Flexural behavior of ribbed CFRP bars in ultra-high-performance fiber-reinforced concrete (UHPFRC) beams with lap-splice connection

Due to transport limitations, lap-splice of CFRP bars is imperative, lap-spliced CFRP bars in ultra-high strength concrete can be an innovative solution by reducing the lap-splice length. This study investigated lap-splice behavior of CFRP bars in UHPFRC and required lap-splice length of CFRP bars by comparing design guidelines. For these purposes, a total of 8 beam specimens were fabricated and subjected to four-point loading. Two beams are control variables, one of which consists of a continuous ribbed CFRP bar, and the other of a mechanical connection by coupler. The main parameters are different lap-splice lengths (20d, 40d, and 60d), and concrete strength (normal strength concrete (NC), high strength concrete (HC), ultra-high-performance fiber-reinforced concrete (UHPFRC)), including one beam with traverse reinforcement in the lap-spliced region. Test results showed that the coupler connection was disadvantageous, with the ultimate load reducing by approximately 76 % compared to the un-spliced beam. A lap-splice length of 60d was determined to be the critical length, resulting in 1.0 % and 6.3 % higher ultimate load and developed tensile strength compared to the un-spliced beam. The ultimate load was increased by about 14 % due to the contribution of transverse reinforcement in the lap-spliced region. Unlike NC and HC, lap-spliced ribbed CFRP bars in UHPFRC can prevent splitting failure with crack localization around the loading points. Current design guideline for lap-splice length of FRP bars does not predict well ribbed CFRP bars in UHPFRC, and the predicted lap-splice length of ribbed CFRP bars in UHPFRC was shown to be about 42d.