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Isolated footing with axial load and moment

Design Input

•Grade of concrete - 35•Grade of steel - 460•Allowable soil pressure – 200 KN/m2

•Column load – 1260 KN(D.L+L.L)•Moment – 100 kN.m•Condition about overburden of soil - No

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Design procedure

•Arrive footing size•Total load=wt of footing+column load•Average soil pressure q= total load / footing area

Allowable soil pressure > Average soil pressureThen footing are is ok

Checking the footing area

By ACI 318

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Finding factored loads

•Factored column load=1.4xdead load+1.7xlive load

•Average factored soil pressure qnet=Factored column load/footing area

•Average dv=total thick – cover - bar dia

•Eccentricity e = Mu/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 section2.find Vu

3.find Vu

If Vu>Vu

Check for Two way shear• Take the critical section as ‘d/2’ distance all around the face of the column (as per ACI 318 )1. find pressure at critical section2. Find the value of bo

2.find Vu

3.find Vu is smallest of these

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dbfV occ

c'4

2

dbfb

dV oc

o

sc

'2

dbfV occ'4

cu VV 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 Mn=Mu/

•Find required Ast

•Min Ast=0.0018bh

•Max spacing=18 in

Development length

'

04.0

c

yd

f

Afl

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Isolated footing with axial load and moment

• Word document (IS Method)• Word document (ACI method)• Spread sheet (ACI method)• STAAD output (ACI method)

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Final comparison

CODE

manual design and spread sheet design

STAAD DESIGN

Area of steel Area of steel

IS 456 3366 mm2 Not available in STAAD

ACI 3185.55 in2

(3580.64 mm2)5.15 in2

(3322.57 mm2)

% difference in steel quantity

10.6% 1.3%

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Thank You