Bond and Development of Straight Reinforcing Bars in Tension

Description

The bond between reinforcing bars and concrete has beenacknowledged as a key to the proper performance of reinforcedconcrete structures for well over 100 years (Hyatt 1877).Much research has been performed during the interveningyears, providing an ever-improving understanding of thisaspect of reinforced concrete behavior. ACI Committee 408issued its first report on the subject in 1966. The reportemphasized key aspects of bond that are now well under-stood by the design community but that, at the time, repre-sented conceptually new ways of looking at bond strength.

The report emphasized the importance of splitting cracks ingoverning bond strength and the fact that bond forces did notvary monotonically and could even change direction inregions subjected to constant or smoothly varying moment.Committee 408 followed up in 1979 with suggested provi-sions for development, splice, and hook design (ACI408.1R-79), in 1992 with a state-of-the-art report on bondunder cyclic loads (ACI 408.2R-92), and in 2001 with design provisions for splice and development design for high relative rib area bars (bars with improved bond characteristics) (ACI408.3-01).

This report represents the next in that line, emphasizing bond behavior and design of straight reinforcingbars that are placed in tension.For many years, bond strength was represented in terms ofthe shear stress at the interface between the reinforcing barand the concrete, effectively treating bond as a material property.

It is now clear that bond, anchorage, development, and splice strength are structural properties, dependent not only on the materials but also on the geometry of the reinforcing bar and the structural member itself. The knowledge base on bond remains primarily empirical, as do the descriptive equations and design provisions. An understanding of the empirical behavior, however, is critical to the eventual development of rational analysis and design techniques.