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ARCH3355_2013_04_16_Foundation_Design

# Wall footings example ld tension in bottom of footing

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Unformatted text preview: ion in bottom of footing face of wall [critical section for moment] f two-way or punching h s is the effective depth “d”hear line distance from top of the shear line one-way footing to the centroid of c d the reinforcing steel g ld one-way shear line c upward soil pressure ld d 3” cover two-way or punching shear line d 3” cover ld e h d distance “d” from the face of the wall [critical section for shear] a face of wall [critical sd/2 for moment] ection d d d distance “d” from the d face of the wall [critical section for shear] column load [P] e g face of wall [critical section for moment] f h d g two-way or punching shear line h c tension reinforcing 12” 36” 5’ below grade c upward soil pressure #8 bar [1in dia] d d d d Step 03: Check for Shear at Critical Section [Face of Wall] d tension reinforcing face of column: [critical section for moment] development length of reinforcing steel tension in bottom of footing Concrete strength: Steel Strength: Dead Load: Live Load: Max Soil Pressure: f’c = 3000psi, 12” fy = 60,000psi, 14,000 lb/ft of wall length, 7,000 lb/ft of wall length, 3,500 lb/ft2 12” ld d = 12in - 3in – 0.5in = 8.5in V = (3ft – d)(1ft)(qs) = (3ft – 0.708ft)(1ft)(4500lb/ft2) = 10,314lb à༎ Actual Shear 12” ld #4 bars [7in o.c.] d 3” cover ld ld 12” Mu = qs(I2)/2 = 4,500(32)/2 = 20,250 ft-lb Allowable Shear [ACI Code]: d d The leg of the footing acts as an inverted cantilever beam: 12” #8 bar [1in dia] d d Step 04: Find the Moment [Face of Wall] ld 12” 36” 5’ below grade d d 3” cover ld 12” #4 bars [7in o.c.] d V = Φ2√fcbd = 0.85(2)√3000(12)(8.5) = 9,497lb à༎ since actual shear > allowable shear à༎ Need to 14” a 14” deep footing d try V = Φ2√fcbd = 0.85(2)√3000(12)(10.5) = 11,732lb #5 bars [8in o.c.] à༎ now actual shear < allowable shear à༎ 14” deep footing OKAY! ARCH3355 | Construction III | Spring 2013 effective depth “d” is th distance from top of th footing to the centroid the reinforcing steel ld Find the required depth, width, and reinforcement for the following load: 12” d 3” cover one-way shear line development length of reinforcing steel tension in bottom of footing f’c = 3000psi, 12” fy = 60,000psi, 14,000 lb/ft of wall length, 7,000 lb/ft of wall length, 3,500 lb/ft2 two-way or punching shear line Designing Wall Footings: Example face of column: [critical section for moment] Find the required depth, width, and reinforcement for the f...
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