Assessment of Development and Lap-Splice Lengths for New Generation GFRP Bars in Flexural Concrete Bridge and Structural Members

This study investigates the development and lap-splice length of high-modulus, high-tensile-strength new generation glass fiber–reinforced polymer (GFRP) bars under tension in concrete bridge and structural members. The bond strength is assessed using the splice beam test method on nine large-scale beams (300 mm × 450 mm cross section, 5,200 mm length) reinforced with spliced GFRP bars. The parameters included different staggering configurations, splicing percentages, and bar diameters. The splicing configurations involved center-to-center staggering distances of zero (not staggered), 1.0ld (partially staggered), and 1.3ld (fully staggered), with splicing percentages of 100%, 50%, and 33%, and bar diameters of 15.9 and 25.4 mm. Four-point bending tests examined load–deflection profiles, failure modes, crack widths, strain values, and bond strengths. Nonstaggered beams experienced very brittle failure due to splitting, while staggered beams exhibited less brittle failure due to multistage failure of the staggered spliced bars. Staggering increased load capacity and ductility, with fully staggered setups maintaining postfailure strength. Staggering also reduced crack width and enhanced bond and splice strength, particularly with lower splicing percentages and greater staggering distances. Although the splice length-to-bar diameter ratio was kept constant, beams containing three No. 5 spliced bars or two No. 8 bars exhibited notably lower average bond strength than those with two No. 5 bars, underscoring the critical role of bar diameter and clear spacing between splice bars in bond behavior. The development length equations in existing North American design codes often overestimate the bond strength of lap splices, particularly for larger bar diameters and smaller bar spacings. To address this anomaly, a new equation has been proposed for predicting the bond strength and splice length of GFRP bars in tension in flexural members, demonstrating improved accuracy compared with current codes. This advancement is essential for robust design practices in flexural GFRP-reinforced concrete bridges and structural members and may inform future revisions of design codes.