Seismic Performance of Concrete Columns Reinforced with Weakly Bonded Ultrahigh-Strength Longitudinal Bars
Takashi Takeuchi, Yuping Sun, Masanori Tani, P. Benson Shing
Abstract
This paper presents an investigation of the seismic performance of concrete columns reinforced longitudinally with steel bars (referred to as UHS-WB bars) that have an ultrahigh strength and a low bond strength. Nine cantilever columns were tested with variables including the type of longitudinal steel reinforcement, the anchorage method for the UHS-WB bars, the axial load ratio, and the shear-span ratio of the columns. The columns with securely anchored UHS-WB bars and shear-span ratios of 2.5 and 3.0 exhibited very stable hysteretic behavior and a mild hardening postyield behavior up to drift ratio of 4%, whereas the lateral resistance of the column with a shear-span ratio of 4.0 had a slight decline beyond a drift ratio of 1.5% due to significant P-δ effect. However, all the columns with securely anchored UHS-WB bars had a residual drift less than 0.5% after unloading from the drift of 3%. The stable response and low residual drift can be attributed to the low bond strength, which delayed the yielding of the UHS-WB bars.