Pipe deflection questions in AWWA M11

[win]

Hi im trying to understand the formula for pipe deflection in the AWWA M11 page 75. Using the metric formula (7-6M), i calculated the deflection to be 2.27mm for a 6m long 250mm OD steel water pipe with 4.55mm wall thickness.

Is this deflection calculation correct? I also cant seem to get the same deflection when using the imperial formula (7-6). I tried using various online pipe deflection calculators and the deflection seems to be more (around 20mm).

The parameters i used is in oage 103
Pipe OD = 250mm
Wall thk = 4.55mm
W = 78.87kg/m x 9.81 x 6m
L = 6m
E = 206.84GPa
I = 2.7725x10^7

 

[robyengIT]

pay attention to the units : 20 mm is almost 9.81 x 2.27 mm

 

[win]

I already multiplied by 9.81 to get the weight in Newtons for the metric formula though.

 

[LittleInch]

Can you post the formula used.

I note the weight you have is a pipe full of water.

Is there a different calculation for single pipe of 6 m or continuous pipe with supports at 6m spacing?

This

http://www.wermac.org/steel/pipesupports_spacing.html

seems to back up the 2.5mm cas as a 10" pipe is around 6m max spacing of supports based on stress but also a max 2.5mm deflection.

Is the pipe really 250mm OD exactly? 10" pipe I use is actually 10.75" OD.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[win]

Does this mean that a deflection of 2.27mm is correct for the above parameters?
The formula used is for ‘maximum theoretical deflection for a simple span’, for uniformly distributed loads and free ends. This formula is from page 75 of AWWA M11 if you have the book.

Metric Y = (5x10^6)/(384) * (WL^3)/EI
Imperial Y = 22.5 * (WL^3)/EI

Y = max deflection at center span (mm) <inches>
W = total load on span (N) <lbf>
L = length of span (m) <Ft>
E = modulus of elasticity (206.84GPa for steel pipe) <30,000,000psi>
I = moment of innertia of pipe (mm4) <in4>


I just took a sample 250mm (10 inch) OD pipe size from Section modulus and inertia table to test out the calculations. This table also contains the size you mentioned 10.75 inches OD

Iam also curious as to why my deflection calculation results are different when using the metric and imperial formulas.

 

[robyengIT]

metric is correct (see hand calc)

 

[robyengIT]

may be it can help too : the front coeff. (5/384) remain the same, provided that the other values are expressed as per page 3 of this doc (so in USA wrote)

PS : when I have to do similar calc I always transform only the result

 

[win]

If the metric calcultions (2.27mmm deflection for 6m span 250mm OD steel pipe filled with water) is correct then i might have to relook at my unit conversions. Thanks!