Influence of Rib Geometry on the Bond Strength of Reinforcing Steel in Coils

The entire construction industry is facing a transition to greater sustainability and resource efficiency. In this effort, the industrial, quality-assured prefabrication of components and structures becomes of major importance. Due to its design and particularly favorable stock keeping, reinforcing steel in coils is suitable for automated reinforcing processes. To ensure a proper bending and straightening, reinforcing steel in coils has a modified rib geometry compared to reinforcing steel in bars. Such wide ribs in combination with small rib spacing result in a large value of relative rib area, but still have a poor impact on the bond behavior. The value of relative rib area itself is not able to predict such unfavorable bond behavior. To meet this concern, an experimental study with pull-out tests is carried out to investigate the influence of rib geometry on the bond strength of reinforcing steel in coils. With large concrete cover, bond is mainly dependent on the load-bearing capacity of the concrete consoles in front of the ribs. Wide ribs and narrow rib spacings generally soften the bond strength due to a reduced load-bearing capacity of the concrete consoles. In pull-out tests, significantly lower bond forces were obtained with reinforcing steel from coils compared with straight reinforcing bars. In concrete beams and tension tie tests with small concrete cover, the bond strength was significantly lower compared to pull-out tests. In addition, a smaller influence of rib geometry was found at lower bond strengths. Although the influence of the rib geometry in concrete structures does not appear to be as severe as pull-out tests would indicate, further research is needed to reliably evaluate all influences on the bond strength of reinforcing steel from coils.