L&T-GES Isolated footing with axial load and moment Design Input Grade of concrete - 35 Grade of...
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Transcript of L&T-GES Isolated footing with axial load and moment Design Input Grade of concrete - 35 Grade of...
L&T-GES
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
L&T-GES
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
L&T-GES
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
L&T-GES
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
L&T-GES
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
L&T-GES
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
L&T-GES
Isolated footing with axial load and moment
• Word document (IS Method)• Word document (ACI method)• Spread sheet (ACI method)• STAAD output (ACI method)
L&T-GES
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%
L&T-GES
Thank You