of Construction Materials (IWB) 19/21 Investigations by Schmid Unconfined Confined

University of Stuttgart Institute of Construction Materials (IWB) 20/21 Investigations by Schmid

University of Stuttgart Institute of Construction Materials (IWB) 21/21 Investigations by Schmid More research necessary