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COMBINED FOOTING FOR 2 COLUMNS-1.xls
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COMBINED FOOTING FOR 2 COLUMNS-1.xls
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Author:
Wanda Beasley
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Combined Articles
Footing 1
Full description
Design Of Combined Foundation
FOR COLUMN C1 & C2 Z
0.6 7
0.75
4.8
2
3
X
2
0.3
1.3 2.5
1.2
Constants :Unit Wt Of Soil =
1.8
T/m3
1
T/m3
Unit Weight Of Concrete =
2.5
T/m3
Comp. strength of concrete fc =
30
N/mm2
Yield strength of steel fy =
500
N/mm2
Coefficient Of Friction m =
0.5
Net SBC =
15
Density Of Water =
T/m2
Gross SBC =
19.5
T/m2 ------ Where increase in SBC is not allowed.
Gross SBC =
23.25
T/m2 ------ Where increase in SBC is allowed.(Wind / EQ 25% increase)
Shape Of Foundation :Length Of Foundation Lf =
7
m
Width Of Foundation Wf =
4.8
m
Thickness Of Foundation Tf =
1.2
m
Founding Depth Df =
2.5
m
Length Of Pedestal Lp =
0.6
m
Width Of Pedestal Wp =
0.75
m
Height Of Pedestal Hp =
0
m
(Support Reaction Considered at Base of footing)
Section Modulus Zxx = 1 / 6 x 7 x 4.8 x 4.8 =
26.88
m3
Section Modulus Zzz = 1 / 6 x 4.8 x 7 x 7 =
39.2
m3
Calculation Of Soil, Fdn & Pedestal Weights :Selfweight Of Foundation = 7 x 4.8 x 1.2 x 2.5 =
100.8
T
Selfweight Of Soil = 1.8 x 1.3 x ( 7 x 4.8 - 0.75 x 0.6 x 2 ) Page 1 of 32
=
76.52
T
Selfweight Of Pedestal = 2.5 x 0.75 x 0.6 x 0 x 2 =
0
T
Buoyant Weight = -1 x 7 x 4.8 x 2.5 =
-84
T
Total weight without buoyancy = 100.8 + 76.52 + 0 =
177.32
T
Total weight with buoyancy = 100.8 + 76.52 + 0 + -84 =
93.32
T
Page 2 of 32
Calculation Of Restoring Moment :-
Due to fdn. Weight = 100.8 x 7 / 2 =
352.8
Tm
Due to fdn. Soil = 76.52 x 7 / 2 =
267.82
Tm
Due to Pedestal = 0 x 1 + 0 x 6 =
0
Tm
Due to Buoyant weight = -84 x 3.5 =
-294
Total moment without buoyancy = 352.8 + 267.82 + 0 =
620.62
Tm
Total moment with buoyancy = 352.8 + 267.82 + 0 -294 =
326.62
Support Reactions :- ( At foundation level) JOINT
LOAD
Tm
All Units in Ton - Meter
FORCE-X FORCE-Y
FORCE-Z MOM-X MOM-Y
MOM Z
1029 50 1.0(DL
-1.215
98.241
0.24
-0.395
0.039
0.854
51 1.0(DL
19.517
134.614
7.981
17.209
2.302
39.691
52 1.0(DL
-22.093
49.571
-7.64
-17.939
-2.231
-37.827
53 1.0(DL
19.37
122.317
7.841
17.268
2.294
39.847
54 1.0(DL
-22.24
37.274
-7.78
-17.88
-2.239
-37.671
55 1.0(DL
5.385
134.345
24.183
53.504
1.42
13.371
56 1.0(DL
-7.961
49.84
-23.842
-54.235
-1.349
-11.507
57 1.0(DL
5.238
122.048
24.043
53.563
1.412
13.527
58 1.0(DL
-8.108
37.543
-23.982
-54.176
-1.357
-11.351
59 1.0(DL
5.13
112.221
7.591
16.29
0.891
12.866
60 1.0(DL
-7.706
71.965
-7.25
-17.02
-0.821
-11.002
61 1.0(DL
4.983
99.923
7.451
16.349
0.884
13.022
62 1.0(DL
-7.853
59.668
-7.389
-16.961
-0.828
-10.847
63 1.0(DL
-2.534
78.387
0.028
-0.325
-0.062
3.057
64 1.0(DL
-0.336
81.204
0.033
-0.288
0.117
-0.882
65 1.0(DL
-2.24
102.982
0.307
-0.443
-0.047
2.746
66 1.0(DL
-0.042
105.798
0.312
-0.406
0.132
-1.194
67 1.0(DL
-1.451
81.643
1.491
2.826
0.027
1.108
68 1.0(DL
-1.419
77.949
-1.43
-3.438
0.028
1.068
69 1.0(DL
-1.158
106.237
1.77
2.708
0.042
0.796
70 1.0(DL
-1.125
102.543
-1.151
-3.556
0.043
0.756
1030 50 1.0(DL
0.207
104.688
-0.728
-1.156
0.05
-0.252
51 1.0(DL
22.464
116.926
6.355
16.275
1.709
39.646
52 1.0(DL
-22.085
78.4
-7.611
-18.3
-1.614
-40.076
53 1.0(DL
22.431
102.876
6.555
16.563
1.704
39.719
54 1.0(DL
-22.119
64.35
-7.411
-18.012
-1.618
-40.003
55 1.0(DL
7.318
105.194
20.513
51.463
1.617
12.562
56 1.0(DL
-6.939
90.133
-21.769
-53.488
-1.521
-12.993
57 1.0(DL
7.285
91.144
20.713
51.751
1.612
12.636
58 1.0(DL
-6.973
76.082
-21.569
-53.2
-1.526
-12.919
59 1.0(DL
7.039
103.963
5.969
15.312
0.807
12.046
60 1.0(DL
-6.66
91.364
-7.224
-17.337
-0.712
-12.476
61 1.0(DL
7.006
89.913
6.169
15.6
0.802
12.12
Page 3 of 32
62 1.0(DL
-6.694
77.313
-7.024
-17.049
-0.716
-12.403
63 1.0(DL
-0.944
84.476
-0.448
-0.774
0.067
1.767
64 1.0(DL
1.256
82.75
-0.408
-0.675
0.019
-2.05
65 1.0(DL
-0.877
112.576
-0.848
-1.349
0.076
1.62
66 1.0(DL
1.323
110.851
-0.808
-1.25
0.028
-2.197
67 1.0(DL
0.14
83.722
0.825
2.184
0.059
-0.122
68 1.0(DL
0.172
83.504
-1.681
-3.633
0.027
-0.161
69 1.0(DL
0.207
111.822
0.425
1.609
0.068
-0.27
70 1.0(DL
0.239
111.604
-2.081
-4.208
0.037
-0.308
Page 4 of 32
Check For stability :a) Against Overturing :- (Check is done only for with buoyancy case) Total O/T Moment Load
Restoring Moment MOM-X
MOM-Z STAAD Due to Fy
50 1.0(
1.106
9.67
1.551
51 1.0(
79.337
26.53
52 1.0(
77.903
43.24
53 1.0(
79.566
29.16
54 1.0(D
77.674
40.61
55 1.0(
25.933
56 1.0(
24.5
57 1.0(
External Soil,Fdn,
Total
Load
Total
F.O.S.
Result
Pedestal
10.89
719.92
326.62
1046.54
96.1
Safe
33.484
111.04
853.86
326.62
1180.48
10.63
Safe
36.239
126.45
491.14
326.62
817.76
6.47
Safe
33.831
113.87
759.01
326.62
1085.63
9.53
Safe
35.892
123.61
396.3
326.62
722.92
5.85
Safe
43.73
104.967
125.99
794.66
326.62
1121.28
8.9
Safe
60.44
107.723
137.19
550.35
326.62
876.97
6.39
Safe
26.163
46.36
105.314
127.87
699.82
326.62
1026.44
8.03
Safe
58 1.0(D
24.27
57.81
107.376
135.16
455.5
326.62
782.12
5.79
Safe
59 1.0(
24.912
12.39
31.602
48.89
744.26
326.62
1070.88
21.9
Safe
60 1.0(
23.478
29.1
34.357
62.81
600.75
326.62
927.37
14.76
Safe
61 1.0(
25.142
15.02
31.949
51.32
649.41
326.62
976.03
19.02
Safe
62 1.0(D
23.25
26.47
34.01
60.24
505.9
326.62
832.52
13.82
Safe
63 1.0(D
4.824
9.13
1.099
14
579.15
326.62
905.77
64.7
Safe
64 1.0(D
2.932
2.32
0.963
5.34
576.16
326.62
902.78
169.06
Safe
65 1.0(D
4.366
14.39
1.792
18.85
768.84
326.62
1095.46
58.11
Safe
66 1.0(D
3.391
7.58
1.656
11.1
765.85
326.62
1092.47
98.42
Safe
67 1.0(D
1.23
3.12
5.01
6.64
581.9
326.62
908.52
136.83
Safe
68 1.0(D
1.229
8.33
7.071
11.9
573.42
326.62
900.04
75.63
Safe
69 1.0(D
1.066
8.38
4.317
10.39
771.58
326.62
1098.2
105.7
Safe
70 1.0(D
1.064
13.59
7.764
16.59
763.11
326.62
1089.73
65.69
Safe
Total
F.O.S.
Result
b) Against Sliding :- (Check is done only for with buoyancy case) Total Sliding Forces Load
Fx
Fz
Resultant
Restoring Forces External Load
Soil,Fdn, Pedestal
50 1.0(
1.422
0.968
1.72
202.93
93.32
148.13
86.12
Safe
51 1.0(
41.981
14.336
44.36
251.54
93.32
172.43
3.89
Safe
52 1.0(
44.178
15.251
46.74
127.97
93.32
110.65
2.37
Safe
53 1.0(
41.801
14.396
44.21
225.19
93.32
159.26
3.6
Safe
54 1.0(D
44.359
15.191
46.89
101.62
93.32
97.47
2.08
Safe
55 1.0(
12.703
44.696
46.47
239.54
93.32
166.43
3.58
Safe
56 1.0(
14.9
45.611
47.98
139.97
93.32
116.65
2.43
Safe
57 1.0(
12.523
44.756
46.47
213.19
93.32
153.26
3.3
Safe
58 1.0(D
15.081
45.551
47.98
113.63
93.32
103.48
2.16
Safe
59 1.0(
12.169
13.56
18.22
216.18
93.32
154.75
8.49
Safe
60 1.0(
14.366
14.474
20.39
163.33
93.32
128.33
6.29
Safe
61 1.0(
11.989
13.62
18.14
189.84
93.32
141.58
7.8
Safe
62 1.0(D
14.547
14.413
20.48
136.98
93.32
115.15
5.62
Safe
63 1.0(D
3.478
0.476
3.51
162.86
93.32
128.09
36.49
Safe
64 1.0(D
1.592
0.441
1.65
163.95
93.32
128.64
77.96
Safe
65 1.0(D
3.117
1.155
3.32
215.56
93.32
154.44
46.52
Safe
66 1.0(D
1.365
1.12
1.77
216.65
93.32
154.99
87.56
Safe
67 1.0(D
1.591
2.316
2.81
165.37
93.32
129.35
46.03
Safe
68 1.0(D
1.591
3.111
3.49
161.45
93.32
127.39
36.5
Safe
69 1.0(D
1.365
2.195
2.58
218.06
93.32
155.69
60.34
Safe
70 1.0(D
1.364
3.232
3.51
214.15
93.32
153.74
43.8
Safe
Page 5 of 32
Page 6 of 32
Check For bearing pressure :Case 1) Without Buoyancy :Total Load pmax
pmin
pall
Result
0.275
11.653
10.987
19.5
Safe
1.246
2.701
16.707
8.813
19.5
Safe
1.349
3.091
13.53
4.65
19.5
Safe
11.98
1.259
2.774
16.013
7.947
19.5
Safe
8.3
1.336
3.018
12.654
3.946
19.5
Safe
416.859
12.41
3.906
1.778
18.094
6.726
19.5
Safe
317.293
9.44
4.008
2.167
15.615
3.265
19.5
Safe
177.32
390.512
11.62
3.918
1.851
17.389
5.851
19.5
Safe
113.625
177.32
290.945
8.66
3.995
2.094
14.749
2.571
19.5
Safe
216.184
177.32
393.504
11.71
1.176
0.952
13.838
9.582
19.5
Safe
163.329
177.32
340.649
10.14
1.279
1.342
12.761
7.519
19.5
Safe
189.836
177.32
367.156
10.93
1.189
1.025
13.144
8.716
19.5
Safe
49.72
136.981
177.32
314.301
9.35
1.266
1.269
11.885
6.815
19.5
Safe
13.954
162.863
177.32
340.183
10.12
0.041
0.356
10.517
9.723
19.5
Safe
5.252
163.954
177.32
341.274
10.16
0.036
0.134
10.33
9.99
19.5
Safe
18.756
215.558
177.32
392.878
11.69
0.067
0.479
12.236
11.144
19.5
Safe
10.971
216.649
177.32
393.969
11.73
0.062
0.28
12.072
11.388
19.5
Safe
4.35
165.365
177.32
342.685
10.2
0.187
0.111
10.498
9.902
19.5
Safe
7.071
9.559
161.453
177.32
338.773
10.08
0.264
0.244
10.588
9.572
19.5
Safe
4.317
9.446
218.059
177.32
395.379
11.77
0.161
0.241
12.172
11.368
19.5
Safe
7.764
14.654
214.147
177.32
391.467
11.65
0.289
0.374
12.313
10.987
19.5
Safe
pmax =
18.094
T/sq.M
pmin =
10.33
T/sq.M
P/A
pmax
pmin
pall
Result
Load
MOM-X
MOM-Z
Fy
Soil,Fdn, Pedestral
Total Load
P/A
50 1.0(
1.551
10.776
51 1.0(
33.484
52 1.0(
36.239
53 1.0( 54 1.0(D
202.929
177.32
380.249
11.32
0.058
105.867
251.54
177.32
428.86
12.76
121.143
127.971
177.32
305.291
9.09
33.831
108.726
225.193
177.32
402.513
35.892
118.284
101.624
177.32
278.944
55 1.0(
104.967
69.663
239.539
177.32
56 1.0(
107.723
84.94
139.973
177.32
57 1.0(
105.314
72.523
213.192
58 1.0(D
107.376
82.08
59 1.0(
31.602
37.302
60 1.0(
34.357
52.578
61 1.0(
31.949
40.162
62 1.0(D
34.01
63 1.0(D
1.099
64 1.0(D
0.963
65 1.0(D
1.792
66 1.0(D
1.656
67 1.0(D
5.01
68 1.0(D 69 1.0(D 70 1.0(D
Bearing Pressure for Without Buoyancy Case :-
Mxx/Zxx Mzz/Zzz
Case 2) With Buoyancy :Total Load Load
MOM-X
MOM-Z
Fy
Soil,Fdn, Pedestral
Total Load
Mxx/Zxx Mzz/Zzz
50 1.0(
1.551
10.776
202.929
93.32
296.249
8.82
0.058
0.275
9.153
8.487
19.5
Safe
51 1.0(
33.484
105.867
251.54
93.32
344.86
10.26
1.246
2.701
14.207
6.313
19.5
Safe
52 1.0(
36.239
121.143
127.971
93.32
221.291
6.59
1.349
3.091
11.03
2.15
19.5
Safe
53 1.0(
33.831
108.726
225.193
93.32
318.513
9.48
1.259
2.774
13.513
5.447
19.5
Safe
54 1.0(D
35.892
118.284
101.624
93.32
194.944
5.8
1.336
3.018
10.154
1.446
19.5
Safe
55 1.0(
104.967
69.663
239.539
93.32
332.859
9.91
3.906
1.778
15.594
4.226
19.5
Safe
56 1.0(
107.723
84.94
139.973
93.32
233.293
6.94
4.008
2.167
13.115
0.765
19.5
Safe
57 1.0(
105.314
72.523
213.192
93.32
306.512
9.12
3.918
1.851
14.889
3.351
19.5
Safe
58 1.0(D
107.376
82.08
113.625
93.32
206.945
6.16
3.995
2.094
12.249
0.071
19.5
Safe
59 1.0(
31.602
37.302
216.184
93.32
309.504
9.21
1.176
0.952
11.338
7.082
19.5
Safe
60 1.0(
34.357
52.578
163.329
93.32
256.649
7.64
1.279
1.342
10.261
5.019
19.5
Safe
61 1.0(
31.949
40.162
189.836
93.32
283.156
8.43
1.189
1.025
10.644
6.216
19.5
Safe
62 1.0(D
34.01
49.72
136.981
93.32
230.301
6.85
1.266
1.269
9.385
4.315
19.5
Safe
63 1.0(D
1.099
13.954
162.863
93.32
256.183
7.62
0.041
0.356
8.017
7.223
19.5
Safe
64 1.0(D
0.963
5.252
163.954
93.32
257.274
7.66
0.036
0.134
7.83
7.49
19.5
Safe
65 1.0(D
1.792
18.756
215.558
93.32
308.878
9.19
0.067
0.479
9.736
8.644
19.5
Safe
66 1.0(D
1.656
10.971
216.649
93.32
309.969
9.23
0.062
0.28
9.572
8.888
19.5
Safe
67 1.0(D
5.01
4.35
165.365
93.32
258.685
7.7
0.187
0.111
7.998
7.402
19.5
Safe
68 1.0(D
7.071
9.559
161.453
93.32
254.773
7.58
0.264
0.244
8.088
7.072
19.5
Safe
Page 7 of 32
69 1.0(D
4.317
9.446
218.059
93.32
311.379
9.27
0.161
0.241
9.672
8.868
19.5
Safe
70 1.0(D
7.764
14.654
214.147
93.32
307.467
9.15
0.289
0.374
9.813
8.487
19.5
Safe
pmax =
15.594
T/sq.M
pmin =
7.83
T/sq.M
Bearing Pressure for With Buoyancy Case :-
Page 8 of 32
Check for Pressure at All Four Corners with Buoyancy Case
Z
X
1-2+3
1+2+3
1-2-3
1+2-3
X
Z
Load
P/A
Mxx/Zxx
Mzz/Zzz
1
2
3
50 1.0(
8.82
0.058
0.275
51 1.0(
10.26
1.246
2.701
52 1.0(
6.59
1.349
3.091
11.03
53 1.0(
9.48
1.259
2.774
13.513
54 1.0(D
5.8
1.336
3.018
10.154
7.482
1.446
4.118
55 1.0(
9.91
3.906
1.778
15.594
7.782
4.226
12.038
56 1.0(
6.94
4.008
2.167
13.115
5.099
0.765
8.781
57 1.0(
9.12
3.918
1.851
14.889
7.053
3.351
11.187
58 1.0(D
6.16
3.995
2.094
12.249
4.259
0.071
8.061
59 1.0(
9.21
1.176
0.952
11.338
8.986
7.082
9.434
60 1.0(
7.64
1.279
1.342
10.261
7.703
5.019
7.577
61 1.0(
8.43
1.189
1.025
10.644
8.266
6.216
8.594
62 1.0(D
6.85
1.266
1.269
9.385
6.853
4.315
6.847
63 1.0(D
7.62
0.041
0.356
8.017
7.935
7.223
7.305
64 1.0(D
7.66
0.036
0.134
7.83
7.758
7.49
7.562
65 1.0(D
9.19
0.067
0.479
9.736
9.602
8.644
8.778
66 1.0(D
9.23
0.062
0.28
9.572
9.448
8.888
9.012
67 1.0(D
7.7
0.187
0.111
7.998
7.624
7.402
7.776
68 1.0(D
7.58
0.264
0.244
8.088
7.56
7.072
7.6
69 1.0(D
9.27
0.161
0.241
9.672
9.35
8.868
9.19
70 1.0(D
9.15
0.289
0.374
9.813
9.235
8.487
9.065
1+2+3
1-2+3
1-2-3
1+2-3
9.153
9.037
8.487
8.603
14.207
11.715
6.313
8.805
8.332
2.15
4.848
10.995
5.447
7.965
Check for Eccentricity without Buoyancy Case:-
P
Mxx
Mzz
ex = Mzz/P
ez = Mxx/P
L/6
B/6
ex < L/6 ez < B/6
380.249
1.551
10.776
0.03
0.01
1.17
0.8
< L/6
51 1.0(
428.86
33.484
105.867
0.25
0.08
1.17
0.8
< L/6
52 1.0(
305.291
36.239
121.143
0.4
0.12
1.17
0.8
< L/6
53 1.0(
402.513
33.831
108.726
0.28
0.09
1.17
0.8
< L/6
54 1.0(D
278.944
35.892
118.284
0.43
0.13
1.17
0.8
< L/6
55 1.0(
416.859
104.967
69.663
0.17
0.26
1.17
0.8
< L/6
56 1.0(
317.293
107.723
84.94
0.27
0.34
1.17
0.8
< L/6
57 1.0(
390.512
105.314
72.523
0.19
0.27
1.17
0.8
< L/6
58 1.0(D
290.945
107.376
82.08
0.29
0.37
1.17
0.8
< L/6
Load 50 1.0(
Page 9 of 32
59 1.0(
393.504
31.602
37.302
0.1
0.09
1.17
0.8
< L/6
60 1.0(
340.649
34.357
52.578
0.16
0.11
1.17
0.8
< L/6
61 1.0(
367.156
31.949
40.162
0.11
0.09
1.17
0.8
< L/6
62 1.0(D
314.301
34.01
49.72
0.16
0.11
1.17
0.8
< L/6
63 1.0(D
340.183
1.099
13.954
0.05
0.01
1.17
0.8
< L/6
64 1.0(D
341.274
0.963
5.252
0.02
0.01
1.17
0.8
< L/6
65 1.0(D
392.878
1.792
18.756
0.05
0.01
1.17
0.8
< L/6
66 1.0(D
393.969
1.656
10.971
0.03
0.01
1.17
0.8
< L/6
67 1.0(D
342.685
5.01
4.35
0.02
0.02
1.17
0.8
< L/6
68 1.0(D
338.773
7.071
9.559
0.03
0.03
1.17
0.8
< L/6
69 1.0(D
395.379
4.317
9.446
0.03
0.02
1.17
0.8
< L/6
70 1.0(D
391.467
7.764
14.654
0.04
0.02
1.17
0.8
< L/6
Page 10 of 32
Check For Shear a) Two Way Shear Limit State Method
d/2
4.8
d/2
2
1.5
Critical Section = At distance d/2 from face of column Concrete Grade =
30
N/mm2
Length =
600
mm
Width =
750
mm
Length =
3500
mm
Width =
4800
mm
Effective Depth =
1125
mm
Percentage Of Steel =
0.22
%
134.614
T
Column Details
Foundation Details
Punching Load Maximum Load on Column =
Punching Shear = 134.614 x ( 3.5 x 4.8 - 1.725 x 1.875 ) 3.5 x 4.8
P=
109
Ton
Shear Resistance Of Concrete (Vc) = vc x bc x d -----Refer to clause no. 31.6.3.1 of IS 456 where vc = ks x tc ks = 0.5 + bc
-----should not be greater than 1
bc = Short Side Of Column Long Side Of Column
= =
600 750 0.8
ks =
1
tc =
1.37
N/mm2
bc = Appropriate perimeter at distance d/2 Length of critical section =
1725
mm
Width of critical section =
1875
mm
Perimeter of critical section =
7200
mm Page 11 of 32
Depth Required = =
1635000 1.37 x7200 165.75
mm
Shear Resistance = 1.37 x 7200 x 1125 / 10000 1109
T
Page 12 of 32
B) One Way Shear
3.5
0.9 d
4.8 d
2
1.5
0
2
3
Critical Section = At distance d from face of column Maximum Pressure =
12.754
T/m2
---- For without Buoynacy Condition
At Length Length at critical section =
4800
mm
Width at critical section =
2000
mm
Shear Force = 12.754 x 4.8 x 2 =
123
T
Length at critical section =
3500
mm
Width at critical section =
900
mm
At Width
Shear Force = 12.754 x 3.5 x 0.9 =
41
T
Designed Shear Stress =
123
T
Corresponding Length =
4800
mm
% Ast =
0.23
Allowable Shear Stress =
0.35
k=
1
tc =
0.354
N/mm2
----Refer Table 21 of IS 456
---- Refer clause no. 40.2 of IS 456 N/mm2
Depth Required = 1845000 0.354 x 4800 =
1086
mm
Design Of Foundation a) Calculation of reinforcement at bottom Maximum Pressure =
18.094
T/m2
--- Without Buoyancy Load Case
Pre. due to pcc & fdn wt = ( 100.8 + 76.52 ) / ( 7 x 4.8 ) =
5.28
T/m2
Net causing moment =
12.814
T/m2
Maximum Projection of fdn =
2.025
m
Bending Moment = 12.814 x 2.025 x 2.025 / 2 = Ast =
26.27
Tm
0.5 x fck x b x d fy
1-
(4.6 x Mu ) 1 - fck x b x d2
Page 13 of 32
Ast = Min. percentage of re-bar = Ast =
815.46 0.2 2400
mm2 % mm2
Use
20
mm dia bars
Area of bar =
314
mm2
Spacing =
125
mm
Provide Spacing =
125
Area Provided =
2512
Hence % of Steel =
0.23
mm2
Provide 20 mm dia Bars @ 125 mm spacing bothways
Page 14 of 32
b) Calculation of reinforcement at top Area Load = Max. Projection of fdn =
12.814
T/m2
3
m
Bending Moment = 12.814 x 3 x 3 / 10 = Ast =
11.53
Tm
0.5 x fck x b x d
1-
Ast = Min. percentage of re-bar =
355.46 0.2
(4.6 x Mu ) 1 - fck x b x d2
fy mm2 % mm2
Ast =
2400
Use
20
mm dia bars
Area of bar =
314
mm2
Spacing =
130
mm
Provide Spacing =
130
mm
Hence % of Steel =
0.22
Area Provided = 2415.3846 mm2 Provide 20 mm dia Bars @ 130 mm spacing bothways
Summary Of Design :Length Of Footing :-
7000
mm
WIdth Of Footing :-
4800
mm
Depth Of Footing :-
1200
mm
Reinforcement :At Top :- Provide 20 mm dia Bars @ 130 mm spacing bothways At Bottom :- Provide 20 mm dia Bars @ 125 mm spacing bothways
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