# Study on Seismic Performance of Steel Fiber Reinforced Concrete Pier Under Bending-Torsion Coupling
## 1 Introduction  
The number of curved girder bridges is increasing with the rapid development of transportation. Due to the influence of curvature, the center of gravity of the curved girder bridge deck deviates from the pier. The pier is typically subjected to complex forces such as compression, bending, shear, and torsion due to earthquakes [1, 2]. [PERSON] [3] carried out quasi-static tests on RC pirs under the coupled effects of compression, bending, shear, and torsion, and the different failure modes of the pirs under various loading conditions were determined. [PERSON] [4] found that the damage of the pirs was increased and the energy dissipation and load-bearing capacities of the pirs were weakened due to torsional and shear effects. [PERSON] [5] performed a series of tests to study the mechanical properties of RC pirs under various loading cycles. The results showed that an increase in the number of loading cycles accelerated damage accumulation and led to the cyclic degradation of RC pirs, which resulted in bending-shear failure. In order to improve the seismic resistance of pirs, [PERSON] [6] proposed the theory of ductile seismic design, emphasizing the formation of plastic hinges through structural plastic deformation to resist seismic forces. Some scholars have aimed to improve the ductility of pirs by increasing the stirrup reinforcement and optimizing the section dimensions [7, 8, 9]. However, these measures might result in increased costs and greater construction difficulty. In recent years, technological innovation in bridge engineering has been promoted by new materials. The seismic performance of RC piers has been improved by several scholars through the use of high-ductility concrete, replacing ordinary concrete at the pier ends [10]. [PERSON] [11] studied the seismic performance of prefabricated piers with ultra-high-performance fiber-reinforced concrete (UHPFRC)-enhanced bottom segments and found that prefabricated piers with UHPFRC bottom segments had higher lateral strength and residual displacement compared to those with ordinary reinforced concrete segments. [PERSON] [12] compared the seismic performance of piers constructed from different fiber-reinforced concrete materials, including steel fiber-reinforced concrete (SFRC), polypropylene fiber-reinforced concrete (PFRC), and high-performance fiber-reinforced concrete (HySPFRC). The results showed that all types of fibers effectively improved the seismic performance of the piers. [PERSON] [13] carried out uniaxial cyclic compression tests on steel fiber-reinforced concrete specimens and found that the specimens had obvious ductility characteristics. [PERSON] [14] studied the effect of fiber-reinforced cement-based composite materials on the mechanical properties of RC piers, and the results showed that the seismic performance of the RC piers was significantly improved after reinforcement. [PERSON] [15] used a glass fiber-reinforced polymer (GFRP) and aramid fiber-reinforced polymer (AFRP) to strengthen the plastic hinge regions of piers, and the test results showed that the specimen reinforced with AFRP had the best seismic performance. [PERSON] [16] found that adding polyvinyl alcohol (PVA) fibers in the concrete could effectively improve the spalling at the base of precast circular hollow piers. [PERSON] [17] established a determination method for the drift ratio limit state and the corresponding strength of an RC circular pier with GFRP. [PERSON] [18] reinforced the wall panel joints using SFRC, and it was indicated that SFRC could delay crack propagation and enhance the deformability of the wall. In summary, while research has been conducted by numerous scholars on the seismic performance of SFRC piers under bending-torsion coupling effects, a systematic analysis of the influence of the component parameters and external load parameters on the mechanical behavior of SFRC circular piers has not been performed.