The stress range to which a reinforcing bar is subjected is the primary factor determining its fatigue life. For design purposes, there is a limiting stress range, the fatigue limit, above which a reinforcing bar will have a finite fatigue life and is certain to fracture. At stress ranges below the fatigue limit, a reinforcing bar will have a long fatigue life and may be able to sustain a virtually unlimited number of stress cycles. The magnitude of the fatigue limit depends on the minimum stress during each stress cycle and on the shape of the deformatins rolled onto the bar surface. It may also depend on the diameter and the grade of the bar. Increasing a tensile minimum stress was found to result in a decrease in fatigue strength. On the other hand the fatigue was found to incrase with an increasing compressive minimum stress. Bar diameter and grade of bar were found to influence the finite-life fatigue strength of reinforcing bars. The existence of a long-life fatigue effect due to these variables could not be established. Larger size bars have a lowered fatigue strength while higher grade bars have an increased fatigue strength. The effect of lug geometry on fatigue strength was found to be coupled with that of bar diameter. The larger the bar diameter, the greater was the effect of lug geometry.
Samenvatting