Strengths

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Footing
2

• Failures
• 1.Bearing failure
• 2.Serviceability failure
• 3.Excessive total settlement

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P
M
Centroidal Axis
P/A
My/I
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Pc0
240 lb/ft2
300 lb/ft2
540 lb/ft2
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Pc
240 lb/ft2
2 ft of soil _at_120 lb/ft3
300 lb/ft2
2 ft of concrete _at_150 lb/ft3
540 lb/ft2
Gross soil pressure 540qn lb/ft3
qnPc/A
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P
M
Net soil pressure
qnPc/A
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Only Dead load and Live load
Area of footing
Including Wind load also
Area of footing
or
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Isolated footing with axial load and moment
Design Input

• Grade of concrete
• Grade of steel
• Allowable soil pressure
• Column load
• Moment
• Condition about overburden of soil

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Design procedure
Checking the footing area

• Assume column size
• Assume footing size
• Total loadwt of footingcolumn load
• Average soil pressure q total load / footing
  area
• Allowable soil pressure gt Average soil pressure
• then footing are is ok

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Finding factored loads

• Factored column load1.4xdead load1.7xlive load
• Average factored soil pressure qnetFactored
  column load/footing area

• Average dvtotal thick cover - bar dia
• Eccentricity eMu/Pu

• Solving two equations to get q1 and q2
• Service load equation
• Vertical equilibrium

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Check for One way shear

• Take the critical section as d distance from
  the
• face of the column (as per ACI 318 )
• 1.find pressure at critical section
• 2.find Vu
• 3.find Vu
• If VugtVu

Check for Two way shear

• Take the critical section as d/2 distance all
  around
• the face of the column (as per ACI 318 )
• find pressure at critical section
• Find the value of bo
• 2.find Vu
• 3.find Vu is smallest of these

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Safe against two way shear Otherwise increase
the depth
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Check for flexural reinforcement
Max moment occurs at the face of the column

• Find average pressure
• Find required moment MnMu/
• Find required Ast
• Min Ast0.0018bh
• Max spacing18 in

Development length
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Thank You
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