Quasi-static experimental study on precast concrete columns reinforced with bundled rebars

Bundled reinforcement is an alternative approach to improve the installation efficiency and structural integrity of precast concrete structures. With higher strength and lighter weight compared with steel bars, basalt fiber reinforced polymer (BFRP) bar is an attractive candidate material for concrete structures. Low-cyclic reversed loading tests on four precast concrete columns reinforced with different arrangements of longitudinal bars were conducted in this paper. The test specimens included singly arranged steel bars (S12-1P, S20-1P), three-bar bundled steel bars (S12-3P), and three-bar bundled hybrid BFRP bars/steel bars (S10/B13-3P). The test results showed that using bundled reinforcement in precast concrete columns could delay the yielding of longitudinal steel bars. Specimens S12-3P and S20-1P not only maintained the inherent bearing capacity and stiffness, but also demonstrated improved deformability of 18.1% and 6.9%, respectively, compared to the conventional precast column S12-1P. S10/B13-3P showed a 5.5% increase in peak load and a 9.1% increase in displacement ductility, which is expected to result in better seismic performance compared to that of the conventional columns. The corresponding repairable limits (based on the drift ratios) for S12-1P, S20-1P, and S10/B13-3P were 2.6%, 2.9% and 4.5%, respectively. In addition, the use of bundled bars could result in a wider curvature concentrated distribution zone, thereby increasing the plastic hinge length and providing a larger deformation capacity with the same peak curvature.