MODELING OF BOND: 1) INFLUENCE OF CORROSION 2) EXPERIMENTAL EVALUATION MODELING OF BOND: 1) INFLUENCE OF CORROSION 2) EXPERIMENTAL EVALUATION Demokritus University of Thrace (DUTh) - Greece S. Tastani, Civil Eng., PhD candidate S. J. Pantazopoulou, Professor Sponsored by the Hellenic General Secretariat for Research and Technology S. Tastani, Civil Eng., PhD candidate S. J. Pantazopoulou, Professor Sponsored by the Hellenic General Secretariat for Research and Technology

DUThDUTh Definition of the problem Bond – slip General Bond Model Splitting resistance Bursting generation Derivation of specific bond models Tension Stiffening & crack control RotationCapacity Laps & anchorages Detailingrules

Frictional Model for Bond transverse reinforcement concrete cover shrinkage stress shrinkage stress Coefficient of Friction =f( slip, corrosion penetration) breaks down quickly – negligible when corrosion starts Adhesion  rad F+FF+F F fbfbfbfb dx dx FsFsFsFs cccc  rad  shr Frictional model + Thick Cover Ring Theory DUThDUTh

at the cross section: thick cover ring model (Pantazopoulou & Papoulia 2001) at the cross section: thick cover ring model (Pantazopoulou & Papoulia 2001) Impose incremental radial displacement at the internal boundary Calculation of strains & stresses at the radial and hoop direction Equilibrium for calculation of the normal pressure required to split the cover urur  rad(0) N …  th(Ν )  rad(0)  th(2)  th(1)  th(0)  rad(1)  rad(2)  rad(N) ssss ssss  shr(1) DUThDUTh cover stirrups shrinkage adhesion

 rib,res =  sm,max  u su = s r u so u so,sm  rib,max  rib,res =  sm,max coefficient of friction:  = f(slip-s, corrosion penetration-X) coefficient of friction:  = f(slip-s, corrosion penetration-X)  rib,max  sm,max  sm,res  X=h r /R b X shr Geometrical relation between radial displacement (u r ) and slip (s): (a=0.5 - Lura et al. 2002) Displacements: u r ≤ h r s DUThDUTh C R cr RrRr RbRb R rb X The model recognizes corrosion influence on every part of the equation

along the bar axis   rad  f b adh  bear Splitting failure: Pullout failure:  rad f b =  ·  rad F between successive cracks:  bear ≤ f c s cr from equilibrium: tensile force = bond force F  rad  bear nnnn fb=·nfb=·nfb=·nfb=·n  tz DUThDUTh Distribution of bearing stresses along the crack spacing Distribution of bearing stresses along the crack spacing Polak & Blackwell 1998

Results of the model DUThDUTh Serviceability limit state ultimate state Residual capacity : domains from analysis (radial displ.) & experimental records f b = g (f t – f c ; c ; A st ; D b ; X ;  (s, X)) performance index {drift, crack width …}

Anchorage occurs in a uniform biaxial tensile stress field without: the uncountable effect of the compr. Stress field the uncountable effect of the compr. Stress field Influence of curvature Influence of curvature F Means of transverse pressure on support bar (preclusion of failure) Means of transfer tension from one bar to the other F Test bar Support bar Cylindrical or orthogonal (with curved corners) pattern: representative for verification of the thick walled cylinder model with test data Direct Tension Pullout Bond test DUThDUTh giving the lower bound properties of steel bars

Setup of loading h r =0.5mm - L b =5D b & L b =12D b h r =1.1mm - L b =5D b & L b =12D b bar geometry over 70 Direct Tension Pullout Bond tests short & long anchorage specimens short & long anchorage specimens Machined & commercial bars Machined & commercial bars Two concrete mixes (with f c and f t ) Two concrete mixes (with f c and f t ) cover cover Passive confinement (FRP + rings) Passive confinement (FRP + rings) specimens’ area Digital image processing DUThDUTh experimental program:

Splitting cracking along the embedded length Splitting cracking along the embedded length Crushing of concrete under the ribs Crushing of concrete under the ribs Dilation due to bond action Dilation due to bond action DUThDUTh

rings no rings 4 rings 2 rings Average bond stress (MPa) Slip mm 4D20 DUThDUTh urur  rad(0)