Is it structural acceptable to use a min. steel reinforcement ratio of 0.0018 for the design of grade beams when using Fy = 60 ksi & F'c = 3 ksi based on ACI 318?
I'm not as familiar with ACI as I am with CSA, but if the member is meant to act like a 'beam' (horizontally oriented flexural member spanning between supports) I believe it should be detailed as one.
My answer is no, If the grade beam is resisting flexure than minimum reinf should be supplied on all tension faces and should be proportioned based on the requirements for beams.