Seismic Resistant Bridge Columns with NiTi Shape Memory Alloy and Ultra-High-Performance Concrete

Reinforced concrete bridge columns often endure significant damages during earthquakes due to the inherent deficiencies of conventional materials. Superior properties of the new materials such as shape memory alloy (SMA) and ultra-high-performance concrete (UHPC), compared to the reinforcing steel and the normal concrete, respectively, are needed to build a new generation of seismic resistant columns. Application of SMA or UHPC in columns has been separately studied, but this paper aims to combine the superelastic behavior of NiTi SMA and the high strength of UHPC, in order to produce a column design with minimum permanent deformation and high load tolerance subjected to strong ground motions. Additionally, the excellent corrosion resistance of NiTi SMA and the dense and impermeable microstructure of UHPC ensure the long-term durability of the proposed earthquake resistant column design. The seismic performance of four columns, defined as steel reinforced concrete (S-C), SMA reinforced concrete (SMA-C), SMA reinforced UHPC (SMA-UHPC), and reduced SMA reinforced UHPC (R-SMA-UHPC) is analyzed through a loading protocol with up to 4% drift cycles. The use of NiTi SMA bars for the SMA reinforced columns is limited to the plastic hinge region where permanent deformations happen. All the columns have 2.0% reinforcement ratio, except the R-SMA-UHPC column that has a 1.33% reinforcement ratio to optimize the use of SMA bars. Unlike the S-C column that showed up to 68% residual deformation compared to peak displacement during the last loading cycle the SMA reinforced columns did not experience permanent deformation. The SMA-C and R-SMA-UHPC columns showed similar strengths to the S-C column, but with about 5.0- and 6.5-times larger ductility, respectively. The SMA-UHPC column showed 30% higher strength and 7.5 times larger ductility compared to the S-C column.

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