Shear Strengths of Prestressed Concrete Beams Part 1: Experiments and Shear Design Equations

In this paper Part I, five full-scale prestressed concrete I-beams were tested to study the effect of three variables: the shear span-depth ratio (a/d), the transverse steel ratio (rho(iota)), and the presence of harped strands on the web shear and the flexural shear capacity The results from these tests, together with those 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 shear span-depth ratio (a/d), the strength of concrete root f(c)', the web area b(w)d, and the rho(iota) 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 for the maximum shear strengths to preclude the web crushing of concrete before the yielding of transverse steel. The ACI minimum stirrup requirement was also evaluated. In the Part 2 paper given in this same journal issue, the proposed shear design method will be compared to the shear provisions in the ACI 318-08 and the 2007 AASHTO LRFD Specifications.