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.