###### Abstract  
Prestressed spun high-strength concrete (PHC) piles are commonly used in various types of structures, including bridges, buildings and marine infrastructures. However, piles installed in aggressive environments are vulnerable to corrosion of the steel, which can lead to rapid degradation of the piles. As a corrosion-resistant material, carbon fiber-reinforced polymer (CFRP) is considered an alternative to steel tendons for durability enhancement. In this study, a new pile system with CFRP was proposed. Experimental tests of three full-scale piles and a numerical analysis of eight piles with various parameters were performed to investigate the flexural performance of CFRP prestressed spun high-strength concrete pile. The proposed piles were loaded under four-point bending after prestressing. The experimental and numerical results verified the feasibility of the proposed system, and the CFRP pile exhibited twice of flexural capacity of that of steel-reinforced piles. The flexural performance of the CFRP PHC pile was significantly affected by the reinforcement ratio, prestressing level and modulus of the CFRP. An analytical approach predicting the flexural capacity of the CFRP PHC pile was proposed based on the parametric study. Ninety percent accuracy was achieved for the proposed analytical approach. The presented study can significantly promote the application of CFRP in pile foundations and improve the durability of PHC piles. CFRP; PHC piles; experimental tests; FE analysis; analytical approach Article  
Flexural Performance of PHCP  
Prestressed spun high-strength concrete PHC piles are extensively utilized in foundations worldwide due to their notable advantages such as high axial capacity, standardized manufacturing processes, assurance of quality, short on-site construction period and low permeability [1; 2]. These piles not only carry vertical loads from superstructures but also carry lateral forces induced by wind, waves and earthquakes [3]. The high strength steel is prestressed to resist the bending moment exerted by lateral loads. The strength of steel used in PHC piles varies in the range of 1420 MPa-1860 MPa, and the concrete grade ranges from 60 MPa to 100 MPa [3]. Despite the above benefits, the application of PHC piles has encountered various challenges over time. Brittle fracture of the high-strength steel limits the flexural capacity of PHC piles, which has led to a series of accidents. During the Hyougoken-Nanbu Earthquake [4] in1995 and the Tohoku Pacific Earthquake [5] in 2011, brittle failure on PHC pile heads was observed. In addition, a 13-story building collapsed in Shanghai due to the lack of flexural capacity of the PHC piles [6]. Many attempts have been made to improve the flexural resistance of PHC piles. Many studies on the effect of additional non-prestressed steel have been conducted. [PERSON] et al. [7] found that the flexural performance of PHC piles was significantly improved with a combination of steel strands and additional deformed bars. The flexural and seismic performance of PHC piles with additional deformed bars was also investigated by [PERSON] et al. [2; 8] and [PERSON] et al. [9]. [PERSON] et al. [10] proposed a PHC pile system with an un-bonded strand at the center of the pile to reinforce the integrity of the pile. Confinementof the PHC piles is considered an effective way to improve their flexural capacity and ductility. [PERSON] et al. attempted to improve the ductility of PHC piles by confining the pile with high-strength steel hoops [11]. [PERSON] et al. [12] investigated the effect of steel jackets on the flexural strengthening of PHC piles. In addition, PHC piles jacketed by various of FRPs were tested and a significant improvement in flexural performance was observed [13; 14; 15]. The other alternative for flexural improvement is infilling concrete. [PERSON] et al. [16] and [PERSON] et al. [17] tested PHC piles with infilled concrete in the core, and the result showed that the flexural ductility was significantly improved.