60 FT SPAN IRON/STEEL PIPE WITH 3 - 20 FT SECTIONS 1

[KirkGH]

Task is to design a 60 ft span, simply supported, pipe using 20 ft sections and mechanically fastened connections (flanged pipes) to create fixity.

I was looking to DIPRA website for guidance, but the "ductile iron on supports" brochure only supports 20 ft sections with 20 ft support spacing....

Where can I find guidance on concentrated stresses at connections? Thermal effects?, since the "longitudinal" movement will be restrained from the fixed connection.

(I've left a message with the DIPRA regional engineering office and am waiting to hear back)

Thanks!

 

[JStephen]

Are you supporting a 60' span of pipe using some other structure, or expecting the pipe to support itself over 60'?

 

[IFRs]

Can the pipe be curve to form an arch?

 

[KirkGH]

Pipe is suspended in air so it will have supports on either end.... other then that it acts as a simply supported 60ft beam. Load = self weight + water inside

The stresses / deflections on the gross section are ok. My heffe just wanted me to consider the stresses at the flange / bolted connection, which will be 10 ft off of C.L. of span.

No, arch is not acceptable.

Additional info: One end is free (it turns down and dumps into a tank), so thermal effects are negligible.

 

[JStephen]

I would probably try to support it by some other structure.

You should be able to calculate an allowable end force on the flanges due to pressure, and then an equivalent moment to give the same longitudinal stress in the pipe. Assuming pressure is pretty well zero when loaded, you could then design for that end force.

Long unsupported pipes can vibrate in the wind.

 

[civilperson]

The answer to your design problem requires varying the diameter and wall thickness of the pipe. The flanged mechanical joints are much stronger than the pipe being connected,(125% and up). Your boss needs to give you the maximum allowable diameter that you can use and the allowable deflection of the center of the span. Combined FL, DL, Wind/Seismic will give maximum flexural moment. Check Aeolean flutter, freezing/insulation and heat trace requirements as well as possible unforeseen added live loads,(teenagers crawling across and then bouncing in unison). A suspended cable with attached lengths dropping down to encircle and support the pipe at 5-7 foot intervals seems a cheaper solution.

 

[gwynn]

What are the pipe diameter, pressures and wall thickness? A 60 foot span means very little without knowing the specifics.

This situation can be modeled fairly easily in most structural programs and is covered by most piping software as well. The flanges should be stiff enough to prevent any transfer of prying forces. In essence the flanges will then behave like spring supports as far as radial pressures are concerned.

Depending on pipe size, a secondary support system may be a waste of time and effort.