The present paper deals with the numerical analysis of tall reinforced concrete chimneys with piled raft foundation subjected to along-wind loads considering the flexibility of soil. The analysis was carried out using finite element method on the basis of direct method of soil-structure interaction (SSI). The linear elastic material behavior was assumed for chimney, piled raft and soil. Four different material properties of soil stratum were selected in order to study the effect of SSI. The chimney elevation and the thickness of raft of piled raft foundation were also varied for the parametric study. The chimneys were assumed to be located in terrain category 2 and subjected to a maximum wind speed of 50 m/s as per IS:875 (Part 3)-1987. The along-wind loads were computed according to IS:4998 (Part 1)-1992. The base moments of chimney evaluated from the SSI analysis were compared with those obtained as per IS:4998 (Part 1)-1992. The tangential and radial bending moments of raft of piled raft foundation were evaluated through SSI analysis and compared with those obtained from conventional analysis as per IS:11089-1984, assuming rigidity at the base of the raft foundation. The settlements of raft of piled raft foundation, deflection of pile and moments of the pile due to interaction with different soil stratum were also evaluated. From the analysis, considerable reduction in the base moment of chimney due to the effect of SSI is observed. Higher radial moments and lower tangential moments were obtained for lower elevation chimneys with piled raft resting on loose sand when compared with conventional analysis results. The effect of SSI in the response of the pile is more significant when the structure-foundation system interacts with loose sand.
. [J]. Frontiers of Structural and Civil Engineering, 2015, 9(3): 307-322.
B. R. JAYALEKSHMI,S.V. JISHA,R. SHIVASHANKAR. Response in piled raft foundation of tall chimneys under along-wind load incorporating flexibility of soil. Front. Struct. Civ. Eng., 2015, 9(3): 307-322.
tangential moment by conventional method as per IS11089/kNm
soil type
SSI analysis
percentage variation of maximum tangential moment/%
Do/t = 12.5
Do/t = 17.5
Do/t = 22.5
100
2682.68
S1
−50.95
−67.05
−78.64
S2
−65.45
−79.78
−86.83
S3
−79.50
−87.45
−91.14
S4
−87.68
−92.18
−94.85
200
8168.06
S1
−54.92
−67.55
−76.58
S2
−66.56
−79.65
−86.50
S3
−79.11
−89.00
−93.23
S4
−89.64
−95.24
−97.23
400
31526.45
S1
18.12
−6.61
−22.87
S2
−6.36
−30.30
−43.27
S3
−30.56
−49.61
−59.52
S4
−51.33
−65.65
−73.16
Tab.4
Fig.5
Fig.6
H/m
radial moment by conventional method as per IS11089/kNm
soil type
SSI analysis
percentage variation of maximum radial moment/%
Do/t = 12.5
Do/t = 17.5
Do/t = 22.5
100
839.62
S1
32.79
−3.61
−29.95
S2
−0.12
−35.14
−55.49
S3
−37.85
−63.29
−75.71
S4
−68.94
−82.70
−89.24
200
3741.32
S1
65.33
36.73
14.68
S2
39.18
6.82
−11.55
S3
7.68
−20.61
−35.73
S4
−24.96
−47.62
−59.94
400
24765.62
S1
11.41
−18.23
−36.94
S2
−18.40
−46.06
−60.28
S3
−46.01
−66.64
−76.60
S4
−67.70
−81.64
−88.30
Tab.5
Fig.7
Fig.8
H/m
soil type
maximum settlement/mm
Do/t = 12.5
Do/t = 17.5
Do/t = 22.5
100
S1
28.57
29.71
30.81
S2
11.42
11.97
12.37
S3
4.20
4.37
4.50
S4
1.25
1.31
1.35
200
S1
36.23
37.89
39.50
S2
14.29
15.21
15.86
S3
5.44
5.77
6.01
S4
1.75
1.86
1.93
400
S1
45.16
49.92
54.06
S2
19.23
21.26
22.76
S3
7.90
8.59
9.10
S4
2.81
3.03
3.19
Tab.6
Fig.9
Fig.10
Fig.11
Fig.12
H/m
soil type
maximum bending moment of pile/kNm
Do/t = 12.5
Do/t = 17.5
Do/t = 22.5
100
S1
687.83
1066.06
1201.15
S2
555.44
676.80
612.72
S3
347.13
304.30
226.64
S4
120.90
79.96
54.71
200
S1
834.58
1407.91
1768.08
S2
647.31
878.15
914.04
S3
430.96
436.59
387.11
S4
168.71
129.29
98.44
400
S1
1501.62
1920.18
2040.73
S2
780.97
829.08
719.13
S3
306.02
217.85
136.55
S4
63.01
26.82
14.99
Tab.7
Fig.13
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