COMBINED FOOTING DESIGN | DESIGN OF COMBINED FOOTING|Combined footing design as per IS code 456 | Design of Combined Footing excel

# Combined footing design as per IS code 456 | Design of Combined Footing excel

## COMBINED FOOTING DESIGN IS 456

#### Footing Size Design

• Moment in x dir Mux
• Moment in y dir Muy
• c/c dist b/w col in x dir
• c/c dist b/w col in y dir
• Col Dim x dir

#### SBC

Footing Size required A   req
Footing Size Provided L B
Area Provided A p COMBINED FOOTING DESIGN

We have uploaded the combined footing design in excel sheet for your reference purpose. this is purely for educational purposes. if some of you have found any doubt kindly comment below so that we will clear your doubts

### why we use a combined footings design?

1. If two footings (isolated footing) overlapped.

2. subsoil condition is poor

3. To balance eccentric isolated footing combined footing excel download

1. slab design

2. shear check

## COMBINED FOOTING DESIGN AS PER EUROCODE

1. Footing has two columns
2. 300mm square column has 100kN and 500kN live and dead loads respectively
3. 400mm square column has 200kN and 800kN live and dead loads respectively
4. Spacing of columns 3m
5. fck = 30N/mm2
6. fyk = 500N/mm2
7. Assumed footing thickness 500mm
8. Allowable bearing pressure 200N/mm2
9. Assume effective depth 440mm for initial calculations

### 2. Calculation of required footing area

Net bearing pressure    = 200-25X.500
= 187.5N/mm2

Service load                 = 100 + 500 + 200 + 800
= 1600kN

Required footing area  = 1600/187.5
= 8.53m2

Select footing dimensions as 4.3m X 2m

### 3. Calculation of center of gravity

Take moment about center of 300mm square column

x          =  (200+800)X3/(100+500+200+800)
= 1.875m

### 4. Calculation of Bearing Pressure

Design Load         = (1.35X800+1.5*200) + 1.35x500+1.5x100)
= 2205kN

Pressure                = 2205/(4.3*2)
= 257N/mm2

### 5. Check for Punching Shear

Max. Shear Resistance   = 0.5ud[0.6(1-fck/250)](fck/1.5)

At 300mm column face
= 0.5*300*4*440*0.6*(1-30/250)*(30/1.5)
= 2788kN > (1.35*500+1.5*100 = 825kN)
At 400mm column face
= 0.5*400*4*440*0.6*(1-30/250)*(30/1.5)
= 3717kN > (1.35*800+1.5*200 = 1380kN)

Hence, Punching Shear is safe

Maximum bending was calculated

It was 209kNm, and it occurred at1.05m from 300mm square column

### 6. Design for Bending

Longitudinal reinforcements

MEd                              = 209kNm
K                                    = M/[b*(d^2)*fck]
K                                    = 209*E6/[1000*(440^2)*30]
K                                    = 0.04

Kbal = 0.167 (balance condition is taken based on x = 0.45d)
Therefore

K<Kbal

Compression reinforcement is not required

z                                     = d[0.5+(0.25-K/1.134)^0.5]
z                                     = 440[0.5+(0.25-0.04/1.134)^0.5]
z                                     = 424mm  (Z/d = 0.96>0.95)
Therefore
Z                                    = 0.95*440
= 418mm
As                                  = M/(0.87*fyk*z)
As                                  = 209*E6/(0.87*500*418)
= 1150mm2

As min.                        = 0.15*b*d/100
= 0.15*1000*440/100
= 660mm2
Therefore,

Proved #16@150mm spacing

### 7. Transverse reinforcements

Bending Moment   = 257*(1^2)/2
MEd                             = 128.5kNm
K                                    = M/[b*(d^2)*fck]
K                                    = 128.5*E6/[1000*(440^2)*30]
K                                    = 0.022

Kbal = 0.167 (balance condition is taken based on x = 0.45d)

Therefore

K<Kbal

Compression reinforcement is not required
z                                     = d[0.5+(0.25-K/1.134)^0.5]
z                                     = 440[0.5+(0.25-0.022/1.134)^0.5]
z                                     = 431mm  (Z/d = 0.97>0.95)
Therefore
Z                                    = 0.95*431
= 409.5mm
As                                  = M/(0.87*fyk*z)
As                                  = 128.5*E6/(0.87*500*409.5)
= 722mm2

As min.                        = 0.15*b*d/100
= 0.15*1000*440/100
= 660mm2

Provide #12@150mm spacing Name

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Combined footing design as per IS code 456 | Design of Combined Footing excel
COMBINED FOOTING DESIGN | DESIGN OF COMBINED FOOTING|Combined footing design as per IS code 456 | Design of Combined Footing excel