Bond Strength of Staggered and Nonstaggered GFRP Lap-Spliced Bars in Normal and Fiber-Reinforced Concrete Beams

This study evaluated the performance of glass fiber–reinforced polymer (GFRP) lap-spliced bars in concrete beams, focusing on the effects of splice configuration and the use of fiber-reinforced concrete using macrosynthetic fibers through large-scale testing of six beam specimens. The investigation compared nonstaggered (100% of bars spliced at the same section) and fully staggered (50% of bars spliced with a center-to-center distance of 1.3ls) splices, using No. 5 sand-coated GFRP bars with a splice length of 38db. Experimental results reveal that, while precracking stiffness was similar across all beams, fully staggered splices enhanced load-carrying capacity by 6.4% and promoted a ductile, multistage failure mechanism, retaining approximately 85% of peak strength postinitial splice failure. The inclusion of synthetic macrofibers at 1.8 and 2.7 kg/m3 dosages increased postcracking stiffness by up to 8% and 18% for nonstaggered and staggered configurations, respectively, and boosted ultimate load capacity by 7.9% and 16.8%. Crack width analysis showed that staggered splices and fiber reinforcement significantly reduced crack propagation, with fully staggered fiber-reinforced beams achieving a 1.0-mm crack width at higher loads (up to 108.5 kN) compared to nonstaggered beams (up to 99.8 kN). Bond strength was enhanced by 5.6%–14.6% in fully staggered and fiber-reinforced beams due to improved stress distribution and crack-bridging effects. Comparisons with the existing design codes revealed limitations in capturing fiber and staggering effects, prompting the development of a modified bond strength equation that incorporates splice staggering and fiber content, achieving the average test-to-prediction ratios of 1.03. These findings offer critical insights for optimizing GFRP-reinforced concrete structures and refining bond strength provisions in design guidelines.