A) Introduction:Two numbers of circular thickeners have been provided as per the process requirement. The wall of the thickener is designed as circular wall as per the coefficents in IS 3370-part IV. 1
The wall is designed as hinged at base for hoop forces and span B.M in the wall . On inner face of the wall steel is provided for 100% fixity condition. B) Geo-technical Investigation & Soil Data Adopted in Design:One number of Bore hole BH10 has been done at thickener location. Average EGL at this location is 595.5 . Refusal strata is met at depth of 1.5 M , N value =112 ( 594 M level). Proposed FGL in this area is 593.0 M . The founadtion is provided 500 mm below FGL on the refulsal strata. The bearing capacity as per the soil report is as follows :1.5 M below EGL
25 T/Sqm
2.5 M below EGL
30T/Sqm
For hard Rock Bearing pressure of 60 T/sqm is adopted.
Note:- The bearing capacities in the table are Net safe bearing Capacities of the soil and gross bearing capacity at founding level are adopted as follows:-
Soil weight T/Cum
Gross Bearing Capacity = Net Bearing Capacity + 1.6 x Depth of Foundation.
( Soil load from Existing Ground level to Finished ground level or above due to plinth filling will be treated as load , with soil weight of 2.0 T/Cum) For the Back fill soil following soil properties are adopted:Soil Properties adopted in the design:- ( Back Fill material)
j
Angle of Internal Friction
30
Degree
( For cantilever walls)
Coefficient Active pressure
0.33
Ka
( For propped / circular Walls)
Pressure at Rest
0.5
Kr
( For Computation of Loads)
Weight of Soil
20
Kn/M3
Submerged Soil Weight
10
Kn/M3
(For stability against Uplift)
Weight of Soil
16
Kn/M3
(For stability against Uplift)
Submerged Soil Weight
8
Kn/M3
Subsoil Water level
Not Present
Force resistance from soil due to friction is computed as per the following equation. F= 2 / 3 ( tan ( )) x W W= Vertical Load on the Slab / Footing 2/3xtan ( )
=0.384
C) Liquid Retaining Structures:All water retaining structure are designed as per the provisions in IS 3370-Part II - 2009 with controlled crack width of 0.1mm as per the specifications. The water level for the design shall be adopted as follows :For strength calculations water shall be taken up to top of the wall assuming all outlets are blocked . For serviceability limit state condition water level is adopted at working top liquid level or the overflow level as appropriate ( refer cl.4.2 of IS 3370-II -2009) Strength Calculations will be carried out using limit state design as per IS456-2000 with load factor of 1.5 . For empty condition soil level will be adopted as applicable.
Non Liquid Retaining Structures and Buildings :All non liquid retaining structures like foundations and columns of
2
elevated tanks and Buildings will be designed as per IS 456-2000. D) Design Idealization , Load Conditions and Load combinations:I) Design Idealization :Rectangular tank's walls will be designed as rectangular plates for 3
the boundary conditions as applicable using MOODY'S charts. Permissible stresses will be adopted as per the material retained. The wall will be treated as fixed at base & common edges with adjacent wall panels as applicable. Walls with aspect ratio greater than 3 , will be designed as one way as per boundary conditions . For walls of rectangular tanks the direct horizontal tension and bending action will be adopted as per IS 3370-partII
Circular tanks Clarifiers , thickeners etc. will be designed for HOOP forces and Bending Moment . The foundation of the wall will provide nominal fixity to the wall , for foundation design 50% fixity is adopted. In the wall vertical span steel and hoop steel is provided for the hinged base condition . However on the inner face of the wall vertical steel at base is provided for fixed base condition. E)
F) Specific Design Requirement as per tender Specifications. E1) Materials for Construction:I) Plain Concrete as Mud mat :PCC as mud mat below RCC , 100mm Thick.
M10
1000 gauge polythene sheet will be provided as sliding layer below base slab and raft slab of water retaining structures. II) Concrete Grades for RCC Structures :Liquid Retaining Structure
M30
Buildings / non Liquid retaining Structures
M25
All structural concrete will be with aggregates 40mm down for Footings and base slab and with 20mm down aggregates for all water retaining and other structures. For screed concrete 12.5mm 4
down size aggregates will be used.
III) Steel as Reinforcement for the Concrete:For Water retaining structures :
CRS Fe 500Grade.
( Steel with corrosion resistant Characteristics)
E2) Minimum Thickness of Reinforced Concrete:Following minimum thicknesses of the members will be provided Walls Liquid retaining Structures
250.00
mm
Bottom Slab liquid retaining structures
250.00
mm
Walls Foundations ( at base slab & wall junction)
250.00
mm
Roof slab of Liquid retaining structures
200.00
mm
Launder base slab & wall
150
mm
Shell roof
100
mm
Floors , roof slab , walkways , canopy slabs
125
mm
Walls of cable & Pipe trenches
200
mm
Under ground Pits etc.
200
mm
Footings at edge
200
mm
Footing at column face
300
mm
Width
300
mm
Depth
300
mm
Width
230
mm
Depth
300
mm
100
mm
Columns:-
Beams:-
Parapets , Chajjas etc.
Preacst Trench covers
75
mm
Free face
30
mm
Face in contact with Soil
40
mm
E3) Minimum Cover to any Reinforcement:Slabs:-
5 Beams:-
Top & Bottom
40
mm
Side / face in Contact with Soil
40
mm
Super Structure 50
mm
Sub. Structure 50
mm
Bottom , Top
50
mm
Sides
50
mm
Face in Contact with Soil
40
mm
Free face
30
mm
Face in contact with liquid
50
mm
Face in contact with Soil
50
mm
Free face
50
mm
10
mm
Main bar
10
mm
Dist. Steel
8
mm
Main bar
12
mm
Links
8
mm
Columns & Pedestals
Foundations :-
Retaining Walls , Basement & Pit Walls:-
Liquid retaining Structures
E4) Minimum Bar Diameter of Reinforcement bars :Major Foundations Block Foundations :-
Columns & Pedestals
Beams:-
Slabs & Base Slabs :-
Walls & Wall Foundations :-
Main bar
12
mm
Stirrups
8
mm
Main bar
10
mm
Dist. Steel
10
mm
Main bar
10
mm
Dist. Steel
8
mm
8
mm
Main bar
10
mm
Dist. Steel
8
mm
Other Minor elements shell roof :-
6
F) Design of The wall of the Thickener :-
7
Typical Wall Section
F1) Design of main wall:Wall top Level=
597.5 M
Base slab level=
593 M
Wall Height =
H=
4.5 M
Wall Th. provided at base t=
0.25 M
Wall Th. provided at span t=
0.25 M
Tank Diameter D=
19.5 M
HxH/Dxt is adopted =
4.15
Design of wall For Bending Moment :Base B.M Tank Full case :-
Coefficient as per IS 3370=
=9.81x4.5
Water pressure at base Triang.
0.026 44.145 Kn/Sqm
Refer table 10 of IS 3370-Part IV for Coefficient B.M= 0.026x44.145x4.5x4.5
23.24234 Kn-M
Ultimate B.M = Mu=1.5 M D ( Cms )=
25
34.86 Kn-M
d=
19.5 Cms
Mu/(bx d x d) Refer Sp16 , Table 4
0.916858
Pt ( required )
0.23 %
Ast=
4.485 Sqcm
Provided on Inner Face Base B.M for Tank Empty Case:-
Y10-175 C/C Not critical
Refer table 13 of IS 3370-Part IV for Coefficient Maximum Span B.M in wall for Hinged Case=0.0118xwxHxHxH D ( Cms )=
25
10.54845 Kn-M
d=
19.5 Cms
Mu/(bx d x d) Refer Sp16 , Table 4
0.416112
Pt ( required )
0.105 %
Ast= Provided on outer face
2.0475 Sqcm Y10-175 C/C
Check for shear force in the wall at base :- Adopted as for fixed base
8
Refer table 11 of IS 3370-Part IV Coefficient for shear Shear force = V
0.23 45.69008 Kn
(Note : Shear will be lesser at critical section " d " from base slab face.) Ultimate shear=1.5 x V D ( Cms )=
25
d= Vu/(b x d)
Refer Sp16 , Table 61
Pt ( required ) Ast= Provided on Inner Face
68.53511 Kn 19.5 Cms 0.351462 0.23 % 4.485 Sqcm Y10-175 C/C
Mimimum Steel Required :Mimimum Pt
0.35 %
Surface zone =25/2=
12.5 Cms
Ast= Provided
4.375 Sqcm Y10-175 C/C B.F
9
Check for Crack width:-
10
As crack width is << 0.1mm section is OK.
Design of Wall For Hoop Forces :Tank Full Condition is Critical :-
Refer table 12 of IS 3370-Part IV
Hoop force in Top 0.0 H to 0.3 H=0.367x4.5x9.75x9.81 = T Tu=T x1.5
157.9618 Kn 236.9428 Kn
=0.87x500
Permissble stress in steel=fst
=Tu/fst
Steel required
5.44696 Sqcm
Steel on each face
2.72348 Sqcn
Provided minimum steel
Hoop force in 0.3 H to 0.8 H=0.58x4.5x9.75x9.81 = T Tu=T x1.5
435 Mpa
Y10-175 C/C B.Faces
249.64 Kn 374.46 Kn
=0.87x500
Permissble stress in steel=fst
=Tu/fst
Steel required
8.608275 Sqcm
Steel on each face
4.304138 Sqcn
Provided minimum steel
Below 0.8H steel is provided nominal Y10-175 C/c B.Faces.
No craking of the section.
435 Mpa
Y10-175C/C B.Faces
11
F2) Design of the launder:Vertical wall of the launder :-
Wall Top level Base Slab level Wall height B.M as cantilever
=((0.35x100000x6/(1000x150^2)
Bending stress developed
597 M 596.4 M 0.6 M 0.35316 Kn-M 0.093 MPA
Nominal Ast=( fst=130,d=7.5) Min steel =0.35x15
0.426136 Sqcm 5.25 Sqcm
Provided
Y10-145 C/C
Provided above minimum steel
Horizontally also.
Design of Base Slab of the launder:Base slab is designed as cantilever from the main wall. B.M due to base slab from vertical wall Self Load of the wall=V
2.25 KN
B.M at wall face=0.375*V
0.84375 Kn-M
Self Load Base slab ( av 0.2th)
0.50625 Kn-M
B.M due to load on the base slab :-
PCC fill ( max =0.2 th) ( ht above PCC)
0.216 Kn-M
Water Load max.(0.4 m )
0.28122 Kn-M
Total B.M =
1.84722 Kn-M
Axial force
0.7848 KN
D provided
25 Cms
=Mx1e6/(0.85x130xdx100)
Ast ( B.M , fst=130,d=19.5)
0.857278 sqcm
= Tx1e3/(130/100/2)
Ast axial force each face
0.030185 Sqcm
Total steel
0.887463 Sqcm
Minimum steel =0.35x12.5 Provided
4.375 Sqcm Y10-175 C/C
12
Y8-110 C/C T & B
Distribution steel F3) Design of Foundation for the Wall :Net safe bearing Capacity at founding level say
25 T/Sqm 250 Kn/sqm 13
Loading :Dead load of the wall:Wall height provided
4.50 M
Thickness provided
0.25 M
Load / Meter
28.13 Kn/m
Dead load from the launder:Wall Load
2.81 Kn/M
Base slab + Water+ Screed
4.12 Kn/M
Total Launder Load
6.93 Kn/M
Self load Footing :Average thickness
0.25 M
Base slab width provided
1.45 M
Load / Meter
9.06 Kn/M
Total Dead load effect =
V d.l.
44.12 Kn/M
say
45.00 Kn/M
Footing width provided Base pressure developed
1.45 M 31.03 Kn/Sqm
Soil Load effect :-
Soil load on external projection:Soil height
0.1 M
Projection width
0.6 M
Load / M @ 20Kn/Cum
1.2 Kn/M
Soil + Slab Load on Internal Projection:-
not present in this case
Soil height
0 M
Projection width
0 M
Load / M @ 20Kn/Cum
0 T/M
Slab Load
0 T/M
Total load on inner Projection Total soil Load
14
0.00
V s.l
1.20 Kn/M
say
1.20 Kn/M
B.M at footing center line
0.51 kn-M
Additional Base pressure out side
2.28 Kn/sqm
Additional Base pressure inside
-0.63 Kn/sqm
( Out side)
Maximum base pressure in combination Dead Load
33.32 Kn/sqm
(Inside)
Maximum base pressure in combination Dead Load
30.41 Kn/sqm
Water Load effect :Water height
4.50
M
Slab projection
0.60
M
26.49
Kn/m
11.26
T-M
B.M due to water pressure
23.24
Kn-M
50 % fixity B.M =23.24/2
11.62
Kn-M
Design B.M
-0.36
Kn-M
Load /M = B.M due to water load Refer page 8
Base pressure developed Inside in combination D.L
48.27 Kn/sqm
Outside in combination D.L
50.34 Kn/sqm
=48.27-0.63
Inside in combination D.L+S.L
47.64 Kn/sqm
=50.34+2.28
Outside in combination D.L+SL
52.62 Kn/sqm
Effect of the Bridge Load :Reaction from Bridge Load after dispersion through
150 Kn
wall at 45 degree=150/(2x4.8)
15.63 Kn/M
Load/ sqm=
10.78 K/sqm
Maximum Base pressure
63.40 Kn/sqm <<<250Kn/sqm OK
Maximum Footing Projection
0.6 M
(Pr=63.4-slab load - soil load)
B.M in Footing
9.926319 kn-M
(Sress forconcrete =2.0MPA)
D rqd for uncraked section
17.25658 cms <<< 30 Cms
d=30-5-0.5 , Ast ( Fst=130)
4.61 Sqcm
Minimum Pt=0.35x15
5.25 Sqcm
Provided Top & bottom
Y10-350+Y12-350C/C
Distribution steel
Y10-145 C/C T & B
F4) Design of The Base Slab:Base Slab Provided
25.00
Cms
Base slab is designed as slab on grade and nominal steel is provided as per IS 3370-Part II
Pt rqd= Surface zone Ast=
Provided in top part as D < 300 mm Refer fig to IS 3370-Part 2
Provided
0.35 12.50
% cms
4.38 Sqcm Y10-175C/C at top
15
F5) Seismic Load Effect :- Seismic load is adopted as per IS 1893-2002 Refer IS-1893 -2000 Part 1 Sa/g=
2.5
Damping
5
Z=
0.16
R=
3
I=
1.5
Ah=
0.1000
Horizontal coefficients are computed as per IS 1893-1984 ( Referred as Part 2 of code is not published , refer page 2 of IS 1893-part 1)
R=
9.75 M
H=
4 M Service Condition
For maximum force Cos ( Phi) = 1 , y= h Pw=0.35x9.81
3.4335 Kn/sqm
As above increase is lesser than the free board , Seismic case not critical
%
16
G) Design of Staircase:-
Staircase is provided with stringer Beam
17
=1.2x(3.739+2.188 +1.2+5)+0.3x0.45x25/0.8
Steel provided
3 nos-Y16 T & B Stps
Y8-150 C/C 2 legged.
Design of column below staircase :Provided 300 mm diameter column . Maximum load on the column
84.6 Kn
As load on column is nominal provided nominal 0.8 % steel Ast=
5.652 Sqcm
Provided
6 Nos Y12
Links
Y8-150C/C
( As the bearing Capacity of the soil 25 T/sqm , area rquired for above load is only 0.34 Sqm , Provided nominal footing )
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