Thum Rule for Footing
1
Dear Sir, In Isolated footing, up to 300mm , uniform depth of footing is adopted and above 300mm, sloped footing is adopted with maximum depth near column suppor t and a minimum of 150mm at free end (200mm is adopted in practice). Footing dep th is arrived based on bending moment, one way shear and two way shear considera tion. For arriving quickly you can follow thumb rule. Thumb rule 1: D=650 times projection of footing in metre and depth of footing D is in mm. For example for a projection of (1.200- 0.230)/2=0.485m, D=309mm. say 300mm (Since depth is more adopt lesser depth than required). Thumb rule 2: Based on SBC of soil SBC in KN/m2 D/A value 50 1/7.5 100 1/5.5 150 1/5.0 200 1/4.5 250 1/4.0 300 1/3.5 For the same example if SBC is 150KN/m2 , A=1200mm D=1200/5.0=240mm. If sloped footing is adopted, increase 20% of this Value =1.20x240=288mm say 300mm. V.M.RAJAN.
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Transcript of Thum Rule for Footing
Dear Sir, In Isolated footing, up to 300mm , uniform depth of footing is adopted and above 300mm, sloped footing is adopted with maximum depth near column support and a minimum of 150mm at free end (200mm is adopted in practice). Footing depth is arrived based on bending moment, one way shear and two way shear consideration. For arriving quickly you can follow thumb rule. Thumb rule 1: D=650 times projection of footing in metre and depth of footing D is in mm. For example for a projection of (1.200- 0.230)/2=0.485m, D=309mm. say 300mm (Since depth is more adopt lesser depth than required). Thumb rule 2: Based on SBC of soil SBC in KN/m2 D/A value 50 1/7.5 100 1/5.5 150 1/5.0 200 1/4.5 250 1/4.0 300 1/3.5 For the same example if SBC is 150KN/m2 , A=1200mm D=1200/5.0=240mm. If sloped footing is adopted, increase 20% of this Value =1.20x240=288mm say 300mm. V.M.RAJAN.
