Splice Strength of Conventional and High Relative Rib Area Bars in Normal and High-Strength Concrete

Abstract

The effects of concrete strength, coarse aggregate quantity and type, and reinforcing bar geometry on splice strength are evaluated. Results for 64 splice specimens with reinforcing 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 0.069 to 0.141, concrete strengths ranging from 4,250 psi to 15,650 psi (29-108 MPa), and quantities of limestone and basalt coarse aggregate ranging from 1,586 lb/cu yd to 1,908 lb/cu yd (941-1,132 kg/cu m) are reported. The results are combined with the American Concrete Institute (ACI) Committee 408 database to develop design equations for development and splice length, which are then compared with the design criteria in ACI 318-99. For splices not confined by transverse reinforcement, the 1/4 power of compressive strength (f'c) best characterizes the effect of concrete strength on splice strength. f'c (3/4 power) characterizes the effect of concrete strength on the additional splice strength provided by transverse reinforcement. The splice strength of bars confined by transverse reinforcement increases with an increase in relative rib area and bar diameter. The use of stronger coarse aggregate results in an increase in splice strength for bars both with and without confining reinforcement. For splices confined by transverse reinforcement, the higher the quantity of coarse aggregate, the greater the contribution of transverse reinforcement to splice strength. The expressions characterizing the splice strength of reinforcing bars accurately represent the development/splice strength of bottom-cast uncoated bars as a function of member geometry, concrete strength, relative rib area, bar size, and confinement, provided by both concrete and transverse reinforcement. The new design expressions are superior to the design criteria in ACI 318-99 in terms of both safety and economy. The criteria in ACI 318-99 for developed bars and Class A splices are unconservative for No. 6 (No. 19) and smaller bars.