Electrical Duct-Bank Concrete Encasement Volume
Concrete for an electrical duct bank - the encasement around a bundle of conduits: net area = bank width x height - conduits x pi/4 x OD^2; volume = net area x length / 27. A 24 x 18 in bank around six 4.5 in-OD conduits over 100 ft is 8.66 cy (9.1 cy with 5% waste); a bigger 30 x 24 in bank is 16 cy - the envelope, not the conduits, drives the pour. Order right so it finishes in one continuous lift with no cold joint; the engineer sets the encasement.
Formula and source
net_area_ft2 = bank_width_ft x bank_height_ft - num_conduits x (PI/4) x (conduit_od_in/12)^2; volume_cy = net_area_ft2 x length_ft / 27; ordered_cy = volume_cy x (1 + waste_pct/100).
Duct-bank encasement identity by name (bank cross-section minus conduits, times the run); first-principles volume arithmetic.
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