Info

strength, fy, psib

Without edge beams

With edge beamsc

Interior panels

Without edge beams

With edge beamsc

Interior panels

4G,GGG

in 33

in 36

in 36

in 36

in 4G

in 4G

6G,GGG

in 3G

in 33

in 33

in 33

in 36

in 36

a Minimum thickness for slabs without drop panels is 5 in. Minimum thickness for slabs with drop panels is 4 in. b For values of reinforcement yield stress between 40,000 and 60,000 psi, minimum thickness shall be obtained by linear interpolation.

c Slabs with beams between columns along exterior edges. The value of a for the edge beam shall not be less than 0.8.

a Minimum thickness for slabs without drop panels is 5 in. Minimum thickness for slabs with drop panels is 4 in. b For values of reinforcement yield stress between 40,000 and 60,000 psi, minimum thickness shall be obtained by linear interpolation.

c Slabs with beams between columns along exterior edges. The value of a for the edge beam shall not be less than 0.8.

ratio l2/l1 = 20/24 = 0.833. From Table 7.3, the column strip moment is 60% of the total moment.

Moment to column strip = 0.60 x 146.5 = 87.9 kip-ft

Moment to middle strip = 0.40 x 146.5 = 58.6 kip-ft

For the distribution of support moment Ms between column and middle strips, use Table 7.4. Since a1 = 0, and l2/l1 = 0.833, from Table 7.4, the column strip moment is 75% of the total moment.

Moment in column strip = 0.75 x 272.2 = 204 kip-ft

Exterior Span. The magnitude of the moments at critical sections in the exterior span is a function of both M0, the simple beam moment, and aec, the ratio of stiffness of exterior equivalent column to the sum of the stiffness of the slab and beam framing into the exterior joint. Instead of computing aec, we use edge condition (d) given in Fig. 7.20 to evaluate the design moments at critical sections. At the exterior column face:

At midspan:

At the interior column face:

Figure 7.20. One-way solid slab, unit quantities: (a) reinforcement; (b) concrete.

At the exterior edge of the slab, the transverse distribution of the design moment to the column strip is given in Table 7.5. Instead of calculating the value of b, we conservatively assign 100% of the exterior moment to the column strip.

The moment to the column strip = 1 x 125.6 kip-ft. The middle strip is assumed to be controlled by the minimum steel requirements, an assumption which is satisfactory in almost all practical designs.

7.2.4. Unit Structural Quantities

Quantities used in cost estimates are physical items of construction to which unit costs are applied to arrive at a total construction cost. These are relatively easy to obtain once complete working drawings and specifications have been prepared. Prior to this point, however, the estimator or engineer must use "conceptual estimating" to determine approximate cost. Conceptual estimates require considerable judgment to correct so-called average unit costs to reflect complexity of construction operations, expected time required for construction, etc.

Typically, in the United States, units of structural quantities are dimensional, based on linear feet, square feet, or cubic feet. These result in unit quantities such as pounds per linear foot (plf), pounds per square foot (psf), etc.

Reinforcement and concrete unit quantities for various concrete floor-framing systems are shown in Figs 7.20-7.25. Live loads shown in the figures are working loads, and range

Figure 7.21. One-way pan joist, unit quantities: (a) reinforcement; (b) concrete.
Figure 7.22. Two-way slab, unit quantities: (a) reinforcement; (b) concrete.

from a typical office live load of 50 psf to a maximum of 200 psf appropriate for heavily loaded warehouse floors. The rebar quantities shown are for reinforcement required by design and do not include bars required for temperature and crack control, support bars, additional lengths required for laps, etc. The engineer should make allowances for these in the preliminary estimates by making appropriate notations on the preliminary drawings.

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