Report on Bond of Steel Reinforcing Bars Under Cyclic Loads

Description

The transfer of forces across the interface between concrete and steel by bond stresses is of fundamental importance to many aspects of reinforced concrete behavior. Satisfactory bond performance is an essential goal in detailing reinforce-ment in structural components. Many detailing provisions in ACI 318 are aimed at preventing bond failures.Bond stresses in reinforced concrete members arise from two distinct situations. The first is anchorage or development where bars are terminated.

The second is flexural bond or the change of force along a bar due to a change in bending moment along the member. Bond performance under static monotonically increasing deformations—referred to as monotonic loading—has been summarized in ACI 352R, ACI 408R, and ACI Committee 408 (1966, 1970, 1979). Bond behavior under cyclic loads received little attention until design for earthquake and wave loads became impor-tant design topics (ACI Committee 408 1979).

Investigations over the past 40 years have clarified some of the important parameters influencing bond behavior under cyclic loads. However, the influence of many of these parameters is understood only qualitatively.In this report, “bar” means “reinforcing bar” and “ribs” refer to the deformations on deformed reinforcing bars. Longitudinal deformations on reinforcing bars are not clas-sified as ribs. “Bond stress” refers to the stresses along the bar-concrete interface. The steel stresses along the length of the reinforcing bar are modified by transfer of force between the bar and the surrounding concrete along the interface (refer to Fig. 1.1)