Above ground Ductile Iron Pipe Seismic Response Factor 1

[strucbells]

I am a structural engineer that recently started doing some pipe support design for some wastewater treatment plant projects with above ground ductile iron piping.

What is the appropriate design value for ductile iron piping under ASCE 7-16 Chapter 13 for seismic response factor (Rp)? Generally I have used Rp = 3 for "Piping and tubing constructed of low-deformability materials, such as cast iron, glass, and nonductile plastics" as it mentions cast iron piping. However, I am wondering if this has been overly conservative and that Rp = 4.5 or even Rp = 6.0 would be more appropriate because of the inherent superior ductility of ductile iron pipe compared to cast iron piping.

As a separate question, if the DI pipe is glass-lined, does that affect the Rp factor selection, or would that be addressed separately through tight deflection limits?

I have reviewed the DIPRA brochures and contacted them about this earlier today, but didn't get a clear response. Their engineer said they were unfamiliar with ASCE7 (!).

Thanks!

 

[HTURKAK]

I will advise the use of Rp=4.5 . Ductile iron should be considered as limited-deformability material. Refer to Table 13.6- 1.
The R values are sensitive not only to type of material , but also type of connection . For your case , most of the connections should be flanged and some of them could be compression coupling. In case of all the connections are flanged, you may use R=6.

Regarding the analysis, you may use formula 13.3-1 and the requirements of 13.6.3 should be satisfied.

If DI pipe glass lined, the deflection limits shall be tightened to a level suitable for glass .

I will suggest you to read Guidelines for seismic evaluation and design of petrochemical facilities ( Seismic Evaluation and Design of the Petrochemical Committee ASCE)

Finally, the basic allowable stress at service conditions should be σt / 3 where σt is tensile strength for DI pipe.

 

[KevinNZ]

While It might not apply to iron pipe, B31E cover steel pressure piping.