KevinNZ
Mechanical
- Jun 12, 2003
- 829
ASME is planning a change to B31. (also B31E & B31.3)
proposed change clause 101.5.2 and 101.5.3. ".. the Allowable Stress Design reduction factor shall not be applied”.
The following is the ASME explanation provided for the item record associated with this revision:
proposed change clause 101.5.2 and 101.5.3. ".. the Allowable Stress Design reduction factor shall not be applied”.
The following is the ASME explanation provided for the item record associated with this revision:
“Some time ago the American Institute of Steel Construction (AISC) and the structural steel industry reduced the allowable stress multiplier of 1.33 to 1.00 for occasional loads such wind or earthquake in concert with moving to strength design methods. The ASME is based on working stress design methods and not strength design methods. The ASCE recognizing that many structural designers still use allowable stress design methods (comparable to ASME’s working stress design methods) adjusted the seismic demand (earthquake force) in the seismic nonstructural components chapter (where B31 is referenced) by multiplying the seismic demand by 0.7 (roughly 1.00/1.33), ostensibly to compensate for the difference in strength design methods and working stress design methods. Further, the same adjustment in the ASCE seismic requirements is inferred in the ASCE wind requirements. Since B31.1 allows the occasional load increase for piping, there is no reason an occasional load increase should not be allowed for structural steel supports.
However, it was pointed out that what was proposed would result in [highlight #FCE94F]double dipping, reducing the load by a 0.7 factor per the ASCE 7 and increasing the allowable per B31.1[/highlight]. I agreed, stating the reference to ASCE 7 for earthquake loads would be augmented by not allowing the Allowable Stress Design factor to be used when developing loads for supplementary structural steel and permitting the occasional load allowable, 1.2Sh, to be used. The ASCE 7 reference for wind loads will similarly be augmented.”
Further, the following is some commentary from the project manager of this item:
“The B31.1 seismic requirement is consistent with the AISC's and ASCE 7's consideration of Allowable Stress Design (and ASME's working stress design) methods. Both B31E and B31.3 are considering whether to conform to B31.1. However, B31E-2010a has lost ANSI approval and the current B31E activity intent is to develop a new standard to incorporate the latest understanding of the seismic failure mechanism of B31 piping which correlates better with fatigue rather than collapse (collapse being the failure mechanism expected by the civil/structural discipline). Further, the civil/structural discipline recognizes the superior performance of B31 piping compared to piping designed to other standards. ASCE 7 reflects this understanding (but currently fails to appropriately compensate for piping support loads and displacements). Finally, the B31E activity realizes that the current design methods of the B31 Books and probably the design methods employed in other countries are overly conservative but B31E has no rational justification to abridge the AISC and ASCE 7 requirements.”
Note this explanation and commentary is being provided for information and should not be considered an official response from the Committee or ASME. .. or if you would like further information or like an official response from the ASME B31.1 Section Committee.
However, it was pointed out that what was proposed would result in [highlight #FCE94F]double dipping, reducing the load by a 0.7 factor per the ASCE 7 and increasing the allowable per B31.1[/highlight]. I agreed, stating the reference to ASCE 7 for earthquake loads would be augmented by not allowing the Allowable Stress Design factor to be used when developing loads for supplementary structural steel and permitting the occasional load allowable, 1.2Sh, to be used. The ASCE 7 reference for wind loads will similarly be augmented.”
Further, the following is some commentary from the project manager of this item:
“The B31.1 seismic requirement is consistent with the AISC's and ASCE 7's consideration of Allowable Stress Design (and ASME's working stress design) methods. Both B31E and B31.3 are considering whether to conform to B31.1. However, B31E-2010a has lost ANSI approval and the current B31E activity intent is to develop a new standard to incorporate the latest understanding of the seismic failure mechanism of B31 piping which correlates better with fatigue rather than collapse (collapse being the failure mechanism expected by the civil/structural discipline). Further, the civil/structural discipline recognizes the superior performance of B31 piping compared to piping designed to other standards. ASCE 7 reflects this understanding (but currently fails to appropriately compensate for piping support loads and displacements). Finally, the B31E activity realizes that the current design methods of the B31 Books and probably the design methods employed in other countries are overly conservative but B31E has no rational justification to abridge the AISC and ASCE 7 requirements.”
Note this explanation and commentary is being provided for information and should not be considered an official response from the Committee or ASME. .. or if you would like further information or like an official response from the ASME B31.1 Section Committee.
