Pull-Out Bond Behavior of Ribbed Bars in Normal and High-Strength Concrete with Various Confinements

When ribbed bars are anchored in linear structural members, the bond-slip behavior and the anchorage capacity is strongly influenced by splitting cracks. Many factors influence the formation of the splitting cracks, among others the anchorage length, the concrete cover, the bar spacing and arrangements, confinement from stirrups, flexural and shear cracks in the vicinity of the anchorage region, transverse pressure from support bearings, etc. These parameters often interact in a complex manner, and common design methods for anchorage regions are derived from empirical evaluations of test data and are often strongly simplified. The present study was carried out with the aim of studying the anchorage behavior of ribbed bars in structural members of high strength concrete and to check the applicability of some common design methods to these new materials. The influence of concrete type, normal or high-strength concrete, and various detailing of the node regions was examined. The tensile force in the active end of the anchorage zones was evaluated from steel strain measurements and was compared with predictions by means of strut and tie models. These models were found to consider the effect of inclined cracks in an appropriate and consistent way. The observed anchorage capacity was compared to some common design methods. It was found that the methods, to a considerable degree, were unable to reflect the real behavior. Further improvement and development of design and analytical tools is required.