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Structural Concrete - Hassoun

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462 Chapter 13 Footings<br />

13 no. 7 bars each direction<br />

Figure 13.18<br />

Example 13.2: Square footing.<br />

3. Net upward pressure equals (factored load)/(area of footing):<br />

P u = 1.2D + 1.6L<br />

= 1.2 × 245 + 1.6 × 200 = 614 K<br />

Net upward pressure, q u = 614 = 6.14 ksf<br />

10 × 10<br />

4. Check depth due to two-way shear. If no shear reinforcement is used, two-way shear determines<br />

the critical footing depth required. For an assumed total depth of 24 in., calculate d to the centroid<br />

of the top layer of the steel bars to be placed in the two directions within the footing. Let the bars<br />

to be used be no. 8 bars for calculating d:<br />

d = 24 − 3(cover)−1.5(bar diameters) =19.5in.<br />

It is quite practical to assume d = h − 4.5 in.<br />

b 0 = 4(c + d) =4(18 + 19.5) =150 in.

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