Long-term behavior of reduced length FRP tendons in post-tensioned steel beam-column connections

The long-term behavior of different fiber reinforced polymer (FRP) tendons has been investigated experimentally up to 2000 h. Seven half-scaled exterior post-tensioned (PT) beam-column connection subassemblies, containing reduced length basalt fiber reinforced polymer (BFRP), carbon fiber reinforced polymer (CFRP), and glass fiber reinforced polymer (GFRP) tendons, were tested. To simulate the actual loading conditions in real buildings, an equivalent gravity load was applied to each connection subassembly. Also, to investigate the PT force level effect, three PT force levels, up to 50 %, were applied to 10 mm BFRP tendons, while two PT force levels were applied to 10 mm CFRP tendons. Besides, a 20 % PT force level was applied to 10 mm GFRP tendons. In addition, to study the effect of tendons’ diameter on the long-term behavior, PT connection subassembly containing 12 mm diameter BFRP tendons with 30 % PT force level was tested. The maximum PT force losses were almost 6.1, 5.8, 4.0 % for BFRP, CFRP, and GFRP, respectively. Finally, according to the experimental test results, unified relaxation equations were proposed to predict the amount of PT force loss. Consequently, the predicted PT force losses for one-million-hour period were approximately 15.3 and 12.2 % for BFRP and CFRP tendons, respectively.