The AWC's Prescriptive Residential Deck Design Guide has a table for footings. Unfortunately, your 20 foot beam span is off the footing sizing charts. Max the table goes up to is 18 ft span. Not to say it can't be done, but thats what the PRDGG maxes out at.
Are you going to cantilever the joists at all? Cantilever the outside end of the beams a foot or two? Read the guide, and you'll get a better idea of what I'm talking about. Page 9. It's free on the internet.
Footing reinforcement calcs come from ACI's SP-17 design handbook. If doing or paying for the calcs isn't in the cards, try talking to the building code official. He might give you some direction and possibly tell you what he'd be comfortable with.
Are you going to cantilever the joists at all? Cantilever the outside end of the beams a foot or two? Read the guide, and you'll get a better idea of what I'm talking about. Page 9. It's free on the internet.
Footing reinforcement calcs come from ACI's SP-17 design handbook. If doing or paying for the calcs isn't in the cards, try talking to the building code official. He might give you some direction and possibly tell you what he'd be comfortable with.
