Well curb is designed for hoop tension,
N =
Referring to Fig. A-5,
, ,
Value of hoop tension being less, minimum reinforcement is provided in well curb Volume of well curb = 97.819 m3
Reinforcement required in well curb = Minimum reinforcement in well curb = 72 X 97.819
= 7043 kg
= (7043/7850) m3 = 0.8972 m3
Provide 50 nos. of 25 mm dia.bar rings distributed along the perimeter of the well curb & 80 nos. of 16 mm dia. bar stirrups enclosing the perimeter of well curb
Volume of rings =
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Total volume of reinforcement provided = 0.9121 m3 > 0.8972 m3 . Hence, OK. 16 mm dia. anchor bars are provided at 300 mm c/c
DESIGN OF WELL STEINING
Before designing the section of steining, stresses in steining are calculated at the level of maximum scour as shown below:
Moment at the section of steining about longitudinal axis = 9881 kNm Moment at the section of steining about transverse axis = 41869 kNm
Vertical load acting on the section at the level of maximum scour, W = 19001 kN
Area of section =
Z =
Hence,
& . Hence, Safe.
Required area of vertical reinforcement in steining = 0.12 % of gross sectional area of steining
= 0.0676 m2 = 67622 mm2 Area of steel required on both the faces of steining = 67622 mm2
Area of steel required on one face of steining = 33811 mm2 Using 16 mm dia. bars in vertical reinforcement,
Spacing of 16 mm dia. bars required =
Effective depth of steining = 1750 – 50-8 = 1692 mm Spacing provided = 150 mm <
Hence, 16 mm dia. bars of vertical reinforcement is provided at 150 mm c/c
Required volume of hoop steel in steining =0.04 % of volume of steining / unit length of steining
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= 0.02254 m3 = 2.254 X 107 mm3
Area of steel required on both face of steining = on each face Area of steel required on each face = 350
Using 10 mm dia. bars in hoop reinforcement, Spacing of 10 mm dia. bars required = Spacing provided = 220 mm <
Hence, 10 mm dia. bars of hoop reinforcement is provided at 220 mm c/c
The thickness of steining is checked for requirement of excessive kentledge during sinking of well.
Thickness,
where, kN/m2
Hence, excessive kentledge is required for sinking the well
DESIGN OF WELL CAP
Over all depth of well cap = 1200 mm
Effective depth = 12000-50-12.5 = 1137.5 mm Vertical load on well cap = 7325.5 kN
Self weight of well cap = 25 X 1.2 = 30 kN/m2
Moment at the base of pier, about transverse axis = 8768 kNm Moment at the base of pier, about longitudinal axis = 1309.6 kNm
Resultant moment, M = =8865.3 kNm
The load from the pier is dispersed at an angle of 45° to the well cap, throughout its effective depth. Area of load dispersion is calculated,
Dispersion width = 2500 + (2 X effective depth of well cap) = 4.775 m
Length of dispersion = 9.6 + (2 X effective depth of well cap) = 11.875 m < Diameter of well cap. Hence, OK.
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Maximum dispersion width available = a
Mean length of dispersion =
Fig. A-7 Load dispersion area in well cap
Hence, dispersion area = 11.44 X 4.775 = 54.636 m2
Diameter of equivalent circle i.e. circle of patch loading = 8.34 m
Since the well-cap is assumed to be partially restrained by the steining, the moments in the well-cap are calculated for circular patch loading and for U.D.L. (self-weight of well cap) for the following two conditions: Well cap freely supported on steining & Well cap fully clamped on steining
Condition 1: Well cap freely supported on steining
(i) For moments beneath loaded area due to circular patch loading
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Hence, = 833.1 kNm
(ii) For moments beneath unloaded area due to circular patch loading
At support, d = h; = 1
Hence,
The radial and tangential moments in the well cap due to U.D.L. are given by
At centre, d = 0; = 0 At support, d = h; = 1
Condition 2: Well cap fully clamped at support (i) For moments beneath loaded area due to circular patch loading
(ii) For moments beneath unloaded area due to circular patch loading
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The radial and tangential moments in the well cap due to U.D.L. are given by
At centre, d = 0; = 0 At support, d = h; = 1
(a) Moments due to Patch load (b) Moments due to Self weight load Fig. A-8 Moments in well-cap when freely supported
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(a) Moments due to Patch load (b) Moments due to Self weight load Fig. A-9 Moments in well-cap when fully clamped
Maximum moment at the centre of well cap due to moments transferred form pier = , where
=
Maximum moment at the edges of well cap due to moments transferred from pier = .
=
Total moment at the centre of well-cap
Due to patch loads =
Due to self weight of well cap =
Due to moment from pier & superstructure =
Hence, total sagging moment = 1469 kNm &
total hogging moment = 780.4 kNm Total moment at the support of well-cap
Due to patch loads =
Due to self weight of well cap = Due to moment from pier & superstructure =
Hence, total hogging moment = 486.16 kNm &
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Total sagging moment at the centre of well cap = 1469 kNm & Total hogging moment at the support of well cap = 486.2 kNm Now, the reinforcement of the well cap is calculated.
Bottom reinforcement of the well cap will be designed for total sagging moment at the centre of well cap = 1469 kNm
0.515%
28 mm dia. bars are used at the bottom of well cap,
Spacing required for 28 mm dia. bars =
Spacing provided to 28 mm dia. bars = 100 mm <
Top reinforcement of the well cap will be designed for total hogging moment at the centre of well cap = 780.4 kNm
0.262%
25 mm dia. bars are used at the top of well cap,
Spacing required for 25 mm dia. bars =
Spacing provided to 25 mm dia. bars = 150 mm <
Hence, 25 mm dia. bars at 150 mm c/c is provided at the top of well cap & 28 mm dia. bars are provided at 100 mm c/c is provided at the bottom of well cap.
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Check for Punching Shear
Total vertical load acting on the well cap = 3533 + 3000 +791 = 7324 kN Hence, Shear stress acting on the well-cap =
Maximum shear stress for M25 Grade concrete = Hence, Safe
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