Analysis and Design of Strap (Cantilever) Footing According to ACI
[email protected]
Footing No 5
Job:
Project :
R
PA
X
Strap Beam
h
C
B1
a c.g
bA
Z
L
L1
q1 e
R1
Values Need to be Intered by the User Characteristic Results
Axial Load on Column A , PA Axial Load on Column B , PB Moment on Column A , MA Moment on Column B , MB
300 200
KN KN KN.m KN.m
Proposed External Footing Length L1 Proposed Footing Thickness h
2 0.4
m m
Concrete Compressive Str Reinforcement Yielding Str
Distance Between Columns (Z)
6.2
m
Net Allowable Soil Bearing
Service Service Service Service
C Column A Width bA Column A Length aB Column A Width bB
Design Summary Required Width of External Footing ( B1 )
1.95
m
Required Area of Internal Footing (AB)
1.73
m2
2
m
0.90
m
Maximum Soil Pressure under footings
98.84
KN/m2
Assumed Width of Strap Beam b strap=
250
mm
Minimum Required Effective Depth of Strap Beam
450
mm
Proposed Length of Internal Footing (L2) Required Width of the internal footing (B2)
10
Shear Forc
-1.00 0.00
1.00
2.00
3.00
Bending Mom -1.00 0.00
1.00
2.00
3.00
Maximum Shear Force in Strap Beam
398.0
KN
Maximum Bending Moment in Strap Beam
298.5
KN
800
mm
1034.4 T20 1.04 4*T12@
mm2 4 mm2/mm 435
Provided Strap Beam Depth Required Longitudinal Reinforcment Area Required Shear Reinforcment Area
Bending Mom -1.00 0.00
1.00
2.00
3.00
Proportion Footing Dimensions
X B The location of forces resultant that give uniform pressure under both footing relative to the center of column
According to the proposed length of footing "A" the eccentricity of footing reactions Taking moments about the center of column B,
R1 =
344.44
KN
Taking moments about the center of column A,
R2 =
155.56
KN
e (
L1 C ) 2
According to the allowable pressure under the footing the minimum width of external footing
Minimum
According to the allowable pressure under the footing the minimum area of internal footing
Minimum
Sequar Foot OR
L2 Acual location of force resultant
A A ( Z e ) (A A A B ) * X X
3.695
Soil pressure under the external footing q1=
98.84
KN/m2
OK
Soil pressure under the external footing q2=
95.29
KN/m2
OK
m
Strap Beam Analysis and Design Considering Ultimate Load Magnification
q1ult * q1
1.5
Therefore the ultimate soil pressu
q 2ult * q 2
259.86 KN/m
R
PA
115.14
X
Strap Beam
h
C
a
B1
c.g
bA
Z
L
L1
qu1 x
Shear Force Diagram
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
Bending Moment Diagram
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
Design of Strap Beam Bending Moment Design
2M u 0.85* fc ` 1 1 2 fy 0.85* * b * d * fc ` strap eff
As *bstrap * d eff
0.0052
1034.44 mm2
>
min
0.0033
4 T20
I recommond to provide of the
Shear Design
V c 0.17 *0.75* fc `*bstrap * d eff (V u V c ) A sv Shear Reinforcement S VS
134.93
KN
Strength of Concrete Se
350.79 KN
1.04
mm2/mm==>
Shear Force need to be
4*T12@ 435
Required Shear Reinfo
Footing Design d e h 75
The effective Depth
325
mm
119.94
KN
438.53
KN
-19.19
KN
438.53
KN
1- Exterior Footing
V u1
q1ult * L1 B 1 b A * d eff B1 2
V c 0.17 * 0.75* fc `* L1 * d eff
> Applied Shear Force =
2- Interior Footing
Vu2
q 2ult * L 2 B 2 b B * d eff B2 2
V c 0.17 *0.75* fc `* L 2 * d eff Punching Shear
> Applied Shear Force =
Will not be considered due to the presence of strap beam
Bending Moment 1- Exterior Footing 2
M u1
q * L1 B 1 b A 1ult * 2* B 1 2
2M u 1 0.85* fc ` 1 1 A s * L1 * d eff 2 fy 0.85* * L * d * fc ` 1 eff
80.04
KN.m
Bottom Flexure Reinforcement
Shrinkage Reinforcement
2- Interior Footing 2
M u2
4
As 0.0018* L1 * d eff
For shrinkage reinforcement in longitudinal direction
q * L2 B 2 bB 2ult * 2* B 2 2
1170.00
8.00
KN.m
6
2M u 2 0.85* fc ` 1 1 A s * L 2 * d eff 2 fy 0.85* * L * d * fc ` 2 eff
Bottom Flexure Reinforcement
1170.00 6
As 0.0018* L 2 * d eff
For shrinkage reinforcement in longitudinal direction
Shrinkage Reinforcement
Developed by Walid Matar Sr. Structural Engineer
[email protected]
6
ilever) Footing According to ACI 318 X Project
R
PB
X
rap Beam
aB c.g
B2
bB
L2
q2
R2 C Column A Width bA Column A Length aB Column A Width bB
0.2 400 200 400
m mm mm mm
Concrete Compressive Strength fc` Reinforcement Yielding Strength fy
28 420
N/mm2 N/mm2
Net Allowable Soil Bearing Capacity
100
KN/m2
Shear Force Diagram
-1.00 0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
7.00
8.00
Bending Moment Diagram -1.00 0.00
1.00
2.00
3.00
4.00
5.00
6.00
Bending Moment Diagram -1.00 0.00
1.00
2.00
3.00
4.00
5.00
6.00
PA * Z PA PB
X B h footing relative to the center of column
7.00
8.00
3.72
m
B1
1.95
m
AB
1.73
m2
1.40
m
0.80
m
Sequar Footing with B = 2.00
Variation =
B2 0.0253 m
0.90
Therefore the ultimate soil pressure under footings KN/m
R
PB
X
trap Beam
aB c.g
B2
bB
L2
q u2
e Diagram
4.00
5.00
6.00
7.00
8.00
6.00
7.00
8.00
ment Diagram
4.00
5.00
OK
I recommond to provide similar steel at top and bottom of the strap beam
Strength of Concrete Section
Shear Force need to be Resisted by Steel
> Applied Shear Force ==> OK
> Applied Shear Force ==> OK
mm2 T20
1170 T16
Along L1 mm2 Along B1
tar Sr. Structural Engineer
[email protected]
mm2 T16
1170 T16
Along L2 mm2 Along B2
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