footing
DESCRIPTION
Footing. Failures 1.Bearing failure 2.Serviceability failure 3.Excessive total settlement. P. M. Centroidal Axis. P/A. My/I. Kern. B. L/6. L/6. L. P c =0. 240 lb/ft 2. 300 lb/ft 2. 540 lb/ft 2. P c. 240 lb/ft 2. 2 ft of soil @120 lb/ft 3. 300 lb/ft 2. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/1.jpg)
Footing
![Page 2: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/2.jpg)
Failures
1.Bearing failure
2.Serviceability failure
3.Excessive total settlementq
FS
qq ultA
![Page 3: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/3.jpg)
P
MCentroidal Axis
P/A
My/I
![Page 4: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/4.jpg)
L/6 L/6
Kern
L
B
6
LeK
I
My
A
Pq
![Page 5: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/5.jpg)
Pc=0
540 lb/ft2
300 lb/ft2
240 lb/ft2
![Page 6: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/6.jpg)
Pc
540 lb/ft2
300 lb/ft2
240 lb/ft2
qn=Pc/A
2 ft of soil @120 lb/ft3
2 ft of concrete @150 lb/ft3
Gross soil pressure =
540+qn lb/ft3
![Page 7: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/7.jpg)
qn=Pc/ANet soil pressure
M
P
![Page 8: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/8.jpg)
Area of footing
aq
LesurchfootingStructureDA
arg,,
Only Dead load and Live load
Including Wind load also
Area of footing
aq
WLesurchfootingStructureDA
33.1
arg,,
A
LstructureDqnu
7.14.1
or
A
WLstructureDqnu
]7.17.14.1[75.0
![Page 9: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/9.jpg)
Isolated footing with axial load and moment
Design Input
•Grade of concrete•Grade of steel•Allowable soil pressure•Column load•Moment•Condition about overburden of soil
![Page 10: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/10.jpg)
Design procedure
•Assume column size•Assume footing size•Total load=wt of footing+column load•Average soil pressure q= total load / footing area
Allowable soil pressure > Average soil pressure
then footing are is ok
Checking the footing area
![Page 11: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/11.jpg)
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
![Page 12: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/12.jpg)
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 section
2.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 section
2. Find the value of bo
2.find Vu
3.find Vu is smallest of these
![Page 13: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/13.jpg)
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
![Page 14: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/14.jpg)
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
![Page 15: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/15.jpg)
Thank You
![Page 16: Footing](https://reader036.vdocuments.site/reader036/viewer/2022062802/5681449c550346895db14bae/html5/thumbnails/16.jpg)