Isolated footing design

Isolated Footing Design (IS 456-2000)

Design For Isolated Footing 1




Isolated Footing 1

Footing No. Group ID Foundation Geometry

- - Length Width Thickness

1 1 1.150m 1.150m 0.230m

Footing No. Footing Reinforcement Pedestal Reinforcement

- Bottom Reinforcement(Mz) Bottom Reinforcement(M

x) Top Reinforcement(M

z) Top Reinforcement(M

x) Main Steel Trans Steel

1 Ø8 @ 140 mm c/c Ø8 @ 140 mm c/c N/A N/A N/A N/A



2 2 1.150m 1.150m 0.230m









7 3 1.150m 1.150m 0.230m









8 4 1.150m 1.150m 0.230m







Page 1 of 42Isolated Footing Design

22/08/2013file:///F:/Staad%20Foundation%20Advanced/CalcXsl/footing.xml

Input Values

Footing Geomtery

Column Dimensions

Pedestal

Design Type : Calculate Dimension

Footing Thickness (Ft) : 230.000mm

Footing Length - X (Fl) : 900.000mm

Footing Width - Z (Fw) : 900.000mm

Eccentricity along X (Oxd) : 0.000mm

Eccentricity along Z (Ozd) : 0.000mm

Column Shape : Rectangular

Column Length - X (Pl) : 0.230m

Column Width - Z (Pw) : 0.230m

Include Pedestal? No

Pedestal Shape : N/A

Pedestal Height (Ph) : N/A

Pedestal Length - X (Pl) : N/A

Pedestal Width - Z (Pw) : N/A



Design Parameters

Concrete and Rebar Properties

Soil Properties

Sliding and Overturning

Global Settings

Unit Weight of Concrete : 25.000kN/m3

Strength of Concrete : 20.000N/mm2

Yield Strength of Steel : 415.000N/mm2

Minimum Bar Size : Ø8

Maximum Bar Size : Ø16

Pedestal Minimum Bar Size : Ø12

Pedestal Maximum Bar Size : Ø32

Minimum Bar Spacing : 50.000mm

Maximum Bar Spacing : 200.000mm

Pedestal Clear Cover (P, CL) : 50.000mm

Footing Clear Cover (F, CL) : 75.000mm

Soil Type : Drained

Unit Weight : 18.000kN/m3

Soil Bearing Capacity : 200.000kN/m2

Soil Bearing Capacity Type: Gross Bearing Capacity

Soil Surcharge : 0.000kN/m2

Depth of Soil above Footing : 2800.000mm

Cohesion : 0.000kN/m2

Min Percentage of Slab in Contact: 0.000

Coefficient of Friction : 0.500

Factor of Safety Against Sliding : 1.500

Factor of Safety Against Overturning : 1.500

Top Reinforcement Option : Calculate only when foundation is subjected to uplift forces

Concrete Design Option : Gross Pressure

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Design Calculations

Load Combination/s- Service Stress Level

Load Combination

Number Load Combination Title

1

2

101 1.000 x DL

102 1.000 x DL+1.000 x LL

Load Combination/s- Strength Level

Load Combination

Number Load Combination Title

1

2

201 1.500 x DL



202 1.500 x DL+1.500 x LL

Applied Loads - Service Stress Level

LC Axial(kN)

Shear X (kN)

Shear Z (kN)

Moment X (kNm)

Moment Z(kNm)

1 86.584 -0.716 -0.716 0.000 0.000

2 18.000 -0.204 -0.204 0.000 0.000

101 86.584 -0.716 -0.716 0.000 0.000

102 104.584 -0.920 -0.920 0.000 0.000

Applied Loads - Strength Level

LC Axial

(kN)

Shear X

(kN)

Shear Z

(kN)

Moment X

(kNm)

Moment Z

(kNm)

1 86.584 -0.716 -0.716 0.000 0.000

2 18.000 -0.204 -0.204 0.000 0.000

201 129.876 -1.074 -1.074 0.000 0.000

202 156.876 -1.380 -1.380 0.000 0.000

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Footing Size

Initial Length (Lo) = 0.900m

Initial Width (Wo) = 0.900m

Uplift force due to buoyancy = 0.000kN

Effect due to adhesion = 0.000kN

Area from initial length and width, Ao = L

o X W

o = 0.810m2

Min. area required from bearing pressure, Amin

= P / qmax

= 0.721m2

Note: Amin

is an initial estimation.

P = Critical Factored Axial Load(without self weight/buoyancy/soil). q

max = Respective Factored Bearing Capacity.

Final Footing Size

Length (L2) = 1.150 m Governing Load Case : # 1

Width (W2) = 1.150 m Governing Load Case : # 1

Depth (D2) = 0.230 m Governing Load Case : # 1

Area (A2) = 1.323 m2

Depth is governed by Ultimate Load Case

(Service check is performed with footing thickness requirements from concrete check)

Final Soil Height = 2.570 m

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Pressures at Four Corner



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.

Load Case

Pressure at

corner 1 (q1)

(kN/m2)

Pressure at

corner 2 (q2)

(kN/m2)

Pressure at

corner 3 (q3)

(kN/m2)

Pressure at

corner 4 (q4)

(kN/m2)

Area of

footing in

uplift (Au)

(m2)

102 130.9101 129.2403 127.5704 129.2403 0.000

102 130.9101 129.2403 127.5704 129.2403 0.000

102 130.9101 129.2403 127.5704 129.2403 0.000

102 130.9101 129.2403 127.5704 129.2403 0.000

Summary of adjusted Pressures at Four Corner

Load Case

Pressure at

corner 1 (q1)

(kN/m2)

Pressure at

corner 2 (q2)

(kN/m2)

Pressure at

corner 3 (q3)

(kN/m2)

Pressure at

corner 4 (q4)

(kN/m2)

102 130.9101 129.2403 127.5704 129.2403

102 130.9101 129.2403 127.5704 129.2403

102 130.9101 129.2403 127.5704 129.2403

102 130.9101 129.2403 127.5704 129.2403

Details of Out-of-Contact Area (If Any)

Governing load case = N/A

Plan area of footing = 1.323sq.m

Area not in contact with soil = 0.000sq.m

% of total area not in contact = 0.000%

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Check For Stability Against Overturning And Sliding

- Factor of safety against sliding Factor of safety against overturning

Load Case

No.

Along X-

Direction

Along Z-

DirectionResultant

W.R.T. X-

Direction

W.R.T. Z-

Direction

1 106.757 106.757 75.489 533.785 533.785

2 206.747 206.747 146.192 1033.733 1033.733

101 106.757 106.757 75.489 533.785 533.785

102 92.875 92.875 65.672 464.373 464.373

Critical Load Case And The Governing Factor Of Safety For Overturning and Sliding X Direction

Critical Load Case for Sliding along X-Direction : 102

Governing Disturbing Force : -0.920kN



Governing Restoring Force : 85.460kN

Minimum Sliding Ratio for the Critical Load Case : 92.875

Critical Load Case for Overturning w.r.t. X-Direction : 102

Governing Overturning Moment : -0.212kNm

Governing Resisting Moment : 98.277kNm

Minimum Overturning Ratio for the Critical Load Case : 464.373

Critical Load Case And The Governing Factor Of Safety For Overturning and Sliding Z Direction

Critical Load Case for Sliding along Z-Direction : 102

Governing Disturbing Force : -0.920kN



Critical Load Case for Overturning w.r.t. Z-Direction : 102

Governing Overturning Moment : 0.212kNm

Governing Resisting Moment : 98.277kNm

Minimum Overturning Ratio for the Critical Load Case : 464.373

Critical Load Case And The Governing Factor Of Safety For Sliding Along Resultant Direction

Critical Load Case for Sliding along Resultant Direction :

102

Governing Disturbing Force : 1.301kN



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Compression Development Length Check

Development length skipped as column reinforcement is not specified in input (Column Dimnesion Task Pane)

Top Reinforcement Design Requirement

Top Reinforcement needs to be provided because of resultant negative pressure coming from net pressure calculations for bending. Please check 'Always Calculate Top Reinforcement Option' from Global Settings

Moment Calculation

Check Trial Depth against moment (w.r.t. Z Axis)

Critical Load Case = #202

Effective Depth = = 0.151m

Governing moment (Mu) = 20.647kNm

As Per IS 456 2000 ANNEX G G-1.1C

Limiting Factor1 (Kumax

) = = 0.479107

Limiting Factor2 (Rumax

) = = 2755.432917kN/m2

Limit Moment Of Resistance (Mumax

) = = 72.249306kNm

Mu <= M

umax hence, safe

Check Trial Depth against moment (w.r.t. X Axis)




Effective Depth = = 0.151m

Governing moment (Mu) = 20.647kNm

As Per IS 456 2000 ANNEX G G-1.1C

Limiting Factor1 (Kumax

) = = 0.479107

Limiting Factor2 (Rumax

) = = 2755.432917kN/m2

Limit Moment Of Resistance (Mumax

) = = 72.249306kNm

Mu <= M

umax hence, safe

------------------------------------------------------

Shear Calculation

Check Trial Depth for one way shear (Along X Axis)

(Shear Plane Parallel to X Axis)

Critical Load Case = # 201

DX = 0.309m

Shear Force(S) = 52.975kN

Shear Stress(Tv) = 305.066010kN/m2

Percentage Of Steel(Pt) = 0.1999

As Per IS 456 2000 Clause 40 Table 19

Shear Strength Of Concrete(Tc) = 326.161kN/m2

Tv< T

c hence, safe

Check Trial Depth for one way shear (Along Z Axis)

(Shear Plane Parallel to Z Axis)



Critical Load Case = # 201

DZ = 0.309m



Percentage Of Steel(Pt) = 0.1999

As Per IS 456 2000 Clause 40 Table 19

Shear Strength Of Concrete(Tc) = 326.161kN/m2

Tv< T

c hence, safe

Check Trial Depth for two way shear




As Per IS 456 2000 Clause 31.6.3.1

Ks = = 1.000

Shear Strength(Tc)= = 1118.0340kN/m2

Ks x T

c = 1118.0340kN/m2

Tv<= K

s x T

c hence, safe

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Reinforcement Calculation



Calculation of Maximum Bar Size

Along X Axis

Bar diameter corresponding to max bar size (db) = 8mm

As Per IS 456 2000 Clause 26.2.1

Development Length(ld) = = 0.360m

Allowable Length(ldb

) = = 0.385m

ldb

>=ld hence, safe

Along Z Axis

Bar diameter corresponding to max bar size(db) = 8mm

As Per IS 456 2000 Clause 26.2.1

Development Length(ld) = = 0.360m

Allowable Length(ldb

) = = 0.385m

ldb

>=ld hence, safe

Bottom Reinforcement Design Along X Axis

For moment w.r.t. X Axis (Mz)

As Per IS 456 2000 Clause 26.5.2.1


Minimum Area of Steel (Astmin

) = 317.400mm2

Calculated Area of Steel (Ast

) = 397.611mm2

Provided Area of Steel (Ast,Provided

) = 397.611mm2

Astmin

<= Ast,Provided

Steel area is accepted

Selected bar Size (db) = Ø8

Minimum spacing allowed (Smin

) = 48.000mm

Selected spacing (S) = 141.714mm



Based on spacing reinforcement increment; provided reinforcement is

Based on spacing reinforcement increment; provided reinforcement is

Smin

<= S <= Smax

and selected bar size < selected maximum bar size...

The reinforcement is accepted.

Ø8 @ 140.000mm o.c.

Bottom Reinforcement Design Along Z Axis

For moment w.r.t. Z Axis (Mx)

As Per IS 456 2000 Clause 26.5.2.1


Minimum Area of Steel (Astmin

) = 317.400mm2

Calculated Area of Steel (Ast

) = 397.611mm2

Provided Area of Steel (Ast,Provided

) = 397.611mm2

Astmin

<= Ast,Provided

Steel area is accepted

Selected bar Size (db) = Ø8

Minimum spacing allowed (Smin

) = = 50.000mm

Selected spacing (S) = 141.714mm

Smin

<= S <= Smax

and selected bar size < selected maximum bar size...

The reinforcement is accepted.

Ø8 @ 140.000mm o.c.

Crack Width Calculation (for Mz)

Modulus of Elasticity of Concrete(Ec) = 22360679.775kN/m2 Clause No. 6.2.3.1

Modulus of Elasticity of Steel(Es) = 200000000.000kN/m2 Annexure F

Depth of Neutral Axis(Xu) = 0.072m

Annexure G, Clause No. G-1.1.a

Effective MOI(Ieff

) = 0.000m4

Average Steel Strain at Considered Level(Ɛm

) = 20.945 X 10-5

Distance from Nearest Tension Rod (acr

) = 0.106m



Crack Width (Wcr

) = 0.048mm Annexure F

From IS 456-2000 Clause No. 35.3.2

Crack Width calculated at critical tension face(bottom face) is less than 0.2 mm...Hence OK.

Crack Width Calculation (for Mx)

Modulus of Elasticity of Concrete(Ec) = 22360679.775kN/m2 Clause No. 6.2.3.1

Modulus of Elasticity of Steel(Es) = 200000000.000kN/m2 Annexure F

Depth of Neutral Axis(Xu) = 0.072m

Annexure G, Clause No. G-1.1.a

Effective MOI(Ieff

) = 0.000m4

Average Steel Strain at Considered Level(Ɛm

) = 20.945 X 10-5

Distance from Nearest Tension Rod (acr

) = 0.106m

Crack Width (Wcr

) = 0.048mm Annexure F

From IS 456-2000 Clause No. 35.3.2

Crack Width calculated at critical tension face(bottom face) is less than 0.2 mm...Hence OK.

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Isolated Footing 2

Input Values

Footing Geomtery

Column Dimensions

Pedestal

Design Type : Calculate Dimension

Footing Thickness (Ft) : 230.000mm

Footing Length - X (Fl) : 900.000mm

Footing Width - Z (Fw) : 900.000mm

Eccentricity along X (Oxd) : 0.000mm

Eccentricity along Z (Ozd) : 0.000mm

Column Shape : Rectangular

Column Length - X (Pl) : 0.230m

Column Width - Z (Pw) : 0.230m

Include Pedestal? No

Pedestal Shape : N/A

Pedestal Height (Ph) : N/A

Pedestal Length - X (Pl) : N/A



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Isolated footing design