Transformer Foundation Design

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CONTRACT NO. : PGCB/DANIDA/1DESIGN-BUILD AND TURNKEY CONTRACT FOR CONSTRUCTION OF 132kV JOYDEVPUR - KABIRPUR - TANGAIL TRANSMISSION LINE PROJECTTITLE :

SCALE :132kV Joydevpur Substation

EMPLOYER :POWER GRID COMPANY OF BANGLADESH LIMITED (PGCB )

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Design Calculation for Foundation of Auto Transformer

DOCUMENT NO. : SUBMITTAL NO. :

JDP/A26/001 SECTION : 12, Building and civil engineering works

DESIGNED BY : Md. Giasuddin CHECKED BY : APPROVED BY :

CONTRACTOR : MTHΦJGAARD A/S - LINDPRO A/S JV

DATE :19 Nov '05 REV. NO. : MANUFACTURER :

E:\PROJECTS FOR EXECUTION\Joydevpur - Kabirpur - Tangail OHL\Joydevpur Substation\Design Calculation\Static Cal of Foundation For Auto Transformer

ID :

MT HΦJGAARD A/S - LINDPRO A/S JV

1. GENERAL1.1 Considerations :

a) Raft foundation is considered for a 132kV Transformer.b) The bottom of the raft is at a depth of 1.0m from existing ground surface.c) Soil bearing capacity is considered 90.04 kN/m2 minimum value from BH-4, BH-5 & BH-7.d) The Top of bund wall is 200mm above the finished switchyard surface level.

1.2 Soil Data:

Allowable bearing capacity of soil is considered : 90.04 kN/sqmUnit weight of soil : 17.94 kN/cum.

Frustum angle : 15.00 Deg.Water Table from EGL : 2.50 m

1.3 Material Properties :Concrete………………...…fc'= 20 N/mm2Reinforcing Steel…………..fy = 415 N/mm2Concrete Clear Cover……….= 60 mmUnit Weight of Concrete…….= 24.0 kN/cum.

2. DESIGN DATA AND FOUNDATION GEOMETRY :( Reference Dwg no. 56.20.3-03-3537)

Transformer's Length = 6.80 mTransformer's Width = 5.10 m

Height of Transformer = 5.00 mTotal Weight of Tx. ( with Oil ) = 72,000 Kg

Weight of Oil = 19,000 KgDensity of Oil = 840 Kg/cum.

Design of Transformer Foundation ; Joydevpur 132/33kV Sub-station

Total volume of oil = 22.62 CumPit volume reqd. below the stone ( 125% of oil vol. ) = 28.27 Cum

Inside length of pit considered = 7.80 mInside width of pit considered = 5.80 m

Surface area of the pit = 41.47 sqm.Width of Tx. Supporting Pedestal = 2.68 m

Length of Tx. Supporting Pedestal = 3.89 mArea of Tx. Supporting Pedestal = 10.4 sqm.

Net surface area of the pit = 31.0 sqm.Average Depth required = 0.9 m

Provided depth below Grating = 0.90 mThickness of grating = 0.05 m

Thickness of gravel layer on top of grating = 0.225 mFree height above gravel top = 0.05 m

Max. height of pit wall above base slab = 1.225 m

Center of Foundation

Center of Tx.

sign By : Md. Giasuddin of 11 Date : 19 Nov '05

MT HΦJGAARD A/S - LINDPRO A/S JVDesign of Transformer Foundation ; Joydevpur 132/33kV Sub-station

3. LOAD CALCULATION

Transformer Length, L = 6.80 mTransformer Width, B = 5.10 m

Transformer Height above top of Pedestal, H = 5.00 mTotal weight of Transformer ( with oil ) = 720.00 kN

3.1 Wind load calculation - as per BNBC

Maximum wind velocity , Vb = 160.0 km/hr ( Specified in the Contract specification)Height of top of transformer from FSYL = 5.20 m

For exposure B , Cz at Top = 0.85For exposure B , Cz at Bottom = 0.801

Velocity to Pressure conversion coefficient, Cc = 4.72E-05Structure Importance Factor CI = 1.25

1.284 kN/m2 ; at Top= 1.210 kN/m2 ; at Bottom

L/B = 1.33H/B = 0.98

Pressure co efficient C = 0 80

( Ref. Bangladesh National Building Code 1993, Chapter 2;Page 6-33)



zq =

2z c I z bq = c c c v

z G p zDesign Wind Pressure, p = c c q

Pressure co-efficient, Cp = 0.80Gust Co-efficient, CG = 1.30

1.335 kN/m2 ; at Top= 1.258 kN/m2 ; at Bottom

Average Pressure , Pz = 1.29671 kN/m2∴ Force results from Wind = 1.297*6.8*5.1 = 44.97 kN

3.2 Seismic load calculation - as per BNBC

Design Base Shear is given by :

Where, Z = Seismic Zone Co-efficient = 0.15 ( for Zone 2 )I = Structure Importance Factor = 1.25 ( with essential Facilities )

R = Response Modification Coefficient = 6 ( For RCC wall System )

C = Numerical coefficient system is given by :

S = Site coefficient for soil characteristics = 1.5

T = Fundamental period of vibration is given by :

Ct = 0.049hn = 5.00 m

∴ T = 0.164 Sec C = 6.262

W = Total Seismic dead load =Transformer Weight = 720.00 kN ∴ Design base shear V = 140.90 kN

4. SOIL STABILITY CHECK

4.1 Check for Soil Bearing Capacity :

Weight of each Transformer with 15% impact = 828.00 kNWeight of Transformer supporting Pedestal = 306.50 kN

Length of foundation pad = 8.800 mWidth of foundation pad = 6.800 m

Thickness of foundation pad = 0.300 m

( For all type of non braced RCC structure )


zDesign Wind Pressure, p =

= ZICWVR

23

1.25= SCT

( )3

4 t nT C h=

828.0 kN

140.0 kN

CL of Foundation

Load Application on Foundation



Weight of Pad = 430.85 kNWidth of Bund Wall = 0.200 m

Total Length of Bund wall = 28.540 mHeight of Bund wall = 1.225 mWeight of Bund wall = 167.82 kN

Total area of the Yard within bundwall = 41.47 m2Area of Tx. supporting Pedestal = 10.43 m2Net area to be filled with gravel = 31.04 m2

Thickness of Gravel = 0.225 mWeight of gravel = 111.76 kN

Total Vertical Load = 828+306.5 +430.85+167.82+111.76 = 1844.93 kNMaximum Moment at base due to Max. Horizontal Load =140.9*1.525 = 214.87 kN.m

Eccentricity for Horizontal load = 214.87/1844.93 = 0.116 mNet Eccentricity = 0.116+0.600 = 0.716 m

Q = Fzb = 1844.93 kN kNsA = LxB = 59.84 m2

e = el = 0.716 m mL /6 = 1.467 >e

qmax = 43.54 kN/m2

Gross allowable soil pressure = 90.04 + γsDf = 107.98 kN/m2 So it's OK.

max

min

Q 6eSo;q = (1+ )A LQ 6eand;q = (1- )A L

CL of Foundation

Load Application on Foundation

Net Upward Pressure = 43.54-γ'sDf = 35.60 kN/m24.2 Check for Settlement :

Settlement of a Soil layer is given by :

Where, Cc = Compression Index = 0.258 From soil test report of BH-4.e0 = Initial Void ratio = 0.989 From soil test report of BH-4.

H = Thickness of the Soil Layer = 5.00 m From soil test report of BH-4.p0 = The original Soil Pressure at the mid point of the

layer = γ∗H/2 = 45.00 kN/m2Δp = Change In Pressure = qmax - γDf = 25.60 kN/m2

∴ S = 0.1269 ft. = 1.524 inch.Which is less than 2.0" , so OK.

5. STRUCTURAL DESIGN

5.1 Design of Pit Wall :Angle of repose for backfilled soil, φ = 0.00 Deg

Coefficient of earth pressure , Ka = ( 1-sin φ ) / ( 1-sin φ ) = 1.00Unit weight of soil = 17.94 kN/cum

Height of soil at toe side above base = 0.000 mHeight of soil at heel side above slab = 0.700 m

PL above heel side soil = 0.200 mThickness of stem = 0.200 m

Thickness of base slab = 0.300 mSuperimposed live load at heel side = 10.00 kN/sqm

Applied Loading :

Unit Weight of Gravel Fill = 16 kN/cum.Unit Weight of Brick = 19 kN/cum.

Unit Weight of Sand Fill = 15 kN/cum.

Pressure due to Backfill P1= 1/2*Kpγh2*1.0 = 4.40 kN ( Per meter of width )

010

0 0

log1

cc p pS He p

+ Δ=

+



Ka = ( 1-Sinφ )/( 1+Sinφ ) = 1.0 ( For Backfill φ is considered 0 Degree )13.75 kN ( Per meter of width )

So Moment about point A = 4.41*0.233+13.75*0.35 = 5.835 kN.m ( Per meter of width )Factored Moment = 5.838*1.5 = 8.752 kN.m "

Let us check with minimum reinforcement. As per ACI code, Ratio of minimum reinforcement ( in SI unit) is given by =1.4/fyρmin= 0.003373494

85 mm 95 mm; OK

5.1.1 - Reinforcement Calculation :

Vertical ReinforcementMdes =Mu/0.9 = 9.725 kN.m

Assuming depth of stress block, a = 6.94 mmArea of steel, As = M*1000000/(0.9*fy*(d-a/2)) = 284.47 mm2

(Ref. -Design of concrete structure, By-Nilson & Winter,Page 83 ,10th Ed.)Check for a

a = As*fy/(.85*fc'*b) = 6.94 mmConsideration is OK, So As = 284.47 mm2/m

As per Code Min Rebar Required = 0.004bt = 400.00 mm2/mConsider bar Size = 10.0 mm

So Nos. of Bars = 5 Nos

; d Provided =200-100-10/2=

Pressure due Surcharge load P2 =10.0+ ( 0.175*16+0.075*19+0.075*15)*0.7 =

y2u y

c

ρfM =φρf bd 1-0.59 ...;Where φ = 0.9

f'⎛ ⎞⎜ ⎟⎝ ⎠

u

yy

c

Md= =ρfφρf b(1-0.59 )

f '

∴

Spacing = 200.00 mmProvide φ 10mm @ 200mm at both face of the wall.

Horizontal Reinforcement :As per Code Min Rebar Required = 0.002bt = 400.00 mm2/m

Consider bar Size = 10.0 mmSo Nos. of Bars = 5 Nos

Spacing = 1000/5 = 200.00 mmProvide φ 10mm @ 200mm at both face of the wall.

Check for shear :

Shear force , V = 18.14 kNFactored shear , Vu = 27.21 kN

Where, b= 1000 mmd = 95 mm

So, vc= Vc/bd = 0.286 N/mm2AS per ACI Shear Stress applied to concrete should be less than N/mm2; In present case which is coming 0.76 Mpa.This is much greater than applied stress so consideration is quite Ok.

5.2 Design of Transformer Supporting Pedestal :

( Reference Dwg no. 56.20.3-03-3537)

Length of Pedestal = 3.890 mWidth of Pedestal = 2.680 mHight of Pedestal = 1.225 m

Weight of Pedestal = 306.50 kNTotal Weight of Tx. ( with Oil ) = 720.00 kN

Design Loads:Compression =720.0+306.5 = 1026.50 kN

Moment M = 172.6025

Max. or Min. stress on the section =

I = bh3/12 = 6.24E+12 mm4Maximum stress on the section = 0.06 Mpa, Compressive

Stresse is within acceptable limit, so no rebar is required from structural point of view.

0.17 'cf

max/ minP McA I

σ = ±



But as per code Minimun Rebar = 0.0018*Ag = 0.0018*3890*2680 mm2. = 18766 mm2.So Use 94 nos. of dia 16mm Bar for Vertical Reinforcement. Use dia 10mm bar @ 200mm c/c for tie.5.3. Design of Base Slab

Foundation Layout

Center of Tx.

5.3.1 Check for Punching of the Base :Base Thickness, t = 300 mm

Clear Cover = 60 mmConsider Max Bar size = 20 mm

d = 300-60-20/2 = 230 mmPunching Perimeter = (2680+3890)*2 = 13140 mm

Punching Area = 13140*230 = 3022200 mm2Vertical Forces = 1026.50 kN

0.340 MpaAS per ACI Shear Stress applied to concrete should be less than MpaIn present case which is coming 1.48 Mpa. So OK.

5.3.2 Bottom Reinforcement Along Long Direction :For right side

Net Upward Pressure by soil = 35.60 kN/m2166.147 kN.m/m

Design moment = 170.42/0.9 = 184.607 kN.m/mBase Thickness, t = 300 mm

Clear Cover = 60 mmConsider Bar size = 20 mmd = 300-60-20/2 = 230 mm


Punching stress developed by Tx. = 1026.5*1000/ 3022200 =

Max Moment Developed at Pedestal face at Bottom = 35.6*3.055^2/2 =

0.33 'cf




Check for stress block,aa = As*fy/(0.85*fc'*b) = 60.39 mm

Consideration is OK, So As = 2473.73 mm2Minimum reinforcement = 0.18 % = 540.00 mm2/m

Consider bar Size = 20 mmSo Nos. of Bars = 7.87 Nos

Spacing = 127 mm Say 120mmFor Left Side

61.257 kN.m/mDesign moment = 61.257/0.9 = 68.063 kN.m/m

Base Thickness, t = 300 mmClear Cover = 60 mm

Consider Bar size = 20 mmd = 300-60-20/2 = 230 mm





Spacing = 379 mm Say 240mm


5.3.3 Bottom Reinforcement Along Short Direction :

Net Upward Pressure by soil = 43.54 -γ'sDf = 35.60 kN/m283.057 kN.m/m


Clear Cover = 60 mmConsider Bar size = 12 mm

d = 300-60-12/2-20 = 214 mm ( Bars to be placed on top of long Bars)Assuming depth of stress block, a = 30.34 mm

Area of steel, As = M*1000000/(0.9*fy*(d-a/2)) = 1242.69 mm2Check for stress block,a

a = As*fy/(0.85*fc'*b) = 30.34 mmConsideration is OK, So As = 1242.69 mm2

Minimum reinforcement = 0.18 % = 540.00 mm2/mConsider bar Size = 12 mm

So Nos. of Bars = 10.99 NosSpacing = 91 mm Say 90 mm

Calculation For Bar Curtailment

35.392 kN.m/mDesign moment = 35.392/0.9 = 39.325 kN.m/m

Base Thickness, t = 300 mmClear Cover = 60 mm

Consider Bar size = 12 mmd = 300-60-12/2-20 = 214 mm ( Bars to be placed on top of long Bars)





Max Moment Developed at 0.75 m far from Pedestal face at Bottom = 35.6*1.41^2/2 =




Spacing = 209 mm Say 180 mmPoint of curtailment = 750+(12 times dia of bar ; i.e 12*12 = 144mm use 250mm) 250 = 1000mm from face of Padestal.

5.3.4 Top Reinforcement Calculation along both direction :

Max Hogging Moment Developed = 35.6*(3.055-0.40)^2/8 = 31.368 kN.m/m


Clear Cover = 60 mmConsider Max Bar size = 12 mm

d = 300-60-12/2 = 234 mmAssuming depth of stress block, a = 9.95 mm

Area of steel, As = M*1000000/(0.9*fy*(d-a/2)) = 407.45 mm2Check for stress block,a

a = As*fy/(0.85*fc'*b) = 9.95 mmConsideration is OK, So As = 407.45 mm2

Minimum reinforcement = 0.18 % = 540.00 mm2/mConsider bar Size = 12 mm

So Nos. of Bars = 4.77 NosSpacing = 209 mm Say 200mm

6. DESIGN OF GRATINGS

Layout of Gratings :

Steel of Fy 275.0 Mpa shall be used for gratings.Main bar : 50X6 Flat

Spacing of main bar : 30 mm c/cSecondary bar dia. = 12 mm



Spacing of secondary bar : 100 mm c/cThickness of gravel paving = 225 mm

Unit weight of gravel = 16.00 kN/cumMax span of main bar = 1.698 m

6.1 Design of main bar :Self weight of grating : 0.56 kN/sqmSelf weight of gravel : 3.60 kN/sqm

Assumed live load : 2.00 kN/sqmTotal load per unit area = 6.16 kN/sqm

Uniform Distributed Load per main bar = 0.185 kN/mCheck for bending stress :

Max bending moment = 0.185*1.6982/8 = 0.067kN.mZxx of main bar = 6*502/6 = 2500 mm3

Max bending stress = 0.067*10^6/2500 = 26.64 MpaAllowable bending stress = 0.6*Fy = 0.6*275 = 165.00 Mpa ; So OK.

Check for shear stress :Max shear force = 0.157 kN

Max shear stress = 0.52 MpaAllowable Shear stress = 0.346*Fy = 0.346*275 = 95.15 Mpa ; So OK.

Check for max deflection :

Ixx of main bar = 6*50^3/12 = 62500 mm4Modulus of elasticity of steel = 200000 Mpa

Max central deflection = 5wl4/384EI = 1 60 mmMax central deflection 5wl /384EI 1.60 mmAllowable Maximum deflection = l/325 = 5.22 mm ; So OK.

6.2 Design of grating supporting channel :

Max span of channel = 2.505 mLoad from grating per channel = 6.16*2.505 = 15.431 kN/m

Max bending moment , M = 12.104kN.mMax end shear, V = 19.327 kN

Provide : ISMC 200

Check for bending stress :

Total depth, D = 200 mmSectional Area, A = 2828 mm2

ryy = 22.3 mm Flange thickness, T = 10.40 mm

Web thickness, tw = 6.1 mm Zxx = 182500 mm3

Ixx = 18251000 mm4Leff / ryy = 2700/22.3= 112.33

Consider ends of channel are not to carry any moment so 2nd and 3rd term of the above equation can be ignored. So Cb = 1.75

Bending Stress = M/Z = 12.1*10^6/182500 = 66.32 Mpa∴ Fb = 0.535*275 = 147.13 Mpa > 66.32 Mpa ; So OK.

Check for shear stress :Shear stress = V/A = 19.327*1000/2828 = 6.83 Mpa

Allowable Shear stress = 0.346*Fy = 0.346*275 = 95.15 Mpa > 6.83 Mpa ; So OK.

( )

3 3

2

3

2b

703 10 3516 10When

2 0.603 10550 10

Where C 1.75 1.05*( 1/ 2) 0.3( 1/ 2)

b b

y y

y

b y yb

X C X ClF r F

lF rF F FX C

M M M M

≤ ≤

⎡ ⎤⎢ ⎥= − ≤⎢ ⎥⎢ ⎥⎣ ⎦

= + +



Check for max deflection :Max central deflection = 5wl4/384EI = 2.17 mm

Allowable Max. deflection = l/325 =2825/325 = 7.71 mm ; So OK.


MT HΦJGAARD A/S - LINDPRO A/S JV

Contents Page No.

1. General 03

1.1 Considerations : 03

1.2 Soil Data: 03

1.3 Material Properties : 03

2. Design Data Foundation Geometry : 03

3. Load Calculation : 04

3.1 Wind load calculation - as per BNBC 04

3.2 Seismic load calculation - as per BNBC 04

4. Soil Stability Check 04

4.1 Check for Soil Bearing Capacity : 04

4.2 Check for Settlement : 05

Design of Transformer Foundation ; Joydevpur 132/33kV Sub-station

5. Structural Design : 05

5.1 Design of Pit Wall : 05

5.1.1 - Reinforcement Calculation : 06

5.2 Design of Transformer Supporting Pedestal : 06

5.3. Design of Base Slab 07

5.3.1 Check for Punching of the Base : 07

5.3.2 Bottom Reinforcement Along Long Direction : 07

5.3.3 Bottom Reinforcement Along Short Direction : 08

5.3.4 Top Reinforcement Calculation along both direction : 09

6. Design of Grating : 09

6.1 Design of main bar : 10

6.2 Design of grating supporting channel : 10

Giasuddin / BEL Date : 19 Nov '05

Transformer Foundation Design

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