Flexural performance of pretensioned centrifugal spun concrete piles with combined steel strands and reinforcing bars

Abstract

Pretensioned spun high-strength concrete (PHC) piles have been widely used in building foundations in many parts of the world. However, PHC piles are also known to have poor lateral deformation and ductility capacity and hence are not suitable for seismic regions. To improve the horizontal load bearing and deformation capacities, pretensioned centrifugal spun concrete piles with steel strands alone (hereafter referred to as PSC piles) or a combination of steel strands and mild steel deformed rebars (referred to as PSRC piles) have been developed. PSRC piles are expected to benefit on the one hand from steel strands with high deformation capacity, and on the other hand from deformed steel bars with good bond with concrete and hence better control of cracks. This paper presents a comprehensive study on the comparative flexural performance of PSC and PSRC piles. The bending tests of PSC piles and PSRC piles were firstly conducted on six full-scale pile specimens with three different pile diameters, respectively. The flexural performances are evaluated in terms of crack resistance, flexural and deformation capacities, as well as crack distribution. The results show that the cracking bending moment of PSRC piles is similar to that of PSC piles, but the ultimate bending moment is about 55% higher due to the addition of deformed rebars. The general cracking behavior of PSRC piles exhibit remarkable improvement comparing to PSC piles, with an extended crack region, denser distribution of cracks, and much reduced maximum crack width. Following the experimental study, a theoretical method is proposed for the calculation of the flexural strength and flexural stiffness of prestressed concrete piles considering the presence of both steel strands and deformed rebars. Furthermore, a finite element (FE) model has been developed to simulate the flexural performance of the piles. The accuracy of the FE model is validated through comparing with the experimental results, and subsequently parametric analyses are conducted to explore the influences of three parameters, including the prestressing level of the prestressing strands, prestressing strand ratio and deformed steel bar ratio, on the flexural performance of PSRC piles.