---Quoted as Client Comments--------
Application for Wind and Seismic specifies that the combined sustained and occasional loads (such as wind or seismic) be limited to 1.33 times the allowable stress at temperature. The document further stipulates the equivalent static seismic load factor to be 70% of the seismic design load. It is therefore wrong to reduce the occasional loads and increase the allowable stress to which the resulting stresses are be compared to at the same time. Although to be fair, of the piping flexibility analyses we have reviewed the 1.33 allowable stress increase was not used; only the seismic equivalent static load was multiplied by 0.7. Even so,this is not in compliance with the B31.3 Code which says to not factor occasionalloads and limits the resulting stresses to 1.33 times the allowable at temperature. It is also slightly un-conservative as 1/0.7=1.43 which is higher than the code permitted factor of 1.33 on stress. The piping flexibility analyses are under-reporting the stresses in occasional load cases for Code evaluation.
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Question
1. As per ASCE, is it wrong application using factor 0.7 as defined on ASD(Allowable Stress Design)in AISC?
In CAESAR Seismic Wizard, the seismic acceleration factor is calculated considered factor 0.7?

2. Is it using duplicated margin in calculating seismic factor using factor 0.7 and pipe stress allowable 1.33h in occasional?

LJK, consider the following references:

Firstly the Power Piping and Process Piping codes:

ASME B31.1-2012
101.5.3 Earthquake. The effect of earthquakes shall be considered in the design of piping, piping supports, and restraints. The analysis considerations and loads may be as described in ASCE/SEI 7. ..........

ASME B31.3-2010
301.5.3 Earthquake. The effect of earthquake loading shall be taken into account in the design of piping. The analysis considerations and loads may be as described in ASCE 7. .............

So these clauses provide a connection between the ASME piping codes and ASCE 7, which states:

ASCE 7-05 – Minimum Design Loads for Buildings and Other Structures
Chapter 13 – Seismic Design Requirements for Nonstructural Components
Clause 13.1.7 Reference Documents Using Allowable Stress Design
Where a reference document provides a basis for the earthquake-resistant design of a particular type of system or component, and the same reference document defines acceptance criteria in terms of allowable stresses rather than strengths, that reference document is permitted to be used. The allowable stress load combination shall consider dead, live, operating, and earthquake loads in addition to those in the reference document. The earthquake loads determined in accordance with Section 13.3.1 shall be multiplied by a factor of 0.7. The allowable stress design load combinations of Section 2.4 need not be used. The component or system shall also accommodate the relative displacements specified in Section 13.3.2.

Also another reference:

American Lifelines Alliance - Seismic Design and Retrofit of Piping Systems (July 2002)
Clause 4.3.2 Seismic Load In-Structure
Step – 6: The total load is the sum of the seismic load E and the weight W. If the allowable stress design method (also called working stress design method) is used to qualify the piping system, as is the common practice, then the seismic load E should be divided by 1.4 (IBC 1605.3.2), the total load is therefore:
FT = W + E/1.4


My understanding is that the modern structural codes such as ASCE 7 use "Strength Design" or "Load and Resistance Factor Design" and that these methods compare the ultimate strength of members with actual gravity plus earthquake loadings. These methods assume that yielding will occur and utilise plastic modulus methods.

ASME piping codes on the other hand use working stress methods (i.e. elastic analysis with no yielding [accepting that there is some elastic shakedown under thermal expansion, but that would complicate this discussion]) and therefore should properly use a reduced seismic loading coefficient.

So if your seismic design load has been determined on the basis of "Strength Design" it is correct to reduce it by a factor of 0.7 for use in a working stress design.

The introduction of the 1.33 factor into this argument is misleading. The allowable stress for the SUS + OCC category is increased because it is an occasional event, and the factor is related to the duration of the event (particularly B31.1).

Allow me to add:
Using 0.7 will give good loads for stress calculation.
But for structural response (that is displacements & support loads), do not use the 0.7.
These issues are currently under review in B31E - the B31 seismic document.

Okay, I have FRP systems. What row in Table 13.6.1 ASCE 7 would apply to determine the ap and Rp values?

Piping and tubing constructed of low-deformability materials, such as cast iron, glass, and nonductile plastics.

or

Piping in accordance with ASME B31, including in-line components, constructed of high or limited deformability materials, with joints made by threading, bonding, compression couplings, or grooved couplings.

Another question. It would seem to me that the (1 + 2 * z/h) term is aimed at computing maximum load at the base of a support, not necessarily the distributed seismic loads acting on the pipe itself.

"z = height in structure of point of attachment of component
with respect to the base. For items at or below the base, z
shall be taken as 0. The value of z/h need not exceed 1.0"

So If I hang a pipe, this factor -> 1, while if its on a T-Pole, this factor -> 3.

Dave,

How about the specific paragraph of B31E sec. 3.1 stated "For the purpose of determining seismic loading, when applicable, the basis for design used in para. 3.3 and 3.4 is allowable stress design"? Does this implies also to use the factor of E/1.4 of ASCE-7, or similar standard like IBC / UBC-1997, when using ASD method of checking the piping stress?

Also, is it MANDATORY (because the code stated "shall") to use of Ap = 2.5, even the project's Ap is different as it based from table of ASCE-7, or similar standard like UBC-1997 or IBC?

My opinion? I would use the lower Rp. For non-B31 piping with bonded joints, Rp=4.5. Even though you are analyzing this system, I say non-B31 because B31 does not directly address FRP pipe.
Some would say for estimating seismic loads and deflections, Rp should be 1.0.
I believe the building codes treat piping as a component in the building - the focus is on the building and building connections, not the response of the piping system. And that contribues greatly to the problems here.

If you hange the pipe, wouldn't Z be based on the elevation within the structure where it hangs? If I hang from the top of a structure, then Z/H=1.
The point is, if the structure can wag in first mode (cantilever) response, then the "free end" (top) of that cantilever structure experiences a much larger acceleration that the fixed end (foundation). This assumes that the structure response is not affected by the piping. Your T-pole example does not abide by this assumption.
Again, ASCE 7 is focused on the building itself and not this "component".
I would agree that all this is not clear if your focus is on the pipe rather than the structure.

B31E is under review to settle these issues - use 0.7? what Rp? what allowable stress?
The approach must be consistent. The answer to one of these questions will establish the proper answer to the others.
At the moment, B31.3 does not specifically point to B31E so I don't think the full "shall"/"may" interpretations apply.
I think the ap=2.5 will stand.

Dave,

Whilst B31.3 does not specifically point to B31E, B31E can clearly be applied to B31.3:

Extract from B31E
1.1 Scope
This Standard applies to above-ground, metallic piping systems in the scope of the ASME B31 Code for Pressure Piping (B31.1, B31.3, B31.4, B31.5, B31.8, B31.9, B31.11). The requirements described in this Standard are valid when the piping system complies with the materials, design, fabrication, examination, testing, and inspection requirements of the applicable ASME B31 Code section.

This maybe out of topic but interesting to be discussed. Based on similar provisions in ASCE 7-10 (sec. 12.12.4 and 13.6) and UBC-1997 (sec. 1633.2.11 and footnote #13 of Table-O); these codes require that piping at "structure support points" shall be designed for the maximum anticipated relative displacements and remain functional following an earthquake. Piping shall be flexible to absorb the structure's anticipated maximum inelastic response displacements. Hence, piping stress analysis shall take the most critical scenario assuming the out-of-phase motions when piping is supported by two different adjacent structures (assuming the two structures are moving in opposite directions). This relative displacement of structure at piping support points specified in the building code is not clearly discussed in the ASME B31 piping codes of occasional stress analysis (esp. in B31.3 where only the occ. stress due to moment effects of sustained and seismic accelerations are considered) and the term "seismic anchor motions" is not mentioned in any of these piping codes. Only in ASME B31E that you can find the term "relative anchor motion" as accounted in the calculation of Occasional stress in sec. 3.4. There is different approach between B31.3 & B31E occasional stress checks and the Ap value varies following the building code used (for B31.3) and the provision in B31E (seismic anchor motion considered).