Steel Deck Diaphragm stress increase
Steel Deck Diaphragm stress increase
(OP)
Some reference material:
In the 2001 AISI Cold-Formed Steel Specification, NASPEC 2001, we are directed to appendix A for provisions applicable to the USA. On page A3, the appendix for code section A4.1.2 "Load Combinations for ASD", the 1/3 stress increase is apparently eliminated and instead the 0.75 load factor is used, as in the ASCE 7. This section also specifically states: "When evaluating diaphragms using the provisions of Section D5, no decrease in forces is permitted for load combinations including wind or earthquake loads." Section D5 is the section with a table giving the required safety factors and resistance factors for diaphragms.
The Vulcraft steel deck catalog shows in the diaphragm notes, page 67 note 10, that the allowable diaphragm loads have already been increased by 1/3.
Because the AISI spec removed the 1/3 increase for steel diaphragms, and moved the increase to the load side of the equation only for two or more loads, do we have to multiply all of the diaphragm capacities listed in the steel deck catalogs by 0.75? It seems to me that we do.
In the 2001 AISI Cold-Formed Steel Specification, NASPEC 2001, we are directed to appendix A for provisions applicable to the USA. On page A3, the appendix for code section A4.1.2 "Load Combinations for ASD", the 1/3 stress increase is apparently eliminated and instead the 0.75 load factor is used, as in the ASCE 7. This section also specifically states: "When evaluating diaphragms using the provisions of Section D5, no decrease in forces is permitted for load combinations including wind or earthquake loads." Section D5 is the section with a table giving the required safety factors and resistance factors for diaphragms.
The Vulcraft steel deck catalog shows in the diaphragm notes, page 67 note 10, that the allowable diaphragm loads have already been increased by 1/3.
Because the AISI spec removed the 1/3 increase for steel diaphragms, and moved the increase to the load side of the equation only for two or more loads, do we have to multiply all of the diaphragm capacities listed in the steel deck catalogs by 0.75? It seems to me that we do.






RE: Steel Deck Diaphragm stress increase
RE: Steel Deck Diaphragm stress increase
I just never noticed the built-in 1/3 increase until recently and I don't think anyone at my company has either, hence I ask you guys.
RE: Steel Deck Diaphragm stress increase
I think I understand then, that with diaphragm design, you aren't really even looking at any roof live or snow loads so there would definitely be just the D+W case and in the IBC then, you can't use the 1/3. So your post sort of woke me up to the fact.