Size effect on failure of bond splices of steel bars in concrete beams

The results of reduced-scale failure tests of simply supported four-point-b end beams of different sizes, containing lapped bond splices of smooth (und eformed) longitudinal reinforcing bars, are reported. The tests consist of two groups, with splices located either in the midspan region with a unifor m bending moment, or in one of the end regions with a uniform shear force. The specimens were made of microconcrete with a maximum aggregate size 4.76 mm. Beams of three different heights (50, 100, and 200 mm) were tested. Th e beams were geometrically similar in three dimensions, and even the bar di ameters and cover thicknesses were scaled in proportion. The reinforcement ratio was 0.31%. The results reveal the existence of a significant size eff ect, which can be approximately described by the size effect law previously proposed by Bazant. The size effect is found to be stronger for splices wi thout any spiral than for splices confined by a spiral, and stronger for sp lices in the maximum shear force region of a beam than for splices in the m aximum bending moment region. Generalization of the existing formula of Ora ngun et al. is proposed and recommended for design. Although the formula pr ovides a safer alternative to the existing approach, further testing is nee ded for better calibration. The size effect on the nominal bond strength im plied by the development length provisions of the current and previous Amer ican Concrete institute code :is discussed and shown to be inadequate.