§27-610 Short-Span Concrete Floor and Roof Construction Supported on Steel Beams

In lieu of analysis, the following empirical procedures may be used for the design of short-span concrete floor and roof slabs containing draped reinforcement and supported on steel beams. The empirical equations described in subdivisions (c) and (d) of this section shall apply only where the steel beams are placed, or are encased, in a manner that will provide section for the transfer of shear from slabs to beams equivalent to, or in excess of, the slab thickness required by said equations.

(a) Concrete. The concrete shall have a minimum compressive strength at twenty-eight days of seven hundred psi.

(b) Reinforcement. Reinforcement shall consist of steel fabric, rods, or other suitable shapes that shall be continuous or successively lapped to function as a continuous sheet. The main reinforcement shall be at least 0.15% of the gross cross section where continuous steel fabric is used and at least 0.25% of the gross cross section where other forms of steel reinforcement are used. All reinforcing shall be draped, with the center of the reinforcement at the center of the span one inch above the bottom of the slab and the center of reinforcement over the support one inch below the top of the slab.

(c) Minimum slab thickness. The minimum total thickness of concrete floor and roof construction shall be determined by the following formula, but shall not be less than four inches:



where:
t = total thickness (in.)
L = clear span between steel flanges (ft.)
w = gross uniform load (dead load plus reduced live load) (psf).


d) Allowable Load. The allowable load shall be determined by the following formula:



where:
w = gross uniform load (psf)
A_s = cross sectional area of main reinforcement (sq. in. per ft. of slab width)
L = clear span between steel flanges in feet. (L shall not exceed ten feet in any case, and when the gross floor load exceeds two hundred psi shall not exceed eight feet)
C = the following coefficient for steel having an ultimate strength of at least fifty-five thousand psi;

1. For lightweight aggregate concrete:
   1. twenty thousand when reinforcement is continuous.
   2. fourteen thousand when reinforcement is hooked or attached to one or both supports.
2. For stone concrete:
   1. twenty-three thousand when reinforcement is continuous.
   2. fifteen thousand when reinforcement is hooked or attached to one or both supports.

(1) When the above formula is used the reinforcement shall be hooked or attached to one or both supports or be continuous.

(2) If steel of an ultimate strength in excess of fifty five thousand psi is used, the above coefficient may be increased in the ratio of the ultimate strength to fifty five thousand but at most by thirty percent.

(e) Openings in floors and roofs. Openings more than one foot six inches on a side shall be framed. All areas encompassing multiple openings aggregating more than one foot six inches in any ten foot width or span of floor or roof slab shall be framed.