Behavior of FRP-RC Columns Using BFRP Ties under Concentric Loading

Abstract

Several studies have investigated the use of Fiber-Reinforced Polymers (FRP) rebars in reinforced concrete (RC) flexural members. However, not enough depth of understanding is currently available with regards to their use in compression members. This research aims at investigating the structural performance of square concrete columns longitudinally-reinforced with Glass FRP (GFRP) and Basalt FRP (BFRP) bars. The use of BFRP ties as a replacement to steel transverse reinforcement in FRP and steel RC columns is also examined. A total of 20 short columns with a cross-section of 180 mm × 180 mm are cast and tested under concentric loading. The specimens included 6 BFRC RC columns, 6 GFRC RC columns and 8 steel RC columns. Half of the columns were transversely-reinforced with BFRP ties while the other similar 10 specimens were reinforced with steel ties. The parameters investigated include: (a) longitudinal reinforcement type (steel versus BFRP versus GFRP), (b) transverse reinforcement type (BFRP versus steel ties), and (c) transverse reinforcement spacing. The effects of the test parameters on the overall response of FRP RC columns including axial load capacity, failure modes, confinement efficiency (EC), ductility, strength contribution of longitudinal rebars, and deformation capacities are discussed and scrutinized. The results showed comparable performance in terms of capacity and ductility between FRP and steel RC columns and between BFRP and steel ties. The contribution of longitudinal steel reinforcement to the ultimate capacity of columns was found to be larger than the contribution of FRP rebars. However, reducing ties spacing by one-third increased the contribution of FRP bars up to 41.6% and consequently improved columns ultimate capacity and ductility. Furthermore, replacing the steel ties with BFRP ties slightly decreased the ductility and the ultimate capacity of FRP and steel RC columns. The main failure mode of all columns was compression-controlled attributed to concrete crushing at strains close to 0.003.