Experimental Study on Seismic Performance of RC Columns Made of Ultra-High-Strength Materials

As recent strong earthquakes have revealed, the excessive deformation of the traditional ductile structures under mega-earthquakes far more than design intensity makes the structures hard to be repaired after earthquakes. To assure sufficient resilience of concrete columns, i.e., stable response and small residual deformation under mega-earthquakes, low-bond and ultra-high-strength (UHS) prestressed concrete (PC) strands rather than deformed reinforcing barsare adopted as the longitudinal reinforcing bars. To verify this method, pseudo-static tests were conducted for five 1/3-scale concrete columns with asquare section of 250 mm × 250 mm, height of 1 000 mm, shear span ratio of 2.0, and axial load ratio of 0.25. The steel amount of UHS PC strand and confinement configuration of transverse reinforcement were experimental variables. Test results indicate that when low-bond and UHS PC strands was used aslongitudinal reinforcement, the lateral resistance of concrete columnskept increasing trend before the drift level reached 3.5%, which effectively reduced residual deformation and limited residual drift below one-fifth of the corresponding peak drift. It is also indicated that carbon fiber reinforced polymer wrapping prevents stripping of concrete cover and further reduces the residual deformation after large deformation of concrete columns.