Next Generation of Bridge Columns for Accelerated Bridge Construction in High Seismic Zones
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Accelerated bridge construction (ABC) utilizes advanced planning, new construction techniques, and innovative detailing to facilitate construction. ABC offers many advantages over conventional construction, the most important of which is the reduction of onsite construction time. Even though ABC has been widely used in low seismic regions of the country mostly in superstructure, application of ABC in seismic areas has been limited due to the lack of seismic performance data regarding substructure connections. The main objective of this study was to develop new ABC connections for bridge columns using novel detailing and advanced materials. Three low-damage materials were incorporated: ultra-high performance concrete (UHPC), Nickel-Titanium shape memory alloy (NiTi SMA), and engineered cementitious composite (ECC). Furthermore, two types of mechanical bar splices, grouted coupler and headed bar coupler, were utilized. UHPC-filled duct connections were developed and evaluated through 14 pullout tests. A new detailing was proposed for grouted coupler column end connections to enhance the drift capacity. Three half-scale precast column models were tested under slow reversed cyclic loading, each with a new precast element connection or low-damage plastic hinge. A material model was developed for reinforcing superelastic NiTi SMA bars. Furthermore, new simple methods were developed to account for bond-slip effects and bar debonding effects in analytical models of reinforced concrete members. It was found that bar bond strength in UHPC is eight times higher than that in conventional concrete. UHPC-filled duct connections exhibited no damage even under 12% drift ratio cycles. The displacement capacity and displacement ductility capacity for the grouted coupler column were respectively increased by 47 and 56% compared to grouted coupler column models investigated previously. Longitudinal bar debonding allowed spread of yielding and prevented premature failure of reinforcements in UHPC-filled duct connections and grouted coupler column pedestal. The SMA-reinforced ECC column showed superior seismic performance compared to a conventional column in which the plastic hinge damage was limited to only ECC cover spalling even under 12% drift ratio cycles. The column residual displacements were 79% lower than CIP residual displacements on average due to the superelastic NiTi SMA longitudinal reinforcement, and higher base shear capacity and higher displacement capacity were observed. The analytical modeling methods were simple and sufficiently accurate for general design and analyses of precast components proposed in the present study. The proposed symmetrical material model for reinforcing NiTi superelastic SMA was found to be a viable alternative to the more complex asymmetrical model. Extensive experimental and analytical investigations performed in the present study led to a new generation of ABC bridge columns in which columns can be built in relatively short time but the seismic performance of these columns is equal or better than columns that are built cast-in-place with conventional materials.