Peer-to-Peer Standards Exchange


  • ASCE Standards
  • ASCE7
  • Seismic
Tyson Stagner's profile image
Tyson Stagner posted 07-01-2022 12:57 PM
Currently API is using chapter 13 of ASCE for design of pipe supports regardless of whether they are attached to a building or not. In my mind pipe supports not attached to a building would be designed per chapter 15 and not chapter 13 as they are not a mechanical/electrical component of a building.

Does anyone know of the rational for this?

Note: I have investigated both approaches for the design of ASME piping in general for chapter 13 vs chapter 15 and the results are markedly similar as the use of Rp= 12 forces the use of Fpmin and when Ie/Ip can be taken as 1.0. Chapter 13 approach is more conservative when Ie- 1.25 and Ip = 1.5. However, ASME piping not supported/attached by a structure does not seem to fit the scope for chapter 13
James Soules's profile image
James Soules

There is overlap between components covered by ASCE Chapters 13 and 15.  Philosophically, Chapter 13 covers relatively small components supported above grade in a building and Chapter 15 covers nonbuilding structures (large components) supported at grade.  As I mentioned there is overlap between the two chapters.  Chapter 13 provisions can be applied to components supported at grade (z = 0) and Chapter 15 Section 15.3 covers nonbuilding structures supported by other structures.  The Section 15.3 rules apply to relatively large nonbuilding structures.  

Piping is specifically addressed in ASCE 7-16 Chapter 13 Table 13.6-1 under distributed systems.  Very large values of Rp are provided for different piping systems (the highest being Rp = 12 for ASME B31 piping).  The use of Rp = 12 generally results in seismic forces (Fp) being governed by the minimum Fp value given by Equation 13.3-3.  The very high value of Rp for ASME B31 piping recognizes the very high ductility of ASME B31.3 piping.  Unfortunately, the very high value of Rp for ASME B31 piping ignores the fairly low ductility of the ordinary structural systems used to support ASME B31 piping.  Piping designers often take the very low forces from Chapter 13 for ASME B31 piping and design their (often small) ground supported pipe supports for these low forces.  This practice is allowed by ASCE 7-16 Chapter 13.  Structural Engineers designing large pipe supports (pipe racks, vertical cantilevers, etc.) generally use the R values for the supporting system and the piping is simply the weight supported by the structural system.  Please note that pipe racks are specifically covered in ASCE 7 Chapter 15.  These two different approaches can give widely different answers when applied to the same pipe support.

The ASCE 7 task committee responsible for Chapter 13 recognized this disconnect.  In ASCE 7-22 Chapter 13 Table 13.6-1, values to determine the seismic force, Fp, are given separately for distributed systems (includes ASME B31 piping) and for distribution system supports.  The forces determined using the values for distributed systems would be used to analyze the component itself, such as ASME B31 piping.  The forces determined using the values for distributed system supports would be used to design the component supports, such as pipe supports for ASME B31 piping.  You will find that the ASCE 7-22 Chapter 13 seismic forces for both distributed systems and distributed system supports have increased over those determined using ASCE 7-16.