The bond between reinforcement and concrete should ensure high structural stiffness and small cracks in the serviceability limit state, generate small splitting forces and allow full utilization of the reinforcement ductility in the ultimate limit state. While bond behavior at service load and splitting behavior has been investigated intensively, bond behavior at large inelastic steel strains is not known very well. Therefore, in this paper the contribution of concrete between cracks at inelastic steel strains is investigated numerically based on a rational mechanical model and using realistic constitutive material laws. The model predictions agree rather well with a large number of test results. According to the results of the parametric study, after steel yielding the ratio of mean steel strain to the steel strain at the crack is mainly influenced by the reinforcement percentage and the shape of the steel stress-strain curve. It is much lower than at service load. Due to this lower ratio of mean steel strain to steel strain at the crack, the rotation capacity of plastic hinges and thus the structural ductility is reduced significantly and may be very low if reinforcement with low ductility is used. Therefore an optimization of bond seems to be necessary. Corresponding extensive numerical and experimental studies are under way in Germany.

This experimental study addresses the performance of reinforced concrete slabs containing epoxy-coated reinforcement subjected to high-cycle/low stress range repeated loading typical of those encountered in bridge decks. The behavior under repeated load indicated that epoxy-coated reinforcement does not significantly increase deflections despite the larger bar slip associated with wider cracks. The wider cracks do increase the potential for increased amount of corrosive agent at the level of the top mat of reinforcement in bridge decks. The average bond strength ratios of coated to uncoated specimens support a proposed single modification factor of 1.35 for specimens with low cover.

Pullout tests were conducted on deeply embedded headed reinforcement to determine the effect of transverse reinforcement and bonded length on the side-blowout capacity and load-slip behavior of the anchorage. It was found that transverse ties or stirrups in the anchorage zone had little effect on the ultimate capacity. Increases in anchorage capacity were only observed when the head was positively anchored in contact behind a large crossing bar. Transverse reinforcement also had little effect on the load-slip behavior before failure. However, when large amounts of transverse reinforcement were placed near the head, the amount of load maintained after the blowout failure occurred was increased. Additional bonded length of a deformed reinforcing bar increased the anchorage capacity and reduced the head slip for a given load. The amount of increase in capacity can be predicted using current ACI provisions for development length. Design procedures taking into account the effects of transverse reinforcement and bonded length were developed.

Fusion bonded epoxy coated reinforcement (FBECR) has been developed ! to help combat problems of corrosion in reinforced concrete structures. The surface i texture of the coating is smoother than the normal mill scale surface of reinforcing bars and alters bond characteristics of the bar. Although FBECR has now been in use for more than 30 years and production Standards have been established, rules for design using the material are not well developed. CEB Task Group 2/5 is currently reviewing data on bond and structural performance of elements reinforced with FBECR with the aim of deriving recommendations for design practice which will enable structures reinforced with FBECR to achieve equivalent performance to that of structures reinforced with millscale surface ribbed bars. This paper presents proposals for amendments to the CEB-FIP Model Code 1990 for design of anchorages and splices of coated bars, and briefly reviews other aspects of structural performance influenced by the different bond characteristics of FBECR.

Characteristic results of more than 100 cyclic pull-out tests are presented including various load histories (simulating realistic load spectra) like random loading or variable amplitude loading with increasing or decreasing tendencies in addition to the constant amplitude loading with different amplitudes. Slip measurements are compared to acoustic emission measurements. Repeated loading produces a progressive deterioration of bond caused by the propagation of micro-cracks and progress of micro-crushing in concrete. Deterioration of bond may be observed by measuring slip or acoustic emission events. It is quantitatively shown that the actual slip is significantly influenced by the load history: maximum and minimum levels of the repeated load, type of amplitude (constant or variable), frequency, sequence of amplitudes and number of load cycles, respectively.