Lap Splicing of Large Steel Reinforcing Bars

Eleven large-scale reinforced concrete beams were tested to failure under four-point bending to investigate tension lap splices of No. 14 and 18 (43 and 57 mm) bars. Additional variables included transverse reinforcement, concrete compressive strength (nominally 5 or 10 ksi [34 or 69 MPa]), and target bar stress at splice failure (60 or 100 ksi [420 or 690 MPa]). Results show that both the ACI 408R-03 and ACI 318-19 bond length equations become less conservative as bar diameter increases, so a bar size factor is proposed for modifying bond length equations to obtain similar conservatism across all diameters. A minimum clear cover of one bar diameter is also recommended for large-bar lap splices. Increasing the limit on (cb + Ktr)/db in the ACI 318-19 development length equation from 2.5 to 4.0 was shown to produce similar mean ratios of test-to-calculated bar stresses across different amounts of transverse reinforcement. Finally, results suggest that development length should be limited to 50db when designing lap splices without transverse reinforcement.