Assume you mean the grade beam has piles supporting it along its length, centered on the width of the grade beam. As long as the piles are located within the tolerance dictated by the grade beam, should be no need for pile caps. The pile is just a column, and the grade beam works like any other beam.
IBC 1808.2.4 states that "pile caps shall have at least 4" beyond the edges of piles". If the grade beam is "integral" with the pile cap, does that mean that the grade beam has to be 8" wider than the pile?
I have an 18" grade bm and a 16" pile and I don't want to make that contractor pour 50 unnecessary pile caps. If the 4" edge requirement is for tolorances, it seems logical to simply provide an alternate detail for misplaced piles.
A single row of piles under a grade beam is considered unstable. The building code that you are working under will likely require some type of restraint against latral movement. This could be intersecting grade beams, pilecaps or corners. If you consider a fairly heavily loaded pile placed at the maximum allowable tolerance there will be a moment generated that has to be resisted by something. If you are able to develop the moment capacity at the interface will the combination of pile/grade beam have sufficient stiffness to resist rotation/translation which will generate even larger stresses.
A single row of piles under a grade beam can be used as long as the piles can resist axial and lateral forces, and moments. Load eccentricity must be assumed to allow for construction tolerance when placing piles. The design eccentricity is typically 75 - 80mm in my experience but your local codes may dictate otherwise.
You may want to pour 24x24 pile caps such that the top of the cap is the bottom of the beam. Bring a couple of U's through the cap to tie into the beam. Then your contractor can run continous forms for the grade beams. Keep the pile caps 2ft square and this should be a prety slick operation.
