COMBINED FOOTING.pdf

COMBINED FOUNDATION DESIGN (ACI 318-05)

Design For Combined Footing 1

Footing No. Left Overhang (m)

Right Overhang (m)

Length (m)

Width (m)

Thickness (m)

1 0.500 0.500 3.000 4.800 0.500

of 13Strip Footing Design

6/3/2011file://C:\Staad.foundation 5\CalcXsl\Combined.xml

Footing No. Footing Reinforcement - Main Steel Top Main Steel Bottom Secondary Steel Top Secondary Steel Bottom

1 #16 @ 4749 mm c/c #16 @ 4749 mm c/c #16 @ 4800 mm c/c #16 @ 4800 mm c/c



Combined Footing 1

Input Data

Geometry of Footing

Column Dimensions

Pedestal

Column Dimensions

Pedestal

For Column 34

Column Shape : Rectangular

Column Length - X (Pl) : 0.00 m

Column Width - Z (Pw) : 0.00 m

Include Pedestal? Yes

Pedestal Shape : Rectangular

Pedestal Height (Ph) : 2.80 m

Pedestal Length - X (Pl) : 0.60 m

Pedestal Width - Z (Pw) : 0.60 m

For Column 28

Column Shape : Rectangular

Column Length - X (Pl) : 0.00 m

Column Width - Z (Pw) : 0.00 m

Include Pedestal? Yes

Pedestal Shape : Rectangular

Pedestal Height (Ph) : 2.80 m



Cover and Soil Properties

Concrete and Rebar Properties

Pedestal Length - X (Pl) : 0.60 m

Pedestal Width - Z (Pw) : 0.60 m

Length of left overhang : 0.50 m

Length of right overhang : 0.50 m

Is the length of left overhang fixed? Yes

Is the length of right overhang fixed? Yes

Minimum Width of footing (Wo) : 2.50 m

Maximum Width of Footing (Wo) : 9000.00 mm

Minimum Thickness of footing (Do) : 500.00 mm

Maximum Thickness of Footing (Do) : 1500.00 mm

Maximum Length of Footing (Lo) : 9000.00 mm

Length Increment : 50.00 mm

Depth Increment : 50.00 mm

Pedestal Clear Cover : 50.00 mm

Footing Clear Cover : 50.00 mm

Unit Weight of soil : 960.00 kg/m3

Soil Bearing Capacity : 78.00 kN/m2

Soil Surcharge : 0.00 N/mm2

Depth of Soil above Footing : 1.30 m

Depth of Water Table : 1.00 m

Unit Weight of Concrete 24.000 kN/m3

Compressive Strength of Concrete : 18.300 N/mm2

Yield Strength of Steel : 392.000 N/mm2

Minimum Bar Size : 6

Maximum Bar Size : 8

Minimum Bar Spacing : 50.00 mm

Maximum Bar Spacing : 250.00 mm

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Design Calculations

Footing size calculations

Final footing dimensions are:

Reduction of force due to buoyancy = -11514.82 kgf

Minimum area required from bearing pressure,Amin = Pcritical/qmax : 12.87 m^2

Area from initial length and width,Ao = L x W: 7.50 m^2

Length of footing, L : 3.00 m

Width of footing, W : 4.80 m

Depth of footing, Do : 0.50 m

Area, A : 14.40 m^2

Length of left overhang, Lleft_overhang : 0.50 m

Length of right overhang, Lright_overhang : 0.50 m

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Applied Loads - Allowable Stress Level

LC Axial (kgf)

Shear X (kgf)

Shear Z (kgf)

Moment X (kNm)

Moment Z (kNm)

-

Column Number : 1

4 10222.026 0.000 0.000 0.000 0.000

5 42901.379 0.000 0.000 0.000 0.000

-

Column Number : 2

4 10222.022 0.000 0.000 0.000 0.000

5 42898.562 0.000 0.000 0.000 0.000



Applied Loads - Strength Level

LC Axial (kgf)

Shear X (kgf)

Shear Z (kgf)

Moment X (kNm)

Moment Z (kNm)

-

Column Number : 1

4 10222.026 0.000 0.000 0.000 0.000

5 42901.379 0.000 0.000 0.000 0.000

-

Column Number : 2

4 10222.022 0.000 0.000 0.000 0.000

5 42898.562 0.000 0.000 0.000 0.000



Calculated pressures at four corners

If Au is zero, there is no uplift and no pressure adjustment is necessary. Otherwise, to account for uplift, areas of

negative pressure will be set to zero and the pressure will be redistributed to remaining corners.

Summary of adjusted pressures at four corners

Load Case

Pressure at corner 1

(q1)

(kgf/m^2)


(q2)

(kgf/m^2)


(q3)

(kgf/m^2)


(q4)

(kgf/m^2)

Area of footing in

uplift (Au)

(sq. m)

5 7910.9153 7910.1328 7910.1328 7910.9153 0.00

5 7910.9153 7910.1328 7910.1328 7910.9153 0.00

5 7910.9153 7910.1328 7910.1328 7910.9153 0.00

5 7910.9153 7910.1328 7910.1328 7910.9153 0.00

Load Case

Pressure at corner 1 (q1)

(kgf/m^2)


(kgf/m^2)


(kgf/m^2)


(kgf/m^2)

5 7910.9153 7910.1328 7910.1328 7910.9153

5 7910.9153 7910.1328 7910.1328 7910.9153

5 7910.9153 7910.1328 7910.1328 7910.9153

5 7910.9153 7910.1328 7910.1328 7910.9153

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Check for stability against overturning:-

Load Case Moment X (kNm)

Moment Z (kNm)

Resisting Moment X

(kNm)

Resisting Moment Z

(kNm) Ratio X Ratio Z

4 0.000 0.000 1142.780 714.236 N/A 21046227.354

5 0.000 0.028 2680.966 1675.602 N/A 60656.672

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Calculations of Footing Thickness

Footing thickness is calculated based on the ultimate load cases

Check for Punching Shear

Effective depth, deff, increased until 0.75*Vc Punching Shear Force

Punchng Shear Force, Vu = 36406.89 kgf

Effective depth, deff, increased until 0.75*Vc Punching Shear Force

Punchng Shear Force, Vu = 36404.64 kgf

Check for One-Way Shear

For Column 1

Total Footing Depth, Do = 0.50m

Calculated Effective Depth,deff = Do - clear cover - Db/2 : 0.44 m

For rectangular column, = Bcol / Dcol : 1

From ACI Cl.11.12.2.1, for column

4.18 m

Equation 11-33, Vc1 402957.28 kgf

Equation 11-34, Vc2 419940.15 kgf

Equation 11-35, Vc3 268638.19 kgf

Punching shear strength,Vc=

0.75 x minimum of (Vc1,Vc2,Vc3) 201478.64 kgf

0.75 * Vc > Vu hence, OK

For Column 2

Total Footing Depth, Do = 0.50m

Calculated Effective Depth,deff = Do - clear cover - Db/2 : 0.44 m

For rectangular column, = Bcol / Dcol : 1

From ACI Cl.11.12.2.1, for column

4.18 m

Equation 11-33, Vc1 402957.28 kgf

Equation 11-34, Vc2 419940.15 kgf

Equation 11-35, Vc3 268638.19 kgf

Punching shear strength,Vc=

0.75 x minimum of (Vc1,Vc2,Vc3) 201478.64 kgf

0.75 * Vc > Vu hence, OK

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Critical load case for maximum shear force along the length of footing :

5

Critical Shear force,Vu For the critical load case: 7321.59 kgf

Point of occurance of Vu Critical one-way shear position: 1.244 m

From ACI c1. 11.3.1.1,Vc154389.76 kgf



0.75 x Vc = 115792.32 kgf

Since 0.75 * Vc > Vu hence, OK

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Design of flexure

Bottom Reinforcement

Top Reinforcement

Distribution Reinforcement

Critical load case : 4

Required Effective Depth : 0.44 m

, from ACI Cl.10.2.7.3 max[0.85-0.05x(Fc-4),0.65]= 0.8500

From ACI Cl. 10.3.2, 0.0204

From ACI Cl. 10.3.3, 0.0153

From ACI Cl. 7.12.2, 0.0020

Modular Ratio,m 25.2009

Ultimate Moment : 7.85 kNm

Point of occurrence of the ultimate moment along the length of footing :

0.48 m

Nominal Moment Capacity : 8.73 kNm

Required : 0.002000

Area of main steel required, As =

* W * deff :

7.44 in2

Critical load case : 4

Required Effective Depth : 0.44 m

, from ACI Cl.10.2.7.3 max[0.85-0.05x(Fc-4),0.65] 0.8500

From ACI Cl. 10.3.2, 0.0204

From ACI Cl. 10.3.3, 0.0153

From ACI Cl. 7.12.2, 0.0020

Modular Ratio,m 25.2009

Ultimate Moment : 25.05 kNm

Point of occurrence of the ultimate moment along the length of footing :

1.52 m

Nominal Moment Capacity : 27.84 kNm

Required : 0.002000

Area of main steel required, As = *

W * deff :

7.44 in2

Critical Moment for distribution steel : 92.0974 kNm

Nominal moment Capacity : 102.3304 kNm

Point of occurance of the critical moment : 0.5000 m

Required : 0.000444

Area of distribution steel required, As = * L *

deff :

4.65 in2

Provided minimum Area for distribution steel along Z(Top reinforcement), Astmin = 0.18% of

c/s :

4.65 in2



Provided Reinforcement

Based on spacing reinforcement increment; provided reinforcement is




Main bar no. for top Reinforcement: 16

Spacing of top reinforcement bar : 187.65 mm

# 16 @ 4749 mm o.c.

Main bar no. for bottom Reinforcement: 16

Spacing of bottom reinforcement bar : 187.65 mm

# 16 @ 4749 mm o.c.

Distribution bar no.: 16

Spacing of distribution bars : 190.00 mm

# 16 @ 4800 mm o.c.

Distribution bar no.(Top): 16

Spacing of distribution bars(Top) : 190.00 mm

# 16 @ 4800 mm o.c.

Print Calculation Sheet



COMBINED FOOTING.pdf

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