Underground Pipe Thk Cal

8/10/2019 Underground Pipe Thk Cal

1/12

JOB No. 99304

BASIC CRITERIA

Route of Pipe Line

Pipe Nominal Diameter 3500 NB

Pipe OD 3556 mm 140 ''

Design Pressure 6 kgf/cm2

Average height of ground above top of pipe 1250 mm 4.1 '

Pipe Material IS 3589 : FE 410

Thickness of Cement Mortar (Internal & External) 0 mm

Allowable stress (50% of yield point) 1200 kgf/cm2 1.7E+04 psi

Modulus of Elasticity of Steel, E 2.1E+06 kgf/cm3 3.0E+07 psi

Poisson's Ratio for steel, n 0.3

900 1700 450

1250

250006625.xls.ms_office 1 of 12 11/3/2014/9:19 PM


2/12

JOB No. 99304

A. CALCULATION FOR INTERNAL PRESSURE

As per ANSI B31.1

Estimation of Thickness due to Internal Pressure

tm(1-m)

Where :

tm= Thickness without Mill Tolerance

t = Thickness after Mill Tolerance

P= Internal Pressure, 6 kgf/cm2

D0= Outside Diameter 3556 mm

S= Allowable stress 1200 kgf/cm2

A= Corrosion Allowance 0 mm Refer 4.4 AWWA M-11

E= Joint Efficiency 80% for ERW Pipe

Y= Factor 0.4 for ERW Pipe

m= Mill Tolerance 10.0% As per Cl 11.2 of IS3589

Calculated Thickness without Mill Tolerance, tm= 11.08 mm

Calculated Thickness with Mill Tolerance, t = 12.32 mm

Nearest Available Plate Thickness 14 mm

Pipe thickness Adopted 14 mm

t =

tm=2(SE+PY)

PD0+A



3/12

JOB No. 99304

B. CHECK FOR EXTERNAL PRESSURE

Step 1

As per IS 2825 (Clause 3.3.3.2)Estimation of Thickness under External Pressure

Maximum Allowable vacuum

tm= 1.03*D0/100*(PK)0.33 for L/D0> 14.4/(PK)

0.166

P= 1/K(t*100/(1.03*Do))3 0.056 kgf/cm2 0.794 psi

Where :

t = Thickness after Mill Tolerance 14.0 mm

P= Minimum Internal Pressure, 1 kgf/cm2

D0= Outside Diameter 3556 mm

A= Corrosion Allowance 0 mm

Step 2

As per Sl. No. 1 of Table XIII of Roark (4th Edition)

External Collapsing Pressure

Where :

t = wall thickness 14 mm

R= Radius of pipe 1778.0 mm

sy= compressive yield point 1200 kgf/cm2

E= Modulus of elasticity 2.1E+06 kgf/cm2

mmK=Elastic Modulus of Steel at Design Temp

Elastic Modulus of Steel at Room Temp1

psitsy

R(1+(4sy/E)(R/t)2)

kgf/cm2p'= 0.250 3.549



4/12

JOB No. 99304

Step 3

Where :

E= Modulus of Elasticity 2.1E+06 kgf/cm2

n= Poisson's Ratio 0.3

t = Pipe Wall thickness 14 mm

D= Neutral Axis Diameter 3528 mm

Collapsing Pressure

Pc= 3 psi 0.221 kgf/cm2

Where :

t = Pipe Wall thickness 0.5512 inch

D= Neutral Axis Diameter 138.9 incht/D=


5/12

JOB No. 99304

C. CHECK AGAINST BUCKLING

As per equation 6-7 of AWWA M-11, 2nd ed 1987

Allowable Buckling Pressure

qa= 1/F(32RwB'E'(EI/D3)) 10.7 psi 0.753541 kgf/cm2

where

F= Design Factor 3 for h/D =2

D= Diameter of Pipe 140 inch

Rw= Water Bouyancy factor 0.736

1-0.33(hw/h)

h= height of ground surface above top of pipe 49.213 inch

hw= height of water surface above top of pipe 39.37 inch 0hwh

h/D= 0.3515

B'= Empirical coefficient of elastic support 0.1644

0.150+0.041(h/D) for 0h/D5

0.150+0.014(h/D) for 5h/D80

E= Modulus of Elasticity 3E+07 for Steel

E'= Modulus of Soil 1750 psiI= Moment of inertia of X-section of Pipe wall 0.014 in4/lin in

=t3/12

t= thickness of pipe 0.5512 inch

Pipe embedded in soil may collapse or buckle from elastic instability resulting from external forces due toearth load and/or internal vacuum.



6/12

JOB No. 99304

Pt= gwhw + RwWc/D + Pi

gw= Specific weight of water 0.0361 lb/in

h= ht. of ground surface above top of pipe 49.213 inch

hw= ht. of water surface above top of pipe 39.37 inch 0hwh

Rw= Water Bouyancy factor 0.736

1-0.33(hw/h)

D= Diameter of Pipe 140 inch

Wc= Weight of Conduit 68.751 lb/lin in

Pi= 100% Vacuum 14.2 psi Case I

Vehicle Load 3 psi Case II

Total Load, Pt(Considering Internal Vacuum) = 15.983 psi 1.124 kgf/cm2Total Load, Pt(Considering Wheel Load) = 4.783 psi 0.336 kgf/cm2

for Case I (Internal Vacuum): Pipe Chosen is liable to fail under Buckling

for Case II (Wheel Load): Pipe Chosen is Safe

Compared to above, the total external pressure on the pipe is



7/12

JOB No. 99304

D. CHECK AGAINST HORIZONTAL DEFLECTION

As per equation 6-1 of AWWA M-11, 2nd ed 1987

Pipe deformation: Sprangler's formula

Marston ditch conduit formula

W= Cdw Bd2 (1)

For a flexible pipe, equation (1) is revised to

Wc= Cdw Bd2(Bc/Bd) when the trench width is less than 2D (2a)

Wc= Hcw Bc when the trench width is more than 2D (2b)

where

Wc= dead load on the conduit 5980.7 lb/ft using (2b)

w= unit weight of fill material 125 lb/ft3

Cd= Load Coefficient based on Hc/Bd 0.5 (Fig 8.3 of AWWA M-11 1st ed)

Bc= Pipe OD 11.667 ft

Bd= width of ditch at top of pipe 14.62 ft

Hc= Height of fill 4.10 ft

W = (WC+WL)/12 918.39 lb/lin in

WL= Live load 5040 lb/lin ft Considering Truck Load

Sprangler's formula for horizontal deflection

Horizontal Deflection of Pipe

Dx= Dl(KWr3)/(EI+0.061E'r3) 1.276 in 0.91%

32.4 mm

where

Dl= Deflection Lag Factor 1.5

K = Bedding Constant 0.1

r = radius of pipe 70 in

t= pipe wall thickness 0.5512 in

E = Modulus of Elasticity 3E+07 psi

I = Moment of Inertia 0.014 in4/lin in

E' = Modulus of Soil 1750 psi

Pipe Chosen is safe under Horizontal Deflection

equations 2(a) or 2(b) are the probable minimum loading. The actual load in a given case will be

intermediate of the two



8/12

JOB No. 99304

E. CHECK AGAINST COMBINED LATERAL STRESS

Bending moment in pipe shell (Considering lateral support is available)

r= Radius of Pipe 177.8 cm

W= Weight of Conduit 12.28 kg/cm

Kb= Bedding Coefficient 0.235

Kq= Coefficient 0.103 for q=30o

E = Modulus of Elasticity 2.1E+06 kgf/cm2

I = Moment of Inertia 0.2287 cm4/lin cm

E' = Modulus of Soil 28.123 kgf/cm2

Pe= External Uniform Pressure 1 kgf/cm2

Compressive Stress

sc= M/z 0.0005 kgf/cm2

z = Section Modulus 0.3267 cm3/lin cm

Longitudinal Stress

sp= PeD/2t 127 kgf/cm2

Total Stress

s = sc+ sp 127.33 kgf/cm2

As total stress is less than the Allowable, hence safe

M= kg cm1.70E-04Kb W r E I

E I+0.061 E'r

3

- 2KqPer

3



9/12

JOB No. 99304

F. CHECK AGAINST COMBINED INT PR & EXTERNAL LOAD

2(E I+0.061 E'r3+ 2KqPer3)

r= radius of Pipe 177.8 cm

W= Weight of Conduit 12.277 kg/cm

Kb= Bedding Coefficient 0.235

Kq= Coefficient 0.103 for q=30o

E = Modulus of Elasticity 2.1E+06 kgf/cm2

I = Moment of Inertia 0.2287 cm4/lin cm

E' = Modulus of Soil 28.123 kgf/cm2

P = Internal Pressure 6 kgf/cm3

Longitudinal Stress

sp= P D/2t 762 kgf/cm2

Total Stress

s = st+ sp 762.00 kgf/cm2

As total stress is less than the Allowable, hence safe

kgf/cm2Kb W r E t

0.003st=



10/12


11/12

JOB No. 99304

Method 1

yh2= [0.7(s1/sa)(Dt)3/2] - [t2S] 388.09 cm3

where:

s1= s

a- P

iD/2t 438

kgf/cm

2

sa= allowable stress in compression 1200 kgf/cm2

Pi= internal Pressure 6 kgf/cm2

D= Diameter 355.6 cm

t= wall thickness 1.4 cm

S= Spacing of reinforcement ring 1250 cm

y= width of stiffener 2.0 cm Assumed

h= height of stiffener 13.9 cm

Method 2

where:

s1= sa- PiD/2t 438 kgf/cm2

sa= Allowable Stress in Compression 1200 kgf/cm2

E= Modulus of Elasticity 2.1E+06 kgf/cm2

E'= Modulus of Elasticity for Soil 28.123 kgf/cm2

Pi= Internal Pressure 6 kgf/cm2

D= Diameter 355.6 cm

t= Wall Thickness 1.4 cm

S= Spacing of Reinforcement Ring 1250 cm

y= Width of Stiffener 12 cm Assumed

h= Height of Stiffener 76.282 cm

cm3- t2S

0.65750.7 (D/t)2

yh2=[s1 (1 + 0.091 (D/t)

3 (E'/E) + 0.325 (p/E)]

[0.7 p D2S]

p=

69826

s1[1 + 0.091(E'/E)(D/t)3+ Pi/E (D/t)

3]kgf/cm2



12/12

14.223418 from to thickness

168.3 406.6 4 5

406.6 559.0 5 6

559.0 914.0 6 7

914.0 1219.0 7 8

1219.0 1620.0 8 10

1620.0 2032.0 10 12

12 14

14 16

16 18

18 20

20 22

22 25

25 2828 32

32 36

Table 3 (IS 3589:1991)

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Underground Pipe Thk Cal