Water line design on steel bridge 4

[gigi02]

If I want to design a 8" PVC line through a steel bridge, would this line need to be encased? Or would I have to replace the PVC with a different material? What can I use for expansion? Is there a helpful book or website for this type of design? The water line is to go between the 1st and 2nd I-beam, then through the wall and back under the ground at each end. The line will be exposed to the weather and I will have to consider the cold and the heat. Does anyone have any advice?

 

[SlideRuleEra]

For the application that you are describing, I suggest that you investigate ductile iron pipe as an alternative. It is much more resistant to damage than PVC & has other good characteristics for exposed pipe runs. Here is a link to the Ductile Iron Pipe Research Association (DIPRA) where you can get more information to make an informed decision.

http://www.dipra.org/

http://www.SlideRuleEra.net

 

[stanier]

Stay away from PVC. Too many risks. The PVC you see on bridges should only be for road drainage not pressure or sewage applications.

 

[Zambo]

HDPE pipe would be suitable for this application. HDPE (black colour) is resistant to UV and will not degrade in hot weather. Cold weather is a different matter and this depends on the expected temperature and the water flow, i.e if the water is constantly flowing it is less likely to freeze. So if the water flow may be much reduced, at night for instance, then insulation would be needed.

 

[stanier]

Problem with PE is that the coeficient of expansion is 20 times that for ferrous products. So how will the thermal strain be accommodated?

In addition the Poissons ratio is only 0.35. Hence when pressurised the pipe will shrink from its anchors and cause local stresses that may fail. It will also need more pipe supports than for a ferrous product.

 

[SoeSoe]

What about other types of plastics and composite type pipes?
It seems like there is stigma against plastic. Would plastic be alright if it was inside a carrier pipe, thus it would have room to expand and contract? I for one would really appreciate some more explanations and comments on this thread. The only thing I have to offer is that steel pipe is also an option.

 

[stanier]

A bridge crossing is an infrastructure asset that is difficult to acces to maintain. There is no stigma against plastic materials however if you are designing for 50 years in an exposed position PVC-U is not the best choice. Use a risk analysis technique to look at likelihood of ailure and consequences of such a failure.

Problems with PVC-U include:-
1) thermal expansion/contraction which can result in failure due to "follow on" strains exceeding the material design parameters. Do NOT assume that the thermal strain will occur linearly along the length of pipe on a bridge crossing. One section may be exposed to the sun, its temperature increases, the material weakens and all the strain occurs in a small section.

2) PVC-U has low fracture toughness below 5C. Wind chill on a bridge can easily get the pipe surface below this figure.

3) Wind loading can cause a pipe surface to fret in a bridge crossing

4) Sunlight and UV can be detrimental to PVC-U in the long run.

5) Vibration due to wind or traffic load can cause problems

If you intend using steel make sure it is epoxy coated on the outside and lined internally either with cement or PE, epoxy etc.

You could consider spiral wound stainless steel, its cheaper than coated carbon steel.

I would stay away from GRP.

There is nothing wrong with ductile iron cement lined pipe. Just because its been around for a long time dont discount it.

 

[Qshake]

Untold numbers of utilities have been run across bridges with a multitude of piping materials.

Unless I'm way out of my league here, the first thing you need to do is determine what the utility company will allow you place on the bridge. I have yet to meet with a utility representative that has left this up to the bridge engineer.

Most utilities are run in between girders for slab and girder bridges so that impact damage is prevented. Most utilties require a single roller type hanger with some companies using double roller hangers. Most of these are hung not from the slab but from special diaphragms attached to girders. The rollers are prefered as they help with expansion and installation. Most contractors like to put the pipe together and push it across the bridge rather than piecemeal it. So if it's a long distance to push, and I've seen 300+ feet tried, there are hang-ups with the double rollers binding.

I have never seen a large utilty on a full depth slab bridge that was not encased in a concrete duct bank.

Most other utilties such that would fit in up to 4" conduit are placed inside the barrier curbs.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[SlideRuleEra]

As stanier says, the varous types of plastic pipe have limitations. Ductile iron has advantages other that toughness:

1. Relatively easy to accommodate pipe movement (both thermal expansion and the deflection / vibration all bridges experience in use).

2. Cement lining has excellent flow characteristics (Hazen & Williams, C = 140) and it maintains a high value over many years.

3. The pipe exterior (iron) is resistant to corrosion.

4. The pipe itself has good structural properties that maximize the spacing of pipe hangers or other supports.

In my previous post I gave a link to DIPRA. Here is specific link (free .pdf download) at the DIPRA website, "Bridge Crossings With Ductile Iron Pipe"

http://www.dipra.org/pdf/bridgeCrossings.pdf

http://www.SlideRuleEra.net

 

[RCEJD]

To: Gigi02

We have done many bridges for various applications and have placed the pipes in different configurations. The advice given by Stanier and SlideRuleEra are on point.

Typically only see pvc for short term applications ... as pointed out by other posts, for the reasonss stated. Good Luck.

 

[DRC1]

Just finished installing 12" main across 60 ft bridge. Typicall set up for our area. 12 pipe was in 20" casing pipe. Carrier wrapped in insulation. Pipe supported on 5 Grinell Roller Pipe hangers. Inserts cast into sidewalk. 22" steel sleeve cast into each backwall. Rollers & casing allow pipe movement. Pipe was ductile iron. Design and materials by water company

 

[egb]

I need to also design two pressure ductile iron pipes across a 250' bridge. One a 12" insulated water and other a 6" non-insulated SS FM. Two questions: a) For the 12", is a secondary encsement necessary between the pipe and the insulation, and b) which insulation is preferrable either a foamglas with metal jacketing or a pre-insulated pipe.

 

[rconner]

egb,
It may be best to address your specific questions with regard to the insulated/pre-insulated piping to those folks who specialize in these aspects and support of same (e.g. Thermacor, Urecon, Perma-Pipe(spellings?)) etc. I believe most at least exterior insulated piping I've seen however does have secondary "jackets" that are often probably firmer/mmore impermeable than the insulation itself, the jackets accomplish varied functions, and sometimes also various "shoes" are used between the insulated pipes and/or jackets that perhaps also help to spread loads/wear etc.

 

[stanier]

Why not consider pre insulated Australian made ABS. Use dextensively in the middle east for reticulation of chilled and condenser water. Available up to DN800.

http://www.tycoflowcontrol.com.au/t...ine_systems/Overview/plastic_products#ABSKFLO

 

[swayze]

I've completed two projects in NJ - one with insulation and one without. Each time the water main was DIP. Recently, for a long span crossing, we used DIP CL 53 with US Pipe xtra flex restrained joint fittings and a tr flex sleeve to allow for movement. The pipe shall be installed on rollers attached to the beams. You may want to contact the agency who owns the bridge to see what they will accept. For us, that was the NJDOT.

 

[RDK]

Where I live we seldom hang pipe on bridges.

It tends to freeze.

A line can be insulated but is is often more economical and maintenance free to bury it in the stream bed or push it under the river.



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[stanier]

Direction drilling under the river or float and sink will be far more costly than spanning a bridge. Factors of 3 or 4 are typical dpending upon the size of the river, closeness of a contractor weho can do this, amount of river traffic etc.