A New Design Method for Shear in Prestressed Concrete Girders

摘要

Five full-scale prestressed concrete I-beams were tested to explore the effect of three variables: the shear-span-to-depth ratio (a/d), the transverse steel ratio ρ_t, and the presence of draped strands, on the web-shear and the flexural-shear capacity. The results from these five tests, together with 143 test beams found in literature, were used to develop an accurate, yet simple, equation for the shear strengths of prestressed concrete beams. This new equation is a function of the a/d ratio, the strength of concrete √f_c', the web area b_wd, and the ρ_t ratio. Although the ACI and AASHTO shear provisions include two other variables, namely, the prestress force and the angle of failure crack, this study showed that these two variables had no significant effect on the shear capacity. In addition, a new formula was derived to preclude the web crushing of concrete before the yielding of transverse steel, and the ACI minimum stirrup requirement was evaluated. The new shear design method has been compared with the shear provisions of the ACI 318-08 and the AASHTO specifications. Finally, the simplicity and rationality of the new method has also been illustrated by a design example.