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Spread Footing Verification ExampleReference: Reinforced Concrete – Mechanics and Design, 5th Edition, by Wright and MacGregor,Prentice Hall, 2009. Example 15-2.A square spread footing supports an 18-in square supporting a service dead load of 400 kips and aservice live load of 270 kips. The column is built with 5000-psi concrete and has 8 #9 longitudinal barswith fy 60 ksi. Design the footing to be constructed using 3000-psi concrete. The top of the footingis covered with 6-in of fill with a density of 120 pcf and a 6-in basement floor with a load of 100 psf.The allowable pressure of the soil is 6000 psf.U 1.4 D 1.4 x 400 560 kipsU 1.2 D 1.6 L 1.2 x 400 1.6 x 270 912 kips (controls)- Try an 11’-2” x 32” thick footing (d 28”). Check punching shear.Factored net soil pressure 912/11.172 7.31 ksfThe critical shear perimeter is a square which side is 18” 28” 46”Vu 7.31[11.172 – (46/12)2] 805 kipsφVc 0.75 x 4 3000 x 46 x 4 x 28 847 kips Vu OK- Check one-way shear.Vu 7.31[11.17 x (30/12)] 204 kipsφVc 0.75 x 2 3000 x 134 x 28 308 kips Vu OK- Design the flexural reinforcement.Mu 7.31[11.17 x (58/12)2 / 2] 954 kipsTry 11 #8 bars each way (As 8.69 in2)a 8.69 x 60 / (0.85 x 3 x 134) 1.53 in (tension controlled)φMn 0.9 x 8.69 x 60 (28 – 1.53/2) 1065 k-ft Mu OKASDIP Foundation is available for purchase online at asdipsoft.comPage 1

- Check the development.The clear spacing exceeds 2db and the clear cover exceeds db, thereforeLd 60000/(20 3000) db 54.8 x 1” 54.8” OK- Design the column-footing joint.The allowable bearing on the footing is 0.85 x 0.65 x 3 x 182 x 2 1070 kipsThe allowable bearing on the base of the column is 0.85 x 0.65 x 5 x 182 895 kips (controls)Area of dowels required (912 – 895)/(0.65 x 60) 0.44 in2Area of dowels minimum 0.005 x 182 1.62 in2 (controls)Use 4 #6 dowels. Extend dowels 25” into column.ASDIP Foundation is available for purchase online at asdipsoft.comPage 2

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