Dowels Needed: Large Pedestal to Mat Foundation
Dowels Needed: Large Pedestal to Mat Foundation
(OP)
I am going to be supporting a piece of equipment (dynamic considerations need not be considered) on a large 17.5' x 10.5' concrete pedestal (more like a mat). That pedestal will be sitting on top of a large concrete mat foundation.
I am needing to prescribe the amount/size of dowels that will be used to secure this pedestal to my foundation.
I feel as though I should not be using ACI's requirement of 0.005*Ag in this case because that would yield roughly 130 in^2 worth of dowels (17.5*10.5*144*0.005).
Has anyone had some experience with this type of situation before? What should I be considering when prescribing the dowels area of steel needed. TIA!
I am needing to prescribe the amount/size of dowels that will be used to secure this pedestal to my foundation.
I feel as though I should not be using ACI's requirement of 0.005*Ag in this case because that would yield roughly 130 in^2 worth of dowels (17.5*10.5*144*0.005).
Has anyone had some experience with this type of situation before? What should I be considering when prescribing the dowels area of steel needed. TIA!






RE: Dowels Needed: Large Pedestal to Mat Foundation
Assume the dowels are located 3" inside the pedestal faces.
Dowel location perimeter is 17'+10'+17'+10' = 54'
Say, a dowel is located every 6" along the dowel perimeter - therefore 108 dowels are needed. 130 in2 / 108 dowels = 1.2 in2 / dowel. This gives #10 bars for dowels @ 6".
I would temper that math with engineering judgement. Consider the size and spacing of rebar used for the pedestal - dowels most likely should be similar size and spacing. So, maybe #6, #7, or #8 dowels with spacing to match pedestal rebar.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Dowels Needed: Large Pedestal to Mat Foundation
RE: Dowels Needed: Large Pedestal to Mat Foundation
RE: Dowels Needed: Large Pedestal to Mat Foundation
I agree. The minimum reinforcing quantity originated as a means of preventing concrete creep from passively yielding the reinforcement in compression members. For that creep to occur, you'd need some minimum amount of compression stress in the concrete. With a 170 SF "pedestal", I doubt that you're there. Consequently, I don't feel that the ACI minimum applies here.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Dowels Needed: Large Pedestal to Mat Foundation
@KootK thank you for shining some light on how the provision came about. I feel better about prescribing a lesser steel amount now.
@SlideRuleEra I like your comments on an effective area. This piece of equipment sits on a skid. The skid runs 2 main beams down the length of the equipment. I am thinking about considering the effective area as the area beneath the 2beams at a 45 deg angle down to the mat because more or less this would be the area which is being engaged.