Fatigue of High Relative Rib Area Reinforcing Bars

Abstract

The fatigue performance of high relative rib area reinforcing bars is compared to that of conventional bars. Fatigue tests involve No. 4 ( 13mm) and No. 5 ( 16rnm) bars with relative rib areas (ratio of projected rib area normal to bar axis to the product of the nominal bar perimeter and the center-to-center rib spacing) ranging from 0.064 to 0.146. The tests include 69 specimens representing 6 deformation patterns [2 for No. 4 (13mm) bars and 4 for No. 5 (16mm) bars] to investigate the effect of deformation pattern on fatigue behavior. The tests were conducted in air using stress ranges of 20, 25, 30, and 35 ksi (138, 172, 207, and 241 MPa) with a minimum stress of zero. Characteristics of fatigue crack zones and the details of lug geometry are provided. The test results indicate that the stress range, bar diameter, and surface geometry, especially the lug base radius-to-height ratio (rib). have significant effects on the fatigue strength of the bars. Fatigue strength and fatigue life decrease with increased stress range and bar diameter and decreased r/h ratio. Relative rib area has no effect on fatigue performance.