Seismic performance and repairability assessment of resilient RAC frame structures employing UHSB in columns

Abstract

To investigate the influence of ultra-high strength steel bars (UHSB) on the seismic performance and repairability of recycled aggregate concrete (RAC) frame structures, low cyclic loading tests were conducted on two frame structures. HRB600-grade steel bars were used as the longitudinal reinforcement in columns of HRB600-reinforced frame structure (HFS), while UHSB were employed as the longitudinal reinforcement in columns of UHSB-reinforced frame structure (UFS). The experimental results indicated that the damage evolution of specimens was similar. However, there was no plastic hinge forming at the column ends in the UFS. The plastic hinge at the column ends in the HFS led to a greater energy dissipation capacity compared to the UFS, particularly beyond 2.0% drift. At a horizontal drift of 1.0%, the HFS and UFS can be reused without any repair. However, at a horizontal drift of 2.5%, the HFS can be reused after repair. The residual drift of UFS was within 0.5%, indicating that UFS can be reused after simple repair. When the horizontal drift reached 3.5%, the HFS was difficult to repair, whereas the residual drift of the UFS was still less than 1.0% and able to repair. Additionally, finite element models, considering the bond-slip behavior between weakly bonded UHSB and RAC, were established by setting nonlinear springs. The influences of varying UHSB ratios and axial compression ratios of columns were analyzed. It is recommended to control both the UHSB ratio and the axial compression ratio in resilient RAC frame structures to mitigate the risk of progressive collapse.